研究生: |
梁祺安 Chi-an Liang |
---|---|
論文名稱: |
聚乳酸-聚丙二醇-聚乳酸三團聯共聚物之硬段長度對結晶成長及表面能量的影響 Effect of Hard Segment Length on Crystallization Growth and Surface Energy in Poly(L-lactide) -Poly(propylene glycol) -Poly(L-lactide) Triblock Copolymers |
指導教授: |
胡孝光
Shiaw-guang Hu |
口試委員: |
何明樺
Ming-hua Ho 許貫中 Kuan-chung Hsu 朱一民 I-ming Chu |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 材料科學與工程系 Department of Materials Science and Engineering |
論文出版年: | 2012 |
畢業學年度: | 100 |
語文別: | 中文 |
論文頁數: | 71 |
中文關鍵詞: | 三團聯共聚物 、聚乳酸 、結晶度 、晶片厚度 、接觸角 、表面能量 |
外文關鍵詞: | triblock copolymer, Poly(L-lactide), Crystallinity, thickness of lamellae, contact angle, surface energy |
相關次數: | 點閱:448 下載:1 |
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本研究合成不同聚合度的聚乳酸( PLLA,聚合度= 59~450 )與聚丙二醇( PPG,分子量= 4000 g/mol )三團聯共聚物( PLLA-PPG-PLLA)。使用DSC觀察共聚物熱性質與PLLA鏈段長度的關係,以實驗求得之熔融焓估算出PLLA鏈段之結晶度,討論PLLA鏈段的結晶度與PLLA鏈段長度的關係。再利用偏光顯微鏡,觀察改變PLLA鏈段長度對球晶成長動力學參數的影響。以Hoffman-Weeks方法估平衡熔點,再估計平衡晶片厚度,討論平衡晶片厚度與PLLA鏈段長度之標度關係。另外,使用接觸角測量儀,觀察不同PLLA鏈段長度的共聚物之接觸角,藉由Girifalco-Good- Fowkes -Young equation 估算共聚物的表面能量及表面能量中極性成份與非極性成份,討論表面能量與PLLA鏈段長度及PLLA鏈段結晶度之關係。
以DSC測量共聚物的熱性質,結果顯示,共聚物的熔融溫度及結晶溫度均隨著PLLA鏈段長度增加而愈大,其共聚物的分子量愈大,熔融溫度愈大。共聚物的結晶溫度大約為其熔融溫度的0.8倍。其熔融焓與結晶焓也隨著PLLA鏈段長度增加而愈大。以△HmPLLA對PLLA鏈段長度作圖,發現△HmPLLA隨著PLLA鏈段長度增加而愈大。共聚物中PLLA鏈段的結晶度會隨著PLLA鏈段愈短而愈小,其PLLA鏈段的結晶度受非晶PPG影響愈大。
根據Lauritzen-Hoffman成核現象理論分析共聚物球晶成長速率,發現隨著PLLA鏈段長度減少,共聚物的球晶成長動力學參數愈小。藉由Gibbs-Thomson-Tammann 及 Hoffman-Weeks方程式其得共聚物的平衡晶片厚度,會隨著PLLA鏈段長度減少而愈小,且求得平衡晶片厚度Lc與PLLA鏈段長度的標度指數α 為1.360,非平衡晶片厚度L與PLLA鏈段長度的標度指數α'為0.733。
在接觸角實驗中,水及甲醯胺與共聚物的接觸角均會隨PLLA鏈段愈短愈大,顯示PLLA鏈段愈短,共聚物的極性愈小。利用Girifalco-Good-Fowkes-Young equation求出共聚物的表面能量,共聚物的總表面能量會隨著PLLA鏈段愈短而減少,約有20%的下降。
以共聚物的總表面能量對非平衡晶片厚度作圖,可知共聚物的總表面能量會隨著非平衡晶片厚度愈厚而愈大。共聚物的總表面能量不但受到PLLA鏈段長度的影響,也會受PLLA鏈段的結晶度影響。
Poly(L-lactide)-poly(propylene glycol)-poly(L-lactide) (PLLA-PPG-PLLA) triblock copolymers with PPG (the number average molecular weight ‾= 4000 g/mol) and various PLLA length (degree of polymerization = 59 to 450 ) were synthesized. We observe the relationship between thermal properties of copolymers and length of PLLA segment with differential scanning calorimetry (DSC). Using the melting enthalpy to estimate crystallinity of PLLA segment we discuss relationship between length of PLLA segments and crystallinity of PLLA segments. The equilibrium melting point and spherulitic growth rate of copolymers were examined with polarizing microscopy. In conjunction with data, the Hoffman nucleation theory was used to obtain kinetic parameters such as nucleation constants (Kg), pre-exponential factor(G0), and fold surface energy(σe). The thickness of equilibrium lamellae was calculated, via equations by Hoffman-Weeks and Gibbs-Thomson-Tammann. In addition, we measure the liquid-drop contact angles of copolymers with goniometry. Finally, using Girifalco-Good-Fowkes-Young equation we calculate the surface energies and discuss the relationship between the surface energy and length of PLLA segments.
DSC measurement showed that the melting temperature and crystallization temperature of copolymers increased with the increasing length of PLLA segments. The crystallization temperature of copolymer is 0.8 times the melting temperature. The melting enthalpy and crystallization enthalpy also increase with the increasing length of PLLA segment. We plot melting enthalpy per unit mass of PLLA (△HmPLLA) versus the length of PLLA segment. It is found that △HmPLLA increases with the increasing length of PLLA segments. The crystallinity of PLLA segment decreases with the decreasing length of PLLA segments, showing that the crystallinity of PLLA segment was affected by amorphous PPG significantly.
According to the Lauritzen-Hoffman nucleation theory we analyze the spherulitic growth rate of copolymers, showing that, as long as length of PLLA segments decrease, Kg and σe of copolymers decrease. The thickness of equilibrium lamellae (Lc) decreases with the decreasing length of PLLA segments. The scaling exponent value α between Lc and length of PLLA segment is 1.360 and the scaling exponent value α' between thickness of non-equilibrium lamellae (L) and length of PLLA segment is 0.733.
In contact angle experiments, the contact angle of copolymers with water and formamide increase with the increasing length of PLLA segments, showing that, as long as length of PLLA segments decrease, the polarity of copolymers becomes smaller. The total surface energy of copolymers decreases with the decreasing length of PLLA segments. There is a 20% decrease.
We plot the total surface energy versus thickness of non-equilibrium lamellae. It is found that the surface energy increases with thickness of non-equilibrium lamellae. The surface energy of copolymers is affected not only by length of PLLA segments but also by the crystallinity of PLLA segments.
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