Investigating the Physical Properties of Poly(L-lactic acid) Modified Using an Aromatics Succinic Dihydrazide Derivative

Abstract

In order to overcome the defect of slow crystallization rate of Poly(L-lactic acid) (PLLA) during manufacturing, a new organic nucleating agent, N,N'-succinic bis(hydrocinnamic acid) dihydrazide (BHSH), was synthesized to evaluate its influence on the crystallization and other physical properties of PLLA in this work. For this purpose, the non-isothermal crystallization, isothermal crystallization of PLLA modified using BHSH were investigated using differential scanning calorimetry and depolarized-light intensity measurement. Additionally, the melting behavior, thermal stability, and optical property of BHSHnucleated PLLA were further studied. The result of the non-isothermal crystallization behavior indicated that BHSH had a distinct accelerating effect for the melt crystallization process of PLLA and the non-isothermal crystallization peak shifted to the higher temperature and became sharper. Meantime, non-isothermal crystallization result further revealed that both the cooling rate and the final set melting temperature affected the non-isothermal crystallization behavior of PLLA. The addition of BHSH could cause the crystallization halftime of PLLA to become shorter, meaning that PLLA/BHSH samples had a faster overall crystallization rate comparing with the pure PLLA. Upon the addition of 2 wt% BHSH, the crystallization half-time of PLLA/BHSH decreased from 575.7 s to the minimum value 48.6 s at 100°C. Melting behavior after crystallization further confirmed the crystallization promoting effect of BHSH for PLLA, and the double-melting peaks were attributed to the melting-recrystallization. Although that the BHSH could improve the crystallization of PLLA, unfortunately, the presence of BHSH decreased the thermal stability and light transmittance of PLLA.