介質研磨及超細纖維素對澱粉薄膜機械性質之影響

Abstract

塑膠是最常使用於食品包裝上的一種材料，塑膠廢棄物的與日俱增，對環境是一沉重負擔。以生物性材料製造環保及特殊用途的包裝或隔絕性薄膜是目前科技發展的重點。生物性材料必須具備生物可降解、生物相容性或可食性等優點。澱粉為可製成薄膜之可食性材料，但無韌性且脆，不利於應用。由於纖維素結構排列緊密，添加纖維素可用來增強澱粉薄膜的機械強度。本研究目的在探討介質研磨及超細纖維素的添加對澱粉薄膜機械性質的影響。以玉米澱粉及棉花纖維素為材料，經介質研磨後利用靜態雷射粒徑分析儀確認懸浮液之顆粒組成大小為奈米/次微米等級。藉由電子顯微鏡觀察奈米/次微米懸浮液顆粒表面樣貌，確定奈米/次微米粒子的存在。 將研磨後澱粉與纖維素懸浮液以不同比例混合，利用動態流變儀進行流動測試，發現研磨會造成澱粉與纖維素的黏度上升。天然玉米澱粉糊化後黏度隨著纖維素的添加而下降，但是研磨後澱粉之糊化後黏度隨著纖維素的添加而上升，兩者變化量呈現線關係。由流動測試結果得知，所有實驗流體隨剪切速率增加而下降，屬切變致稀性流體，其流體行為可用Herschel-Bulkley模型描述。將澱粉與超細纖維素依不同比例混合成膜，使用質地分析儀測定薄膜機械強度，澱粉經研磨後之薄膜機械強度增加，楊氏模數(Young’s Modulus)由743增加至1505 MPa；添加11%的超細纖維素，澱粉膜由743 MPa 提高到1075 MPa，顯示介質研磨及超細纖維素皆能改善澱粉薄膜機械強度。

Plastic materials are generally applied matters in food packaging; however, it resulted in an environmental impact or pollution. Recently, environment friend materials from natural and renewable resources, which are biodegradable and biocompatible, have received great attention. Starch, an edible material with thermoplastic characteristics, is suitable for film formation; however, the starch-based film is too brittle to processing. Cellulose is an abundant polysaccharide in nature with high crystallinity, which has the potential to enhance the mechanical properties of starch-based film. In the present study, the influence of addition of ultrafine cellulose in starch-based film was studied by the application of media milling technique. Corn starch and cotton cellulose were fractured by media milling, and the static-light-scattering particle analyzer was applied to check the nano/submicron particles. Also, the scanning and transmission electron microscopes were used to observe the image of particles in nano/submicron scales. The rheological properties of milled starch and cellulose suspension were evaluated by dynamic rheometer. The apparent viscosity of starch and cellulose suspension was increased after media milling. Addition of ultrafine cellulose drove the decrease of apparent viscosity of native gelatinized corn starch. But, the apparent viscosity of gelatinized milled starch increased with ultrafine cellulose addition. The suspensions appeared to be a shear-thinning fluid and can be described by Herschel–Bulkley model. The suspensions were used to prepared starch-based film using casting method. The mechanical properties of films were studies by texture analyzer with tensile test. The Young’s modulus increased from 743 MPa for the native starch film to 1505 MPa for the milled starch film. The Young’s modulus increased from 743 to 1075 MPa as the addition of ultrafine cellulose. increased from 0 to 11% (w/w, base on the weight of starch). Media milling as well as the addition of ultrafine cellulose can enhanced mechanical properties of starch based film.