**Table 3.**

*Preparation of the eight kinds of kenaf-imbedded specimen.*

**91**

**Figure 6.**

*2.2.3 Porosity*

**Figure 5.**

**Figure 4.**

pressure (1b/(in)<sup>2</sup>

a 20 cm<sup>2</sup>

*2.2.4 Air permeability*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

The pore size (diameter, D, μm) was measured using a capillary flow porometer (CFP-1200AE PMI Co., USA). The measured pore diameter (D) was calculated using Eq. (1) with the median value of the graph between the air flow and pressure.

where C is a constant, τ the surface tension of the liquor (dyne/cm), and ρ the

The air permeability (R) was measured using Fx3300 (TEXTEST, Switzerland) according to the KSK ISO 9237 method. An air pressure of 100 Pa was applied to

following Eq. (2). **Figure 8** shows the air permeability measuring apparatus:

*FAST-1 system for measuring compressibility [28]. (a) Image of FAST-1 and (b) Schematic diagram.*

Air permeability (R, cm3/cm2/g) = \_\_

area of the specimen, and the air permeability was calculated using the

). **Figure 7** shows the capillary flow porometer.

Cτ

Q

<sup>ρ</sup> (1)

<sup>A</sup> <sup>×</sup> <sup>167</sup> (2)

The mean and largest pore diameters were measured for each specimen:

Pore diameter (D) = \_\_\_

*Measured orientation angle of the fibers in the nonwoven.*

*Preparation of specimens for measuring tensile property of nonwoven fabric.*

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

#### **Figure 4.**

*Generation, Development and Modifications of Natural Fibers*

**90**

**No.**

1 2 3 4 5 6 7 8 *Note: o, treated; x, non-treated.*

**Table 3.**

*Preparation of the eight kinds of kenaf-imbedded specimen.*

Laminated by

40:40:20 40:40:20 40:40:20 40:40:20

2

3 layers

16 mm

170°C, 7.2 m/min

2

3 layers

16 mm

170°C, 7.2 m/min

o X

500

3.17

500

1.53

2

3 layers

16 mm

170°C, 7.2 m/min

2

3 layers

16 mm

170°C, 7.2 m/min

o X

420

2.53

420

1.34

PU film

Nonlaminated

40:40:20 40:40:20 40:40:20 40:40:20

2

3 layers

16 mm

170°C, 7.2 m/min

2

3 layers

16 mm

170°C, 7.2 m/min

o X

320

2.75

320

0.82

2

3 layers

16 mm

170°C, 7.2 m/min

2

3 layers

16 mm

170°C, 7.2 m/min

o X

240

2.10

240

0.60

**Lamination**

**Kenaf:PP:LM** 

**No. of carding** 

**Layer of web**

**Needle** 

**Thermocompression** 

**Powder** 

**Weight** 

**Thickness** 

**(g/m2**

**)**

**(mm)**

**treatment**

**bonding roller** 

**treatment**

**depth**

**treatment**

**PET (blend** 

**ratio)**

*Preparation of specimens for measuring tensile property of nonwoven fabric.*

#### **Figure 5.**

*Measured orientation angle of the fibers in the nonwoven.*

#### *2.2.3 Porosity*

The pore size (diameter, D, μm) was measured using a capillary flow porometer (CFP-1200AE PMI Co., USA). The measured pore diameter (D) was calculated using Eq. (1) with the median value of the graph between the air flow and pressure. The mean and largest pore diameters were measured for each specimen:

$$\text{Pore diameter (D)} = \frac{\text{C}\pi}{\text{P}} \tag{1}$$

where C is a constant, τ the surface tension of the liquor (dyne/cm), and ρ the pressure (1b/(in)<sup>2</sup> ). **Figure 7** shows the capillary flow porometer.

#### *2.2.4 Air permeability*

The air permeability (R) was measured using Fx3300 (TEXTEST, Switzerland) according to the KSK ISO 9237 method. An air pressure of 100 Pa was applied to a 20 cm<sup>2</sup> area of the specimen, and the air permeability was calculated using the following Eq. (2). **Figure 8** shows the air permeability measuring apparatus:

**Figure 6.** *FAST-1 system for measuring compressibility [28]. (a) Image of FAST-1 and (b) Schematic diagram.*

#### **Figure 7.** *Image of capillary flow porometer, CFP-1200AE.*

where Q is the arithmetic mean of air flow (cm3 /min), A the area of the specimen (cm2 ), and 167 the conversion constant.

#### *2.2.5 Water absorption property*

The water absorption property was assessed by KSK ISO 9073-6. The liquid absorption capacity (LAC) was calculated by Eq. (3):

1 the water absorption property was assessed by KSR ISO 90/3-6. I the liquidorption capacity (LAC) was calculated by Eq. (3):

$$\text{LAC} = \frac{\text{weight of specimen absorbed (B)} - \text{weight of dried specimen (A)}}{\text{weight of dried specimen (A)}} \times 100 \qquad (3)$$

A square specimen of dimensions 100 mm × 100 mm was prepared and conditioned under 20 ± 1°C and 65 ± 5% RH. After its dry weight (A) was measured, the specimen was submersed to a depth of 20 mm in the water bath for 60 s, then taken out, and hung horizontally for 120 s, and finally its weight (B) was measured again, and LAC was calculated by Eq. (3) as the average value of five measurements.

#### *2.2.6 Sound absorption property*

The sound absorption coefficient of the nonwoven specimen was measured using acoustic duct (SCIEN-9301, USA) according to KSF2814-2: 2002. **Figure 9** shows the acoustic duct apparatus.

**93**

**Figure 10.**

*Image of the KES-F7 measuring apparatus.*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

The specimen was fastened at the impedance tube's left wall, and a loudspeaker was attached at its right wall. Sound waves of well-defined frequencies were emitted by a loudspeaker. The nodes and antinodes of the standing waves emitted from the loudspeaker and those reflected from the specimens were detected by two small microphones, from which the sound absorption coefficient was calculated by frequency response transfer function from two microphone channels. The frequency used was between 100 and 1600 Hz for low frequency and between 500 Hz and

The thermal conductivity (K) of the nonwoven specimen was measured using KES-F7 (Thermolabo, Kato Tech. Co. Ltd., Japan) and calculated using Eq. (4):

A fogging test of the nonwoven specimen was performed to examine the emission of volatile organic compounds (VOC) using the gravimetric method according to KSM ISO 6452. A circular specimen of diameter 80 ± 1 mm was prepared and put

A ∙ △ T

), and ΔT the temperature difference. **Figure 10** shows an image

*<sup>d</sup>* (4)

), d the specimen thickness (cm), A the area of

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

6.3 kHz for high frequency.

**Figure 9.**

the specimen (cm<sup>2</sup>

*2.2.8 Fogging test*

*2.2.7 Measurement of thermal conductivity*

where *Q* is the heat loss (W/cm2

of the KES-F7 measuring apparatus.

Q = K\_\_\_\_\_\_

*Acoustic duct, SCIEN-9301. (a) Low Frequency and (b) High Frequency.*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

**Figure 9.** *Acoustic duct, SCIEN-9301. (a) Low Frequency and (b) High Frequency.*

The specimen was fastened at the impedance tube's left wall, and a loudspeaker was attached at its right wall. Sound waves of well-defined frequencies were emitted by a loudspeaker. The nodes and antinodes of the standing waves emitted from the loudspeaker and those reflected from the specimens were detected by two small microphones, from which the sound absorption coefficient was calculated by frequency response transfer function from two microphone channels. The frequency used was between 100 and 1600 Hz for low frequency and between 500 Hz and 6.3 kHz for high frequency.

#### *2.2.7 Measurement of thermal conductivity*

The thermal conductivity (K) of the nonwoven specimen was measured using KES-F7 (Thermolabo, Kato Tech. Co. Ltd., Japan) and calculated using Eq. (4):

$$\mathbf{Q} = \mathbf{K} \frac{\mathbf{A} \cdot \triangleleft \mathbf{T}}{d} \tag{4}$$

where *Q* is the heat loss (W/cm2 ), d the specimen thickness (cm), A the area of the specimen (cm<sup>2</sup> ), and ΔT the temperature difference. **Figure 10** shows an image of the KES-F7 measuring apparatus.

#### *2.2.8 Fogging test*

*Generation, Development and Modifications of Natural Fibers*

where Q is the arithmetic mean of air flow (cm3

), and 167 the conversion constant.

absorption capacity (LAC) was calculated by Eq. (3):

The water absorption property was assessed by KSK ISO 9073-6. The liquid

LAC <sup>=</sup> weight of specimen absorbed (B) <sup>−</sup> weight of dried specimen (A) \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ weight of dried specimen (A) <sup>×</sup> 100 (3)

A square specimen of dimensions 100 mm × 100 mm was prepared and conditioned under 20 ± 1°C and 65 ± 5% RH. After its dry weight (A) was measured, the specimen was submersed to a depth of 20 mm in the water bath for 60 s, then taken out, and hung horizontally for 120 s, and finally its weight (B) was measured again, and LAC was calculated by Eq. (3) as the average value of five measurements.

The sound absorption coefficient of the nonwoven specimen was measured using acoustic duct (SCIEN-9301, USA) according to KSF2814-2: 2002. **Figure 9**

/min), A the area of the speci-

**92**

**Figure 8.** *Image of FX 3300.*

men (cm2

**Figure 7.**

*2.2.5 Water absorption property*

*Image of capillary flow porometer, CFP-1200AE.*

*2.2.6 Sound absorption property*

shows the acoustic duct apparatus.

A fogging test of the nonwoven specimen was performed to examine the emission of volatile organic compounds (VOC) using the gravimetric method according to KSM ISO 6452. A circular specimen of diameter 80 ± 1 mm was prepared and put

**Figure 10.** *Image of the KES-F7 measuring apparatus.*

into a thermostatic bath covered with aluminum foil which was boiled for 16 hours at 100°C. The fogging value was calculated using the mass of aluminum foil wrapped on the beaker in the thermostatic bath before and after the experiment.

#### *2.2.9 Measurement of the surface texture of the nonwoven*

The surface texture of the nonwoven specimen was measured by SEM (S-4300, Hitachi Co., Japan) and optical microscopy (I Camscope 305A, Korea).

#### **3. Results and discussion**

#### **3.1 Physical properties of kenaf-imbedded nonwoven according to the processing conditions**

#### *3.1.1 Breaking and tearing strengths of the nonwoven*

**Table 4** lists the physical properties of the ten kinds of nonwoven specimen. **Figure 11(a)** and **(b)** shows the breaking and tearing strengths of the nonwoven specimens. Specimens 3 and 10 showed the highest breaking and tearing strengths. As shown in **Table 4**, specimens 3 and 10 had a smaller mean pore size and higher weight than the other specimens. Therefore, the effect of the mean pore size and weight on the breaking and tearing strengths of the nonwoven was investigated. **Figure 12** shows a diagram of the breaking and tearing strengths according to the weight of the nonwoven specimens.

The breaking and tearing strengths of the MD and CD direction of the nonwoven specimen were increased with increasing weight of the nonwoven. This was attributed to the more numbers of fibers per unit area in the nonwoven specimens according to the increase of weight, which results in higher breaking and tearing strengths due to the more contribution of the fibers to the resistance from external load. **Figure 13** shows a diagram of the breaking and tearing strengths according to the mean pore size. The breaking and tearing strengths of the nonwoven specimens were decreased with increasing mean pore size of the nonwoven specimen, possibly due to the weakened resistance from external force due to the large pore size in the nonwoven. In addition, the breaking and tearing strengths of nonwoven specimen 2, as shown in **Figure 11**, were the lowest, which was attributed to its lowest weight and largest mean pore size as shown in **Table 4**.

On the other hand, the orientation factor and the distribution of the fibers in the nonwoven specimens were measured and discussed to examine their effect on the breaking and tearing strengths of the nonwoven. **Figure 14** presents the fiber orientation distribution of the ten types of nonwoven specimen.

As shown in **Figure 14**, the fiber orientation distributions of specimens 1, 2, 6, and 8 exhibited the shape of a quasi-Gaussian distribution, whereas that of specimens 3 and 10 exhibited a double quasi-normal distribution. Furthermore, specimens 4, 5, 7, and 9 exhibited a random distribution of fiber orientation in the nonwoven, i.e., the number of fibers according to the orientation angle was randomly distributed. As shown previously in **Figure 11**, specimens 3 and 10 exhibited the highest tearing and breaking strengths, respectively, whereas specimen 2 showed the lowest breaking and tearing strengths. This means that the fiber distribution in the nonwoven does not directly affect the breaking and tearing strengths, because specimen 2 with high distribution of fibers between 60° and 120° as a normal distribution exhibited low breaking strength, but specimens 1, 6, and 8 with the same normal distribution as specimen 2 showed higher breaking strength than that of the specimen 2. Furthermore, it was assumed

**95**

**Specimen no.**

**Breaking strength (kgf/mm2**

**Tearing strength** 

**Air permeability** 

**Water** 

**Sound** 

**Mean** 

**Largest pore** 

**Thickness** 

**Weight** 

**(g/m2**

**)**

**(mm)**

**diameter (μm)**

**pore size** 

**(μm)**

**absorption** 

**coefficient**

**absorption** 

**(%)**

**(cm3/cm2/g)**

**(N)**

**)**

**MD**

> 1

2 3 4 5 6 7 8 9 10

41.3 *Note: MD, machine direction; CD, cross direction.*

**Table 4.**

*Physical properties of the nonwoven specimens (first batch of specimens).*

44.8

30.3

44.3

37.6

37.4

0.14

51.0

114.4

0.597

300

26.2

22.3

25.3

30.7

89.9

41.7

0.11

68.0

556.4

0.557

258.4

18.1

19.8

24.0

26.6

125.6

59.3

0.1

61.9

256.3

0.632

221.2

21.2

23.4

25.0

29.5

64.9

50.5

0.12

35.8

157.0

0.738

234.2

22.0

30.0

27.2

27.1

59.3

65.4

0.1

73.4

211.9

0.636

251.4

19.7

20.8

26.5

25.9

69.2

72.7

0.11

62.3

408.4

0.598

245.6

21.8

24.1

26.7

32.6

58.9

44.3

0.11

50.5

177.4

0.554

245.8

38.4

40.5

41.9

55.5

26.0

51.3

0.25

38.6

402.5

0.942

363.6

9.9

11.2

21.5

25.5

238

55.2

0.14

105.3

407.6

0.713

209.8

22.6

22.9

27.0

27.7

51.4

48.7

0.12

34.6

414.4

0.739

254.6

**CD**

**MD**

**CD**

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

*DOI: http://dx.doi.org/10.5772/intechopen.85367*


*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

> **Table 4.**

*Physical properties of the nonwoven specimens (first batch of specimens).*

*Generation, Development and Modifications of Natural Fibers*

*2.2.9 Measurement of the surface texture of the nonwoven*

*3.1.1 Breaking and tearing strengths of the nonwoven*

**3. Results and discussion**

**processing conditions**

weight of the nonwoven specimens.

largest mean pore size as shown in **Table 4**.

into a thermostatic bath covered with aluminum foil which was boiled for 16 hours at 100°C. The fogging value was calculated using the mass of aluminum foil wrapped on the beaker in the thermostatic bath before and after the experiment.

The surface texture of the nonwoven specimen was measured by SEM (S-4300,

Hitachi Co., Japan) and optical microscopy (I Camscope 305A, Korea).

