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研究生:蔡芃芬
研究生(外文):Peng-Fen Tsai
論文名稱:利用正子湮滅光譜技術探討聚乳酸膜材之降解行為
論文名稱(外文):Degradation Behavior of Poly(L-lactic acid) Membranes by Positron Annihilation Spectroscopy Analysis
指導教授:孫一明
學位類別:碩士
校院名稱:元智大學
系所名稱:化學工程與材料科學學系
學門:工程學門
學類:綜合工程學類
論文種類:學術論文
論文出版年:2009
畢業學年度:97
語文別:英文
論文頁數:69
中文關鍵詞:聚乳酸正子湮滅光譜儀水解
外文關鍵詞:PLLAhydrolysispositron annihilation spectroscopy
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此研究主要是利用正子湮滅光譜儀來探討聚乳酸膜材的降解行為。透過溶鑄法得到聚乳酸膜材後,將其置於PBS buffer中,觀察膜材在37 oC下水解的行為。利用正子湮滅光譜儀,透過分析膜材自由體積的變化,以探討水解過程中材料微觀上的變化。此外,藉由慢速正子束湮滅光譜儀,可以對膜材做縱深分析,呈現材料水解過程中不同深度的變化。
透過正子湮滅光譜,可得到o-Ps lifetime, o-Ps intensity。由結果發現,在水解初期,o-Ps 特性與自由體積特性有直接關聯。因此,藉由追蹤o-Ps特性可進一步探討無定型區高分子鏈堆疊的變化。由o-Ps lifetime變化,可知自由體積尺寸隨降解時間增加而下降。o-Ps intensity亦有下降的趨勢,並且與結晶度變化走向相反。然而,到了水解後期,o-Ps intensity除了受到自由體積特性影響外,還需考慮化學環境的變化。當膜材經過長時間水解後,高分子鏈大量被切斷,材料內部產生許多含氧末端基。因氧分子上帶有許多為共用電子,會抑制Ps的形成,進而造成o-Ps intensity明顯下降。整體來說,結合結晶度增加及自由體積特性的變化,可知水解的過程中整體分子鏈排列變的較為緻密。
研究結果亦發現,自由體積分率與膜材的含水量有直接的關聯。在水解前期,自由體積分率與含水量呈現正比關係。
最後,由慢速正子束湮滅光譜儀結果可知,在水解過程中,在膜材每個深度的變化是一致的。藉由慢速中子正子湮滅光譜儀,材料在水解過程中縱深的變化得以被更清楚地呈現
The hydrolysis of cast poly(L-lactic acid) (PLLA) membranes in PBS buffered solution at 37 oC was investigated in this study. The hydrolyzed PLLA membranes were characterized in the molecular level in terms of free volume properties by using positron annihilation spectroscopy (PAS) technique. Through PAS, the change of free volume properties during degradation could be observed. In addition to the bulk free volume properties measured by conventional PAS, the change in depth profile in polymeric materials during hydrolysis was observed by the slow positron beam technique. This study provides further information on the structure change, bulk free volume properties and change in depth profile, so that the degradation mechanism can be better illustrated.
PAS results indicated that, indeed, the free volumes properties changed with hydrolysis time. In the early stage, the polymer chains tended to pack densely and result in the decrease of free volume size in amorphous region due to chain scission and existence of water molecules. The chain packing of whole PLLA membrane became more and more dense. In the later stage of hydrolysis, the crystallinity didn’t change even a weight loss occurred. Therefore, we could reasonably suggest that the chains in amorphous region were dissolved into the PBS buffered solution and some part of the crystalline structure was destroyed at the same time. Moreover, the abundant oxygenated chain ends might cause a decrease in o-Ps intensity due to the inhibition effect of Ps formation. According to fractional free volume and cross section morphology of PLLA membranes, the water sorption was influenced by the free volume properties and the formation of pores in the early and the later stage, respectively. Finally, according to slow positron beam results, the variations during hydrolysis of different locations in PLLA membranes were the same.
ABSTRACT...................................................I
LIST OF FIGURES...........................................VI
LIST OF TABLES............................................IX
CHAPTER 1 INTRODUCTION....................................1
1.1 Degradation of polymers..............................1
1.2 Application of positron annihilation spectroscopy in
polymers.............................................2
1.3 Poly(lactic acid) (PLA)..............................3
1.3.1 Introduction.....................................3
1.3.2 Hydrolysis of biodegradable polymers.............4
1.3.3 Recent studies of PLA hydrolysis.................5

CHAPTER 2 POSITRON ANNIHILATION SPECTROSCOPY..............9
2.1 Free volume theory of polymer........................9
2.2 Positron and positronium chemistry..................10
2.3 Positron annihilation lifetime spectroscopy.........12
2.4.1 Finite term lifetime analysis...................13
2.4.2 Continuous lifetime analysis....................14
2.5 Application of positron annihilation lifetime
spectroscopy in free volume properties of polymer...17
2.6 Slow positron Beam..................................18
2.6.1 Slow positron based Doppler Broadening Energy
Spectroscopy....................................18
2.6.2 Application of slow positrons to polymeric
surfaces........................................20

CHAPTER 3 EXPERIMENTS AND DATA ANALYSIS..................26
3.1 Materials...........................................26
3.2 Instruments and equipments..........................26
3.3 Preparation of cast PLLA films......................27
3.4 Hydrolysis..........................................27
3.5 Measurement of molecular weight (Mw)................27
3.5.1 Equipments......................................28
3.5.2 Operating conditions............................28
3.6 Bulk free volume measurement........................28
3.6.1 Equipments......................................28
3.6.2 Procedures......................................29
3.6.3 Data analysis...................................29
3.7 Depth profile of free volume by slow positron beam..30
3.8 Crystalline structure analysis – wide X-ray
diffraction (WXRD)..................................30
3.8.1 Operating conditions............................31
3.8.2 Data analysis...................................31
3.9 Thermal analysis-differential scanning calorimeter
(DSC)...............................................31
3.9.1 Introduction....................................31
3.9.2 Procedures.....................................32

CHAPTER 4 RESULTS AND DISCUSSIONS.........................33
4.1 Properties of cast PLLA membranes...................33
4.2 Weight loss and change of molecular weight..........33
4.3 Physical structure changes.........................33
4.3.2 The later stage of hydrolysis...................36
4.4 Relationship between fractional free volume and water
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