Polylactic Acid Based Nanocomposites And Fiber Properties

Polylactic acid(PLA)is a biopolymer which has excellent biocompatibility and biodegradability.However,it possesses several shortcomings,such as low crystallization speed,poor mechanical strength and bad flexibility.In this work,we carried out the modification research of PLA by selecting carbon nanotubes(CNT)and cellulose nanocrystal(CNC)as nano-reinforcement materials and nucleating agents,and amorphous poly(vinyl acetate)(PVAc)as the toughening phase.PLA/CNT nanocomposites were prepared by twin-screw melt blending method.PLA/PVAc/mCNC nanocomposites were fabricated by solution casting.Further,PLA/CNT composite fibers were prepared by melt spinning.The structure and performance of the nanocomposites and composite fibers were characterized by SEM,TEM,POM,DSC,XRD,FTIR and tensile testing.The results showed that:In the preparation of PLA/CNT nanocomposites,the optimal blending temperature was 185 ℃,and the optimum screw speed was 120 rpm,and the optimum blending time was 6 min.CNT could provide heterogeneous nucleation sites for PLA crystallization.The crystallization speed of PLA could be elevated.The tensile strength of PLA/CNT 0.5 nanocomposites was improved by 46.60%compared with that of pure PLA,which showed the strong interfacial interactions between CNT and PLA.In the PLA/CNT composite fibers,higher tensile speed and stress could promote the molecular orientation and crystallization of PLA moleculer chains.As a result,the crystallinity and tensile strength of composite fibers with high spinning speeds were higher than that with low spinning speeds.Through the surface treatment of dodecyltrimethylaimmonium chloride(DTAC),the dispersion of the modified CNC(mCNC)was significantly improved,resulting in its good dispersion in PLA matrix.mCNC can provide heterogeneous nucleation sites and accelerate the crystallization of PLA.The tensile strength of PLA/mCNC nanocomposites were significantly increased by 71.70%compared with that of pure PLA showing the nano-reinforcement effect of mCNC.However,the elongation at break and brittleness of the nanocomposites were increased.In PLA/PVAc/mCNC composite materials,The amorphous PVAc could dilute the crystallization of PLA,resulting in the decrease of PLA crystallinity.At the same time,the movement ability of PLA moleculer chains was increased and its toughness was strengthened.In the combination of CNC and PVAc,the reinforcement and toughening of PLA could be realized simultaneously.So the novel PLA/PVAc/mCNC ternary biocomposites were developed.