Effects of NANH as a nucleation agent on the performance of PLLA

In this research, N,N′-bis(nicotinic) 1,4-naphthalenedicarboxylic acid dihydrazide (NANH) as a new synthetic organic nucleating agent was employed to overcome the slow crystallization rate of poly(L-lactide) (PLLA). Melt crystallization showed that the crystallization ability of PLLA was significantly enhanced by NANH, with NANH still being able to accelerate PLLA crystallization at a cooling rate of 50°C/min. Additionally, when the final melting temperature was 170°C, the onset melt-crystallization temperature and melt-crystallization peak temperature of PLLA/3% NANH were up to 160.0 and 155.1°C, respectively. Isothermal crystallization showed that the half-time of the overall crystallization of PLLA/3% NANH was dramatically reduced, from 71.9 min at 135°C for the virgin PLLA to the minimum value of 0.3 min. This advanced nucleation effect was speculated to be due to chemical nucleation through the theoretical analysis of frontier orbital energy. Melting behaviors under different conditions further confirmed the crystallization-accelerating effect of NANH for PLLA crystallization, and the melting processes were affected by the crystallization temperature and heating rate. Although NANH decreased the thermal decomposition temperature of PLLA in air, the thermal decomposition temperatures of all PLLA/NANH blends were higher than 330°C, which could meet daily usage requirements. Finally, the addition of NANH enhanced PLLA fluidity; however, light transmittance was seriously weakened.