不同溶劑效應及製備條件對聚乳酸奈米纖維之形態與物性結構分析研究

Effect of Solvent and Preparation Condition on the Morphology and Physical Properties of Poly(lactic acid)(PLA) Nanofibers

管柏弘(Bo-Hong Kuan)

指導教授 ： 陳建宏

崑山科技大學/工程學院/材料工程研究所/碩士(2011年)

https://doi.org/10.6828/KSU.2011.00066

摘要

本論文利用靜態光散射儀(SLS)、動態光散射儀(DLS)、光學顯微鏡(OM)、偏光顯微鏡(POM)、掃描式電子顯微鏡(SEM)、掃描式熱卡分析儀(DSC) 及X-光繞射儀(WAXD)進行一系列不同的溶劑及加工條件對聚乳酸奈米纖維的形態(morphology)、微細結構(microstructure)等性質影響的研究。本研究結果獲得以下的結論：在第二章節利用光學顯微鏡(OM)及偏光顯微鏡(POM)觀測不同溶劑(THF、Chloroform、及Dioxane)所製備之PLA電紡奈米纖維中發現PLA奈米纖維均為一連續性且直徑分佈均勻隨溶劑而異的纖維絲並發現電紡PLA奈米纖維均具有明顯的雙折射現象表示所製備之PLA奈米纖維中PLA分子鏈受靜電牽伸力的拉伸使PLA分子鏈延纖維軸方向排列。在不同製備條件(高分子濃度為(cp)，施加電壓為(Va)，以及收集板距離為(D))對纖維直徑及分佈分析中獲得：(a) PLA/THF 溶液系統為df~cp-1.478、df~Ef -0.635、df~D-0.013；(b) PLA/Chloroform 溶液系統為df~cp1.192、df~Ef -0.340、df~D-0.440；以及(c) PLA/Dioxane 溶液系統為df~cp2.655、df~Ef -1.015、df~D-0.034。由以上分析資料中發現利用Dioxane溶劑所製備之PLA纖維品質較佳。但不同溶劑效應對PLA奈米纖維外觀型態的影響得知13.0 wt% PLA/THF奈米纖維的外觀型態為一明顯的凹凸不平的結構；PLA/Chloroform奈米纖維的外觀為一多孔洞的纖維結構；以及PLA/Dioxane奈米纖維的外觀為一光滑平面的纖維結構。這現象意味在電紡過程中不同PLA溶液呈現不同的相分離行為所導致。利用WAXD分析不同溶劑效應及熱處理溫度對PLA奈米纖維的微結構的影響，發現PLA初紡奈米纖維微結構主要為一非晶的結構以及局部的PLA分子鏈在靜電紡絲過程中因為牽伸力導致PLA分子鏈延纖維軸方向排列所形成的順向性微結晶(??-結晶)，這現象證明在PLA初紡纖維的表層為PLA分子鏈延纖維軸方向排列所形成的??-結晶；相對的內層為較不規則的順向性非結晶分子鏈結構。因此在DSC熱分析變化分析發現PLA奈米纖維在約57oC有一應力釋放峰，並且在Tg以上溫度有一熱誘導結晶峰，最後在約163oC有一結晶熔融峰。證明在PLA纖維中有利用靜電紡絲牽伸力所導致的PLA分子鏈延PLA纖維軸排列的應力殘留。相對的WAXD分析證明PLA奈米纖維在不同溫度熱處理下，PLA奈米纖維的微結構由??-結晶轉變成結合??-結晶與??-結晶的結構，這現象證明在PLA奈米纖維內層的順向性非結晶分子鏈經由熱運動轉變成??-結晶。因此DSC證明PLA奈米纖維之應力殘留峰及熱誘導結晶化行為均消失。這現象意味PLA纖維的應力殘留在較高溫度中產生應力緩和並利用熱運動促進PLA纖維形成較完整的結晶。
第三章節利用靜態光散射探討PLA高分子鏈在PLA/THF、PLA/Chloroform及PLA/Dioxane稀薄溶液中探討高分子鏈與溶劑間的作用力指標A2及環動半徑Rg的變化證明在室溫條件下(20±0.2 oC)針對PLA高分子鏈在PLA/THF、PLA/Chloroform稀薄溶液呈現一不良溶劑性質(第二維里係數(A2)分別為-1.922×10-6、-3.507×10-4 mol dm3 g-2)；相對的PLA分子鏈在PLA/Dioxane溶劑中呈現出良溶劑行為(第二維里係數(A2)為1.027×10-3 mol dm3 g-2)。另一方面，相對的PLA在不同溶劑中的環動半徑(Rg)表示PLA在不良溶劑中有分子鏈間的聚集因此呈現較大的Rg值。最後利用動態光散射分析PLA/THF、PLA/Chloroform、及PLA/Dioxane等電紡溶液隨時間的光強度變化以探討高分子溶液的液-液相分離行為發現在室溫條件下(20±0.2 oC) 之13wt% PLA分子鏈在不同溶劑中發現PLA分子在PLA/THF溶液系統將隨老化時間增加在約80~90min之間產生凝膠化，相對的PLA在PLA/Chloroform及PLA/Dioxane溶液系統中將隨老化時間增加幾乎不變，這現象可能因為分子間有明顯的糾結導致無法明顯觀測到PLA溶液的液-液相分離行為。最後分析1.0 wt% PLA分子鏈在不同溶劑中的散射光隨老化時間的影響實驗中發現，PLA分子鏈在PLA/THF及PLA/Chloroform半稀薄溶液的光強度隨老化時間之增加呈現明顯的上升而後續再下降的變化表示PLA/THF及PLA/Chloroform半稀薄溶液隨老化時間將呈現亞穩態微相分離(spinodal decomposition)並伴隨後續的粗化現象所導致。而PLA/Dioxane半稀薄溶液隨老化時間增加幾乎不變表示PLA在PLA/Dioxane半稀薄溶液呈現一均勻且呈現分子級的分散歸因於較佳的高分子-溶劑間交互作用力(正的第二維里作用力A2)。

