鈉蒙特石-幾丁聚醣-TEMPO觸媒氧化澱粉抗菌複合膜之製備及性質分析

Abstract

本試驗擬以TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)/NaClO/NaClO2氧化系統製備三種不同氧化度(degrees of oxidation, DO)，分別為5、10及15%的氧化澱粉(oxidized starch, OS)，添加經簡易離心純化及超音波震盪分散之蒙特石(montmorillonite, MMT)懸浮液以製成複合膜。為使其具有抗菌能力，並於成膜溶液中添加幾丁聚醣(chitosan, CS)作為抗菌物質，以鑄模法(casting film method)製備蒙特石-幾丁聚醣-氧化澱粉抗菌複合膜。氧化澱粉物化性質測定結果發現，隨著氧化度的增加，澱粉粒變得較容易膨潤，結晶性、熱焓值以及糊化溫度皆降低，表示天然澱粉(native starch, NS)經過氧化之後，結晶結構受到破壞，並有分子降解的情形發生。蒙特石經過簡易純化後，其純度從87.09%上升至99.55%，表示藉由離心步驟可以得到純度高的蒙特石；將純化後的蒙特石經過超音波處理，可使其平均粒徑從2.77 μm下降到0.99 μm，表示超音波處理可以達到讓蒙特石分散的目的。當以5%氧化度之氧化澱粉製備澱粉膜時，其較天然澱粉膜有較光滑的表面、顯著較高的楊氏模數(Young’s modulus, YM)、透光度(light transmittance)以及較佳的紫外光阻隔性。但隨著氧化度(5-15%)增加，氧化澱粉膜的機械性質以及阻擋紫外光的能力呈下降趨勢，此乃澱粉分子降解程度提高與澱粉分子負電斥力增強，使澱粉鏈排列不緊密所致。蒙特石-氧化澱粉複合膜試驗結果顯示，隨著蒙特石添加量(0-10%)的提高，透光度及水氣滲透性(water vapor permeability, WVP)顯著降低，表示分散在基質中的蒙特石已成功扮演阻隔光線及水氣的角色，機械性質的表現則是以2.5%添加量為最佳條件。蒙特石-幾丁聚醣-氧化澱粉抗菌複合膜的結果顯示，幾丁聚醣可以增加複合膜的紫外光及水氣阻隔性，且透過離子鍵結增強了氧化澱粉膜的YM及抗拉強度(tensile strength, TS)，並在蒙特石-幾丁聚醣-天然澱粉抗菌複合膜中表現出對Escherichia coli及Staphylococcus aureus的抗菌活性。

Three different degrees of oxidation (DO) of 5, 10, and 15% of oxidized starch (OS) were prepared through TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) / NaClO / NaClO2 oxidized system. Montmorillonite (MMT) was purified by simple centrifugation method and dispersed by ultrasonication. MMT suspension was added to the OS film-forming solution to make a composite. Chitosan (CS) was added as an antibacterial substance, and MMT-CS-OS antibacterial composite was prepared by casting film method. The experimental results show that as the DO increased, the starch granules became easier to swell, and the crystallinity, enthalpy and gelatinization temperature decreased, indicating that the crystal structure of the native starch (NS) was damaged, and the molecules of starch was degradated after oxidation. After purification, the purity of MMT has increased from 87.09% to 99.55%, which means that the high purity MMT can be obtained by the simple centrifugation method. The purified MMT was subjected to ultrasonic treatment, and the average particle size was reduced from 2.77 μm to 0.99 μm, which indicates that the ultrasonic treatment can achieve the purpose of dispersing the MMT. When the starch film is prepared with OS with a DO of 5%, it has a smoother surface, significantly higher Young's modulus (YM) and light transmittance than native starch films. However, with the increase of the DO (5-15%), the mechanical and ultraviolet light barrier properties of the oxidized starch films tend to decrease. It may be caused by the degradation of starch molecules and the negative electrostatic repulsion of starch molecules, as a result, the starch chains is not tightly arranged. The experimental results of MMT-OS composite show that with the increase of MMT content (0-10%), the light transmittance and water vapor permeability (WVP) are significantly reduced while mechanical properties performed best with 2.5% of MMT. The results of MMT-CS-OS antibacterial composite show that CS can increase the ultraviolet light and water vapor barrier properties, and enhance the YM and tensile strength (TS) of the oxidized starch film at the same time. Furthermore, CS shows antibacterial activity against Escherichia coli and Staphylococcus aureus in MMT-CS-NS antibacterial composite.