分子链有序化混合对PLLA/PDLA共混物熔融稳定性的影响

Effect of Chain Mixing Degree on the Melt Stability of PLLA/PDLA Blends

左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)可通过共结晶形成兼具高强、耐热、耐水解等优异特性的立构复合聚乳酸(SC-PLA),在工程塑料领域展现出广阔的应用前景。然而,由于PLLA/PDLA共混物的熔融稳定性很差(即PLLA/PDLA分子链对或链簇在熔融时易解离、甚至发生微相分离),导致在熔融结晶过程中会同时形成大量的SC和均质(HC)晶体,制品性能远不及预期。针对这一问题,尝试采用溶液混合-沉淀、熔融混合和静电纺丝等方法来调控共混物中分子链的有序化混合程度(即有序配对的PLLA/PDLA链簇的数量),并研究了链混合对熔融稳定性的影响规律,发现链有序混合是提高熔融稳定性的关键。随着分子链有序混合程度的提高,共混物的熔融稳定性得到明显改善,因此在熔融结晶时形成的SC晶体的含量显著增加,这可为高性能SC-PLA制品的开发提供新思路。

Stereocomplex-type polylactic acid(SC-PLA)prepared from poly(L-lactide)/poly(D-lactide)(PLLA/PDLA)blends showed huge potential applications in engineering field,owing to its outstanding mechanical properties,heat resistance and hydrolysis resistance.However,the poor melt stability of the PLLA/PDLA blends(namely the PLLA/PDLA chains could be decoupled from their chain pairs or clusters upon complete melting and even phase-separated into PLLA-and PDLA-rich regions)led to the predominant formation of homocrystallites(HC)over SC crystallites in final melt-processed SC-PLA products with impaired properties.Three different mixing methods including solution mixing and co-precipitation,melt blending,and electrospinning were used to prepare the PLLA/PDLA blends with various degrees of chain mixing,and the effect of chain mixing on the melt stability had been investigated.It is found that interchain ordering plays a decisive role in improving the melt stability.With the increase in the degree of interchain ordering,the melt stability is greatly improved and thus more SC crystallites are formed during the melt-crystallization process.This could open a new horizon for the fabrication of high-performance SC-PLA products.