**3.1 Physical properties of kenaf-imbedded nonwoven according to the** 

**Table 4** lists the physical properties of the ten kinds of nonwoven specimen. **Figure 11(a)** and **(b)** shows the breaking and tearing strengths of the nonwoven specimens. Specimens 3 and 10 showed the highest breaking and tearing strengths. As shown in **Table 4**, specimens 3 and 10 had a smaller mean pore size and higher weight than the other specimens. Therefore, the effect of the mean pore size and weight on the breaking and tearing strengths of the nonwoven was investigated. **Figure 12** shows a diagram of the breaking and tearing strengths according to the

The breaking and tearing strengths of the MD and CD direction of the nonwoven specimen were increased with increasing weight of the nonwoven. This was attributed to the more numbers of fibers per unit area in the nonwoven specimens according to the increase of weight, which results in higher breaking and tearing strengths due to the more contribution of the fibers to the resistance from external load. **Figure 13** shows a diagram of the breaking and tearing strengths according to the mean pore size. The breaking and tearing strengths of the nonwoven specimens were decreased with increasing mean pore size of the nonwoven specimen, possibly due to the weakened resistance from external force due to the large pore size in the nonwoven. In addition, the breaking and tearing strengths of nonwoven specimen 2, as shown in **Figure 11**, were the lowest, which was attributed to its lowest weight and

On the other hand, the orientation factor and the distribution of the fibers in the nonwoven specimens were measured and discussed to examine their effect on the breaking and tearing strengths of the nonwoven. **Figure 14** presents the fiber

As shown in **Figure 14**, the fiber orientation distributions of specimens 1, 2, 6, and 8 exhibited the shape of a quasi-Gaussian distribution, whereas that of specimens 3 and 10 exhibited a double quasi-normal distribution. Furthermore, specimens 4, 5, 7, and 9 exhibited a random distribution of fiber orientation in the nonwoven, i.e., the number of fibers according to the orientation angle was randomly distributed. As shown previously in **Figure 11**, specimens 3 and 10 exhibited the highest tearing and breaking strengths, respectively, whereas specimen 2 showed the lowest breaking and tearing strengths. This means that the fiber distribution in the nonwoven does not directly affect the breaking and tearing strengths, because specimen 2 with high distribution of fibers between 60° and 120° as a normal distribution exhibited low breaking strength, but specimens 1, 6, and 8 with the same normal distribution as specimen 2 showed higher breaking strength than that of the specimen 2. Furthermore, it was assumed

orientation distribution of the ten types of nonwoven specimen.

**94**

**Figure 11.** *Breaking and tearing strengths of the nonwoven specimens. (a) Breaking strength and (b) Tearing strength.*

that high breaking and tearing strengths of specimens 3 and 10, which showed a double quasi-normal distribution, were attributed to the processing conditions of nonwoven. In addition, the breaking and tearing strengths of nonwoven specimen 2 were measured and discussed according to the cut direction of the nonwoven specimens. **Figure 15** shows the tensile property of specimen 2 according to the cut direction of the specimen. The breaking strength, breaking strain, and initial modulus of the specimens cut along MD, i.e., perpendicular to the cross direction (CD), exhibited maximum values, which was attributed to the many fibers distributed and oriented perpendicular to the CD.

#### *3.1.2 Air permeability*

**Figure 16(a)** presents the air permeability and mean pore size of the nonwoven specimens. Specimens 2 and 8 showed high air permeability, which was attributed to the large pore size and low weight of the nonwoven, as shown in **Table 4**. These specimens were processed under the double-carding treatment in the multi-opener with three

#### **Figure 12.**

*Diagram of the breaking and tearing strengths according to the weight of the nonwoven specimens. (a) Breaking strength(MD) vs weight, (b) Breaking strength(CD) vs weight, (c) Tear strength(MD) vs weight and (d) Tear strength(CD) vs weight.* 

**97**

*3.1.3 Water absorption*

**Figure 13.**

*3.1.4 Sound absorption coefficient*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

layers of web and needle depth of 16 or 14.4 mm. According to two previous studies [26, 27], nonwoven prepared using circular cross-sectional fibers exhibited the highest air permeability than nonwoven with noncircular fiber cross section, which was attributed to the highest pore diameter of nonwoven with circular fibers. These results were similar to our own. **Figure 16(b)** shows a correlation diagram between the mean pore diameter and air permeability of the ten different nonwoven specimens. The air permeability was highly dependent on the mean pore diameter of the nonwoven, and the correlation coefficient between the two parameters was 0.85, which was relatively high.

*vsmean pore size and (d) Tear strength(CD) vsmean pore size.* 

*Diagram of the breaking and tearing strengths according to the mean pore size of the nonwoven specimens. (a) Breaking strength(MD) vsmean pore size, (b) Breaking strength(CD) vsmean pore size, (c) Tear strength(MD)* 

**Figure 17** shows the LAC of the nonwoven specimens. Specimens 2, 5, 6, and 8 showed high liquid absorption, which was related with their large mean pore size. Furthermore, specimens 2, 5, 6, and 8 had larger pore diameter than specimens 4, 7, and 9, as shown in **Table 4**. In particular, the air permeability (**Figure 16**) and liquid absorption (**Figure 17**) of specimen 10 were the lowest, which was attributed to its high percentage of LM PET, i.e., the voids in the nonwoven were blocked by the LM PET that was heat melted on the thermo-compression bonding roller, which shrunk the voids and reduced the air and water flows and hence reduced the air permeability and liquid absorption. According to a previous study [27], high-volume porosity

**Figure 18(a)** and **(b)** presents the sound absorption coefficient according to the high frequency between 500 and 6300 Hz and the average sound absorption coefficient

gives high vertical wicking rate, which was a similar result to our own.

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

#### **Figure 13.**

*Generation, Development and Modifications of Natural Fibers*

that high breaking and tearing strengths of specimens 3 and 10, which showed a double quasi-normal distribution, were attributed to the processing conditions of nonwoven. In addition, the breaking and tearing strengths of nonwoven specimen 2 were measured and discussed according to the cut direction of the nonwoven specimens. **Figure 15** shows the tensile property of specimen 2 according to the cut direction of the specimen. The breaking strength, breaking strain, and initial modulus of the specimens cut along MD, i.e., perpendicular to the cross direction (CD), exhibited maximum values, which was attributed to the many fibers distributed and oriented perpendicular to the CD.

*Breaking and tearing strengths of the nonwoven specimens. (a) Breaking strength and (b) Tearing strength.*

**Figure 16(a)** presents the air permeability and mean pore size of the nonwoven specimens. Specimens 2 and 8 showed high air permeability, which was attributed to the large pore size and low weight of the nonwoven, as shown in **Table 4**. These specimens were processed under the double-carding treatment in the multi-opener with three

*Diagram of the breaking and tearing strengths according to the weight of the nonwoven specimens. (a) Breaking strength(MD) vs weight, (b) Breaking strength(CD) vs weight, (c) Tear strength(MD) vs weight and (d) Tear* 

**96**

**Figure 12.**

*strength(CD) vs weight.* 

*3.1.2 Air permeability*

**Figure 11.**

*Diagram of the breaking and tearing strengths according to the mean pore size of the nonwoven specimens. (a) Breaking strength(MD) vsmean pore size, (b) Breaking strength(CD) vsmean pore size, (c) Tear strength(MD) vsmean pore size and (d) Tear strength(CD) vsmean pore size.* 

layers of web and needle depth of 16 or 14.4 mm. According to two previous studies [26, 27], nonwoven prepared using circular cross-sectional fibers exhibited the highest air permeability than nonwoven with noncircular fiber cross section, which was attributed to the highest pore diameter of nonwoven with circular fibers. These results were similar to our own. **Figure 16(b)** shows a correlation diagram between the mean pore diameter and air permeability of the ten different nonwoven specimens. The air permeability was highly dependent on the mean pore diameter of the nonwoven, and the correlation coefficient between the two parameters was 0.85, which was relatively high.

#### *3.1.3 Water absorption*

**Figure 17** shows the LAC of the nonwoven specimens. Specimens 2, 5, 6, and 8 showed high liquid absorption, which was related with their large mean pore size. Furthermore, specimens 2, 5, 6, and 8 had larger pore diameter than specimens 4, 7, and 9, as shown in **Table 4**. In particular, the air permeability (**Figure 16**) and liquid absorption (**Figure 17**) of specimen 10 were the lowest, which was attributed to its high percentage of LM PET, i.e., the voids in the nonwoven were blocked by the LM PET that was heat melted on the thermo-compression bonding roller, which shrunk the voids and reduced the air and water flows and hence reduced the air permeability and liquid absorption. According to a previous study [27], high-volume porosity gives high vertical wicking rate, which was a similar result to our own.

#### *3.1.4 Sound absorption coefficient*

**Figure 18(a)** and **(b)** presents the sound absorption coefficient according to the high frequency between 500 and 6300 Hz and the average sound absorption coefficient

#### *Generation, Development and Modifications of Natural Fibers*

#### **Figure 14.**

*Orientation of the fibers in the nonwoven specimens. (a) specimen 1, (b) specimen 2, (c) specimen 3, (d) specimen 4, (e) specimen 5, (f) specimen 6, (g) specimen 7, (h) specimen 8, (i) specimen 9 and (j) specimen 10.*

of the nonwoven specimens, respectively. Specimens 2, 3, and 10, which had either high thickness and low weight or low thickness and high weight, showed a high sound absorption coefficient. The sound absorption coefficient under high frequency was highly dependent on the thickness and weight of the nonwoven and also partly affected by the pore diameter [19–21]. The sound absorption coefficient of specimen 3 was the largest, which was attributed to its high weight and low pore diameter.

**99**

**Figure 16.**

*vs Mean pore size.*

**Figure 15.**

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

**Table 5** shows the correlation coefficient between the sound absorption coefficient under high frequency and the thickness and weight of the kenaf-imbedded nonwoven specimens. The sound absorption coefficient was highly correlated with

*Air permeability of the nonwoven specimens. (a) Air permeability of each specimens and (b) Air permeability* 

*Tensile property of the specimen (no. 2). (a) Breaking strength, (b) Breaking strain and (c) Initial modulus.*

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

**Figure 15.** *Tensile property of the specimen (no. 2). (a) Breaking strength, (b) Breaking strain and (c) Initial modulus.*

**Table 5** shows the correlation coefficient between the sound absorption coefficient under high frequency and the thickness and weight of the kenaf-imbedded nonwoven specimens. The sound absorption coefficient was highly correlated with

#### **Figure 16.**

*Air permeability of the nonwoven specimens. (a) Air permeability of each specimens and (b) Air permeability vs Mean pore size.*

*Generation, Development and Modifications of Natural Fibers*

of the nonwoven specimens, respectively. Specimens 2, 3, and 10, which had either high thickness and low weight or low thickness and high weight, showed a high sound absorption coefficient. The sound absorption coefficient under high frequency was highly dependent on the thickness and weight of the nonwoven and also partly affected by the pore diameter [19–21]. The sound absorption coefficient of specimen 3 was the

*Orientation of the fibers in the nonwoven specimens. (a) specimen 1, (b) specimen 2, (c) specimen 3, (d) specimen 4, (e) specimen 5, (f) specimen 6, (g) specimen 7, (h) specimen 8, (i) specimen 9 and (j) specimen 10.*

largest, which was attributed to its high weight and low pore diameter.

**98**

**Figure 14.**

**Figure 17.** *Liquid absorption of specimens.*

the thickness and weight, indicating that the nonwoven specimens with high thickness, high weight, and small pore size have a high sound absorption coefficient. In addition, these nonwoven specimens were made under manufacturing conditions of high needle depth or high blend ratio of LM PET. Lee and Joo [20] found that the sound absorption coefficient of nonwoven mixed with a large amount of fine fibers is high due to the friction of viscosity through the vibration of the air. Another study [21] attributed the increases in thickness and in the amount of the fiber per unit area to an increase in the sound absorption property of the nonwoven. These previous results were similar to our own.

#### *3.1.5 Fogging property*

A fogging test was carried out to determine the emission of volatile organic compounds (VOC) from automotive interior materials with increasing interior temperature during the summer time. **Figure 19** presents the fogging values of the nonwoven specimens. Specimen 1 treated with a single opener, specimen 4 treated with the one-time carding process, and specimen 5 treated with four layers of web showed high fogging values, whereas specimens 2, 6, and 8, with large mean pore size and high air permeability and water absorption, exhibited low fogging values. This was attributed to the easy flow of VOC gases developed from the nonwoven due to their large pores.

#### **Figure 18.**

*Sound absorption coefficient of the nonwoven specimens. (a) Sound absorption coefficient and (b) Average sound absorption coefficients.* 

**101**

**Figure 19.**

*Fogging values of the nonwoven specimens.*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

Sound absorption coefficient High frequency 0.91 0.83

*Correlation coefficient between physical properties and sound absorption coefficient of nonwoven.*

**3.2 Physical properties of the kenaf-imbedded nonwoven according to powder** 

**Table 6** shows the physical properties of the kenaf-imbedded nonwoven speci-

**Figure 20** presents the breaking and tearing strengths of the kenaf-imbedded

θ of each specimens, i.e., unity of this value means

**Thickness (mm) Weight (g/m2**

**)**

nonwoven specimens treated and non-treated with laminated PU film. The breaking and tearing strengths of the laminated specimens were higher than those of the non-treated specimens, which was attributed to the PU film laminated on the nonwoven surface, resulting in higher weight and thickness. In addition, as shown in **Figure 20(b)** and **(d)**, the non-powder-treated specimens (6 and 8) exhibited higher breaking and tearing strengths than the powdertreated specimens (5 and 7), which were assumed to be weakened by adhesion between the PE powder and PU film by the heat on the laminating roller. On the other hand, as shown in **Figure 20(a)**, powder-treated specimens (1 and 3) exhibited higher breaking strength than the non-treated specimens (2 and 4), which was attributed to the enhancement of coherence between PE powder and LM PET fibers that were heat melted on the thermo-compression bonding roller. **Figure 21** presents a diagram of the fiber orientation of the nonlaminated nonwoven specimens (1–4). The degree of fiber orientation in the nonwoven was

orientation of fiber along the machine direction (MD) in the nonwoven, whereas zero value means fiber orientation along the cross direction (CD) in the nonwoven. Of these specimens, specimen 3 showed the highest value as a 0.46, and specimen 4 exhibited the lowest value as a 0.33, which resulted in the high difference between MD and CD in the breaking strength of this specimen 4 as shown in

mens treated with powder and laminated by PU film, respectively.

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

**treatment and laminated PU coating**

*3.2.1 Breaking and tearing strengths*

**Table 5.**

calculated as the mean of cos2

**Figure 20(a)** and **(c)**.

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*


**Table 5.**

*Generation, Development and Modifications of Natural Fibers*

previous results were similar to our own.

*3.1.5 Fogging property*

**Figure 17.**

*Liquid absorption of specimens.*

the thickness and weight, indicating that the nonwoven specimens with high thickness, high weight, and small pore size have a high sound absorption coefficient. In addition, these nonwoven specimens were made under manufacturing conditions of high needle depth or high blend ratio of LM PET. Lee and Joo [20] found that the sound absorption coefficient of nonwoven mixed with a large amount of fine fibers is high due to the friction of viscosity through the vibration of the air. Another study [21] attributed the increases in thickness and in the amount of the fiber per unit area to an increase in the sound absorption property of the nonwoven. These

A fogging test was carried out to determine the emission of volatile organic compounds (VOC) from automotive interior materials with increasing interior temperature during the summer time. **Figure 19** presents the fogging values of the nonwoven specimens. Specimen 1 treated with a single opener, specimen 4 treated with the one-time carding process, and specimen 5 treated with four layers of web showed high fogging values, whereas specimens 2, 6, and 8, with large mean pore size and high air permeability and water absorption, exhibited low fogging values. This was attributed to the easy flow of VOC gases developed from the nonwoven due to their large pores.

