3. Results and discussion

#### 3.1 Natural fibers characterization

The proximate analysis of CCF and CHF is presented in Table 6. Comparing the obtained values, it is observed that the fiber with the highest moisture content is the


Table 6.

Proximate analysis of the natural fibers.

The tests were carried out on bars of rectangular cross section at 23°C and at a rate of crosshead motion between 1.34 and 1.44 mm/min. This rate was determined based on the dimensions of the specimens. Also, the distance between the supports was 50 mm and the tests were conducted up to 5% strain. All the results were taken

Pendulum type impact test machine used for the notched IZOD impact measurements.

The impact strength of PP and biocomposites was determined with an Izod Tinius Olsen impact pendulum equipped with a 4.53 N pendulum. Prior to the test, the materials were subjected to conditioning for 48 hours at 50% relative humidity and a temperature of 25°C. The specimens were made following the standard ASTM D256, and the starting angle of the test was 150° as shown in Figure 3. All the results

DSC test was carried out using a TA Q2000 differential scanning calorimeter under nitrogen atmosphere at a scanning rate of 10°C/min, with a sample of 10 mg in aluminum pans. The thermal history of the samples was erased by a preliminary heating cycle at 10°C/min from 20 to 200°C and maintaining it at that temperature for 10 min to melting residual crystals, cooling at 10°C/min to 0°C, and finally, they

as the average value of five samples.

Assembly used for flexural test (according to ASTM D790).

were taken as the average value of five samples.

2.4.2 Impact properties

Figure 2.

Thermosoftening Plastics

Figure 3.

94

2.4.3 Thermal characterization

CCF. This parameter is directly related to the dispersion of the fibers in a polymer matrix during the melting processing [39]. Higher moisture content causes lower dispersion of a lignocellulosic material in a polymer matrix. This effect can be related with the final properties of the obtained biocomposites. Also, CHF presented the highest volatile matter value. Volatile matter is related to the cellulose and hemicellulose percentage in the fibers. It is reported that hemicellulose influences the distance of interfibrillary cellulose, impacting fiber stiffness [40]. For that reason, a higher content of volatile matter represents a significant proportion of holocellulose in the fiber and represents higher toughness and a better fatigue behavior in the fiber [40]. Therefore, better results can be expected in the mechanical properties of a biocomposite obtained from CHF compared to a CCF-based biocomposite. The results show that the moisture content value in CCF is higher than the data presented by several authors [38, 41–43]. Also, CHF volatile matter content is higher in comparison with the values reported in literature [35–37]. On the other hand, ash, fixed carbon percentages, and calorific value lower of CHF are lower than the values reported in literature [35–37, 41, 43–45].

3.2 Characterization of the biocomposites

The influence of CHF, CCF fibers, and MAPP addition on the r-PP flexural and impact properties was evaluated. The tensile behavior of the materials is shown in Figure 4. Table 9 presents flexural modulus, flexural strength, and impact strength

CHF 33.38 0.89 13.06 0.60 17.31 0.68 1.84 0.06 34.42 0.94 Obtained

Recycled Polypropylene-Coffee Husk and Coir Coconut Biocomposites: Morphological…

CCF 22.24 1.46 15.62 1.25 25.42 0.81 3.71 0.08 33.00 0.28 Obtained

29.17 35.4 18.2 28.96 22.35 23.2 1.4 4.6 17.67 21.8 [49, 50]

30.22 47.7 21.9 25.9 17.8 39.66 0.8 5.56 6.8 18.66 [8, 38, 51]

Lignin (%) Ashes (%) Extractives

(%)

References

values

values

The results show that CHF and CCF fibers incorporation induce a significant improvement of flexural properties of r-PP. r-PP-CHF and r-PP-CCF biocomposites flexural modulus (FM) increased 97 and 13%, respectively, in comparison with r-PP. Although the FM values were improved in both biocomposites, the effect was sharper for r-PP-CHF. This can be explained with the structural analysis of the fibers (Section 3.1). The cellulose content is related to the oxygen proportion and is associated with the resistance degree of the fiber. In this sense, lignocellulosic materials with a higher oxygen content or a higher value in the O/C ratio will have a better mechanical performance [54–57]. CHF presented a higher cellulose content

3.2.1 Mechanical properties

Structural analysis of the natural fibers.

