**4. Results and discussion**

#### **4.1 Fibres properties**

The SPF yarn was made from cotton type soybean fibres of 1.27 dtex with an average length of 39.5 cm. Fibres were thermoplastic with melting point at 224ºC. Dry fibres absorbed 2.47% of moisture when exposed for 48 hours to the air of relative humidity 50% and temperature of 23 °C.

The cross-section shape of used soybean protein fibres was bean-shaped with diameter of 11-20 µm in longer axle and 6-7 µm in shorter axle (Fig. 5). A very smooth surface of fibres imparted high lustre to fibres. On the longitudinal view irregular grooves and wrinkles can be seen. These grooves can help to transport moisture along fibres. On the optical microscope photograph a nonhomogeneous structure with many voids is seen.

Fig. 5. Scanning electron microscope view of soybean protein fibre: top: longitudinal view at magnification of 4.000 and bottom: cross-section at magnification of 3.000. Right: optical microscope longitudinal view of soybean protein fibre.

Soybean Protein Fibres (SPF) 513

Fig. 7. Stress-elongation curves of dry and wet SPF yarns

**Properties of** 

**Breaking** 

could enable bacteria to penetrate into the fibres.

yarns from soya protein fibres, they didn't change essentially.

them (Δ).

experiment.

**Specific breaking** 

**Initial modulus** 

**Specific work of** 

**yarns from SPF DRY WET** 

**stress (cN/dtex)** 2.16 1.58 -26.9

**elongation (%)** 37.75 42.05 +11.4

**(GPa)** 5.08 3.25 -36.0

**rupture (mJ/kg)** 39.81 22.71 -43.0

purpose of comparison, cotton yarn was buried at the same time in the soil. After 7 days cotton yarn degraded very intensively and only small remains of yarn were left in the soil. Tensile properties of biodegraded cotton yarn could be measured only after 2 days. Biodegradation of cotton showed that microorganisms in the soil were active during the

The microphotographs of SPF yarns in Fig. 8 show that the quantity of bacteria and fungus, present on the surface of soybean protein fibres, increased with time of biodegradation. After 21 days in the soil, it is hard to say that there are any physical degradations of the fibre's surface because the fibres have natural irregular grooves and wrinkles (0 days). Soybean protein fibres in comparison to the mid-twentieth century protein fibres (Fig. 1) have essentially smoother surface and relatively lower quantity of surface grooves that

Specific tensile stress-elongation curves of biodegraded cotton yarns (Fig. 9 and 10) show a significant decrease of breaking force and breaking elongation after 2 days, while for the

Table 3. Tensile properties of dry and wet SPF yarns and relative differences between

**Δ (%)** 

Soybean protein fibres are composed of a mixture of two polymers, soybean proteins and polyvinyl alcohol. Protein and polyvinyl alcohol macromolecules are connected by intermolecular interactions like hydrogen bonds (Fig. 3) and van der Waals hydrophilic and hydrophobic forces.

The soybean protein fibres, used in experiment, consisted of polyvinyl alcohol and soybean proteins. The SPF FT-IR spectrum (Fig. 6) has very intensive peaks at 3301 cm-1, which is typical for stretching O-H bonds, and at 1408 cm-1 and 1327 cm-1, which corresponds to N-H stretching in amide III. FT-IR absorption spectrum of SPF is different to FT-IR spectrum of PVA fibres at peaks 1644 cm-1 and 1535.32 cm-1.

Fig. 6. FT-IR/ATR absorption spectra of soybean protein fibres (SPF) and PVA Kuralon®.

Pure soybean protein isolate has typical infrared absorption bands at 1636-1680 cm-1 and 1533-1559 cm-1 that are attributable to the –NH- bonds of amide I at 1640 cm-1 and at 1550 cm-1 for amide II in peptide bonds forming primary backbone of proteins. The absorption peak at 3294 cm-1 refers to the hydrogen-bond association between protein chains and moisture in protein. The absorption band at 1241–1472 cm-1 is attributable to the (C)O-O and C-N stretching and N-H bending (amide III) vibrations (Su et al., 2008).

At room temperature pure polyvinyl alcohol powder with –OH groups on carbon chains has a typical infrared absorption band at 2918-3565 cm-1, which corresponds to –OH absorption (Su et al., 2008).

#### **4.2 Yarns properties**

#### **4.2.1 Tensile properties of SPF yarn in dry and wet state**

Water has a significant influence on tensile properties of the SPF yarn (Fig. 7, Tab. 3). After an hour in distilled water, the yarn lost its specific breaking stress for almost one third. Wet yarn had lower modulus then dry yarn in the whole deformation range and attained by 11.4% higher breaking elongation than dry yarn.