*Sound absorption coefficient of the nonwoven specimens. (a) Sound absorption coefficient and (b) Average* 

**100**

**Figure 18.**

*sound absorption coefficients.* 

*Correlation coefficient between physical properties and sound absorption coefficient of nonwoven.*

#### **3.2 Physical properties of the kenaf-imbedded nonwoven according to powder treatment and laminated PU coating**

#### *3.2.1 Breaking and tearing strengths*

**Table 6** shows the physical properties of the kenaf-imbedded nonwoven specimens treated with powder and laminated by PU film, respectively.

**Figure 20** presents the breaking and tearing strengths of the kenaf-imbedded nonwoven specimens treated and non-treated with laminated PU film. The breaking and tearing strengths of the laminated specimens were higher than those of the non-treated specimens, which was attributed to the PU film laminated on the nonwoven surface, resulting in higher weight and thickness. In addition, as shown in **Figure 20(b)** and **(d)**, the non-powder-treated specimens (6 and 8) exhibited higher breaking and tearing strengths than the powdertreated specimens (5 and 7), which were assumed to be weakened by adhesion between the PE powder and PU film by the heat on the laminating roller. On the other hand, as shown in **Figure 20(a)**, powder-treated specimens (1 and 3) exhibited higher breaking strength than the non-treated specimens (2 and 4), which was attributed to the enhancement of coherence between PE powder and LM PET fibers that were heat melted on the thermo-compression bonding roller.

**Figure 21** presents a diagram of the fiber orientation of the nonlaminated nonwoven specimens (1–4). The degree of fiber orientation in the nonwoven was calculated as the mean of cos2 θ of each specimens, i.e., unity of this value means orientation of fiber along the machine direction (MD) in the nonwoven, whereas zero value means fiber orientation along the cross direction (CD) in the nonwoven. Of these specimens, specimen 3 showed the highest value as a 0.46, and specimen 4 exhibited the lowest value as a 0.33, which resulted in the high difference between MD and CD in the breaking strength of this specimen 4 as shown in **Figure 20(a)** and **(c)**.

**Figure 19.**

*Fogging values of the nonwoven specimens.*


*Physical properties of the kenaf-imbedded nonwoven specimens (second batch of specimens).*

**Table 6.**

**103**

**Figure 21.**

**Figure 20.**

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*3.2.2 Air permeability and water absorption*

*Orientation of nonlaminated nonwoven specimens.*

**Figure 22** shows the air permeability and water absorption of the kenafimbedded nonwoven specimens treated and nonlaminated with laminated PU film. The differences of the air permeability and water absorption between the laminated and nonlaminated specimens were much lower than those between the

*strength of nonlaminated specimens and (d) Tearing strength of laminated specimens.* 

*Breaking and tearing strengths of the kenaf-imbedded nonwoven specimens (second group of specimens). (a) Breaking strength of nonlaminated specimens, (b) Breaking strength of laminated specimens, (c) Tearing* 

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

**Figure 20.**

*Generation, Development and Modifications of Natural Fibers*

**102**

**Specimen** 

**Lamination**

**Powder** 

**Blend ratio** 

**Mean** 

**Largest** 

**Strength**

**LAC** 

**Thermal** 

**Sound** 

**Air** 

**Thickness** 

**Weight** 

**(%)**

**conductivity** 

**absorption** 

**permeability** 

**(mm)**

**(g/m2**

**)**

**(cm3/cm2/s)**

**coefficient**

**(W/m°C)**

**treatment**

**(kenaf:**

**pore**

**pore** 

 **size** 

**diameter** 

**Breaking** 

**Tearing (N)**

**(kgf/mm2**

**)**

**(mm)**

**(mm)**

**MD**

**CD**

**MD**

**CD**

**Low** 

**High** 

**freq.**

**freq.**

**PP:LM PET)**

**no.**

1 2 3 4 5 6 7 8 *Note: O, treated; X, non-treated.*

**Table 6.**

*Physical properties of the kenaf-imbedded nonwoven specimens (second batch of specimens).*

Laminated

O

40:40:20

35.9

117.8

27.412

26.753

106.832

97.39

25.3

0.056

0.055

0.24

63.2

1.3

420

by PU film

X O X

40:40:20

83.8

230.1

40.715

24.136

142.402

200.036

253.6

0.059

0.128

0.54

88.6

3.2

500

40:40:20

49.2

196.5

31.253

26.458

138.78

103.013

20.6

0.056

0.082

0.33

27.6

1.5

500

40:40:20

59.0

180.7

35.534

31.763

127.353

163.11

177.2

0.061

0.096

0.42

98.5

2.5

420

Nonlaminated

O X O X

40:40:20

100.3

314.3

4.959

11.502

55.537

96.278

327.7

0.054

0.088

0.37

172.6

2.8

320

40:40:20

65.1

215.5

14.076

16.840

25.872

27.194

31.8

0.055

0.033

0.11

67.4

0.8

320

40:40:20

92.8

282.7

2.723

6.255

27.48

52.574

285.7

0.047

0.073

0.24

284.6

2.1

240

40:40:20

34.0

199.6

13.314

12.532

33.617

46.144

34.4

0.057

0.054

0.16

40.8

0.6

240

*Breaking and tearing strengths of the kenaf-imbedded nonwoven specimens (second group of specimens). (a) Breaking strength of nonlaminated specimens, (b) Breaking strength of laminated specimens, (c) Tearing strength of nonlaminated specimens and (d) Tearing strength of laminated specimens.* 

#### *3.2.2 Air permeability and water absorption*

**Figure 22** shows the air permeability and water absorption of the kenafimbedded nonwoven specimens treated and nonlaminated with laminated PU film.

The differences of the air permeability and water absorption between the laminated and nonlaminated specimens were much lower than those between the

**Figure 21.** *Orientation of nonlaminated nonwoven specimens.*

**Figure 22.**

*Air permeability and water absorption of the kenaf-imbedded nonwoven treated and non-treated with laminated PU film. (a) Air permeability and (b) Water absorption.* 

powder-treated and non-treated specimens, i.e., the air permeability and water absorption of the non-powder-treated specimens (2, 4, 6, and 8) were much higher than those of the powder-treated specimens (1, 3, 5, and 7). Furthermore, the nonlaminated specimens (1–4) exhibited higher air permeability and water absorption than did the laminated specimens (5–9). This was attributed to the small pore size of the powder-treated and laminated specimens, which was caused by the blockage of the pores in the nonwoven by melted powder in the thermo-compression bonding process and partly melted PU in the laminating process. This was verified by the mean pore and largest pore diameters of the kenaf-imbedded nonwoven specimens, as shown in **Figure 23**.

The mean pore and largest pore diameters of the non-powder-treated (2, 4, 6, and 8) and nonlaminated (1, 2, 3, and 4) specimens were much larger than those of the powder-treated (1, 3, 5, and 7) and laminated (5, 6, 7, and 8) specimens, respectively.

#### *3.2.3 Thermal conductivity*

**Figure 24** shows the thermal conductivity of the kenaf-imbedded nonwoven specimens treated and non-treated with laminated PU film. The thermal conductivities of the powder-treated (1, 3, 5, and 7) and laminated (5–8) nonwoven specimens were higher than those of the non-powder-treated (2, 4, 6, and 8) and nonlaminated (1–4) specimens, respectively, which was attributed to less obstruction of heat particles' flow due to less air film in the smaller pores due to blockage of pores in the nonwoven by melted powder in the thermo-compression bonding process.

**105**

**Figure 25.**

*frequency, (c) low frequency and (d) high frequency.*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

**Figure 25** shows the sound absorption coefficients of the laminated and nonlaminated nonwoven specimens at low and high frequencies. The sound absorption coefficients of the laminated specimens (5, 6, 7, and 8) were higher than those of the nonlaminated specimens (1, 2, 3, and 4), which was attributed to the increased thickness of the nonwoven due to the laminated film on its surface. Furthermore, the sound absorption coefficients of the powder-treated specimens (1, 3, 5, and 7)

*Sound absorption coefficients of the kenaf-imbedded nonwoven specimens. (a) low frequency, (b) high* 

*Thermal conductivity of the laminated and nonlaminated nonwoven specimens.*

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*3.2.4 Sound absorption*

**Figure 24.**

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

**Figure 24.** *Thermal conductivity of the laminated and nonlaminated nonwoven specimens.*

#### *3.2.4 Sound absorption*

*Generation, Development and Modifications of Natural Fibers*

*laminated PU film. (a) Air permeability and (b) Water absorption.* 

powder-treated and non-treated specimens, i.e., the air permeability and water absorption of the non-powder-treated specimens (2, 4, 6, and 8) were much higher than those of the powder-treated specimens (1, 3, 5, and 7). Furthermore, the nonlaminated specimens (1–4) exhibited higher air permeability and water absorption than did the laminated specimens (5–9). This was attributed to the small pore size of the powder-treated and laminated specimens, which was caused by the blockage of the pores in the nonwoven by melted powder in the thermo-compression bonding process and partly melted PU in the laminating process. This was verified by the mean pore and largest pore diameters of the kenaf-imbedded nonwoven specimens,

*Air permeability and water absorption of the kenaf-imbedded nonwoven treated and non-treated with* 

The mean pore and largest pore diameters of the non-powder-treated (2, 4, 6, and 8) and nonlaminated (1, 2, 3, and 4) specimens were much larger than those of the powder-treated (1, 3, 5, and 7) and laminated (5, 6, 7, and 8) specimens,

**Figure 24** shows the thermal conductivity of the kenaf-imbedded nonwoven specimens treated and non-treated with laminated PU film. The thermal conductivities of the powder-treated (1, 3, 5, and 7) and laminated (5–8) nonwoven specimens were higher than those of the non-powder-treated (2, 4, 6, and 8) and nonlaminated (1–4) specimens, respectively, which was attributed to less obstruction of heat particles' flow due to less air film in the smaller pores due to blockage of pores in the

*Mean pore and largest pore diameters of the nonwoven specimens. (a) Mean pore dia and (b) Largest pore dia.*

nonwoven by melted powder in the thermo-compression bonding process.

**104**

**Figure 23.**

as shown in **Figure 23**.

*3.2.3 Thermal conductivity*

respectively.

**Figure 22.**

**Figure 25** shows the sound absorption coefficients of the laminated and nonlaminated nonwoven specimens at low and high frequencies. The sound absorption coefficients of the laminated specimens (5, 6, 7, and 8) were higher than those of the nonlaminated specimens (1, 2, 3, and 4), which was attributed to the increased thickness of the nonwoven due to the laminated film on its surface. Furthermore, the sound absorption coefficients of the powder-treated specimens (1, 3, 5, and 7)

**Figure 25.**

*Sound absorption coefficients of the kenaf-imbedded nonwoven specimens. (a) low frequency, (b) high frequency, (c) low frequency and (d) high frequency.*

were lower than those of the non-treated ones (2, 4, 6, and 8), which was attributed to the thinner nonwoven and partly affected by its smaller pores due to blockage of the pores in the nonwoven by melted powder in the thermo-compression bonding process. In addition, the sound absorption coefficient of thick and heavy specimen 8, which was non-powder-treated and PU-laminated, was the highest, whereas those of thin and light specimens 1 and 3, which were powder-treated and non-PU-treated, exhibited lower value than others. The sound absorption coefficients of the laminated and nonlaminated nonwoven specimens according to the sound frequency during measurement exhibited a rapid increase around 630 Hz in the low-frequency experiment but showed a rapid increase around 1, 600 Hz in the high-frequency experiment.

#### *3.2.5 Correlation between the physical properties and structural parameters of the kenaf-imbedded nonwoven specimens*

**Table 7** presents the correlation coefficient between physical properties and structural parameters of the kenaf-imbedded nonwoven specimens.

The breaking and tearing strengths of the kenaf-imbedded nonwoven specimens were highly correlated with weight of the nonwoven and inversely correlated with mean pore diameter in the kenaf-imbedded nonwoven and the orientation factor of its fibers. In particular, tensile property of the nonwoven according to the orientation factor exhibited a similar result to that of Rawal et al. [29]. The air permeability was highly correlated with the mean pore diameter as a porosity in the kenaf-imbedded nonwoven, which can be compared with those of the previous findings [26, 30]. The water absorption was also highly correlated with the mean pore diameter of the kenaf-imbedded nonwoven, and the thickness of the kenaf-imbedded nonwoven strongly affected its water absorption. This is in accordance with that of Das et al. [23]. They analyzed that more air trapped within the nonwoven with high porosity allows faster movement of water through pores. Furthermore, they suggested that this is in accordance with the theory of capillarity. The thermal conductivity of the nonwoven was dependent on its weight and was inversely correlated with its mean pore diameter. In addition, the sound absorption was highly correlated with thickness of the kenaf-imbedded nonwoven, and its


#### **Table 7.**

*Correlation coefficient between physical properties and structural parameters of the kenaf-imbedded nonwoven specimens.*

**107**

**4. Conclusion**

**Figure 26.**

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application*

weight affected the sound absorption, but its mean pore diameter did not. This was

*Surface images of the kenaf-imbedded nonwoven specimens. (a) Optical microscopy (x100) and (b) SEM (x50).*

**Figure 26** presents surface images of the kenaf-imbedded nonwoven specimens

The large pores observed for specimens 2, 6, and 9 resulted in high air permeability and water absorption, and these large pore diameters affected the breaking and tearing strengths. In addition, the thermal conductivity was inversely affected

This study examined the relationship between the physical properties of kenafimbedded nonwoven and its structural factors according to the needle-punching

a similar result to those of previous studies [20, 21].

taken by SEM and optical microscopy.

*3.2.6 Surface images of the kenaf-imbedded nonwoven specimens*

by the pore diameter. Specimens 1, 3, and 7 had small pore.

*DOI: http://dx.doi.org/10.5772/intechopen.85367*

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

**Figure 26.** *Surface images of the kenaf-imbedded nonwoven specimens. (a) Optical microscopy (x100) and (b) SEM (x50).*

weight affected the sound absorption, but its mean pore diameter did not. This was a similar result to those of previous studies [20, 21].

#### *3.2.6 Surface images of the kenaf-imbedded nonwoven specimens*

**Figure 26** presents surface images of the kenaf-imbedded nonwoven specimens taken by SEM and optical microscopy.

The large pores observed for specimens 2, 6, and 9 resulted in high air permeability and water absorption, and these large pore diameters affected the breaking and tearing strengths. In addition, the thermal conductivity was inversely affected by the pore diameter. Specimens 1, 3, and 7 had small pore.

#### **4. Conclusion**

This study examined the relationship between the physical properties of kenafimbedded nonwoven and its structural factors according to the needle-punching

*Generation, Development and Modifications of Natural Fibers*

high-frequency experiment.

*kenaf-imbedded nonwoven specimens*

were lower than those of the non-treated ones (2, 4, 6, and 8), which was attributed to the thinner nonwoven and partly affected by its smaller pores due to blockage of the pores in the nonwoven by melted powder in the thermo-compression bonding process. In addition, the sound absorption coefficient of thick and heavy specimen 8, which was non-powder-treated and PU-laminated, was the highest, whereas those of thin and light specimens 1 and 3, which were powder-treated and non-PU-treated, exhibited lower value than others. The sound absorption coefficients of the laminated and nonlaminated nonwoven specimens according to the sound frequency during measurement exhibited a rapid increase around 630 Hz in the low-frequency experiment but showed a rapid increase around 1, 600 Hz in the

*3.2.5 Correlation between the physical properties and structural parameters of the* 

structural parameters of the kenaf-imbedded nonwoven specimens.