Natural Fiber

Table 8.

Cellulose (%)

DOI: http://dx.doi.org/10.5772/intechopen.81635

Hemicellulose (%)

values of the materials.

Figure 4.

97

Average flexural stress vs. deformation of r-PP and r-PP biocomposites.

The elemental analysis values of the fibers are presented in Table 7. The results show that the carbon content in the CCF (53.88%) was higher in comparison with the reported values in literature, while the oxygen content was lower. On the other hand, CHF elemental analysis values are within the ranges established by other authors. Atomic ratios O/C and H/C obtained for CHF and CCF were 0.61, 0.54, 1.63, and 1.45, respectively. These results are in accordance with the values of biomass established in the Van Krevelen diagram [31]. The values of the O/C ratio obtained can be attributed to a high content of cellulose and hemicellulose in the biomass [3, 47]. This O/C relationship can be used as a parameter to evaluate the polarity of fibers in the production of biocomposites materials, being related to the content of hydroxyl groups. These groups are reactive centers of high polarity, which influence the formation of hydrogen bonds and the compatibility between fibers and a polymer [48]. For this reason, the O/C ratio allows to estimate the interaction degree between the lignocellulosic reinforcement and the polar polymeric matrix used [3], and its value is higher for CHF compared to CCF.

The structural compositions of the fibers are presented in Table 8. CHF presented a higher cellulose content (33.38%) compared to CCF (22.24%). Cellulose is considered as a semicrystalline biopolymer with a fibrous and rigid structure, which positively affects the stiffness in biocomposites materials [52]. Also, a greater amount of cellulose is related to better compatibility between the fibers and the polymeric matrix and a better mechanical performance of the biocomposite [53]. Regarding the lignin content, CCF shows a greater quantity (25.42%) compared to CHF (17.31%). This type of compound is considered as an amorphous polymer with chemical heterogeneity and a low physical consistency. Bajwa et al. [48] mentioned that increase in the lignin content decreases the mechanical resistance of thermoset biocomposites.


#### Table 7. Elemental analysis of the natural fibers.



Table 8.

CCF. This parameter is directly related to the dispersion of the fibers in a polymer matrix during the melting processing [39]. Higher moisture content causes lower dispersion of a lignocellulosic material in a polymer matrix. This effect can be related with the final properties of the obtained biocomposites. Also, CHF

presented the highest volatile matter value. Volatile matter is related to the cellulose and hemicellulose percentage in the fibers. It is reported that hemicellulose influences the distance of interfibrillary cellulose, impacting fiber stiffness [40]. For that reason, a higher content of volatile matter represents a significant proportion of holocellulose in the fiber and represents higher toughness and a better fatigue behavior in the fiber [40]. Therefore, better results can be expected in the mechanical properties of a biocomposite obtained from CHF compared to a CCF-based biocomposite. The results show that the moisture content value in CCF is higher than the data presented by several authors [38, 41–43]. Also, CHF volatile matter content is higher in comparison with the values reported in literature [35–37]. On the other hand, ash, fixed carbon percentages, and calorific value lower of CHF are

The elemental analysis values of the fibers are presented in Table 7. The results show that the carbon content in the CCF (53.88%) was higher in comparison with the reported values in literature, while the oxygen content was lower. On the other hand, CHF elemental analysis values are within the ranges established by other authors. Atomic ratios O/C and H/C obtained for CHF and CCF were 0.61, 0.54, 1.63, and 1.45, respectively. These results are in accordance with the values of biomass established in the Van Krevelen diagram [31]. The values of the O/C ratio obtained can be attributed to a high content of cellulose and hemicellulose in the biomass [3, 47]. This O/C relationship can be used as a parameter to evaluate the polarity of fibers in the production of biocomposites materials, being related to the content of hydroxyl groups. These groups are reactive centers of high polarity, which influence the formation of hydrogen bonds and the compatibility between fibers and a polymer [48]. For this reason, the O/C ratio allows to estimate the interaction degree between the lignocellulosic reinforcement and the polar poly-

lower than the values reported in literature [35–37, 41, 43–45].

