Effect of thermal history on nucleation and crystallization of poly(lactic acid)
Effect of thermal history on nucleation and crystallization of poly(lactic acid)
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DOI：
10.1007/s10853-016-0059-5
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发表时间：
2016-08-01
影响因子：
4.5
通讯作者：
Elkoun, Said
中科院分区：
文献类型：
--
作者：
Jalali, Amirjalal;Huneault, Michel A.;Elkoun, Said
本文设计了一种连续加热和冷却的方案来研究聚乳酸的自成核行为。这项研究的主要目的是研究聚乳酸的α和α‘晶型修饰的效率。这是通过比较先前在80到130摄氏度的不同等温温度下结晶的样品在自成核后冷却时的结晶温度来实现的。在加热到部分熔化范围期间，观察到结晶样品的三种不同的机制。对于100℃以下结晶的样品，在主熔融峰之前检测到一个放热峰，该峰被归因于α‘-α固态转变。对于100-120℃结晶的样品，观察到了熔融再结晶机制。最后，对于在120摄氏度以上结晶的样品，只检测到阿尔法相的熔化。在部分熔融后冷却时，发现含有α和α‘混合物的样品具有最高的晶化温度、最高的晶核密度和最小的球晶尺寸。此外，还观察到在100-120℃之间等温结晶，加热到部分熔融，然后冷却到室温的样品在100℃和120℃有两个特殊的结晶峰，这一现象归因于X射线衍射所揭示的α和α‘晶相的形成。此外，通过在自核化温度范围内略微改变温度，观察到每个峰的比例发生了变化。
In this paper, a successive heating and cooling protocol was designed to investigate the self-nucleation behavior of poly(lactic acid), PLA. The main objective of this investigation was to study the efficiency of the alpha and alpha' crystalline modifications of PLA. This was carried out by comparing crystallization temperatures upon cooling after self-nucleation of samples previously crystallized at various isothermal temperatures ranging from 80 to 130 degrees C. During heating to the partial melting range, three different mechanisms were observed for crystallized samples. For samples crystallized below 100 degrees C, an exothermic peak was detected prior the main melting peak which is ascribed to the alpha'-alpha solid-state transition. For samples crystallized between 100 and 120 degrees C, a melt recrystallization mechanism was observed. Finally, for samples crystallized above 120 degrees C, only melting of the alpha phase was detected. Upon cooling after partial melting, it was found that samples comprising a mixture of alpha and alpha' exhibited the highest crystallization temperature, the highest nuclei density, and the smallest spherulite size. Moreover, it was observed that samples that were isothermally crystallized between 100 and 120 degrees C, heated up to partial melting, and then cooled back to room temperature exhibited two peculiar crystallization peaks at 100 and 120 degrees C. This phenomenon was ascribed to the formation of alpha and alpha' crystalline phases as revealed by X-ray diffraction. In addition, by slightly changing the temperature within the self-nucleation temperature range, a change of the proportion of each peak was observed.