**Mean pore diameter (μm)**

Air permeability 0.85 0.49 0.44 −0.65

Thermal conductivity −0.62 0.75

*Correlation coefficient between physical properties and structural parameters of the kenaf-imbedded* 

Water absorption 0.91 0.68 0.84

Low frequency

High frequency

**Largest pore diameter (μm)**

Breaking strength −0.55 0.25 0.88 −0.59 Tearing strength −0.48 0.59 0.98 −0.55

0.43 0.60 0.90 0.65

0.41 0.48 0.91 0.83

**Table 7** presents the correlation coefficient between physical properties and

The breaking and tearing strengths of the kenaf-imbedded nonwoven specimens were highly correlated with weight of the nonwoven and inversely correlated with mean pore diameter in the kenaf-imbedded nonwoven and the orientation factor of its fibers. In particular, tensile property of the nonwoven according to the orientation factor exhibited a similar result to that of Rawal et al. [29]. The air permeability was highly correlated with the mean pore diameter as a porosity in the kenaf-imbedded nonwoven, which can be compared with those of the previous findings [26, 30]. The water absorption was also highly correlated with the mean pore diameter of the kenaf-imbedded nonwoven, and the thickness of the kenaf-imbedded nonwoven strongly affected its water absorption. This is in accordance with that of Das et al. [23]. They analyzed that more air trapped within the nonwoven with high porosity allows faster movement of water through pores. Furthermore, they suggested that this is in accordance with the theory of capillarity. The thermal conductivity of the nonwoven was dependent on its weight and was inversely correlated with its mean pore diameter. In addition, the sound absorption was highly correlated with thickness of the kenaf-imbedded nonwoven, and its

**Porosity Thickness Weight Orientation** 

**(mm) (g/m2**

**)**

**factor**

**106**

**Table 7.**

*nonwoven specimens.*

Sound absorption nonwoven processing conditions. The physical properties of kenaf fiber-imbedded nonwoven were measured and compared according to the blend ratio of the constituent fibers and the different nonwoven processing conditions. The results are summarized as follows.

The breaking and tearing strengths of the kenaf-imbedded nonwoven were dependent on its weight and its mean pore size. Nonwoven specimens with high needle depth and/or a large amount of LM PET exhibited high breaking and tearing strengths. The air permeability was highly dependent on the mean pore diameter of the kenaf-imbedded nonwoven. Nonwoven specimens processed with double carding, three layers of web, and with a needle depth of 16 mm exhibited high air permeability, which was due to high mean pore diameter and low weight. The water absorption of the kenaf-imbedded nonwoven was highly correlated with its mean pore diameter and thickness. A high blend percentage of LM PET fibers reduced the pore size, which resulted in low air permeability and water absorption. The sound absorption coefficient of the kenaf-imbedded nonwoven under high frequency was highly dependent on its thickness and weight and was also partly affected by the pore diameter, i.e., the kenaf-imbedded nonwoven with high thickness and weight exhibited a high sound absorption coefficient, and small-pore nonwoven showed a low sound absorption coefficient, manufactured with high needle depth and/or a high blend ratio of LM PET. In addition, the large-pore nonwoven specimen with high air permeability and water absorption exhibited a low fogging value, which was attributed to the easy flow of VOC gases developed from the nonwoven due to its large pores. Regarding the effects of powder and laminated PU treatment on the physical properties of the kenaf-imbedded nonwoven fabric, the breaking and tearing strengths of the laminated specimens were higher than those of the nonlaminated specimens, and the non-powder-treated specimens exhibited higher breaking and tearing strengths than the powder-treated specimens after PU laminating. The air permeability and water absorption of the non-powder-treated specimens were much higher than those of the powder-treated specimens. Moreover, the laminated and non-powder-treated specimens exhibited higher sound absorption coefficient than did the nonlaminated and powder-treated specimens. On the other hand, the thermal conductivities of the powder-treated and PU-laminated specimens were higher than those of the non-powder-treated and nonlaminated ones.

#### **Author details**

Seung Jin Kim1 \* and Hyun Ah Kim2

1 Department of Fiber System Engineering, Yeungnam University, Gyeongsan, Korea

2 Korea Research Institute for Fashion Industry, Daegu, Korea

\*Address all correspondence to: sjkim@ynu.ac.kr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**109**

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Cotton Science. 1999;**3**:60-70

Journal. 1999;**69**:720-724

[7] Zhang X. Investigation of biodegradable nonwoven composite based on cotton, bagasse and other annual plants [thesis]. Louisiana: Louisiana State University; 2004

[8] Jung JS, Song KH, Kim SH. Mechanical properties and

biodegradability of enzyme-retted kenaf fiber composites. Textile Research Journal. 2018. DOI: 10.1177/0040517518779996

[9] Dunne R, Desai D, Sadiku R, Jayaramudu J. A review of natural fibers, their sustainability and

*Characteristics of Eco-friendly Kenaf Fiber-Imbedded Nonwoven for Automotive Application DOI: http://dx.doi.org/10.5772/intechopen.85367*

#### **References**

*Generation, Development and Modifications of Natural Fibers*

summarized as follows.

nonwoven processing conditions. The physical properties of kenaf fiber-imbedded nonwoven were measured and compared according to the blend ratio of the constituent fibers and the different nonwoven processing conditions. The results are

The breaking and tearing strengths of the kenaf-imbedded nonwoven were dependent on its weight and its mean pore size. Nonwoven specimens with high needle depth and/or a large amount of LM PET exhibited high breaking and tearing strengths. The air permeability was highly dependent on the mean pore diameter of the kenaf-imbedded nonwoven. Nonwoven specimens processed with double carding, three layers of web, and with a needle depth of 16 mm exhibited high air permeability, which was due to high mean pore diameter and low weight. The water absorption of the kenaf-imbedded nonwoven was highly correlated with its mean pore diameter and thickness. A high blend percentage of LM PET fibers reduced the pore size, which resulted in low air permeability and water absorption. The sound absorption coefficient of the kenaf-imbedded nonwoven under high frequency was highly dependent on its thickness and weight and was also partly affected by the pore diameter, i.e., the kenaf-imbedded nonwoven with high thickness and weight exhibited a high sound absorption coefficient, and small-pore nonwoven showed a low sound absorption coefficient, manufactured with high needle depth and/or a high blend ratio of LM PET. In addition, the large-pore nonwoven specimen with high air permeability and water absorption exhibited a low fogging value, which was attributed to the easy flow of VOC gases developed from the nonwoven due to its large pores. Regarding the effects of powder and laminated PU treatment on the physical properties of the kenaf-imbedded nonwoven fabric, the breaking and tearing strengths of the laminated specimens were higher than those of the nonlaminated specimens, and the non-powder-treated specimens exhibited higher breaking and tearing strengths than the powder-treated specimens after PU laminating. The air permeability and water absorption of the non-powder-treated specimens were much higher than those of the powder-treated specimens. Moreover, the laminated and non-powder-treated specimens exhibited higher sound absorption coefficient than did the nonlaminated and powder-treated specimens. On the other hand, the thermal conductivities of the powder-treated and PU-laminated specimens were

**108**

**Author details**

Seung Jin Kim1

Gyeongsan, Korea

provided the original work is properly cited.

\* and Hyun Ah Kim2

\*Address all correspondence to: sjkim@ynu.ac.kr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

higher than those of the non-powder-treated and nonlaminated ones.

1 Department of Fiber System Engineering, Yeungnam University,

2 Korea Research Institute for Fashion Industry, Daegu, Korea

[1] Ramaswamy GN, Craft S, Wartelle L. Uniformity and softness of kenaf fibers for textile products. Textile Research Journal. 1995;**65**:765-770. DOI: 10.1177/004051759506501210

[2] Tao W, Moreau JP, Calamari TA. Properties of nonwoven mats from kenaf fibers. Technical Association of Pulp & Paper. Industry Journal. 1995;**78**:165-169

[3] Lee H, Ahn C, Kim J, Yoo H, Han Y, Song K. The characteristics of kenaf/ rayon fabrics. Journal of the Korean Society of Clothing and Textiles. 2004;**20**:1282-1291

[4] Lee H, Yoo H, Han Y. The properties of kenaf/polyester blended nonwovens. Journal of the Korean Society of Clothing and Textiles. 2007;**31**:1696-1706

[5] Bel-Berger P, Hoven TV, Ramaswamy GN, Kimmel L, Boylston E. Textile technology cotton/kenaf fabrics: A viable natural fabrics. The Journal of Cotton Science. 1999;**3**:60-70

[6] Weiying T, Calamari TA. Preparing and characterizing kenaf/cotton blended fabrics. Textile Research Journal. 1999;**69**:720-724

[7] Zhang X. Investigation of biodegradable nonwoven composite based on cotton, bagasse and other annual plants [thesis]. Louisiana: Louisiana State University; 2004

[8] Jung JS, Song KH, Kim SH. Mechanical properties and biodegradability of enzyme-retted kenaf fiber composites. Textile Research Journal. 2018. DOI: 10.1177/0040517518779996

[9] Dunne R, Desai D, Sadiku R, Jayaramudu J. A review of natural fibers, their sustainability and

automotive applications. Journal of Reinforced Plastics & Composites. 2016;**35**:1041-1050

[10] Thilagavathi G, Pradeep E, Kannaian T, Sasikala L. Development of natural fiber nonwovens for application as car interiors for noise control. Journal of Industrial Textile. 2010;**39**:267. DOI: 10.1177/1528083709347124

[11] Moreau JP, Bel-Berger P, Tao W. Mechanical Processing of Kenaf for Nonwovens. Tappi Journal. 1995;**78**:96-105

[12] Yang JQ, Morisawa J, Sameshima YQ. Kenaf bast fiber treatment for nonwoven fabrics. Sen'l Gakkaichi. 2001;**57**:88-93

[13] Tao W, Calamari TA, Shih FF, Cao C. Characterization of kenaf fiber bundles and their nonwoven mats. Tappi Journal. 1997;**80**:162-166

[14] Tao W, Calamari TA, Crook L. Carding kenaf for nonwovens. Textile Research Journal. 1998;**68**:402-406. DOI: 10.1177/004051759806800603

[15] Fatima S, Mohanty AR. Acoustical and fire-retardant properties of jute composite materials. Applied Acoustic. 2011;**72**:108-114. DOI: 10.1016/j. apacoust.2010.10.005

[16] Fouladi MH, Ayub M, Nor MJM. Analysis of coir fiber acoustical characteristics. Applied Acoustic. 2011;**72**:35-42. DOI: 10.1016/j. apacoust.2010.09.007

[17] Parikh VD, Chen Y, Sun L. Reducing automotive interior noise with natural fiber nonwoven floor covering systems. Textile Research Journal. 2006;**76**:813-820. DOI: 10.1177/0040517506063393

[18] Nick A, Becker U, Thoma W. Improved acoustic behavior of interior parts of renewable resources in the automotive industry. Journal of Polymers and the Environment*.* 2002;**10**:115-118. DOI: 10.1023/A:1021124214818

[19] Lou CW, Lin JH, Su KH. Recycling polyester and polypropylene nonwoven selvages to produce functional sound absorption composites. Textile Research Journal. 2005;**75**:390-394. DOI: 10.1177/0040517505054178

[20] Lee YN, Joo CW. Sound absorption properties of recycled polyester fibrous assembly absorbers. AUTEX Research Journal. 2003;**3**:78-84

[21] Byun HS, Lee TG. A study on the characteristic of sound absorption of the polyester non-woven fabrics used for the automobile sound absorption material. POLYMER-KOREA. 2001;**25**:427-434

[22] Kücük M, Korkmaz Y. The effect of physical parameters on sound absorption properties of natural fiber mixed nonwoven composites. Textile Research Journal. 2012;**82**:2043-2053. DOI: 10.1177/0040517512441987

[23] Dubrovski PD, Brezocnik M. Porosity and nonwoven fabric vertical wicking rate. Fibers and Polymers. 2016;**17**:801-808. DOI: 10.1007/ s12221-016-6347-5

[24] Soukupova V, Boguslavsky L, AnandJiwala RD. Studies on the properties of biodegradable wipes made by the hydroentanglement bonding technique. Textile Research Journal. 2007;**77**:301-311

[25] Dubrovski PD, Brezocnik M. The modelling of porous properties regarding PES/CV-blended nonwoven wipes. Fibers and Polymers. 2012;**13**:363-370. DOI: 10.1177/0040517507078239

[26] Das D, Ishtiaque SM, Das S. Influence of fiber cross-sectional shape on air permeability of nonwovens.

Fibers and Polymers. 2005;**16**:79-85. DOI: 10.1007/s12221-015-0079-9

[27] Tascan M, Vaughn EA. Effects of total surface area and fabric density on the acoustical behavior of needlepunched nonwoven fabrics. Textile Research Journal. 2008;**78**:289-296. DOI: 10.1177/0040517507084283

[28] CSIRO Division of Wool Technology. The FAST system for the objective measurement of fabric properties. Operation. Interpretation and Application, CDW Technology. Geelong, Australia; 1989

[29] Rawal A, Lomov S, Ngo T, Verpoest I, Vankerre brouck J. Mechanical behavior of thru-air bonded nonwoven structures. Textile Research Journal. 2007;**77**:417-431

[30] Das D, Ishtiaque SM, Ajab Rao SV, Pourdeyhimi B. Modelling and experimental studies of air permeability of nonuniform nonwoven fibrous porous media. Fibers and Polymers. 2013;**14**:494-499

**111**

**Chapter 6**

**Abstract**

biomaterials

**1. Introduction**

*and Hem Raj Pant*

3D Nonwoven Fabrics for

*Mahesh Kumar Joshi, Rajeshwar Man Shrestha*

Fibrous materials are attractive for biomedical applications owing to their structural superiorities, which include large surface-area-to-volume ratio, high porosity, and pore interconnectivity in a controlled manner. Among the various methods of fiber fabrication, electrospinning has emerged as an attractive nanotechnology to produce ultrafine fibrous materials for myriad applications, including tissue scaffolding. In this technique, processing parameters, such as the solution properties, tip-to-collector distance, applied voltage, etc., can be tailored to obtain the fibers of the desired morphology and physicochemical properties. Ideal scaffolds should meet the basic requirements, such as three-dimensional (3D) architecture, proper mechanical properties and biodegradability, and the sufficient surface characteristics for cell adhesion and proliferation. However, most of the electrospun nanofiber-based scaffolds have densely packed two-dimensional (2D) array which hinders the cell infiltration and growth throughout the scaffolds, thereby limiting their applicability in tissue regeneration. To overcome this problem, several attempts have been made to develop a biomimetic three-dimensional, nanofibrous scaffold. This chapter deals with noble techniques including gas foaming (GF), charge repulsion-assisted fabrication, post-processing, liquid-assisted collection, collector modification, and porogen-assisted methods for the fabrication of 3D

**Keywords:** electrospinning, tissue engineering, nano−/microfiber, 3D scaffold,

The fields of tissue engineering and regenerative medicine aim at promoting the regeneration of tissues or replacing the malfunctioning organs using a scaffold material. The development of scaffolds that mimic the composition and structure of natural extracellular matrix (ECM) is highly demanded in biomedical sciences. A scaffold used for tissue engineering is considered as an artificial extracellular matrix that provides mechanical support for neo-tissue formation in vitro and/or through the initial period after implantation during cell proliferation and differentiation. In addition to contributing to mechanical integrity, the ECM has an important role in signaling and regularity functions in development, maintenance, and regeneration of tissues [1]. It has long been demonstrated that the composition and architecture of a scaffold influence the cell-environment interactions that determine the effectiveness

Biomedical Applications

nanofibrous scaffold for biomedical applications.