meric matrix used [3], and its value is higher for CHF compared to CCF. The structural compositions of the fibers are presented in Table 8. CHF presented a higher cellulose content (33.38%) compared to CCF (22.24%). Cellulose is considered as a semicrystalline biopolymer with a fibrous and rigid structure, which positively affects the stiffness in biocomposites materials [52]. Also, a greater amount of cellulose is related to better compatibility between the fibers and the polymeric matrix and a better mechanical performance of the biocomposite [53]. Regarding the lignin content, CCF shows a greater quantity (25.42%) compared to CHF (17.31%). This type of compound is considered as an amorphous polymer with chemical heterogeneity and a low physical consistency. Bajwa et al. [48] mentioned that increase in the lignin content decreases the mechanical resistance of thermoset

Natural Fiber C (%) H (%) N (%) O (%) S (%) Reference CHF 50.72 6.88 1.07 41.27 0.06 Obtained values

CCF 53.88 6.51 0.68 38.84 0.08 Obtained values

40.1–52.56 4.9–7.08 0–5.2 39.54–49.1 0–0.35 [35–37, 46]

47.25–48.58 5.7–6.74 0–3.04 43.74–45.6 0 [38, 46]

biocomposites.

Thermosoftening Plastics

Table 7.

96

Elemental analysis of the natural fibers.

Structural analysis of the natural fibers.

#### 3.2 Characterization of the biocomposites

#### 3.2.1 Mechanical properties

The influence of CHF, CCF fibers, and MAPP addition on the r-PP flexural and impact properties was evaluated. The tensile behavior of the materials is shown in Figure 4. Table 9 presents flexural modulus, flexural strength, and impact strength values of the materials.

The results show that CHF and CCF fibers incorporation induce a significant improvement of flexural properties of r-PP. r-PP-CHF and r-PP-CCF biocomposites flexural modulus (FM) increased 97 and 13%, respectively, in comparison with r-PP. Although the FM values were improved in both biocomposites, the effect was sharper for r-PP-CHF. This can be explained with the structural analysis of the fibers (Section 3.1). The cellulose content is related to the oxygen proportion and is associated with the resistance degree of the fiber. In this sense, lignocellulosic materials with a higher oxygen content or a higher value in the O/C ratio will have a better mechanical performance [54–57]. CHF presented a higher cellulose content

Figure 4. Average flexural stress vs. deformation of r-PP and r-PP biocomposites.


Mean of five replications standard deviation.

#### Table 9.

Flexural and impact properties of r-PP and r-PP-natural fiber biocomposites.

in comparison with CCF (33.38 and 22.24%, respectively), which could explain the greater improvement in FM values with this fiber. It was also observed that MAPP addition did not generate significant differences (p ≥ 0.05) on the FM values compared to r-PP-Fiber biocomposites.

On the other hand, CHF and CCF fibers addition generate slight improvements (1 and 8%) on the flexural strength (FS) compared to neat r-PP. These results agree with previous studies found in literature [58–60]. However, for both r-PP-fiber biocomposites, MAPP addition causes an increase in FS of 16% in comparison with r-PP.