#### **4.2.2 Biodegradation of SPF yarns**

Biodegradation of SPF yarn was studied after the yarn had been buried for 2, 7, 11, 16 and 21 days in the soil with temperature about 30 ºC and 65% relative humidity (Fig. 8). For the

Soybean protein fibres are composed of a mixture of two polymers, soybean proteins and polyvinyl alcohol. Protein and polyvinyl alcohol macromolecules are connected by intermolecular interactions like hydrogen bonds (Fig. 3) and van der Waals hydrophilic and

The soybean protein fibres, used in experiment, consisted of polyvinyl alcohol and soybean proteins. The SPF FT-IR spectrum (Fig. 6) has very intensive peaks at 3301 cm-1, which is typical for stretching O-H bonds, and at 1408 cm-1 and 1327 cm-1, which corresponds to N-H stretching in amide III. FT-IR absorption spectrum of SPF is different to FT-IR spectrum of

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 500

Wavenumber (cm-1) Fig. 6. FT-IR/ATR absorption spectra of soybean protein fibres (SPF) and PVA Kuralon®.

Pure soybean protein isolate has typical infrared absorption bands at 1636-1680 cm-1 and 1533-1559 cm-1 that are attributable to the –NH- bonds of amide I at 1640 cm-1 and at 1550 cm-1 for amide II in peptide bonds forming primary backbone of proteins. The absorption peak at 3294 cm-1 refers to the hydrogen-bond association between protein chains and moisture in protein. The absorption band at 1241–1472 cm-1 is attributable to the (C)O-O and

At room temperature pure polyvinyl alcohol powder with –OH groups on carbon chains has a typical infrared absorption band at 2918-3565 cm-1, which corresponds to –OH

Water has a significant influence on tensile properties of the SPF yarn (Fig. 7, Tab. 3). After an hour in distilled water, the yarn lost its specific breaking stress for almost one third. Wet yarn had lower modulus then dry yarn in the whole deformation range and attained by

Biodegradation of SPF yarn was studied after the yarn had been buried for 2, 7, 11, 16 and 21 days in the soil with temperature about 30 ºC and 65% relative humidity (Fig. 8). For the

1325.25 2846.36

1642.47

1534.94

1427.411405.91

1233

1169

1142 1091 1064

1010

<sup>916</sup> <sup>844</sup> 798

693

hydrophobic forces.

0.003 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22

absorption (Su et al., 2008).

**4.2 Yarns properties** 

A

3353.09

PVA

3283.01

SPF

2905.66

C-N stretching and N-H bending (amide III) vibrations (Su et al., 2008).

**4.2.1 Tensile properties of SPF yarn in dry and wet state** 

11.4% higher breaking elongation than dry yarn.

**4.2.2 Biodegradation of SPF yarns** 

PVA fibres at peaks 1644 cm-1 and 1535.32 cm-1.

Fig. 7. Stress-elongation curves of dry and wet SPF yarns


Table 3. Tensile properties of dry and wet SPF yarns and relative differences between them (Δ).

purpose of comparison, cotton yarn was buried at the same time in the soil. After 7 days cotton yarn degraded very intensively and only small remains of yarn were left in the soil. Tensile properties of biodegraded cotton yarn could be measured only after 2 days. Biodegradation of cotton showed that microorganisms in the soil were active during the experiment.

The microphotographs of SPF yarns in Fig. 8 show that the quantity of bacteria and fungus, present on the surface of soybean protein fibres, increased with time of biodegradation. After 21 days in the soil, it is hard to say that there are any physical degradations of the fibre's surface because the fibres have natural irregular grooves and wrinkles (0 days).

Soybean protein fibres in comparison to the mid-twentieth century protein fibres (Fig. 1) have essentially smoother surface and relatively lower quantity of surface grooves that could enable bacteria to penetrate into the fibres.

Specific tensile stress-elongation curves of biodegraded cotton yarns (Fig. 9 and 10) show a significant decrease of breaking force and breaking elongation after 2 days, while for the yarns from soya protein fibres, they didn't change essentially.

0 days 2 days

Soybean Protein Fibres (SPF) 515

Fig. 9. Stress-elongation curves of cotton yarns after having been buried for 0 (CO 0) and 2

Fig. 10. Stress-elongation curves of cotton yarns after having been buried for 0 (SPF 0) to 21

Woven fabrics were buried at the same time as yarns into the soil at temperature 30°C and relative humidity 65% for 2, 7, 11, 16 and 21 days. Fabric samples (Fig. 11) changed the colour and became browner with many colour spots on the surface, which confirmed the

Pure cotton fabrics degraded in one weak to such degree that they broke up into pieces when we tried to dig them out of the soil. After 21 days only very little remains were found in the soil. Fabrics with yarns from soybean protein fibres in weft direction were more compact in weft direction than pure cotton fabrics. But in warp direction from cotton yarns

**4.3 Biodegradation of fabrics with SPF yarns in weft direction** 

the fabrics lost their strength and were easily torn (Fig. 11).

(CO 2) days in the soil.

(SPF 21) days in the soil.

existence of fungus.

