A generalizable strategy toward highly tough and heat-resistant stereocomplex-type polylactide/elastomer blends with substantially enhanced melt processability
A generalizable strategy toward highly tough and heat-resistant stereocomplex-type polylactide/elastomer blends with substantially enhanced melt processability
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一种可推广的策略，旨在实现高韧性和耐热立体络合物型聚丙交酯/弹性体共混物，并显着增强熔融加工性能
DOI：
10.1016/j.polymer.2021.123736
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发表时间：
2021-04-12
期刊：
影响因子：
4.6
通讯作者：
Fu, Qiang
中科院分区：
文献类型：
--
作者：
Deng, Shihao;Yao, Ju;Fu, Qiang
可持续的立体复合型聚乳酸（SC-PLA）已被认为是一些传统工程塑料的潜在替代品，然而其广泛应用仍然面临主要与差的熔融加工性（即，SC结晶中不利的熔体记忆效应以及低熔体强度）和不足的断裂韧性。为了克服这些障碍，已选择用聚（乙烯-共-乙酸乙烯酯）（伊娃）增韧的等摩尔聚（L-丙交酯）/聚（D-丙交酯）（PLLA/PDLA）共混物作为模型系统，并设计了一种简单的策略，通过掺入痕量（即，0.5 wt%）的环氧官能化的低聚（苯乙烯-丙烯酸）（ESA）到PLLA/PDLA/弹性体共混物通过直接熔融共混在200？C.这种一锅法共混不仅有利于PLLA和PDLA链之间的立体络合，而且还允许一些对映体PLA的末端羟基与ESA的环氧基之间在它们的立体络合之前进行高效反应。这导致在SC-PLA基质中原位产生大量的长链支化PLA-接枝-ESA共聚物。非常令人印象深刻的是，这种PLA-接枝-ESA共聚物的产生引起SC-PLA基质的熔体记忆效应的实质性改善。该共聚物作为相容剂，以稳定共混物熔体中的规则PLLA/PDLA链簇，从而刺激在熔融加工的共混物产品中的SC微晶的排他性形成。此外，长的PLA分支赋予基质由于链间缠结密度增加而显著增强的熔体粘度。因此，高度立体复合的SC-PLA/伊娃产品具有优异的冲击韧性和耐热性以及强大的机械强度已通过注射成型制备。更值得注意的是，这种策略可以推广到各种SC-PLA基共混物，无论弹性体是否具有反应性基团。总的来说，这些令人兴奋的发现说明了通过生成具有长PLLA和PDLA分支的独特接枝共聚物，具有优异熔融加工性的高性能SC-PLA基材料的设计和应用的有希望的途径。
Sustainable stereocomplex-type polylactide (SC-PLA) has been recognized as a potential substitute for some traditional engineering plastics, however its widespread application still faces several hurdles primarily related to poor melt processability (i.e., the unfavorable melt memory effect in SC crystallization as well as the low melt strength) and insufficient fracture toughness. To overcome these hurdles, an equimolar poly(L-lactide)/poly(Dlactide) (PLLA/PDLA) blend toughened with poly(ethylene-co-vinyl acetate) (EVA) has been chosen as a model system and a facile strategy has been devised by incorporating trace amounts (i.e., 0.5 wt%) of epoxyfunctionalized oligo(styrene-acrylic) (ESA) into the PLLA/PDLA/elastomer blends through direct meltblending at 200 ?C. Such a one-pot blending not only facilitates the stereocomplexation between PLLA and PDLA chains but also permits the highly efficient reaction between terminal hydroxyl groups of some enantiomeric PLAs and epoxy groups of ESA before their stereocomplexation. This results in the in situ generation of large amounts of long-chain-branched PLA-graft-ESA copolymer in the SC-PLA matrix. Very impressively, the generation of this PLA-graft-ESA copolymer gives rise to a substantial improvement in the melt memory effect of the SC-PLA matrix. This copolymer behaves as a compatibilizer to stabilize regular PLLA/PDLA chain clusters in blend melts and hence to stimulate the exclusive formation of SC crystallites in melt-processed blend products. In addition, long PLA branches endow the matrix with a considerably enhanced melt viscosity owing to the increased interchain entanglement density. Consequently, highly stereocomplexed SC-PLA/EVA products with exceptional impact toughness and heat resistance as well as robust mechanical strength have been prepared by injection molding. More notably, this strategy can be generalized to various SC-PLA-based blends, irrespective of whether the elastomers have reactive groups. Overall, these exciting findings illustrate a promising avenue toward the design and applications of high-performance SC-PLA-based materials with excellent melt-processability via the generation of unique graft copolymers having long PLLA and PDLA branches.