Impact test results shows that CHF and CCF addition cause a decrease on the impact strength of 37 and 6%, respectively, in comparison with the r-PP. Similar results were reported by several studies about the morphology and mechanical properties of PP-natural fiber biocomposites [60–63]. However, for r-PP-CHF and r-PP-CCF, an increase on the impact strength of 35 and 44% was observed. This result shows that MAPP addition increases the capacity of r-PP to absorb energy. This phenomenon can be explained by a possible energy absorption promoted by fracture mechanisms, which involve detachment, slippage, and fragmentation of the fiber. Mechanisms are not present on the r-PP and r-PP biocomposites without MAPP.

temperature of r-PP was observed. This decrease indicates that natural fibers in biocomposites can act as a nucleation agent. The second heating runs of r-PP and r-PP biocomposites were shown in Figure 5b. All samples exhibit an endothermic peak between 162 and 165°C corresponding to the melting of the PP matrix. These results indicate that the addition of the CHF and CCF fibers does not disturb the melting processes of the PP matrix. Also, it is observed that PP crystalinity fraction melted during heating was 40%. For r-PP biocomposites, the crystalline phase content increases slightly up to 44%. These results show that CHF and CCF fibers

r-PP 116 165 82 40 r-PP-CHF 121 164 64 44 r-PP-CHF-MAPP 122 162 63 44 r-PP-CCF 118 165 61 42 r-PP-CCF-MAPP 119 164 63 44

biocomposites. Some reports that were related to fiber-reinforced composites have found that the fibers act as nucleation points that increase the crystallinity of the

TG and DTG curves were used to determine the thermal stability of coffee husk (CHF) and coir coconut fibers (CCF). The results are shown in Figure 6. Also, main thermal parameters obtained from these curves are summarized in Table 11. As shown in TG curve (Figure 6a), fibers present three weight loss regions which are located around 60–100°C, 240–350°C, and 350–600°C. The first weight loss region below 100°C can be attributed to the evaporation of superficial water present in the sample, while the other regions might be associated with the decomposition of the fiber constituents. DTG curves (Figure 6b) show a first decomposition peaks at 299 and 284°C for CHF and CCF, respectively. These peaks correspond

promote the formation of crystalline phases in the r-PP present in the

(a) Cooling and (b)second heating DSC curves for r-PP and r-PP biocomposites.

\*Tc and Tm were taken at the maximum peak of crystallization and melting peaks.

Thermal properties on cooling and second heating DSC scans of the samples.

Sample Cooling Second heating

Recycled Polypropylene-Coffee Husk and Coir Coconut Biocomposites: Morphological…

DOI: http://dx.doi.org/10.5772/intechopen.81635

Tc\* (°C) Tm\* (°C) ΔHm (J/g) χ (%)

polymer phase [64].

99

Figure 5.

Table 10.

3.2.2.2 Thermogravimetric analysis (TGA)

The improvements in FS and impact strength with MAPP can be explained with the improved interfacial adhesion that MAPP caused. MAPP addition influences the chemical interaction between the hydrophobic matrix and the hydrophilic fiber through the formation of covalent bonds between the maleic anhydride groups and the hydroxyl groups present on the surface of the cellulosic fiber [57, 60]. In addition, Migneault et al. [55] mentioned that esterification reactions produced by the interaction between the natural fiber and the compatibility agent increase with the oxygen content of the fiber. Oxygen is directly related to the proportion of carbohydrates present in the surface of the fiber, creating a greater number of polar sites (hydroxyl groups) to react.

#### 3.2.2 Thermal characterization

#### 3.2.2.1 Differential scanning calorimetry (DSC)

DSC curves for r-PP and their biocomposites with CHF and CCF are shown in Figure 5. Numerical values of the thermal events are shown in Table 10.

The DSC cooling curve of r-PP (Figure 5a) shows a main exothermic peak located around 116°C corresponding to the crystallization of PP chains. When CHF, CCF, and MAPP were added into r-PP, a 3–6°C shift in the crystallization

Recycled Polypropylene-Coffee Husk and Coir Coconut Biocomposites: Morphological… DOI: http://dx.doi.org/10.5772/intechopen.81635

#### Figure 5.

in comparison with CCF (33.38 and 22.24%, respectively), which could explain the greater improvement in FM values with this fiber. It was also observed that MAPP addition did not generate significant differences (p ≥ 0.05) on the FM values

Flexural properties Impact properties

)

