Toughening polylactide by dynamic vulcanization with castor oil and different types of diisocyanates

Dynamic vulcanization of polylactide (PLA) with castor oil (CO) and three different diisocyanates, namely 4,4′-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), was performed to study the effect of diisocyanate type on the vulcanization process and on the morphology as well as mechanical properties of the PLA/CO-based polyurethane blends. The reactivity of the three diisocyanate followed the order of MDI > HDI > IPDI when reacting with castor oil. Interfacial compatibilization between PLA and the CO-based polyurethane occurred when the less reactive HDI and IPDI was used. Among all the blends, PLA/CO-IPDI showed the finest morphology and the best toughening efficiency. Incorporation of 20 wt% CO-IPDI increased the elongation at break and notched impact strength of PLA by 47.3 and 6.6 times, respectively. Cavitation induced matrix plastic deformation was observed as the toughening mechanism for the PLA blends with CO-based polyurethane. The effect of CO-IPDI content on the morphology and mechanical properties of PLA was studied in detail. The particle size of dispersed CO-IPDI and the elongation at break increased gradually, the tensile strength and Young's modulus decreased gradually, while the impact strength first increased and then decreased with increasing CO-IPDI content from 5 to 30 wt%. The maximum impact strength appeared for the blends with 20 wt% CO-IPDI.     

高分子材料烧结成型研究进展

高分子材料烧结成型是借鉴粉末冶金技术而形成的一种特殊的成型加工方法,特别适合熔体粘度极大、高温易分解的高分子材料的成型加工。传统高分子材料的烧结成型温度在熔点以上,通过粉末的熔融和界面扩散将粉末烧结在一起。本文首先对聚四氟乙烯和超高分子量聚乙烯这两种常用于烧结成型的高分子材料的烧结成型工艺条件、成型机理及其多功能材料的制备等方面进行了系统的介绍;最后,重点分析了我们组最近针对立构复合型聚乳酸熔融稳定性差、熔融加工易降解的问题而提出的一种低温(低于立构复合晶体熔点)烧结成型新方法,即通过在粉末表面形成新立构复合晶体将粉末烧结在一起,并对其研究进展进行了综述。