Thermal performances and optical property of poly(L-lactic acid) under the influence of N,N'-dodecanedioic bis(3-phenylpropionic acid) dihydrazide as a crys­tal­lization promoter

Abstract

Poly(L-lactic acid) (PLLA) as an important biodegradable polymer suffers from slow crystallization rate and poor heat resistance. An organic compound N,N'-dodecanedioic bis(3-phenylpropionic acid) dihydrazide (BHADD) was synthesized to evaluate its general influences on the physical properties of PLLA. The melt-crystallization process indicated that BHADD could serve as a heterogeneous nucleating agent for improving the crystallization of PLLA, and PLLA/1%BHADD exhibited the sharpest melt-crystallization peak located at the highest temperature, as well as an increase of cooling rate weakened the crystallization ability of BHADD-nucleated PLLA. And the final melting temperature also displayed the significant effect on the crystallization process of PLLA. For the cold-crystallization process, both BHADD concentration and heating rate affected the cold-crystallization behavior of PLLA/BHADD, the increasing of BHADD concentration caused the cold-crystallization peak to shift to the lower temperature; in contrast, a higher heating rate during heating leaded to the peak's shift toward the higher temperature because of the thermal inertia. The melting behavior of PLLA/BHADD depended on the crystallization temperatures and heating rates, and the double melting peaks were attributed to the melting-recrystallization. Thermal decomposition experiment showed all PLLA/BHADD samples as the pure PLLA only exhibited one thermal decomposition stage, but PLLA/BHADD had a lower thermal stability than the pure PLLA. Additionally, the addition of BHADD seriously decreased the light transmittance of PLLA.

The Performance Investigation of PLLA/PPAPH: The Influence of PPAPH as Heterogeneous Crystal Nuclei

“…Among all PLLA/PPAPH, PLLA/1%PPAPH exhibits the highest Toc at 138.8°C and the highest Tmc at 135.7°C, as well as the largest ΔHc of 52.5 J/g which means that PLLA/1%PPAPH's crystallinity is up to 57.0% through calculation [24]. These results also show that, upon the addition of 1 wt% nucleating agent, the Toc, Tmc and ΔHc of PLLA/PPAPH are higher than PLLA/BHADD [25]. PPAPH's crystallization accelerating role has been confirmed in previous melt-crystallization section upon cooling at 1°C/min, but the cooling rate is very slow, which is insufficient to demonstrate PPAPH powerful role in accelerating PLLA's crystallization rate, because the actual manufacturing process often requires a higher cooling rate.…”