Investigating the crystallization, melting behavior, and thermal stability of poly(L-lactic acid) using aromatic isoniazid derivative as nucleating agent

The poor crystallization performance is the common challenge for semicrystalline polymers. In this work, a aromatic isoniazid derivative (DI), derived from isoniazid and 1,4-dicarboxybenzene, was synthesized to serve as a nucleating agent for poly(l-lactic acid) (PLLA), and the crystallization behavior, melting behavior, and thermal stability of PLLA/DI were investigated through a series of measurements. The non-isothermal crystallization behavior showed that the incorporation of DI significantly promoted the crystallization of PLLA in cooling of 1 degrees C/min; however, the nucleating effectiveness was also evidently affected by the cooling rate. The effect of DI concentration on non-isothermal crystallization of PLLA indicated that 3 wt% DI exhibited the best crystallization acceleration effectiveness, and the non-isothermal crystallization enthalpy of PLLA/3% DI in cooling was considerably enhanced up to 330 times with respect to the primary PLLA. Both XRD and the relevant melting behavior measurements further confirmed the advanced promoting crystallization effect of DI for PLLA. In addition, the measurement also showed that the addition of DI could not change the crystalline form of PLLA, and the double melting peaks were attributed to the melting-recrystallization mechanism. Thermal stability indicated that the thermal decomposition behavior of PLLA did not depend on the DI concentration; however, the onset decomposition temperature decreased with the increase of DI concentration.