Modulus (MPa) Strength (MPa) Impact strength (kJ/m2

On the other hand, CHF and CCF fibers addition generate slight improvements (1 and 8%) on the flexural strength (FS) compared to neat r-PP. These results agree with

biocomposites, MAPP addition causes an increase in FS of 16% in comparison with r-PP. Impact test results shows that CHF and CCF addition cause a decrease on the impact strength of 37 and 6%, respectively, in comparison with the r-PP. Similar results were reported by several studies about the morphology and mechanical properties of PP-natural fiber biocomposites [60–63]. However, for r-PP-CHF and r-PP-CCF, an increase on the impact strength of 35 and 44% was observed. This result shows that MAPP addition increases the capacity of r-PP to absorb energy. This phenomenon can be explained by a possible energy absorption promoted by fracture mechanisms, which involve detachment, slippage, and fragmentation of the fiber. Mechanisms are not present on the r-PP and r-PP biocomposites without MAPP.

The improvements in FS and impact strength with MAPP can be explained with the improved interfacial adhesion that MAPP caused. MAPP addition influences the chemical interaction between the hydrophobic matrix and the hydrophilic fiber through the formation of covalent bonds between the maleic anhydride groups and the hydroxyl groups present on the surface of the cellulosic fiber [57, 60]. In addition, Migneault et al. [55] mentioned that esterification reactions produced by the interaction between the natural fiber and the compatibility agent increase with the oxygen content of the fiber. Oxygen is directly related to the proportion of carbohydrates present in the surface of the fiber, creating a greater number of polar

DSC curves for r-PP and their biocomposites with CHF and CCF are shown in

The DSC cooling curve of r-PP (Figure 5a) shows a main exothermic peak located around 116°C corresponding to the crystallization of PP chains. When CHF,

Figure 5. Numerical values of the thermal events are shown in Table 10.

CCF, and MAPP were added into r-PP, a 3–6°C shift in the crystallization

previous studies found in literature [58–60]. However, for both r-PP-fiber

Sample Flexural and impact properties\*

<sup>a</sup>–c Different letters in the same column indicate significant differences (p <sup>&</sup>lt; 0.05). \*

Flexural and impact properties of r-PP and r-PP-natural fiber biocomposites.

r-PP <sup>1193</sup> 50a 37.1 1.7a 11.5 1.8a r-PP-CHF <sup>2350</sup> 71b 37.2 0.3<sup>a</sup> 7.3 0.4b r-PP-CHF-MAPP 2309 <sup>114</sup><sup>b</sup> 43.1 0.9b 15.5 1.3c r-PP-CCF <sup>1349</sup> <sup>10</sup><sup>c</sup> 40.1 0.7<sup>c</sup> 10.7 1.2<sup>a</sup> r-PP-CCF-MAPP <sup>1351</sup> 12c 43.3 0.4<sup>b</sup> 16.5 0.7<sup>c</sup>

compared to r-PP-Fiber biocomposites.

Mean of five replications standard deviation.

Thermosoftening Plastics

Table 9.

sites (hydroxyl groups) to react.

3.2.2.1 Differential scanning calorimetry (DSC)

3.2.2 Thermal characterization

98

(a) Cooling and (b)second heating DSC curves for r-PP and r-PP biocomposites.


#### Table 10.

Thermal properties on cooling and second heating DSC scans of the samples.

temperature of r-PP was observed. This decrease indicates that natural fibers in biocomposites can act as a nucleation agent. The second heating runs of r-PP and r-PP biocomposites were shown in Figure 5b. All samples exhibit an endothermic peak between 162 and 165°C corresponding to the melting of the PP matrix. These results indicate that the addition of the CHF and CCF fibers does not disturb the melting processes of the PP matrix. Also, it is observed that PP crystalinity fraction melted during heating was 40%. For r-PP biocomposites, the crystalline phase content increases slightly up to 44%. These results show that CHF and CCF fibers promote the formation of crystalline phases in the r-PP present in the biocomposites. Some reports that were related to fiber-reinforced composites have found that the fibers act as nucleation points that increase the crystallinity of the polymer phase [64].