7 days 11 days

Fig. 8. SEM microphotographs of SPF yarns after having been buried for 0, 2, 7, 11, 16 and 21 days in the soil (at magnification 2500-x).

0 days 2 days

7 days 11 days

16 days 21 days

Fig. 8. SEM microphotographs of SPF yarns after having been buried for 0, 2, 7, 11, 16 and 21

days in the soil (at magnification 2500-x).

Fig. 9. Stress-elongation curves of cotton yarns after having been buried for 0 (CO 0) and 2 (CO 2) days in the soil.

Fig. 10. Stress-elongation curves of cotton yarns after having been buried for 0 (SPF 0) to 21 (SPF 21) days in the soil.

#### **4.3 Biodegradation of fabrics with SPF yarns in weft direction**

Woven fabrics were buried at the same time as yarns into the soil at temperature 30°C and relative humidity 65% for 2, 7, 11, 16 and 21 days. Fabric samples (Fig. 11) changed the colour and became browner with many colour spots on the surface, which confirmed the existence of fungus.

Pure cotton fabrics degraded in one weak to such degree that they broke up into pieces when we tried to dig them out of the soil. After 21 days only very little remains were found in the soil. Fabrics with yarns from soybean protein fibres in weft direction were more compact in weft direction than pure cotton fabrics. But in warp direction from cotton yarns the fabrics lost their strength and were easily torn (Fig. 11).

Soybean Protein Fibres (SPF) 517

cotton - 0 days cotton - 21 days

soybean protein fibres - 0 days soybean protein fibres - 21 days

Fig. 12. SEM microphotographs of CO fabrics and SPF/CO woven fabrics (magnification

Fig. 13. Stress-elongation curves for cotton woven fabrics.

1500-x).

Fig. 12 shows that after 21 days in the soil the cotton cuticle was destroyed. On the soybean protein fibres the quantity of fungus and bacteria increased, but the surface of fibres was not damaged.

Fig. 11. Fabric samples after having been buried in the soil for 0 to 21 days. (Photo: Marica Starešinič)

The longer was the time of being buried in the soil, the greater was the loss of tensile strength of cotton fabrics: by 12% after 2 days and by 62% after 7 days of being buried in the soil. Breaking elongation decreased also rapidly: from 23% of the unburied fabric to only 8% after 7 days of being buried in the soil (Fig. 13).

Degradation of cotton yarns in warp direction affected tensile strength of SPF/CO fabrics in weft direction (Fig. 14). Fabrics buried in the soil for 7 days lost 12% of their tensile force, but after 21 days of being buried in the soil their breaking force decreased by additional 13% in comparison to unburied fabrics. Breaking elongation in weft direction of SPF/CO fabrics did not change significantly.

Fig. 12 shows that after 21 days in the soil the cotton cuticle was destroyed. On the soybean protein fibres the quantity of fungus and bacteria increased, but the surface of fibres was not

Fig. 11. Fabric samples after having been buried in the soil for 0 to 21 days. (Photo: Marica

The longer was the time of being buried in the soil, the greater was the loss of tensile strength of cotton fabrics: by 12% after 2 days and by 62% after 7 days of being buried in the soil. Breaking elongation decreased also rapidly: from 23% of the unburied fabric to only 8%

Degradation of cotton yarns in warp direction affected tensile strength of SPF/CO fabrics in weft direction (Fig. 14). Fabrics buried in the soil for 7 days lost 12% of their tensile force, but after 21 days of being buried in the soil their breaking force decreased by additional 13% in comparison to unburied fabrics. Breaking elongation in weft direction of SPF/CO fabrics

damaged.

Starešinič)

after 7 days of being buried in the soil (Fig. 13).

did not change significantly.

Fig. 12. SEM microphotographs of CO fabrics and SPF/CO woven fabrics (magnification 1500-x).

Fig. 13. Stress-elongation curves for cotton woven fabrics.

Soybean Protein Fibres (SPF) 519


Polyvinyl alcohol was used, because it is a water-soluble polymer, it dissolves at similar conditions as proteins and when added to proteins, it increases the fibre's strength.

The combination of cotton yarns and the yarns from soybean proteins in woven fabrics imparts comfort, soft hand and good moisture absorption properties to undergarments, outerwear, infants' wear, towels and beddings. Biodegradation of contemporary soybean protein fibres in early phase, up to 21 days in the soil at 30 ºC and 65% relative humidity, is a

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spinning dopes had homogenous structure.

Polyvinyl alcohol is also biodegradable in the soil (Brooks, 2005).

fibre's sheath from polyvinyl alcohol.

slow, hardly perceivable process.

p. 4, ISSN 1367-1308

ISSN 1434-3584

ISSN 0947-9163

US Patent 2,377,854

za tekstilstvo, Ljubljana

0947-9163

**6. References** 

polymer polyvinyl alcohol or cellulose or zein proteins. Single fibres made from such

Fig. 14. Stress-elongation curves for woven fabrics with SPF yarn in weft.