#### **Chapter 6**

*Generation, Development and Modifications of Natural Fibers*

Fibers and Polymers. 2005;**16**:79-85. DOI: 10.1007/s12221-015-0079-9

[27] Tascan M, Vaughn EA. Effects of total surface area and fabric density on the acoustical behavior of needlepunched nonwoven fabrics. Textile Research Journal. 2008;**78**:289-296. DOI: 10.1177/0040517507084283

[28] CSIRO Division of Wool Technology. The FAST system for the objective measurement of fabric properties. Operation. Interpretation and Application, CDW Technology.

Geelong, Australia; 1989

2007;**77**:417-431

2013;**14**:494-499

[29] Rawal A, Lomov S, Ngo T, Verpoest I, Vankerre brouck J. Mechanical behavior of thru-air bonded nonwoven structures. Textile Research Journal.

[30] Das D, Ishtiaque SM, Ajab Rao SV,

experimental studies of air permeability of nonuniform nonwoven fibrous porous media. Fibers and Polymers.

Pourdeyhimi B. Modelling and

parts of renewable resources in the automotive industry. Journal of Polymers and the Environment*.* 2002;**10**:115-118.

[19] Lou CW, Lin JH, Su KH. Recycling polyester and polypropylene nonwoven selvages to produce functional sound absorption composites. Textile Research

[20] Lee YN, Joo CW. Sound absorption properties of recycled polyester fibrous assembly absorbers. AUTEX Research

[21] Byun HS, Lee TG. A study on the characteristic of sound absorption of the polyester non-woven fabrics used for the automobile sound absorption material. POLYMER-KOREA.

[22] Kücük M, Korkmaz Y. The effect of physical parameters on sound absorption properties of natural fiber mixed nonwoven composites. Textile Research Journal. 2012;**82**:2043-2053. DOI: 10.1177/0040517512441987

[23] Dubrovski PD, Brezocnik M. Porosity and nonwoven fabric vertical wicking rate. Fibers and Polymers. 2016;**17**:801-808. DOI: 10.1007/

[24] Soukupova V, Boguslavsky L, AnandJiwala RD. Studies on the

properties of biodegradable wipes made by the hydroentanglement bonding technique. Textile Research Journal.

[25] Dubrovski PD, Brezocnik M. The modelling of porous properties regarding PES/CV-blended nonwoven wipes. Fibers and Polymers. 2012;**13**:363-370. DOI: 10.1177/0040517507078239

[26] Das D, Ishtiaque SM, Das S.

Influence of fiber cross-sectional shape on air permeability of nonwovens.

DOI: 10.1023/A:1021124214818

Journal. 2005;**75**:390-394. DOI: 10.1177/0040517505054178

Journal. 2003;**3**:78-84

2001;**25**:427-434

s12221-016-6347-5

2007;**77**:301-311

**110**

## 3D Nonwoven Fabrics for Biomedical Applications

*Mahesh Kumar Joshi, Rajeshwar Man Shrestha and Hem Raj Pant*

#### **Abstract**

Fibrous materials are attractive for biomedical applications owing to their structural superiorities, which include large surface-area-to-volume ratio, high porosity, and pore interconnectivity in a controlled manner. Among the various methods of fiber fabrication, electrospinning has emerged as an attractive nanotechnology to produce ultrafine fibrous materials for myriad applications, including tissue scaffolding. In this technique, processing parameters, such as the solution properties, tip-to-collector distance, applied voltage, etc., can be tailored to obtain the fibers of the desired morphology and physicochemical properties. Ideal scaffolds should meet the basic requirements, such as three-dimensional (3D) architecture, proper mechanical properties and biodegradability, and the sufficient surface characteristics for cell adhesion and proliferation. However, most of the electrospun nanofiber-based scaffolds have densely packed two-dimensional (2D) array which hinders the cell infiltration and growth throughout the scaffolds, thereby limiting their applicability in tissue regeneration. To overcome this problem, several attempts have been made to develop a biomimetic three-dimensional, nanofibrous scaffold. This chapter deals with noble techniques including gas foaming (GF), charge repulsion-assisted fabrication, post-processing, liquid-assisted collection, collector modification, and porogen-assisted methods for the fabrication of 3D nanofibrous scaffold for biomedical applications.

**Keywords:** electrospinning, tissue engineering, nano−/microfiber, 3D scaffold, biomaterials

#### **1. Introduction**

The fields of tissue engineering and regenerative medicine aim at promoting the regeneration of tissues or replacing the malfunctioning organs using a scaffold material. The development of scaffolds that mimic the composition and structure of natural extracellular matrix (ECM) is highly demanded in biomedical sciences. A scaffold used for tissue engineering is considered as an artificial extracellular matrix that provides mechanical support for neo-tissue formation in vitro and/or through the initial period after implantation during cell proliferation and differentiation. In addition to contributing to mechanical integrity, the ECM has an important role in signaling and regularity functions in development, maintenance, and regeneration of tissues [1]. It has long been demonstrated that the composition and architecture of a scaffold influence the cell-environment interactions that determine the effectiveness

of the scaffold [2]. The scaffold material must be able to interact with cells in three dimensions and should facilitate the communication. The main goal of tissue engineering is to enable the body to heal itself by regenerating "neo-native" functional tissues [3, 4]. A highly porous scaffold is necessary to control tissue formation in three-dimensional (3D) architecture in a typical tissue engineering approach. The scaffolds provide the microenvironment (synthetic temporary extracellular matrix) for cell attachment, proliferation, differentiation, and neo-tissue genesis. Therefore, the material used for tissue scaffolding must function without interrupting other physiological processes, that is, the scaffold must not promote or initiate any adverse tissue reaction [5]. Furthermore, the scaffold must have an ability to promote normal cell growth and differentiation while maintaining a three-dimensional orientation/ space for the cells.

Recently, various materials including ceramics, metals, and polymers have been exploited to develop the scaffolds for tissue regeneration. Although the inorganic/ ceramic materials such as hydroxyapatite (HAP) or calcium phosphates are excellent choices for medical implants due to their good osteoconductivity and studied for mineralized tissue engineering, they are disadvantageous due to poor processability into highly porous structures and brittleness. Certain metals have superior mechanical properties and are preferred for medical implants. However, the lack of degradability in a biological environment limits their applications for tissue scaffolding [6]. In contrast, polymers have been extensively studied in various tissue engineering applications, including bone tissue engineering, due to the great design flexibility and structure which can be tailored to the specific needs [6, 7].

Recently, researches in biomaterials have turned to nanotechnology, specifically nanofibers, as the solution to the development of tissue engineering scaffolds and wound repair/care products. At present, few processing techniques are successful in producing nonwoven fibers and subsequent scaffolds on the nanoscale [8]. In basic terms, a nonwoven is a fabric or web composed of fibers. The orientation and properties of the fibers and fabric can be controlled to mimic the native cellular structures, such as collagen fibers of the extracellular matrix. Development and characterization of these nanofibrous structures for tissue engineering applications is crucial in understanding the cell-ECM interactions. Conventional polymer processing techniques are efficient in producing fibers, which are several orders of magnitude larger than the native ECM. Therefore, there has been a concerted effort to develop methods of producing nanofibers that closely mimics to the ECM geometry. In this endeavor, five distinct techniques have proven successful in producing nanofibrous tissue engineering structures: self-assembly, phase separation, melt blowing, drawing, and electrospinning.

Melt blowing and spunbond nonwovens are composed of continuous fiber filaments fabricated by forcing molten thermoplastic polymer through very fine orifices arranged in a spin beam. Melt blowing is a simple, versatile, and one-step process for the production of polymeric fibers in micrometer and smaller scale. During melt blowing and spunbond process, fibers are produced in a single step by extruding a polymer melt through an orifice die. In the melt blowing process, the filaments are drawn and accelerated toward the collector screen via hot air knives, keeping the filaments in a molten state, allowing for fine fiber attenuation. Collected fibers are still in a tacky state, allowing self-bonding between fibers. Conversely, in the spunbond process, as the filaments exit the spin beam, they are rapidly solidified by cool air before being drawn pneumatically. Spunbond and melt blowing techniques can be implemented from lab, pilot, and full production scale. Another method for generation of nonwoven fabric is carding technology. This is a mechanical process that disentangles, cleans, and intermixes fibers to produce a continuous web. In the carding process, short fibers of a few inches

**113**

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

the three-dimensional electrospun nanofibrous scaffolds.

**2. Electrospinning**

Manley [10, 11].

during the past decade.

in length (staple fibers) are separated and entangled by a series of specialized combed rollers to form an unbonded web. Unlike spunbond and melt-blown processing that require a thermoplastic polymer for melt spinning, a variety of fiber materials can be processed via carding technology, including natural and synthetic polymers, glass, and metal fibers. The high-speed, repeatable, economical production capabilities of these techniques make them attractive candidates for the commercial production of nonwoven-based tissue engineering scaffolding materials. The main disadvantages of nonwoven webs generated by these techniques are their large fiber diameters which hinder the cell attachment, proliferation, and neotissue generation, thereby limiting their application as tissue scaffolding material. Among the various techniques, electrospinning is the facile nonwoven manufacturing method and has recently gained significant interest as a method of scaffold fabrication. The size scale of electrospun fibers mimics to the native ECM and provides an ideal environment for cell proliferation, attachment, and differentiation into the target tissue. However, the fabrication of large-scale electrospun scaffolds using conventional technique is time-consuming and difficult to generate 3D microstructures. This chapter focuses on recent advances in the fabrication of

Electrospinning employs electrostatic force to draw a fiber from a spinneret. This fiber solidifies and lies down on a collector in the form of a nonwoven fibrous mesh. Recently, electrospinning has attracted much attention because of its low processing cost and tailorable fiber morphology and fiber diameter. Furthermore, synthetic and natural polymers can be processed into the fiber of different diameters at ambient conditions. However the electrospinning technology has been known for a long time; the practice of this technology remained largely dormant until the 1970s. Morton received the first US patent for the electrospinning of artificial fibers in 1902. Zeleny presented one of the earliest studies of the electrified jetting phenomenon in 1914 [9]. Later on, Formhals filed a series of patents on the processing and apparatus in the decades of the 1930s and 1940s to produce electrospun fibers. Only a few publications appeared in electrospinning research during the 1970s and 1980s, notably by Baumgarten and by Larrondo and St. John

The electrospinning research has gained significant interest when Doshi and Reneker prepared submicron fibers in the 1990s [12]. Since then it has been demonstrated that almost all materials that can be spun from melt or solution by conventional methods can be electrospun into fibers. On account of the remarkable simplicity, versatility, and potential applications of this technique in a variety of fields, the number of publications in this field has been increasing exponentially

The principle of electrospinning involves a high voltage applied between a pendant polymer droplet and a metal target as the counter electrode [13]. Under the electrostatic force, the pendant polymer droplet is deformed from a hemispherical shape to a conical shape which is called as Taylor cone [14]. A thin polymer jet is initiated and travels toward the metal target once the electrostatic force reaches a critical value to overcome the surface tension of the polymer droplet. The charged thin polymer jet is elongated and undergoes a bending instability region where it whips swiftly in the air by the electric field [15]. The thin polymer jet is further stretched due to the evaporation of the solvent during this period and finally deposits on the metal target

as a randomly oriented nanofibrous membrane as shown in **Figures 1** and **2**.

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*Generation, Development and Modifications of Natural Fibers*

space for the cells.

of the scaffold [2]. The scaffold material must be able to interact with cells in three dimensions and should facilitate the communication. The main goal of tissue engineering is to enable the body to heal itself by regenerating "neo-native" functional tissues [3, 4]. A highly porous scaffold is necessary to control tissue formation in three-dimensional (3D) architecture in a typical tissue engineering approach. The scaffolds provide the microenvironment (synthetic temporary extracellular matrix) for cell attachment, proliferation, differentiation, and neo-tissue genesis. Therefore, the material used for tissue scaffolding must function without interrupting other physiological processes, that is, the scaffold must not promote or initiate any adverse tissue reaction [5]. Furthermore, the scaffold must have an ability to promote normal cell growth and differentiation while maintaining a three-dimensional orientation/

Recently, various materials including ceramics, metals, and polymers have been exploited to develop the scaffolds for tissue regeneration. Although the inorganic/ ceramic materials such as hydroxyapatite (HAP) or calcium phosphates are excellent choices for medical implants due to their good osteoconductivity and studied for mineralized tissue engineering, they are disadvantageous due to poor processability into highly porous structures and brittleness. Certain metals have superior mechanical properties and are preferred for medical implants. However, the lack of degradability in a biological environment limits their applications for tissue scaffolding [6]. In contrast, polymers have been extensively studied in various tissue engineering applications, including bone tissue engineering, due to the great design

Recently, researches in biomaterials have turned to nanotechnology, specifically nanofibers, as the solution to the development of tissue engineering scaffolds and wound repair/care products. At present, few processing techniques are successful in producing nonwoven fibers and subsequent scaffolds on the nanoscale [8]. In basic terms, a nonwoven is a fabric or web composed of fibers. The orientation and properties of the fibers and fabric can be controlled to mimic the native cellular structures, such as collagen fibers of the extracellular matrix. Development and characterization of these nanofibrous structures for tissue engineering applications is crucial in understanding the cell-ECM interactions. Conventional polymer processing techniques are efficient in producing fibers, which are several orders of magnitude larger than the native ECM. Therefore, there has been a concerted effort to develop methods of producing nanofibers that closely mimics to the ECM geometry. In this endeavor, five distinct techniques have proven successful in producing nanofibrous tissue engineering structures: self-assembly, phase separation, melt

Melt blowing and spunbond nonwovens are composed of continuous fiber filaments fabricated by forcing molten thermoplastic polymer through very fine orifices arranged in a spin beam. Melt blowing is a simple, versatile, and one-step process for the production of polymeric fibers in micrometer and smaller scale. During melt blowing and spunbond process, fibers are produced in a single step by extruding a polymer melt through an orifice die. In the melt blowing process, the filaments are drawn and accelerated toward the collector screen via hot air knives, keeping the filaments in a molten state, allowing for fine fiber attenuation. Collected fibers are still in a tacky state, allowing self-bonding between fibers. Conversely, in the spunbond process, as the filaments exit the spin beam, they are rapidly solidified by cool air before being drawn pneumatically. Spunbond and melt blowing techniques can be implemented from lab, pilot, and full production scale. Another method for generation of nonwoven fabric is carding technology. This is a mechanical process that disentangles, cleans, and intermixes fibers to produce a continuous web. In the carding process, short fibers of a few inches

flexibility and structure which can be tailored to the specific needs [6, 7].

blowing, drawing, and electrospinning.

**112**

in length (staple fibers) are separated and entangled by a series of specialized combed rollers to form an unbonded web. Unlike spunbond and melt-blown processing that require a thermoplastic polymer for melt spinning, a variety of fiber materials can be processed via carding technology, including natural and synthetic polymers, glass, and metal fibers. The high-speed, repeatable, economical production capabilities of these techniques make them attractive candidates for the commercial production of nonwoven-based tissue engineering scaffolding materials. The main disadvantages of nonwoven webs generated by these techniques are their large fiber diameters which hinder the cell attachment, proliferation, and neotissue generation, thereby limiting their application as tissue scaffolding material.

