Morphologies and Crystallization Behaviors in Melt-Miscible Crystalline/Crystalline Blends with Close Melting Temperatures but Different Crystallization Kinetics

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• 作者：Lijun Ye ; Cuicui Ye ; Kangyuan Xie ; Xianchun Shi ; Jichun You ; Yongjin Li
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：December 8, 2015
• 年：2015
• 卷：48
• 期：23
• 页码：8515-8525
• 全文大小：1101K
• ISSN：1520-5835

文摘

Poly(l-lactic acid) (PLLA) and poly(oxymethylene) (POM), with very close melting temperatures (T_m), can crystallize simultaneously or separately in their blends depending on composition and crystallization temperature (T_c), resulting in various types of morphology. It is mainly attributable to the greatly different crystallization kinetics of PLLA and POM. At a content of POM (蠁_POM), 3 wt % < 蠁_POM < 20 wt %, PLLA crystallization kinetics are comparable to POM, and therefore two type spherulites exhibit 鈥渟ide-by-side鈥?simultaneous growth with the penetration of PLLA spherulites into POM crystals. Although crystal growth rate (v_c) of POM is still a bit faster than that of PLLA, for 蠁_POM = 3 wt %, the nucleation of POM is restrained and POM spherulites can only develop on the propagating PLLA growth fronts with the generation of novel 鈥渃ore鈥搒hell鈥?blended spherulites. For 20 wt % 鈮?蠁_POM < 80 wt %, interspherulitic growth of PLLA inside the pre-existing matrix of POM spherulites causes the formation of interpenetrated blended spherulites, owing to the large discrepancy in kinetics. At 蠁_POM 鈮?80 wt %, PLLA molecular chains are redistributed into the interlamellar level regimes within the POM spherulites and can only crystallize into tiny crystals (owing to strong confinement). PLLA/POM blends provide a perfect example and new insights for understanding the crystallization of miscible crystalline/crystalline polymer blends (with very similar T_m鈥檚), in which kinetic factors could play a significant role in crystallization behaviors and morphology.