添加硬脂酸與纖維素奈米結晶粒子對澱粉膜性質之影響

Abstract

天然的生物高分子相較於合成高分子具有生物可分解性、可再生性及可食性。然而，生物高分子膜由於機械性質及水汽阻隔性較差，在工業應用上受到嚴重的限制。在本試驗中希望藉由添加纖維素奈米結晶粒子(cellulose nanocrystal, CNC)及硬脂酸(stearic acid, SA)以改善玉米澱粉膜的水汽敏感性以及機械性質。以濾紙為原料經酸水解所製得的CNC可提升膜的機械強度及降低膜在高相對濕度(97% RH)下的吸水量，但對於膜的水汽通透性則無顯著影響。1-胺基-2-丙醇(1-amino-2-propanol, AP)在澱粉膜中可作為塑化劑，並提高膜的水汽通透性，且即便添加至8%亦未對膜截面的微細結構產生影響。在澱粉膜中添加SA及AP可製備出不同形態的AP/SA-澱粉膜，表面平滑、乾爽的均質膜可藉由添加SA(10%)/ AP(2-5%)、SA(20%)/AP(3-7%)、SA(30%)/AP(4-9%)及SA(40%)/ AP(5-9%)之比例而獲得。在AP/SA-澱粉膜的X-ray繞射圖譜中發現新的繞射峰，推測可能是由SA及AP所形成之鹽類產生。AP/SA-澱粉膜的SEM截面呈現層狀結構，此結構隨SA的添加量與AP/SA莫耳比值不同而有所改變，進而影響膜的機械性質及水汽通透性。在高SA添加量(40%)及AP/SA莫耳比值(1.01)之AP/SA-澱粉膜有較佳的水汽通透性，但膜變得硬脆。添加CNC (5、15及25%)於AP/SA-澱粉膜成膜溶液中形成之AP/SA/CNC-澱粉膜，對水汽通透性影響不顯著，且由於AP/SA/CNC-澱粉膜的結構因AP及SA的交互作用而改變，干擾CNC與澱粉基質之相容性，致使添加CNC以改善AP/SA/CNC-澱粉膜機械強度之效果不顯著。

Natural biopolymers have advantages, including biodegradable and renewable as well as edible, over synthetic polymers. However, relatively poor mechanical and water vapor barrier properties of biopolymer films limit their applications in industry. In this study, cellulose nanocrystals (CNC) and stearic acid (SA) were introduced into corn starch film to improve its mechanical properties and water sensitivity. Adding CNC, which obtained by hydrolyzing filter paper, did improve the mechanical properties and decrease the water adsorption at high relative humidity (97% RH) of starch composite film, although its water vapor permeability (WVP) did not significantly change. Adding 1-amino-2-propanol (AP), a plasticizer, would increase the WVP of starch film, but no significant differences in the microstructure of film cross section could be investigated even adding up to 8%. Adding SA and AP into starch film resulted in different morphologies of AP/SA-film depending on the amounts of AP and SA additions. The smooth, dry homogenous films could be obtained by introducing SA(10%)/AP(2-5%), SA(20%)/AP(3-7%), SA(30%)/AP(4-9%), and SA(40%)/AP(5-9%). A new X-ray diffraction pattern could be the evidence of the salt formed from SA and AP in starch composite film. The lamellar structure on the cross section of AP/SA-starch film was observed by using a scanning electron microscopy. In addition, the structure changes of cross section on AP/SA-starch film, depending on the amount of SA added and the AP/SA molar ratio, would affect the mechanical properties and WVP of film. High amount of SA (40%) and AP/SA molar ratio (1.01) in AP/SA-starch film had better WVP, but caused film brittle. The WVP of AP/SA/CNC-starch films, made by adding CNC (5%, 15%, and 25%) into AP/SA-starch film forming solution, were insignificantly different. The compatibility of CNC and starch molecules was disturbed due to the interaction of AP and SA which modified the microstructure of AP/SA/CNC-starch film. This might be the reason why the proposed improvement on the mechanical properties by introducing the CNC on the starch film could not be approached.