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CFF/PLA biocomposites

Mixing CFF with biopolymers, e.g., PLA, can form a biodegradable composite used for plastic products and implant applications. In preparation of the composite, chicken feather was immersed in alcohol for 24 h, then washed in a water-soluble organic solvent, and dried under 60°C for 24 h [38]. CFF with a diameter of about 5 цш and length of 10—30 mm were separated from the quill and then used. Fig. 1.4 shows an SEM photograph of a CFF. Fig. 1.7 shows the relations between CFF content and peak stress and modulus of elasticity, respectively. The modulus of elasticity of CFF/PLA composite increases with the CFF content and reaches the

Relationship between tensile properties and CFF content

Figure 1.7 Relationship between tensile properties and CFF content.

Stress—strain curves of (A) pure PLA sample; (B) 5 wt% CFF/PLA composite

Figure 1.8 Stress—strain curves of (A) pure PLA sample; (B) 5 wt% CFF/PLA composite.

maximum modulus of 4.38 GPa (increment up to 35.6%) at the CFF content of 5 wt %. This reveals that the incorporation of CFF into the matrix is quite effective for reinforcement. The decrease of modulus for the composite with the CFF content above 5 wt% will be due to the insufficient filling of the matrix resin, designating 5 wt% CFF to be the critical content.

It also can be found from the peak stress that the tensile strength of PLA after the addition of CFF is lower than that of pure PLA. This phenomenon, also reported by other researchers [26,39], is an indication of poor adhesion between the CFF and the matrix. Although the CFF surface is rough, the hydrophobic properties of CFF and PLA would highly affect their bonding efficiency. Therefore, the adhesion property between them is an issue. And the stress could not be transferred from the matrix to the stronger fibers. Another possible explanation of this phenomenon could be that the CFFs were randomly oriented inside the composite; the failure of the composite might be initiated by the failure of the matrix and then followed by fiber breakage. Fig. 1.8 shows the stress—strain curves of the pure PLA and 5 wt% CFF/PLA composite. It is observed that a much longer plateau is located between a strain where the peak stress is reached and the strain at break. It can be concluded that the proper content addition of CFF shows a positive effect on elongation to break for PLA, which was expected because of CFFs acting as bridges to prolong the fracture process of the CFF/PLA composite, and that the failure of the composite was controlled by the bridging effect of CFF inside the composite. These conclusions could be proved by the fractured morphology of the microstructures observed by SEM. The thermal properties, such as glass transition temperature (Tg), crystallization temperature (Tc), melting temperature (Tm), crystallization enthalpy (AHc), and melting enthalpy (AHm), obtained from the DSC studies are summarized in Table 1.3.

Table 1.3 DSC results for pure PLA and CFF/PLA composites

CFF content (wt%)

Tg (°C)

Tc (°C)

AHc (J/g)

Tm (°C)

AHm (J/g)

0

58.7

112.9

38.8

163.4

169.5

43.2

2

59.8

112.2

42.1

164.0

171.9

44.7

5

59.2

112.4

42.6

163.7

170.0

43.7

8

59.3

112.0

43.5

163.5

170.0

44.7

10

57.5

102.9

44.5

166.7

46.9

 
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