Among the various techniques, electrospinning is the facile nonwoven manufacturing method and has recently gained significant interest as a method of scaffold fabrication. The size scale of electrospun fibers mimics to the native ECM and provides an ideal environment for cell proliferation, attachment, and differentiation into the target tissue. However, the fabrication of large-scale electrospun scaffolds using conventional technique is time-consuming and difficult to generate 3D microstructures. This chapter focuses on recent advances in the fabrication of the three-dimensional electrospun nanofibrous scaffolds.

#### **2. Electrospinning**

Electrospinning employs electrostatic force to draw a fiber from a spinneret. This fiber solidifies and lies down on a collector in the form of a nonwoven fibrous mesh. Recently, electrospinning has attracted much attention because of its low processing cost and tailorable fiber morphology and fiber diameter. Furthermore, synthetic and natural polymers can be processed into the fiber of different diameters at ambient conditions. However the electrospinning technology has been known for a long time; the practice of this technology remained largely dormant until the 1970s. Morton received the first US patent for the electrospinning of artificial fibers in 1902. Zeleny presented one of the earliest studies of the electrified jetting phenomenon in 1914 [9]. Later on, Formhals filed a series of patents on the processing and apparatus in the decades of the 1930s and 1940s to produce electrospun fibers. Only a few publications appeared in electrospinning research during the 1970s and 1980s, notably by Baumgarten and by Larrondo and St. John Manley [10, 11].

The electrospinning research has gained significant interest when Doshi and Reneker prepared submicron fibers in the 1990s [12]. Since then it has been demonstrated that almost all materials that can be spun from melt or solution by conventional methods can be electrospun into fibers. On account of the remarkable simplicity, versatility, and potential applications of this technique in a variety of fields, the number of publications in this field has been increasing exponentially during the past decade.

The principle of electrospinning involves a high voltage applied between a pendant polymer droplet and a metal target as the counter electrode [13]. Under the electrostatic force, the pendant polymer droplet is deformed from a hemispherical shape to a conical shape which is called as Taylor cone [14]. A thin polymer jet is initiated and travels toward the metal target once the electrostatic force reaches a critical value to overcome the surface tension of the polymer droplet. The charged thin polymer jet is elongated and undergoes a bending instability region where it whips swiftly in the air by the electric field [15]. The thin polymer jet is further stretched due to the evaporation of the solvent during this period and finally deposits on the metal target as a randomly oriented nanofibrous membrane as shown in **Figures 1** and **2**.

**Figure 1.** *Schematic illustration of electrospinning setups.*

**Figure 2.** *(a) Photograph of electrospinning jet. (b) Schematic representation for the formation of electrospun nanofibers.*

The electrospinning process is characterized by three major regions: (1) the cone region, (2) the steady jet region, and (3) the instability region. A pendant drop of a fluid is charged at the tip of the nozzle at the initial stage of electrospinning which deforms the droplet into a conical shape, just before jetting occurs. The conical shape is called the Taylor cone, named after G**.** Taylor who has studied this electrified fluid phenomenon [14]. At a critical electrical stress, a fluid jet is ejected from the apex of the cone. The diameter of the jet at the apex is about 100 micrometers. In the steady jet region, the jet can travel in a straight path anywhere from 1 to 20 centimeters. For a fluid that is a solution, real-time spectroscopic data shows that the loss of solvent due to evaporation in this portion of the jet is negligible. In the

**115**

nutrients and waste.

**4. Gas-foaming technique**

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

uniformity, and porosity.

**3. Development of 3D scaffolds**

categories and functions of the original native tissues [17].

called bending or whipping instability (**Figure 2**) [15].

final region, the jet deviates from its straight path and undergoes an instability

Several parameters influence the electrospinning process: polymer solution parameters, processing parameters, and ambient parameters. Extensive polymer chain entanglement is necessary for the fiber formation during electrospinning process; otherwise the polymer solution is electrosprayed into small droplets or forms fibers with large beaded polymer aggregates. Low molecular weight polymers are often difficult to electrospun because of their inability for chain entanglements, while higher molecular weight polymers often cause large changes in solution viscosity, thus increasing the surface tension of the droplet and limiting the ability to electrospun. The choice of solvent is another important processing parameter; the solvent should be nontoxic and should evaporate within the distance from the spinneret to the grounded collector. The processing parameters such as distance between spinneret and collector, solution flow rate, humidity, and voltage intensity (∼a few kV–40 kV) have substantial influence on the morphology, fiber size and

The tissue engineering scaffolds should closely resemble to native extracellular matrices (ECMs) that provide structural support to cells. The primary role of the scaffold is to provide the temporary support until the neo-tissue formation. The scaffolds that closely mimics to the topographies and spatial structures of ECM are efficient for the cell proliferation and differentiation. The morphologies of ECMs vary according to the functions of the target tissues. Fibrous structures with 3D orientation and random distribution are found in native ECMs in the breast, liver, bladder, lung, and many other organs and tissues [16]. Therefore, it is reasonable to fabricate scaffolds with particular morphologies and structures according to

Electrospinning is a simple method to fabricate the nano−/microfibers in a continuous process. The electrospinning parameters and instrumental setups can be tailored to fabricate micro−/nanofibers with desired morphologies, such as aligned fibrous array, fiber diameter, and fibrous patterns. Therefore, electrospinning has gained significant attention to fabricate tissue engineering scaffolds composed of nano- or submicrometer fibers from numerous materials [18]. However, the conventional electrospinning method produces two-dimensional (2D) sheet-like membranes with small pore and tightly packed fibrous layers that limits the cell infiltration and growth to the depth of the scaffolds [19–22]; cells mainly spread and distribute on the surface of 2D nanofibrous membrane [23]. Since most human tissues and organs possess three-dimensional microgeometry holding intrinsic functionality, developing three-dimensional structure has drawn a great interest in the search of the tissue surrogates. 3D fibrous scaffolds with macroporous, open structure facilitate the neo-tissue formation, thereby providing biomimetic environment for the cell infiltration, the cell proliferation, and the transportation of

Among the process technologies that have been developed and successfully implemented for the design of TE scaffolds, gas foaming (GF) has recently attracted much attention. The gas-foaming technique utilizes the nucleation and

#### *3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*Generation, Development and Modifications of Natural Fibers*

The electrospinning process is characterized by three major regions: (1) the cone region, (2) the steady jet region, and (3) the instability region. A pendant drop of a fluid is charged at the tip of the nozzle at the initial stage of electrospinning which deforms the droplet into a conical shape, just before jetting occurs. The conical shape is called the Taylor cone, named after G**.** Taylor who has studied this electrified fluid phenomenon [14]. At a critical electrical stress, a fluid jet is ejected from the apex of the cone. The diameter of the jet at the apex is about 100 micrometers. In the steady jet region, the jet can travel in a straight path anywhere from 1 to 20 centimeters. For a fluid that is a solution, real-time spectroscopic data shows that the loss of solvent due to evaporation in this portion of the jet is negligible. In the

*(a) Photograph of electrospinning jet. (b) Schematic representation for the formation of electrospun nanofibers.*

**114**

**Figure 2.**

**Figure 1.**

*Schematic illustration of electrospinning setups.*

final region, the jet deviates from its straight path and undergoes an instability called bending or whipping instability (**Figure 2**) [15].

Several parameters influence the electrospinning process: polymer solution parameters, processing parameters, and ambient parameters. Extensive polymer chain entanglement is necessary for the fiber formation during electrospinning process; otherwise the polymer solution is electrosprayed into small droplets or forms fibers with large beaded polymer aggregates. Low molecular weight polymers are often difficult to electrospun because of their inability for chain entanglements, while higher molecular weight polymers often cause large changes in solution viscosity, thus increasing the surface tension of the droplet and limiting the ability to electrospun. The choice of solvent is another important processing parameter; the solvent should be nontoxic and should evaporate within the distance from the spinneret to the grounded collector. The processing parameters such as distance between spinneret and collector, solution flow rate, humidity, and voltage intensity (∼a few kV–40 kV) have substantial influence on the morphology, fiber size and uniformity, and porosity.

#### **3. Development of 3D scaffolds**

The tissue engineering scaffolds should closely resemble to native extracellular matrices (ECMs) that provide structural support to cells. The primary role of the scaffold is to provide the temporary support until the neo-tissue formation. The scaffolds that closely mimics to the topographies and spatial structures of ECM are efficient for the cell proliferation and differentiation. The morphologies of ECMs vary according to the functions of the target tissues. Fibrous structures with 3D orientation and random distribution are found in native ECMs in the breast, liver, bladder, lung, and many other organs and tissues [16]. Therefore, it is reasonable to fabricate scaffolds with particular morphologies and structures according to categories and functions of the original native tissues [17].

Electrospinning is a simple method to fabricate the nano−/microfibers in a continuous process. The electrospinning parameters and instrumental setups can be tailored to fabricate micro−/nanofibers with desired morphologies, such as aligned fibrous array, fiber diameter, and fibrous patterns. Therefore, electrospinning has gained significant attention to fabricate tissue engineering scaffolds composed of nano- or submicrometer fibers from numerous materials [18]. However, the conventional electrospinning method produces two-dimensional (2D) sheet-like membranes with small pore and tightly packed fibrous layers that limits the cell infiltration and growth to the depth of the scaffolds [19–22]; cells mainly spread and distribute on the surface of 2D nanofibrous membrane [23]. Since most human tissues and organs possess three-dimensional microgeometry holding intrinsic functionality, developing three-dimensional structure has drawn a great interest in the search of the tissue surrogates. 3D fibrous scaffolds with macroporous, open structure facilitate the neo-tissue formation, thereby providing biomimetic environment for the cell infiltration, the cell proliferation, and the transportation of nutrients and waste.

#### **4. Gas-foaming technique**

Among the process technologies that have been developed and successfully implemented for the design of TE scaffolds, gas foaming (GF) has recently attracted much attention. The gas-foaming technique utilizes the nucleation and growth of gas bubbles dispersed into a viscous polymer solution for the creation of porosity [24]. The gas bubbles are generated in situ either via chemical reaction or by adding inert gases to the polymer phase at different physical environments. The gas-foaming agents are generally released from a pre-saturated gas-polymer mixture resulting in the formation of 3D porous architectures [24]. A supercritical fluid, that is, a fluid above its critical point, such as carbon dioxide, is commonly used for gas-foaming purpose because of its non-flammability, non-toxicity, and moderate critical point (31.1°C and 73.8 bar). Supercritical fluids can be used to form gas-saturated polymer phase by varying the temperature and pressure [25]. In the process, high-pressure CO2 gas is subjected to solid polymer disks to allow saturation of CO2 in the polymer. In this process, the nucleation and growth of CO2 gas bubbles in the material creates the thermodynamic instability and yields mostly a nonporous surface with closed-pore structure. The main limitation of this technique is that it produces the nonporous surface with closed-pore structure with only 10–30% of interconnected pores [26]. Recently, particulate leaching technique has been combined with the gas-foaming process to improve the inter-pore connectivity, although completely eliminating closed pores remains challenging [26].

Recently, Joshi et al. have developed the novel gas-foaming technique to modify the densely packed 2D electrospun membranes into low-density three-dimensional nanofibrous scaffolds [19, 27]. In this technique, authors put the electrospun nanofibrous mat in an aqueous sodium borohydride (SB) solution where the interconnected pores of a mat were filled with the SB solution. The SB solution undergoes the hydrolysis in situ in the nano−/micropores of the nanofibrous mat and produces the hydrogen gas. As generated H2 gas molecules nucleated to form clusters that reorganize the nanofibers into multilayered 3D scaffold with low-density, macroporous spongy structure (**Figure 3**). In their study, nanofibrous membranes of various polymers were prepared via electrospinning and treated with sodium borohydride solution that was prepared in different solvents. They demonstrate that the solvent for sodium borohydride (either water or methanol) plays a crucial role in the fabrication of 3D scaffolds. The electrospun membranes of polar polymers were processed into 3D architecture in aqueous SB solution, while methanolic solution of SB can be used for both polar and nonpolar polymers. The fabrication process is fast in methanol solution compared to an aqueous solution which is attributed due to the

#### **Figure 3.**

*Schematic illustration for the formation of low-density, macroporous, spongy, and multilayered 3D scaffolds. Reproduced with permission from Ref. [19].*

**117**

**Figure 4.**

*[31] and right [19].*

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

fibrous scaffold [30].

**5. Multilayering electrospinning**

rapid evolution of hydrogen gas from the methanolysis reaction compared to the hydrolysis reaction. This method forms the large pores with multilayered structure that mimics to the ECM. Similarly, Zhao et al. immersed the 2D PCL nanofibrous mat in a NaBH4/methanol solution inside a 3D-printed mold and obtained the 3D nanofibrous scaffolds with controllable geometric shapes [28]. Xie et al. also used the NaBH4 solution as gas source to expand the 2D PCL electrospun mat followed by freeze-drying and obtained 3D PCL scaffolds with highly ordered architecture with controllable gas widths and layered structure as a result [29]. Lee et al. combined electrospinning with salt leaching/gas foaming and developed micro-sized pores in poly(L-lactic acid) (PLLA)/montmorillonite (MMT) nanocomposite

The thickness of the electrospun can be increased by increasing the spinning time during the conventional electrospinning process, leading to the 3D fibrous structure. 3D multilayered fibrous membranes of different materials can be fabricated by a sequential electrospinning or co-electrospinning, and post-processing and sometimes an auxiliary electric field is even used to converge the collected fibers into a confined space to produce 3D fibrous structures [19] (**Figure 4**). Pham et al. [32] prepared layer-on-layer stacks including alternating layers of PCL microfibers and PCL nanofibers. This proposed 3D structure combined the beneficial properties of nanofibers with that of microfibers. The thickness of the nanofiber layers is modulated by electrospinning the nanofiber layers for different lengths of time. They demonstrated that cell infiltration and growth in a multilayered scaffold depends upon the thickness of each layer; increasing the thickness of the nanofiber layer reduced the cell infiltration of the scaffold. Han et al. [33] fabricated the electrospun 3D scaffold of cellulose acetate with three different layers (dense layer, cellular layer, and porous layer) by varying the solutions and processing parameters. In this technique, the total number of layers in multilayered scaffold can be controlled. Furthermore, the composition, the fiber diameter, and the porosity of each electrospun fiber layer can be tailored that affects cell proliferation, migration, and/or differentiation on a scaffold. Erisken et al. [34] reported the functionally graded electrospun PCL and β-tricalcium phosphate (β-TCP) nanocomposites using a hybrid twin-screw extrusion/electrospinning process. Soliman et al. [35] fabricated 3D scaffolds of layered composites with mixed nano- and microscale PCL fibers by modifying the electrospinning setup with two parallel syringes and an actuated collector (co-electrospin-

ning with scalability and modularity from an industrial perspective).

*SEM images showing the cross-sectional view of the multilayered scaffold. Reproduced with permission from* 

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*Generation, Development and Modifications of Natural Fibers*

growth of gas bubbles dispersed into a viscous polymer solution for the creation of porosity [24]. The gas bubbles are generated in situ either via chemical reaction or by adding inert gases to the polymer phase at different physical environments. The gas-foaming agents are generally released from a pre-saturated gas-polymer mixture resulting in the formation of 3D porous architectures [24]. A supercritical fluid, that is, a fluid above its critical point, such as carbon dioxide, is commonly used for gas-foaming purpose because of its non-flammability, non-toxicity, and moderate critical point (31.1°C and 73.8 bar). Supercritical fluids can be used to form gas-saturated polymer phase by varying the temperature and pressure [25]. In the process, high-pressure CO2 gas is subjected to solid polymer disks to allow saturation of CO2 in the polymer. In this process, the nucleation and growth of CO2 gas bubbles in the material creates the thermodynamic instability and yields mostly a nonporous surface with closed-pore structure. The main limitation of this technique is that it produces the nonporous surface with closed-pore structure with only 10–30% of interconnected pores [26]. Recently, particulate leaching technique has been combined with the gas-foaming process to improve the inter-pore connectivity, although completely eliminating closed pores remains challenging [26].