關鍵字

聚乳酸 ； 奈米纖維 ； 電紡絲

並列摘要

In this work, we provided insights into effect of solvent and preparation condition on the morphology and physical properties of poly(lactic acid)(PLA) nanofibers through the static light scattering (SLS), dynamic light scattering(DLS), optical microscope (OM), polarized optical microscope (POM), scanning electron microscope (SEM), differential scanning calorimeter (DSC), and Wide angle X-ray Diffraction (WAXD). The PLA solutions were prepared in different solvents; such as tetrahydrofuran (THF), Chloroform, and Dioxane, subsequent electrospinning directly. In the next chapter, the morphology of PLA nanofibers in which prepared by different solvents showed the long continuous nanofibers with distinct surface morphologies of electrospun nanofibers, however the PLA electrospun nanofibers presented a clear birefringence image meant that the PLA polymer chains were high-orientated/high-extended and aligned along the fiber axes. In the work, the results of relationship of prepation conditions; such as polymer concentration (cp), applied voltage (Va), distance between ITO glass and pipette tip (D), on the diameter (df) of PLA nanofiber as shown in bellow. (a) The PLA/THF solution was df~cp-1.478、df~Ef -0.635、df~D-0.013; (b) The PLA/Chloroform solution was df~cp1.192、df~Ef -0.340、df~D-0.440; and (c) The PLA/Dioxane solution system was df~cp2.655、df~Ef -1.015、df~D-0.034. The surface morphology of 13.0 wt% PLA electrospun nanofiber indicated that the PLA electrospun nanofibers were the scraggy surface, pores surface, and smooth surface morphologies, resepectively, prepared by PLA/THF, PLA/Chloroform, and PLA/Dioxane solutions. The distinct surface morphologies of electrospun nanofibers corresponded to different phase-separation behaviors of PLA solutions during solification because the various interactions between polymer and solvents. The result of WAXD indicated that the microstructure of PLA electrospun nanofibers was conbined major part amorphous structure and minor part ??-phase crystalline; crystallized from the extended PLA chain and aligned along the fiber axes, therefore, the thermal behavior of PLA electrospun nanofiber showed a clearly stress-relief peak at 57oC and a heating-induced crystallization exothermic peak followed by multi-melting endothermic peaks at 163oC. Moreover, the anneaed PLA electrospun nanofiber showed a remarkable crystalline changed from ??-phase to ??-phase corresponded to significant premelting and reorganization of the extended PLA polymer chain and aligned along the fiber axes, in which induced that the stress-relief peak and heating-induced crystallization exothermic peak disappeared after anneaed process of PLA electrospun nanofiber.
In the chapter three, the static light scattering indicated that the Zimm plot of PLA/THF and PLA/Chloroform dilute solutions exhibetd a poor solvent system (the valves of A2 of the PLA/THF and PLA/Chloroform were -1.922×10-6 and -3.507×10-4 mol dm3 g-2, respectively), which imply the aggregated or contracted PLA chains in PLA/THF and PLA/Chloroform dilute solutions at 20±0.1oC. Whereas, the Zimm plot of PLA/Dioxane dilute solutions presented an good solvent at 20±0.1oC (the valve of A2 of the PLA/Dioxane was 1.027×10-3 mol dm3 g-2), meant that the individual PLA polymer chain was dissolvent in dioxane. On the other hand, the values of Rg in PLA/THF and PLA/Chloroform dilute solutions larger than that in PLA/Dioxane dilute solution proved that the aggregated PLA clusters is formed in PLA/THF and PLA/Chloroform dilute solutions. The dynamic light scattering of 13.0 wt% PLA/THF semidilute solution indicated that the scattering intensity increased at ageing time above 100min corresponded to formed the gel-state in PLA/THF semidilute solution. Whereas that the scattering intensity of 13.0 wt% PLA/Chloroform and PLA/Dioxane semidilute solution presented a lower intensity and maintained the same with ageing time corresponded to thelarger amount of entangle structures between PLA polymer chains to hinder liquid-liquid phase separation occurred in semidilute solutions. Finerly, the scattering intensity of 1.0 wt% PLA/THF and PLA/Chloroform dilute solutions increased and then decreased with increasing ageing time. It is maybe indicated that the PLA/THF and PLA/Chloroform presented the spinodal decomposition/liquid-liquid phase separation and then conbined coarsening behavior as ageing time was increased. While the scattering intensity of PLA/Dioxane dilute solution maintained the same distributed to the highter interaction force between PLA polymer and Dioxane promoted PLA polymer chain dissolvent and form the molecular level individual polymer chain in dioxane.

並列關鍵字

(Polylactides (PLA) ； nanofiber ； electrospun

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