#### 3.2.2.2 Thermogravimetric analysis (TGA)

TG and DTG curves were used to determine the thermal stability of coffee husk (CHF) and coir coconut fibers (CCF). The results are shown in Figure 6. Also, main thermal parameters obtained from these curves are summarized in Table 11.

As shown in TG curve (Figure 6a), fibers present three weight loss regions which are located around 60–100°C, 240–350°C, and 350–600°C. The first weight loss region below 100°C can be attributed to the evaporation of superficial water present in the sample, while the other regions might be associated with the decomposition of the fiber constituents. DTG curves (Figure 6b) show a first decomposition peaks at 299 and 284°C for CHF and CCF, respectively. These peaks correspond

#### Figure 6.

(a) TG and (b) DTG curves of CHF and CCF fibers at heating rates of 10°C/min.


r-PP phase. As shown in Table 12, To increases between 34 and 60°C. Also, Tmax increases between 33 and 28°C in comparison to r-PP (as indicates in the orange area). This increment in the thermal stability of the biocomposites has been previously observed in different studies, indicating that the incorporation of fibers in the material induces spherulite nucleation points, increasing the crystallinity of the

Sample Degradation stage Tonset (°C) Tmax (°C) Residual Char (%)

2 402 445

2 428 460

2 427 460

2 411 453

r-PP 1 368 428 0.4 r-PP-CHF 1 260 354 8.4

Recycled Polypropylene-Coffee Husk and Coir Coconut Biocomposites: Morphological…

r-PP-CHF-MAPP 1 264 355 8.2

r-PP-CCF 1 243 327 11.9

r-PP-CCF-MAPP 1 259 360 7.4

Figure 8a and b shows SEM images of the fractured surfaces of r-PP-CHF and r-PP-CCF, respectively. In these images, gaps between the fibers and the surrounding r-PP matrix can be clearly observed, which indicate a poor interfacial adhesion between the r-PP matrix and the natural fibers [65]. For Figure 9a and b, with the MAPP addition, gaps between natural fibers and r-PP were significantly reduced, and as a consequence, an improvement over the interface for the composite can be appreciated. This result confirms that MAPP addition improved the interfacial property of the hydrophobic PP matrix and the hydrophilic natural fibers. Also, this

When assessing the carbon footprint of the material, the stages of the life cycle

were limited to raw material acquisition, transport, and processing. Since the

can be related with mechanical properties enhancement observed in the

polymer and improving its thermal properties [64].

Thermal degradation data of r-PP and r-PP biocomposites.

DOI: http://dx.doi.org/10.5772/intechopen.81635

biocomposites after the MAPP addition.

SEM pictures for rPP-CHF and rPP-CCF biocomposites.

3.2.4 Environmental characterization of the materials

3.2.3 Morphology

Figure 8.

101

Table 12.

#### Table 11.

Thermal degradation data of the fibers at 10°C/min in nitrogen atmosphere.

#### Figure 7.

(a) TG and (b) DTG curves of r-PP and r-PP biocomposites at heating rates of 10°C/min.

to the temperature of maximum weight loss rate (Tmax) of hemicellulose, while the second peaks located at 358°C and 328°C (for CHF and CCF) are related to the Tmax of α-cellulose. The residual weights of CHF and CCF have also been measured and are equal to 25 and 31% for CHF and CCF at 600°C. This results show that CHF possesses a better thermal stability compared to CCF.

TG and DTG curves for r-PP and r-PP biocomposites are shown in Figure 7. Also, main thermal parameters obtained from these curves are summarized in Table 12.

Recycled PP degradation occurs in a single step process with an onset temperature (To) located at 368°C and a Tmax of 428°C. The residue after final degradation was 0.4%. Regarding biocomposites, TG and DTG show that the addition of coffee husk and coir coconut fibers produces an increase in the thermal stability of the


Recycled Polypropylene-Coffee Husk and Coir Coconut Biocomposites: Morphological… DOI: http://dx.doi.org/10.5772/intechopen.81635