Recently, Joshi et al. have developed the novel gas-foaming technique to modify the densely packed 2D electrospun membranes into low-density three-dimensional nanofibrous scaffolds [19, 27]. In this technique, authors put the electrospun nanofibrous mat in an aqueous sodium borohydride (SB) solution where the interconnected pores of a mat were filled with the SB solution. The SB solution undergoes the hydrolysis in situ in the nano−/micropores of the nanofibrous mat and produces the hydrogen gas. As generated H2 gas molecules nucleated to form clusters that reorganize the nanofibers into multilayered 3D scaffold with low-density, macroporous spongy structure (**Figure 3**). In their study, nanofibrous membranes of various polymers were prepared via electrospinning and treated with sodium borohydride solution that was prepared in different solvents. They demonstrate that the solvent for sodium borohydride (either water or methanol) plays a crucial role in the fabrication of 3D scaffolds. The electrospun membranes of polar polymers were processed into 3D architecture in aqueous SB solution, while methanolic solution of SB can be used for both polar and nonpolar polymers. The fabrication process is fast in methanol solution compared to an aqueous solution which is attributed due to the

*Schematic illustration for the formation of low-density, macroporous, spongy, and multilayered 3D scaffolds.* 

**116**

**Figure 3.**

*Reproduced with permission from Ref. [19].*

rapid evolution of hydrogen gas from the methanolysis reaction compared to the hydrolysis reaction. This method forms the large pores with multilayered structure that mimics to the ECM. Similarly, Zhao et al. immersed the 2D PCL nanofibrous mat in a NaBH4/methanol solution inside a 3D-printed mold and obtained the 3D nanofibrous scaffolds with controllable geometric shapes [28]. Xie et al. also used the NaBH4 solution as gas source to expand the 2D PCL electrospun mat followed by freeze-drying and obtained 3D PCL scaffolds with highly ordered architecture with controllable gas widths and layered structure as a result [29]. Lee et al. combined electrospinning with salt leaching/gas foaming and developed micro-sized pores in poly(L-lactic acid) (PLLA)/montmorillonite (MMT) nanocomposite fibrous scaffold [30].

#### **5. Multilayering electrospinning**

The thickness of the electrospun can be increased by increasing the spinning time during the conventional electrospinning process, leading to the 3D fibrous structure. 3D multilayered fibrous membranes of different materials can be fabricated by a sequential electrospinning or co-electrospinning, and post-processing and sometimes an auxiliary electric field is even used to converge the collected fibers into a confined space to produce 3D fibrous structures [19] (**Figure 4**). Pham et al. [32] prepared layer-on-layer stacks including alternating layers of PCL microfibers and PCL nanofibers. This proposed 3D structure combined the beneficial properties of nanofibers with that of microfibers. The thickness of the nanofiber layers is modulated by electrospinning the nanofiber layers for different lengths of time. They demonstrated that cell infiltration and growth in a multilayered scaffold depends upon the thickness of each layer; increasing the thickness of the nanofiber layer reduced the cell infiltration of the scaffold. Han et al. [33] fabricated the electrospun 3D scaffold of cellulose acetate with three different layers (dense layer, cellular layer, and porous layer) by varying the solutions and processing parameters. In this technique, the total number of layers in multilayered scaffold can be controlled. Furthermore, the composition, the fiber diameter, and the porosity of each electrospun fiber layer can be tailored that affects cell proliferation, migration, and/or differentiation on a scaffold. Erisken et al. [34] reported the functionally graded electrospun PCL and β-tricalcium phosphate (β-TCP) nanocomposites using a hybrid twin-screw extrusion/electrospinning process. Soliman et al. [35] fabricated 3D scaffolds of layered composites with mixed nano- and microscale PCL fibers by modifying the electrospinning setup with two parallel syringes and an actuated collector (co-electrospinning with scalability and modularity from an industrial perspective).

#### **Figure 4.**

*SEM images showing the cross-sectional view of the multilayered scaffold. Reproduced with permission from [31] and right [19].*

## **6. Post-processing after electrospinning**

With a subsequent post-process after electrospinning such as folding/rolling up, the aforementioned 3D multilayer fibrous structures, even the as-spun 2D layer-on-layer mats, can turn into a desired morphology for further application. Recently, Duan et al. [37] reported the ultralight highly porous 3D polymer sponges of extremely low-density and low-specific surface area from dispersions of short electrospun fibers in an attempt to mimic the design principle of natural sponges. Short electrospun fibers were first prepared by cutting of electrospun nonwoven and then dispersed in dioxin in different concentrations. Sponges of different densities were prepared from these dispersions by freeze-drying. Such sponge showed tunable cellular infiltration and growth. Ryu et al. [36] developed a three-dimensional scaffolds of carbonized polyacrylonitrile for bone tissue regeneration. PAN fibers were formed by electrospinning onto a Petri dish containing water, and PAN/water was lyophilized for 48 h. Performing the lyophilization step prior to the carbonization process created the micro-sized pores between the electrospun PAN fibers leading to the cotton ball-like 3D scaffolds (**Figure 5**). The scaffolds were carbonized under 800°C in argon atmosphere and then further modified into a 3D cylindrical geometry. Wang et al. [38] fabricated the electrospun chitosan nano−/microfiber mesh tubes by controlling the spinning parameters. The nonwoven or oriented fibers of the chitosan were deposited and reeled on the bar as the drum rotates. Furthermore, by folding the aligned electrospun nanofibrous meshes several times, a 3D nonwoven macroporous nanofibrous scaffold was manufactured. However, 3D structures generated by this method usually cannot put into use as scaffolds directly because they often have a large space or distance between adjacent fibrous surfaces. 3D electrospun poly(L-lactic acid) (PLLA) microfibrous scaffolds with 5 mm in thickness were fabricated by using a subsequent mechanical expansion process [39]. 3D scaffolds demonstrated a high level of osteoblast proliferation (1.8-fold higher than nanofibrous membranes in a week), actively penetrated the inside of the 3D scaffold, and showed a spatial cell distribution. Sintering after electrospinning is another way to fabricate 3D macrostructures. 3D electrospun scaffolds of pure PLGA and composites of PLGA/hydroxyapatite were

**Figure 5.**

*Schematic illustration showing the fabrication process of cPAN scaffolds. Reproduced with permission from Ref. [36].*

**119**

**Figure 6.**

**8. Liquid-assisted collection**

*with permission from Ref. [40].*

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

**7. Charge repulsion-assisted fabrication**

thereby generating the fluffy-type nanofibrous mesh [43].

fabricated by a two-step process: electrospun meshes were first stacked and then sintered using pressurized gas which improved the mechanical properties and porosity.

Fabrication of fluffy nanofibrous mesh using the cosolvent that induces the charge repulsion during the spinning has been employed in recent studies [40, 41]. Lee et al. developed a novel strategy to fabricate highly porous poly(L-lactide) (PLLA)-based fibrous scaffold for bone tissue engineering. Blending of PLLA with its monomer, lactic acid (LA) produced the fluffy-type highly porous nanofibrous mesh (**Figure 6**). Their study revealed that the LA component in the blend solution assisted the formation of the macroporous spongy fibrous scaffold. The repulsion between the as-spun fibers occurs due to the interaction between the electric field formed by high voltage and the negative charge on LA due to the functional group (COOH), thereby generating fluffy fibrous mesh [40–42]. Similarly, Xu et al. fabricated a fluffy-type nanofibrous mesh by electrospinning the blend solution of PCL and polystyrene (PS) [42]. In another study, Lee et al. fabricated a core-sheath-type fibrous scaffold (PCL as the core and PS as shell) with fluffy-type architecture using coaxial electrospinning. The PS in the sheath was removed out to avoid its drawbacks associated with scaffold activity [43]. They reported that the negative charge accumulated on the surface of the nanofiber due to the PS (sheath) caused the repulsion between nanofibers under the influence of the strong electric field,

The highly porous three-dimensional nanofibrous scaffolds can be obtained using bath collectors containing a low surface tension solvent, and this technique

*Diagrammatic representation showing the fabrication of three-dimensional fluffy fibrous scaffolds. Reproduced* 

*Generation, Development and Modifications of Natural Fibers*

With a subsequent post-process after electrospinning such as folding/rolling up, the aforementioned 3D multilayer fibrous structures, even the as-spun 2D layer-on-layer mats, can turn into a desired morphology for further application. Recently, Duan et al. [37] reported the ultralight highly porous 3D polymer sponges of extremely low-density and low-specific surface area from dispersions of short electrospun fibers in an attempt to mimic the design principle of natural sponges. Short electrospun fibers were first prepared by cutting of electrospun nonwoven and then dispersed in dioxin in different concentrations. Sponges of different densities were prepared from these dispersions by freeze-drying. Such sponge showed tunable cellular infiltration and growth. Ryu et al. [36] developed a three-dimensional scaffolds of carbonized polyacrylonitrile for bone tissue regeneration. PAN fibers were formed by electrospinning onto a Petri dish containing water, and PAN/water was lyophilized for 48 h. Performing the lyophilization step prior to the carbonization process created the micro-sized pores between the electrospun PAN fibers leading to the cotton ball-like 3D scaffolds (**Figure 5**). The scaffolds were carbonized under 800°C in argon atmosphere and then further modified into a 3D cylindrical geometry. Wang et al. [38] fabricated the electrospun chitosan nano−/microfiber mesh tubes by controlling the spinning parameters. The nonwoven or oriented fibers of the chitosan were deposited and reeled on the bar as the drum rotates. Furthermore, by folding the aligned electrospun nanofibrous meshes several times, a 3D nonwoven macroporous nanofibrous scaffold was manufactured. However, 3D structures generated by this method usually cannot put into use as scaffolds directly because they often have a large space or distance between adjacent fibrous surfaces. 3D electrospun poly(L-lactic acid) (PLLA) microfibrous scaffolds with 5 mm in thickness were fabricated by using a subsequent mechanical expansion process [39]. 3D scaffolds demonstrated a high level of osteoblast proliferation (1.8-fold higher than nanofibrous membranes in a week), actively penetrated the inside of the 3D scaffold, and showed a spatial cell distribution. Sintering after electrospinning is another way to fabricate 3D macrostructures. 3D electrospun scaffolds of pure PLGA and composites of PLGA/hydroxyapatite were

*Schematic illustration showing the fabrication process of cPAN scaffolds. Reproduced with permission from Ref. [36].*

**6. Post-processing after electrospinning**

**118**

**Figure 5.**

fabricated by a two-step process: electrospun meshes were first stacked and then sintered using pressurized gas which improved the mechanical properties and porosity.

## **7. Charge repulsion-assisted fabrication**

Fabrication of fluffy nanofibrous mesh using the cosolvent that induces the charge repulsion during the spinning has been employed in recent studies [40, 41]. Lee et al. developed a novel strategy to fabricate highly porous poly(L-lactide) (PLLA)-based fibrous scaffold for bone tissue engineering. Blending of PLLA with its monomer, lactic acid (LA) produced the fluffy-type highly porous nanofibrous mesh (**Figure 6**). Their study revealed that the LA component in the blend solution assisted the formation of the macroporous spongy fibrous scaffold. The repulsion between the as-spun fibers occurs due to the interaction between the electric field formed by high voltage and the negative charge on LA due to the functional group (COOH), thereby generating fluffy fibrous mesh [40–42]. Similarly, Xu et al. fabricated a fluffy-type nanofibrous mesh by electrospinning the blend solution of PCL and polystyrene (PS) [42]. In another study, Lee et al. fabricated a core-sheath-type fibrous scaffold (PCL as the core and PS as shell) with fluffy-type architecture using coaxial electrospinning. The PS in the sheath was removed out to avoid its drawbacks associated with scaffold activity [43]. They reported that the negative charge accumulated on the surface of the nanofiber due to the PS (sheath) caused the repulsion between nanofibers under the influence of the strong electric field, thereby generating the fluffy-type nanofibrous mesh [43].

**Figure 6.**

*Diagrammatic representation showing the fabrication of three-dimensional fluffy fibrous scaffolds. Reproduced with permission from Ref. [40].*

## **8. Liquid-assisted collection**

The highly porous three-dimensional nanofibrous scaffolds can be obtained using bath collectors containing a low surface tension solvent, and this technique is also helpful for fabricating 3D fibrous macrostructures. It is known that aligned electrospun micro−/nanofibrous arrays can be collected with the help of a water reservoir collector or a water vortex. Teo et al. [44] fabricated hierarchically organized 3D nanofibrous meshes of PCL using a water vortex. As-collected 3D PCL nanofibrous meshes were either freeze-dried or dried in a mold under ambient condition. The freeze-dried 3D meshes showed visible pores on the surface of the mesh, while the 3D meshes dried in room condition were densely packed without any apparent pores on the surface. Yokoyama et al. [45] fabricated the poly(glycolic acid) (PGA) 3D spongy nanofibrous mesh by combining electrospinning with wet spinning. The spongy-type 3D PGA nanofiber fabric showed a low apparent density and high porosity compared to the usual PGA nanofiber nonwoven mats prepared by conventional electrospinning method.

## **9. Collector modification**

3D fibrous macrostructures fabricated by modifying collector are common. Zhang et al. [47] obtained tubular structures through designing the collectors. The collectors used in fabricating the electrospun fibrous tubes are static 3D columnar collectors. The schematic illustration and the photos of the relevant fibrous tubes are separately shown in **Figure 7A** (**a** and **b**). Tubes with different patterned architectures can also be obtained using collectors with two different patterns as displayed in **Figure 7B**(**c–g**). Moreover, crossing tubes with interconnected tubular structures are made using this static collecting method, which are difficult to obtain by other strategies. Similar to 2D assembly, the 3D collecting template is also based on the manipulation of electric field and electric

#### **Figure 7.**

*(A) Schematics of rotary jet-spinning process. Rotary jet spinning consisted of a perforated reservoir. Photographic image of 3D nanofiber structure produced by rotary jet spinning and corresponding SEM image. (B) (a) schematic illustration of collecting process using a cylindrical collector with equally spaced circular protrusions. (b) a fibrous tube with patterned architectures (scale bar = 5 mm). (c) Magnified image of panel b (scale bar = 200 μm). (d) Schematic illustration of collectors with two different patterns and relevant fibrous tube (pc, patterned collector; ft., fibrous tube). (e) a fibrous tube with two different patterns (scale bar = 5 mm). (f,g) Magnified images of two different patterns of panel. Reproduced with permission from Refs. [46, 47].*

**121**

addition and proliferation.

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

cell adhesion and proliferation.

