Conductivity and mechanical properties of carbon black-reinforced poly(lactic acid) (PLA/CB) composites

The effects of carbon black (CB) content on the mechanical properties, hydrophobicity, electrical conductivity, morphology, and thermodynamic properties of the poly(lactic acid) (PLA/CB) composites were studied. The results showed that adding an appropriate amount of CB improved both the mechanical properties and hydrophobicity of PLA, but an excessive addition of CB reduced the mechanical properties of PLA/CB composites. The conductivity test results showed that when CB content was exceeded than12 wt%, there was no significant changes. The results of analyzing the barrier performance showed that less CB content helped to extend the path of water molecules; thus, the water barrier performance was slightly improved. However, CB and PLA had no chemical bonding reaction, thus, the oxygen permeability was greatly increased with increase of the CB content. The XRD results showed that an appropriate amount of CB could improve the crystallinity of PLA. It was shown by scanning electron microscopy (SEM) inspection that when the filler content increased from 4 to 12 wt%, the cross-sections of the PLA/CB composites became wavy and coarser, indicating that the morphology of the PLA/CB composites was gradually changed and became more and more brittle. Thermogravimetric analysis showed that thermal stability of PLA could be improved when CB <= 8 wt%. Differential scanning calorimetry (DSC) analysis showed that the glass transition temperature of PLA/CB composites was slightly higher than that of the pure PLA, whereas the melting temperature was slightly lower than that of the pure PLA. This new composite material with optimized CB content showed excellent properties.

Automated summary

Appropriate amount of carbon black can improve the mechanical properties and hydrophobicity of PLA, but excess addition can reduce mechanical properties. A lower amount of carbon black enhances water barrier performance but also increases oxygen permeability. Crystallinity of PLA can be improved with suitable amount of carbon black, while increasing filler content makes the composite material more brittle.