- 學位論文
增塑聚乳酸介穩態的形成及其冷結晶行為
The mesophase formation of plasticized PLLA and its cold crystallization behavior.
摘要
本研究主要探討聚乳酸(PLLA)介穩態形成的條件及其等溫冷結晶行為。我們利用開環聚合法合成出以分子量為 4,600 及 2,000 的聚乙二醇、乙二醇以及己二醇不同中間鏈段的聚乳酸三嵌段共聚物(triblock copolymer)，以聚乙二醇(PEG)做為塑化劑與共聚物混摻或已以足夠比例存在於共聚物內，改變玻璃轉移溫度，使得聚乳酸可以在更低的溫度形成介穩態，發現介穩態的形成僅與玻璃轉移溫度是否足夠低有關。當 DSC 升溫時觀察到在約 50 °C 及 100 °C 有單獨結晶放熱峰，或者 100 °C 放熱峰前有微量吸熱峰，即可判斷此系統有介穩態。我們以熱微差掃描分析儀及廣角 X 光散射儀觀察介穩態、α’結構以及α結構在等溫冷結晶時結構存在的溫度區間以及三者之間的共存關係。研究結果顯示，最低溫形成介穩態單一結構，較高溫會有一溫度區間為介穩態及α’結構共存，次高溫度區間為α’結構與α結構共存，最高溫度則為單一α結構。介穩態及α’結構共存時互為競爭關係。此外，本研究也探討已在低溫形成介穩態單一結構後，對於介穩態在各共存區持溫的結構變化，發現在介穩態及α’結構共存區介穩態並無變化，而在α’結構與α結構共存區，介穩態則會熔化再結晶形成α結構。
並列摘要
The research is focused on the criteria of the formation of PLLA mesophase and its cold crystallization behavior. In this study, PLLA triblock copolymers with four different central block, including PEG (Mn = 2,000 and 4,600), ethylene glycol and hexanediol, were synthesized by the ring-opening polymerization method. PEG is used as a plasticizer to blend with PLLA or embedded in the PLLA copolymer for the reduction the glass transition temperature of PLLA and the formation of PLLA mesophase at low temperature. It was found that the formation of the PLLA mesophase solely depends on the glass transition temperature.The PLLA system can be cofirmed the exist of mesophase if there are two independently exothermic peaks observed at about 50 °C and 100 °C or an endothermic peak before 100 °C exothermic peak in heating process of differential scanning calorimetry.Both differential scanning calorimetry and wide angle X-ray scattering are applied to observe the exist temperature of α phase, α’ phase and mesophase through cold crystallization. PLLA forms mesophase at the lowest crystallization temperature, α’ phase and mesophase coexist at relatively higher crystallization temperature, α’ and α phases coexist at temperature higher than α’ and mesophase, and α exist at the highest crystallization temperature. α’ phase and mesophase compete with each other at their co-existed T_c.We also observe the influence of PLLA mesophase, which is formed at low temperature in advance, on the formation of other phases and their coexistent temperatures. The results revealed no influence of PLLA mesophase on the coexistent temperature of the mesophase and α’ phase. PLLA mesophase melt and recrystallized to form α phase at coexistent temperature of the α’ and α phases.