Non-isothermal melt- and cold-crystallization, melting process, and optical and mechanical properties of PLLA: the effect of TAPH

We synthesized a new phenylacetic hydrazide derivative (TAPH) by acylation and amination to prepare modified poly(L-lactide) (PLLA) materials. The non-isothermal melt- and cold-crystallization, melting process, optical and mechanical properties of modified PLLA were studied with the objective of correlating TAPH to PLLA crystallization and other performances. Non-isothermal melt crystallization showed that TAPH as a heterogeneous additive was able to promote crystallization and accelerate the crystallization rate of PLLA. Unfortunately, an increase in the cooling rate during cooling led to a decrease in crystallization ability. Non-isothermal cold-crystallization results disclosed that PLLA/TAPH’s cold-crystallization behavior depended on the heating rate; and upon a given heating rate, with an increase in TAPH loading, a shift toward the low-temperature side of the cold-crystallization peak further confirmed the nucleation effect of TAPH. The melting processes of PLLA/TAPH effectively depended on TAPH, the heating rate, and previous crystallization behaviors including non-isothermal crystallization and isothermal crystallization. Additionally, the double-melting peaks that appeared during the melt were thought to be due to melting-recrystallization. In terms of the optical property, the influence of TAPH on PLLA’s transparency was extremely negative as 2 wt% TAPH caused PLLA’s transparency to be zero. A comparative study on mechanical properties showed that TAPH could enhance PLLA’s tensile modulus and tensile strength, but elongation at break of any PLLA/TAPH was lower than that of pure PLLA.