添加非溶劑對聚乳酸靜電紡絲纖維之影響

Abstract

本研究探討非溶劑在靜電紡絲扮演的角色，有別於以往的濕式靜電紡絲是將高分子溶液紡入非溶劑中，我們選擇將非溶劑直接添加到靜電紡絲溶液中，藉此去觀察其對纖維的影響。 我們所使用的高分子為聚乳酸，溶劑為氯仿，經過實驗發現，10wt%的聚乳酸-氯仿溶液可以紡出均勻且無串珠的絲，這是由於足夠濃度的高分子使得溶液有足夠的黏度，並且有足夠的糾纏使得溶液在靜電紡絲的過程中可以克服表面張力而不形成串珠。而我們藉由在電紡絲溶液中添加非溶劑，在非溶劑的比例達到一定的區間時，可以在更低的高分子濃度下紡成均勻的無串珠纖維。藉由不同成分比例下紡出的結果以及斷面分析，認為是非溶劑在高分子溶液中造成了相分離，此相分離非傳統上肉眼可觀的相分離，其形成的範圍很小，卻貢獻了物理上的交聯，使得在較低的高分子濃度下，仍能夠克服表面張力而抑制串珠的形成。我們也認為由於添加與氯仿互溶的非溶劑，會使得氯仿的揮發變得較慢，因此延遲了皮層固化的時間，溶劑持續的揮發造成了纖維體積的收縮，同時還有電廠拉伸的效應，使得纖維的直徑變得更小。 接著我們調整了靜電紡絲時所使用的工作電壓，結果發現在較低電壓的情況下反而有利於串珠的形成，透過DSC的分析，認為在較高電壓下容易形成較為有序排列的結構，使得纖維的機械強度較強，因此較不容易因為表面張力而生成串珠。

The effect of adding nonsolvent to the polymer solution in electrospinning, which is different from wet electrospinning, was studied in this research. The polymer used in this work was PLA, and the solvent was chloroform. By experiment result, uniform fibers without a bead could be synthesized by electrospinning with 10wt% PLA-chloroform solution. Upon this concentration, the viscosity of the solution is high enough so that polymer has enough entanglement to resist surface tension when electrospinning, causing uniform beadless fibers. In addition, we successfully synthesized uniform beadless fibers at a lower concentration by adding a nonsolvent THF. Using morphology and cross-section analysis, we believe it was due to undersized phase separation caused by nonsolvent. The undersized phase separation was not visible with naked eyes; instead, it contributed to physical linking. Thus, the polymer still had enough entanglement at a lower concentration. We also believed that by adding THF, which was completely miscible with chloroform, the volatilization of chloroform became slower and the solidification of skin became slower, too. Therefore, the fiber suffered more effect of stretching, causing the fiber diameter smaller. Additionally, we tried to change the working voltage, and we found beads formed when lower working voltage. Using DSC analysis, fibers synthesized under higher voltage was believed to possess a better mechanical strength to resist the surface tension.