Non-isothermal Crystallization, Melting Behavior, Thermal Decomposition, Fluidity and Mechanical Properties of Melt Processed Poly(L-lactic acid) Nucleated by N,N'-Adipic Bis(piperonylic acid) Dihydrazide

Abstract

Enhancing on the crystallization ability of poly(L-lactic acid) (PLLA) during practical processing is one of the most effective way to overcome the poor heat resistance. In this work, N,N '-adipic bis(piperonylic acid)dihydrazide (PAAH) was synthesized to be firstly used as a heterogeneous nucleating agent to evaluate its influence on the performances, including the crystallization, melting behavior, thermal stability, fluidity and mechanical property, of PLLA. The nucleation effect of PAAH was determined via the melt-crystallization of PLLA with various PAAH concentrations from 0.5 to 3 wt % at different cooling rates, as well as the different final melting temperature Tf . The results revealed that the PAAH could significantly accelerate the crystallization of PLLA in cooling, and the melt-crystallization peak shifted toward the higher temperature with increasing of PAAH concentration, resulting from an increase of nucleation density in PLLA matrix. Additionally, both the cooling rate and Tf were two critical factors to crystallization, a higher cooling rate could weaken the crystallization ability of PLLA/PAAH, and the 200°C was the optimum melting process temperature. For cold-crystallization, PAAH had an inhibition for the cold-crystallization of PLLA, but the cold-crystallization peak moved toward the higher temperature with increasing of heating rate because of thermal inertia. There existed only a single melting peak after melt-crystallization at cooling of 1°C, which further confirmed the advanced nucleation effect of PAAH, but the double-melting peaks appeared after isothermal crystallization at 110°C, which was attributed to the melt-recrystallization. The other measurements showed that, compared to the neat PLLA, the addition of PAAH decreased the thermal stability and tensile modulus of PLLA, but PLLA/PAAH samples had the better fluidity, the higher tensile strength and the longer elongation at break.