旋轉塗佈法製備聚丁二酸丁二醇酯薄膜之結晶型態與降解研究

Abstract

聚丁二酸丁二醇酯自1990年晚期開始被學者廣泛研究及討論，為生物可分解高分子。因其可在自然環境下分解成水及二氧化碳，並且越來越多研究提出聚丁二酸丁二醇酯可以完全從生物基原料合成。在當今各國越來越重視環保議題的潮流下，聚丁二酸丁二醇酯市占率在未來五年內預估可以達十五倍的成長。 至今我們可以從文獻找到很多關於聚丁二酸丁二醇酯的降解研究。然而，少有研究針對聚丁二酸丁二醇酯在微結構下的降解機制。從球晶中心和球晶邊界開始降解是目前被大家所接受的觀點。因為觀察降解型態屬於動態的實驗手法，資訊取得的難易度會大大影響實驗的流暢度。 本研究以偏光顯微鏡及原子力顯微鏡作為檢測工具，設計出合適的降解觀察手法。我們將聚丁二酸丁二醇酯製作成薄膜，目的是要降低空間維度易於觀察。然而，根據文獻及實作經驗，顯示出聚丁二酸丁二醇酯相當容易結晶，可長單層球晶的聚丁二酸丁二醇酯不易製作。因此，在實驗前半部分，我們探討了聚丁二酸丁二醇酯的熱性質。並且結合等溫結晶的實驗，我們模擬了聚丁二酸丁二醇酯在各個結晶溫度的球晶成長速率，也預測出低溫區的結晶成長情形。 我們使用旋轉塗佈法製作薄膜。過程中發現溶劑的選用、溶液的濃度和給料的時間點，都會影響薄膜最終的品質。經過調整，我們認為溶劑選用1,1,2,2-四氯乙烷，給料的時間點選擇轉速穩定後再進行，得到的薄膜品質會最好。此外， 2% 的溶液濃度可以製作出能用偏光顯微鏡解析到的厚度，也能順利長出平整的單層球晶薄膜。 從偏光顯微鏡的分析結果，可發現聚丁二酸丁二醇酯薄膜隨著溶液越偏鹼性，則越容易發生降解。原子力顯微鏡也呈現出類似的趨勢。不過，在整個降解實驗，我們並沒有觀察到從球晶中心開始降解的現象。溶液先破壞球晶邊界的連接伸直晶體鏈，再沿著邊界快速破壞薄膜。我們所使用的基板是親水性的玻璃，且聚丁二酸丁二醇酯具有疏水性，因此浸泡在水溶液的環境下會加速破裂的發生。

Polybutylene succinate(PBS), which has been widely studied and discussed since the late 1990s, was a biodegradable polymer. It can be decomposed into H2O and CO2 in the natural environment, and more and more studies suggest that PBS can be synthesized entirely from bio-based materials. With the increasing emphasis on environmental issues worldwide, the market share of PBS is expected to grow 15 times in the next five years. We can find many studies on the degradation of PBS today. However, the degradation mechanism of microstructure is less studied. The degradation from the center and boundary of the spherulites is widely accepted. Because the degradation morphology is a dynamic observation experiment, the way of obtaining information affects the experimental efficiency. In this study, we used polarized optical microscopy(POM) and atomic force microscopy(AFM) as detection tools and successfully designed a suitable degradation technique. We fabricated PBS thin films to reduce the dimensionality for observation. However, according to literature and our experience, the single-layer spherulite of PBS was hard to manufacture because PBS crystallized quickly. Therefore, we first investigated the thermal properties of PBS. In addition, we simulated the growth rate of spherulites at various crystallization temperatures in combination with isothermal crystallization experiments, and also predicted the crystallization growth in the low-temperature zone. We fabricated our films using spin coating and found that the choice of solvent, the solution's concentration, and the dispensing timing influenced the film's final quality. After optimization, we concluded that the best film was made by dynamic dispense spin coating with 1,1,2,2-tetrachloroethane. In addition, the concentration of 2% PBS could produce a flat film with single-layer spherulites, which could be measured using POM. From the degradation results of POM, we found that the PBS degradability increased with a higher pH value. A similar trend was observed using AFM. However, we did not observe the degradation from the center of the spherulites. The damage started at the spherulite boundary, and then expanded rapidly along the boundary. The glass substrate was hydrophilic and PBS was hydrophobic. Hence the immersion in the aqueous solution would accelerate the rupture rate.