**10. Porogen leaching**

force. Some key factors, especially the design and configurations of the collector, should be well-tailored, which are critical for tubular structures. Moreover, feasible strategies for fabricating 3D structures are still in demand. Blakeney et al. [20] designed a collector with a network of stainless steel needles on the concave side of a foam half-sphere shell. The fibers were collected randomly between the arrays of needles, thereby generating 3D fluffy, "cotton ball-like" PCL scaffolds. As-fabricated scaffolds showed enhanced cellular infiltration compared with 2D scaffolds produced using traditional collectors [20]. Badrossamay et al. [46] prepared 3D fibrous structure using a rotary jet spinning combined with the hydrostatic pressure with centrifugal pressure, 3D nanofiber structures from poly(lactic acid) (PLA) have been fabricated under a proper rotation speed, and the contained aligned nanofibers were similar to that of the conventional 2D mats (**Figure 7A**). The rotating collector assists the collection of 3D nanofibrous tubular scaffolds. Cai et al. [16] fabricated 3D zein and PEG electrospun scaffolds with three-dimensionally and randomly oriented fibers and large interconnected pores by reducing surface resistivity of materials. The 3D structures are also fabricated via a hybrid technique that combines traditional electrospinning with other methods such as prototyping, polymer/fiber deposition, melt electrospinning, and so on. Park et al. [48] developed a nano- and microhybrid process incorporating direct polymer melt deposition (DPMD) and an electrospinning process. DPMD process was employed to prepare the microfiber layer with computer-aided design modeling data considering some structural points such as pore size, pore interconnectivity, and fiber diameter. The polycaprolactone/collagen nanofiber matrices were deposited between the layers of the three-dimensional structure via an electrospinning process. They found that the polymeric scaffolds with nanofiber matrices provided favorable conditions for

Another technique for the fabrication of highly porous 3D structure is the use of porogens. Materials such as ice crystals, salt particles, polymers (e.g., poly(ethylene oxide) (PEO)), which acts as porogens, usually are mixed simultaneously with the precursor during electrospinning to enable rapid buildup of the nanofibrous volume and then washed away or dried after a desired thickness is reached [49]. For example, Baker et al. [50] demonstrated that inclusion and subsequent removal of a sacrificial fiber population within a fiber-aligned fibrous scaffold enhance cellular infiltration. Poly(ɛ-caprolactone) (a slow-degrading polyester) and poly(ethylene oxide) (a water-soluble polymer) were co-electrospun from two separate spinnerets to form dual-polymer composite fiber-aligned scaffolds, and PEO is washed out. Removal of these sacrificial elements (PEO fibers) preserved structural and mechanical anisotropy and tuned to generate composites with varying mechanical properties. Kim et al. [51] fabricated a 3D macroporous and nanofibrous hyaluronic acid (HA) scaffold by combining the electrospinning process with a salt leaching technique (**Figure 8**). The salt particulates, as a porogen, deposited during electrospinning were leached which produced water-soluble HA-based scaffold with macroporous and nanofibrous geometry. Ki et al. [52] developed 3D nanofibrous fibroin scaffold with high porosity by electrospinning. The electrospun SF nanofiber dispersion was collected in 1,4-dioxane having NaCl particles (300–500 μm) as porogen. The scaffold was cross-linked, lyophilized, and washed with PBS solution several times that was effective for cell

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*Generation, Development and Modifications of Natural Fibers*

by conventional electrospinning method.

**9. Collector modification**

is also helpful for fabricating 3D fibrous macrostructures. It is known that aligned electrospun micro−/nanofibrous arrays can be collected with the help of a water reservoir collector or a water vortex. Teo et al. [44] fabricated hierarchically organized 3D nanofibrous meshes of PCL using a water vortex. As-collected 3D PCL nanofibrous meshes were either freeze-dried or dried in a mold under ambient condition. The freeze-dried 3D meshes showed visible pores on the surface of the mesh, while the 3D meshes dried in room condition were densely packed without any apparent pores on the surface. Yokoyama et al. [45] fabricated the poly(glycolic acid) (PGA) 3D spongy nanofibrous mesh by combining electrospinning with wet spinning. The spongy-type 3D PGA nanofiber fabric showed a low apparent density and high porosity compared to the usual PGA nanofiber nonwoven mats prepared

3D fibrous macrostructures fabricated by modifying collector are common. Zhang et al. [47] obtained tubular structures through designing the collectors. The collectors used in fabricating the electrospun fibrous tubes are static 3D columnar collectors. The schematic illustration and the photos of the relevant fibrous tubes are separately shown in **Figure 7A** (**a** and **b**). Tubes with different patterned architectures can also be obtained using collectors with two different patterns as displayed in **Figure 7B**(**c–g**). Moreover, crossing tubes with interconnected tubular structures are made using this static collecting method, which are difficult to obtain by other strategies. Similar to 2D assembly, the 3D collecting template is also based on the manipulation of electric field and electric

*(A) Schematics of rotary jet-spinning process. Rotary jet spinning consisted of a perforated reservoir. Photographic image of 3D nanofiber structure produced by rotary jet spinning and corresponding SEM image. (B) (a) schematic illustration of collecting process using a cylindrical collector with equally spaced circular protrusions. (b) a fibrous tube with patterned architectures (scale bar = 5 mm). (c) Magnified image of panel b (scale bar = 200 μm). (d) Schematic illustration of collectors with two different patterns and relevant fibrous tube (pc, patterned collector; ft., fibrous tube). (e) a fibrous tube with two different patterns (scale bar = 5 mm). (f,g) Magnified images of two different patterns of panel. Reproduced with permission from* 

**120**

*Refs. [46, 47].*

**Figure 7.**

force. Some key factors, especially the design and configurations of the collector, should be well-tailored, which are critical for tubular structures. Moreover, feasible strategies for fabricating 3D structures are still in demand. Blakeney et al. [20] designed a collector with a network of stainless steel needles on the concave side of a foam half-sphere shell. The fibers were collected randomly between the arrays of needles, thereby generating 3D fluffy, "cotton ball-like" PCL scaffolds. As-fabricated scaffolds showed enhanced cellular infiltration compared with 2D scaffolds produced using traditional collectors [20]. Badrossamay et al. [46] prepared 3D fibrous structure using a rotary jet spinning combined with the hydrostatic pressure with centrifugal pressure, 3D nanofiber structures from poly(lactic acid) (PLA) have been fabricated under a proper rotation speed, and the contained aligned nanofibers were similar to that of the conventional 2D mats (**Figure 7A**). The rotating collector assists the collection of 3D nanofibrous tubular scaffolds. Cai et al. [16] fabricated 3D zein and PEG electrospun scaffolds with three-dimensionally and randomly oriented fibers and large interconnected pores by reducing surface resistivity of materials. The 3D structures are also fabricated via a hybrid technique that combines traditional electrospinning with other methods such as prototyping, polymer/fiber deposition, melt electrospinning, and so on. Park et al. [48] developed a nano- and microhybrid process incorporating direct polymer melt deposition (DPMD) and an electrospinning process. DPMD process was employed to prepare the microfiber layer with computer-aided design modeling data considering some structural points such as pore size, pore interconnectivity, and fiber diameter. The polycaprolactone/collagen nanofiber matrices were deposited between the layers of the three-dimensional structure via an electrospinning process. They found that the polymeric scaffolds with nanofiber matrices provided favorable conditions for cell adhesion and proliferation.

#### **10. Porogen leaching**

Another technique for the fabrication of highly porous 3D structure is the use of porogens. Materials such as ice crystals, salt particles, polymers (e.g., poly(ethylene oxide) (PEO)), which acts as porogens, usually are mixed simultaneously with the precursor during electrospinning to enable rapid buildup of the nanofibrous volume and then washed away or dried after a desired thickness is reached [49]. For example, Baker et al. [50] demonstrated that inclusion and subsequent removal of a sacrificial fiber population within a fiber-aligned fibrous scaffold enhance cellular infiltration. Poly(ɛ-caprolactone) (a slow-degrading polyester) and poly(ethylene oxide) (a water-soluble polymer) were co-electrospun from two separate spinnerets to form dual-polymer composite fiber-aligned scaffolds, and PEO is washed out. Removal of these sacrificial elements (PEO fibers) preserved structural and mechanical anisotropy and tuned to generate composites with varying mechanical properties. Kim et al. [51] fabricated a 3D macroporous and nanofibrous hyaluronic acid (HA) scaffold by combining the electrospinning process with a salt leaching technique (**Figure 8**). The salt particulates, as a porogen, deposited during electrospinning were leached which produced water-soluble HA-based scaffold with macroporous and nanofibrous geometry. Ki et al. [52] developed 3D nanofibrous fibroin scaffold with high porosity by electrospinning. The electrospun SF nanofiber dispersion was collected in 1,4-dioxane having NaCl particles (300–500 μm) as porogen. The scaffold was cross-linked, lyophilized, and washed with PBS solution several times that was effective for cell addition and proliferation.

#### **Figure 8.**

*(A) Diagrammatic illustration showing the polymer jet evolution; (B) digital image showing the vertical growth of solidified fibers; (C) the polymer solution from the needle tip was immediately split into minijets (arrows indicate minijets); and (D) fluffy-type nanofiber mesh. Reproduced with permission from Ref. [50].*

#### **11. Conclusion**

In conclusion, it is evident from the foregoing examples that the diversity in biomaterials is immense. The utilization of electrospun nanofibers as tissue scaffold is challenging. A great deal of effort has been put in to prepare the biomimetic 3D nonwoven scaffolds based on natural as well as synthetic polymers. Different processing routes have been proposed to produce 3D nanofibrous scaffolds with a great variety of architectures. Many clever approaches to mimicking the structure and, more importantly, the function of the ECM have been devised. Different fabrication methods have their own merits and demerits. However, despite all the extensive literature containing references to the so-called biomimetic three-dimensional scaffolds, it is the authors' opinion that much work is still needed to obtain clinically successful materials. Various types of bioactive components, such as peptides (e.g., RGD) and hydroxyapatite, may be incorporated/integrated to enhance the cellular response and biocompatibility of the 3D nanofibrous scaffolds. More importantly, the real-time monitoring/control systems may be established by integrating either electronic components or magnetic responsive elements with 3D nanofibrous mesh, enabling remote actuation and thus with an active role in the modulation of the host response on implantation that can revolutionize human therapies toward successful regeneration. It is imperative that these important technologies continue to be investigated for their ability to interact in biological systems. It will be most interesting to follow the further progress and the expected and unexpected leaps forward that will be shaping the field in the coming years.

**123**

**Author details**

Mahesh Kumar Joshi1

Kathmandu, Nepal

Kathmandu, Nepal

provided the original work is properly cited.

\*, Rajeshwar Man Shrestha<sup>2</sup>

1 Department of Chemistry, Trichandra Multiple Campus, Tribhuvan University,

2 Department of Applied Sciences, Institute of Engineering, Tribhuvan University,

\*Address all correspondence to: joshimj2003@yahoo.com and hempant@ioe.edu.np

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Hem Raj Pant2

\*

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*3D Nonwoven Fabrics for Biomedical Applications DOI: http://dx.doi.org/10.5772/intechopen.88584*

*Generation, Development and Modifications of Natural Fibers*

In conclusion, it is evident from the foregoing examples that the diversity in biomaterials is immense. The utilization of electrospun nanofibers as tissue scaffold is challenging. A great deal of effort has been put in to prepare the biomimetic 3D nonwoven scaffolds based on natural as well as synthetic polymers. Different processing routes have been proposed to produce 3D nanofibrous scaffolds with a great variety of architectures. Many clever approaches to mimicking the structure and, more importantly, the function of the ECM have been devised. Different fabrication methods have their own merits and demerits. However, despite all the extensive literature containing references to the so-called biomimetic three-dimensional scaffolds, it is the authors' opinion that much work is still needed to obtain clinically successful materials. Various types of bioactive components, such as peptides (e.g., RGD) and hydroxyapatite, may be incorporated/integrated to enhance the cellular response and biocompatibility of the 3D nanofibrous scaffolds. More importantly, the real-time monitoring/control systems may be established by integrating either electronic components or magnetic responsive elements with 3D nanofibrous mesh, enabling remote actuation and thus with an active role in the modulation of the host response on implantation that can revolutionize human therapies toward successful regeneration. It is imperative that these important technologies continue to be investigated for their ability to interact in biological systems. It will be most interesting to follow the further progress and the expected and unexpected leaps

*(A) Diagrammatic illustration showing the polymer jet evolution; (B) digital image showing the vertical growth of solidified fibers; (C) the polymer solution from the needle tip was immediately split into minijets (arrows indicate minijets); and (D) fluffy-type nanofiber mesh. Reproduced with permission from Ref. [50].*

forward that will be shaping the field in the coming years.

**122**

**11. Conclusion**

**Figure 8.**

## **Author details**

Mahesh Kumar Joshi1 \*, Rajeshwar Man Shrestha<sup>2</sup> and Hem Raj Pant2 \*

1 Department of Chemistry, Trichandra Multiple Campus, Tribhuvan University, Kathmandu, Nepal

2 Department of Applied Sciences, Institute of Engineering, Tribhuvan University, Kathmandu, Nepal

\*Address all correspondence to: joshimj2003@yahoo.com and hempant@ioe.edu.np

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[20] Blakeney BA et al. Cell infiltration and growth in a low density, uncompressed three-dimensional electrospun nanofibrous scaffold. Biomaterials. 2011;**32**(6):1583-1590

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[29] Jiang J et al. Expanding twodimensional electrospun nanofiber membranes in the third dimension by a modified gas-foaming technique. ACS Biomaterials Science & Engineering. 2015;**1**(10):991-1001

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[31] Woodfield TBF et al. Polymer scaffolds fabricated with pore-size gradients as a model for studying the zonal organization within tissueengineered cartilage constructs. Tissue Engineering. 2005;**11**(9-10):1297-1311

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[9] Zeleny J. The electrical discharge from liquid points, and a hydrostatic method of measuring the electric intensity at their surfaces. Physical

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1981;**19**(6):909-920

1995;**35**(2-3):151-160

2017;**66**(10):514-520

1964;**280**(1382):383-397

[12] Doshi J, Reneker DH. Electrospinning process and applications of electrospun fibers. Journal of Electrostatics.

[13] Han SW, Joshi MK, Kim CS. Fabrication and characterization of silver nanoparticle-incorporated bilayer electrospun–melt-blown micro/ nanofibrous membrane AU - Kim, Han Joo. International Journal of Polymeric Materials and Polymeric Biomaterials.

[14] Taylor G. Disintegration of water drops in an electric field. Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences.

[15] Reneker DH et al. Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. Journal of Applied Physics. 2000;**87**(9):4531-4547

[16] Cai S et al. Novel 3D electrospun scaffolds with Fibers oriented randomly and evenly in three dimensions to closely mimic the unique architectures of extracellular matrices in soft tissues:

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2017;**65**:66-76

2005;**26**(1):37-46

2004;**32**(3):477-486

perspectives. Applied Microbiology and

[2] Joshi MK et al. In situ generation

Polycaprolactone nanofibers: Effects on crystallinity, mechanical strength, biocompatibility, and biomimetic mineralization. ACS Applied Materials & Interfaces. 2015;**7**(35):19672-19683

[4] Maharjan B et al. In-situ synthesis of AgNPs in the natural/synthetic hybrid nanofibrous scaffolds: Fabrication, characterization and antimicrobial activities. Journal of the Mechanical Behavior of Biomedical Materials.

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[6] Liu XH, Ma PX. Polymeric scaffolds for bone tissue engineering. Annals of Biomedical Engineering.

[7] Huang LH et al. Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer. Biomaterials. 2007;**28**(10):1741-1751

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## *Edited by Mudassar Abbas and Han-Yong Jeon*

This book covers natural fibers at the basic level as well as a few advanced approaches for recent trends in natural fibers. The core chapters include an introduction to cellulosic fibers like cotton, protein fibers like silk, and other natural fibers. Overall the book provides comprehensive knowledge of natural fibers.

Published in London, UK © 2020 IntechOpen © Steve Johnson / unsplash

Generation, Development and Modifications of Natural Fibers

Generation, Development

and Modifications of Natural

Fibers

*Edited by Mudassar Abbas and Han-Yong Jeon*