Crystallization and morphology of stereocomplexes in nonequimolar mixtures of poly(l-lactic acid) with excess poly(d-lactic acid)
Crystallization and morphology of stereocomplexes in nonequimolar mixtures of poly(l-lactic acid) with excess poly(d-lactic acid)
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DOI：
10.1016/j.polymer.2011.11.002
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发表时间：
2011-12
期刊：
影响因子：
4.6
通讯作者：
E. Woo;L. Chang
中科院分区：
文献类型：
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作者：
E. Woo;L. Chang
聚（d-乳酸）与低分子量聚（l-乳酸）（PDLA/LMw-PLLA）共混物的非等摩尔组合物的结晶导致形成立体络合PLA（sc晶）和同晶（PDLA或PLLA）的各种级分。对于 LMw-PLLA 含量在 30 至 50wt% 之间的组成窗口内的 PDLA/LMw-PLLA 共混物，仅存在单晶，不存在同晶。另一方面，对于含有过量 PDLA 的 PDLA/LMw-PLLA 混合物，例如PDLA/LMw-PLLA=90/10，对 sc-PLA 晶体与 PDLA 同晶的各个结晶阶段的原子力显微镜 (AFM) 表征显示，过量的 PDLA 在作为结晶模板的预成型 sc-PLA 晶体上重复堆积。结晶最初从线状（原纤维状）PDLA 片层开始，随后 PDLA 在 sc-PLA 晶体上聚集成串珠晶体，然后生长为更厚的不规则形状的面团状片层。从线到串珠片层的重复生长循环在面团状片层的顶部继续作为新的基底，直到 PDLA 球晶的撞击结束。
Crystallization of nonequimolar compositions of poly(d-lactic acid) with low-molecular-weight poly(l-lactic acid) (PDLA/LMw-PLLA) blends leads to formation of various fractions of stereocomplexed PLA (sc-crystallites) and homocrystallites (PDLA or PLLA). For the PDLA/LMw-PLLA blends within the composition window of LMw-PLLA content between 30 and 50wt%, only sc-crystal exists and no homocrystal is present. On the other hand, for PDLA/LMw-PLLA blends with excess PDLA, e.g. PDLA/LMw-PLLA=90/10, atomic-force microscopy (AFM) characterization on various stages of crystallization of sc-PLA crystal with PDLA homocrystal shows a repetitive stacking of excess PDLA on pre-formed sc-PLA crystal serving as crystallizing templates. The crystallization initially begins with string-like (fibril-like) PDLA lamellae, followed with PDLA aggregating on sc-PLA crystal into a bead-on-string crystal, then growing to thicker irregularly-shaped dough-like lamellae. Repetitive growth cycle from strings to bead-on-string lamellae continues on top of the dough-like lamellae as new substrates, until ending impingement of the PDLA spherulites.