Study On Crystallization Properties Of Pla/CNTs Composites

Poly-lactic acid (PLA) is a biocompatible and biodegradable biopolymer though, slow crystallization speed and brittleness severely limits its applications. In this paper, carbon nanotubes(CNTs) were compounded with PLA via solution blending to improve PLA's properties. The time-temperature synchronous FTIR and DSC were used to study the isothermal or non-isothermal crystallization properties of the PLA/CNTs composites. The emphasis was put on the influences of the CNTs'types, tube diameter, tube length, mass fraction and also the molecular weight of PLA on the crystallization properties of the composite. The influence of the isothermal crystallization treatment on the tensile properties of PLA/CNTs composites was also studied. The different CNTs used, as heterogeneous nucleation agent, could speed up the isothermal crystallization process of PLA. Different CNTs have different impacts on the isothermally melt crystallization or cold crystallization at different temperatures and multi-walled carbon nanotubes(MWCNTs) with a larger diameter tend to accelerate especially the melt crystallization of PLA, and longer CNTs promotes the crystallization, especially the cold crystallization. The addition of 0.1wt% CNTs could accelerate the crystallization of PLA, but when CNTs increased up to 1wt%, the accelerating effects were weakened obviously. Besides, PLA containing less CNTs content crystallized isothermally faster under higher crystallization temperature. At lower crystallization temperature, PLA-1 with a lower molecular weight crystallized isothermally faster than PLA-2 with a higher molecular weight and all the CNTs used had a more obvious accelerating action on the crystallization of PLA-2. Different CNTs showed varied enhancement for the mechanical properties of PLA, and the isothermal crystallization treatment could further lift the tensile strength of PLA composites at the cost of toughness. CNTs could promote the non-isothermal crystallization process of PLA, the addition of CNTs resulted in an obvious increase in the relative crystallization degree of PLA at a heating speed of 5℃/min, and MWCNTs showed a more obvious acceleration for the non-isothermal crystallization of PLA than singled-walled carbon nanotubes(SWCNTs) or double walled carbon nanotubes(DWCNTs) while shorter MWCNTs showed a more obvious acceleration than longer MWCNTs.