Biocomposites including nano-scale dispersed phase and polymers from renewable resources

摘要

Poly(lactic acid) (PLA) was physically modified by filling with an inorganic additive, natural fibres as well as with a tributyl citrate (TBC). PLA composites were prepared with a film stacking method and analysed by scanning electron microscopy (SEM), thermogravimetry (TGA), thermomechanometry and differential scanning calorimetry (DSC) to investigate the physical and mechanical properties of the hybrid composites. PLA composites reinforced with hemp fibres in combination with nanosilica are thermally stable as the maximum rate of weight loss of the composites shifted to the highest temperature observed in TGA results. Dynamic mechanical properties of PLA composites showed that the reinforcement of hemp fibre and nanosilica strongly affected the mechanical properties of the composites. The highest storage modulus improvements were reached by addition of hemp fibre and nanosilica without plasticiser. An increase in storage modulus monitored in the temperature region from 70 to 100 °C reflected an increase in structural stiffness due to recrystallisation activity in the composites. The addition of TBC reduced the modulus though initiated the crystallisation on cooling, enhanced the nucleating ability of the fillers and chain mobility in PLA composites. The melting and crystallisation behaviour of PLA composites was explored with non isothermal DSC at various scanning rates. The characteristics of the crystallisation and melting behaviour of PLA composites were explained by the slow rate of crystallisation and recrystallisation, which is in agreement with DMA results. Non-isothermal crystallization kinetics shows that the crystallization rate of PLA composites was higher than of neat PLA and further increased with presence of TBC, indicating that the addition of plasticiser and nucleating agents enhanced the transportation ability of polymer chains. SEM revealed a good distribution of nanosilica for composites with and without TBC. A great transfer of stress between hemp fibres and PLA nanosilica matrix resulted in improved of physical and mechanical properties as evidenced by DMA and DSC results.