二氧化矽與星狀構型對左旋聚乳酸結晶行為的影響

Abstract

本研究主要探討添加無機物SiO2以及星狀聚乳酸，對左旋聚乳酸兩結晶結構α與α’結晶行為以及結晶型態學上的影響。 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。我們將左旋聚乳酸混摻二氧化矽，以及合成三臂的星狀左旋聚乳酸，利用POM、DSC、XRD等儀器觀察其結晶共存區間的有何改變。 當左旋聚乳酸加入SiO2顆粒，其提供了異質成核的表面，加速結晶晶核的形成；星狀左旋聚乳酸則因為含有核心結構，在結晶時核心會被視為雜質而排到晶片之外，不易形成穩定的晶核，結晶時需要更久的時間進行，兩種結晶結構受到的影響程度不同，導致共存區的結晶競爭能力改變，PLLA/SiO2系統的α與α’共存區溫度範圍跟單純PLLA系統比較似乎沒有差異，而星狀左旋聚乳酸的共存區溫度範圍則劇烈下移，為了更進一步了解線性與星狀構型之間的差異，我們做了不同比例的線性與星狀PLLA混摻系統來連結兩者，並藉由玻璃轉移溫度、平衡熔點等提供的訊息，由分子鏈運動能力、過冷度與結晶時晶片摺疊鏈端表面自由能來探討競爭的差異。 結晶型態方面，摻入SiO2顆粒後的左旋聚乳酸仍是典型黑十字球晶，星狀PLLA則在較高結晶溫度球晶會開始出現環狀結構，線性與星狀PLLA混摻系統球晶環狀結構出現的溫度則隨線性PLLA比例增加而提高。

The focus of this research is how SiO2-added and architecture affect α and α’crystal structures 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 structures changes of PLLA/ SiO2 and 3-ram PLLA, then compared with typical linear PLLA system.

When SiO2 is added, it provides heterogenous nucleation surface to accelerate the formation of crystal nuclei; in the contrast, star-shaped PLLA is difficult to form stable nuclei and requires longer crystallization time due to the core unit which is considered as impurity and is excluded from lamellae. The two factors affect the two crystal structures in varying degree, resulting in coexistence zone change. The α and α’ coexistence zone of PLLA/SiO2 system seems the same to pure PLLA system and that is much lower of star-shaped PLLA system. In order to further understand the variations from linear to star-shaped PLLA, different proportion blends of linear and star PLLA are used to link the relationship. Furthermore, it is discussed by the aspects of chain mobility, degree of undercooling and surface free energy of chain folding from the information of glass transition temperature, equilibrium melting temperature and the other basic physical properties. On the morphology of PLLA, it is typical Maltese cross type spherulite in PLLA/SiO2 system, while there is ring-banded type spherulite appearing in Star-shaped PLLA system. In the blended system of linear and star PLLA, the temperature of ring-banded spherulite appearing is rasing with the proportion of linear PLLA increasing.