左右旋聚乳酸摻合物對左旋聚乳酸結晶行為的影響

Abstract

本研究利用POM、DSC與XRD來探討當左旋聚乳酸(PLLA)添加左右旋聚乳酸摻合物(Stereocomplex)後，左旋聚乳酸的結晶行為以及形態學上會有如何的改變。 聚乳酸結晶時，會因結晶溫度的不同而產生不同的結晶結構，在較高的結晶溫度下形成排列較緊密的α晶體結構；在較低的結晶溫度下，形成排列相對較鬆散的α’晶體結構；而在這之間的溫度，則形成兩相共存的晶體結構。我們將左旋聚乳酸添加左右旋聚乳酸摻合物後，利用POM、DSC、XRD等儀器觀察其結晶共存區間有何改變。 由於受到Stereocomplex的影響，使PLLA的共存區從原本的120℃~105℃擴大到135℃~95℃；由於Stereocomplex會幫助PLLA成核，使得以成核能力為影響主因的α’結構，可以在較高溫時獲得較大的成核能力。再者由於我們在PLLA中添加了一些不純物(PDLA-PEG-PDLA)，使得PLLA的球晶在成長時會遭遇一些阻礙，因此使球晶成長速率降低，讓α’結構競爭能力減少；另一方面我們發現添加Stereocomplex後PLLA的α結構與α’結構的動力學競爭模式並沒有改變，因此就是上述這兩種因素使得PLLA的共存區發生改變。 我們在POM中觀察到PLLA會在Stereocomplex球晶的晶束與晶束之間結晶；我們改變了混摻比例後，觀察到了三種不同位置生成的PLLA結晶，Internal - PLLA、SC - PLLA以及amorphous - PLLA，藉由這三種結晶，我們可以知道使PLLA球晶成長速率降低的主因為添加了不純物，而幫助PLLA成核的主因為Stereocomplex的結晶。

This research focuses on the Stereocomplex addition how to affect crystal behavior and morphology of PLLA. PLLA polymer chains packed closely α form crystal structure at higher crystallization temperature, and loosely α’ form crystal structure at lower crystallization temperature. Two crystal structures can co-exist at moderate temperatue. It is investigated by POM, DSC and XRD to observe the crystal behavior changes of PLLA/Stereocomplex.

Due to the effect of Stereocomplex, the α and α’ coexistence zone of PLLA/ Stereocomplex system changes from 120℃~105℃ to 135℃~95℃. Because Stereocomplex can help PLLA nucleate, the α’ form crystal structure, which is nucleation control, can have more ability to nucleate at higher temperature. Furthermore, we add some impurity in PLLA, PLLA spherulite may encounter some obstacles, thus making growth rate decreases. On the other hand, the α and α’ kinetic competition model does not change when we add Stereocomplex into PLLA. As the above mentioned, the two factors make the coexistence zone change. In POM, PLLA spherulite crystallizes between the Stereocomplex spherulite's bundle; when we change the Stereocomplex amounts, internal - PLLA、SC - PLLA and amorphous - PLLA can be observed. Because of these three crystal, we can know the impurity-added effect is the main factor resulting in growth rate decreament, and Stereocomplex crystal is the main factor to assist PLLA to nucleate.