纖維素懸浮液之粒徑與濃度對薄膜性質之影響

Abstract

生物可分解聚合物係指可透過酵素或微生物，分解成二氧化碳、甲烷、水、無機化合物或生質能源等之材料，達到垃圾減量、永續性與友善環境的目標。一般使用纖維素原料或製備纖維素衍生物時，須先使用化學溶劑將其溶解，才可進行加工。這些方法使用了大量的化學溶劑，具有毒性，會破壞環境生態，更增加了處理大量廢水的成本。本研究以水與纖維素為原料，透過物理加工–介質研磨的方法，製作纖維素薄膜，探討纖維素經介質研磨之粒徑變化及濃度對薄膜性質的影響，與探討乾燥條件對薄膜之成膜性質。結果顯示，纖維素之平均粒徑會隨著研磨時間增加而減小，研磨時間 10分鐘至 60分鐘，體積平均粒徑由 11.37±0.34 μm下降至 4.03±0.03 μm，數量平均粒徑則由 3.72±0.50 μm下降至 0.14±0.02 μm。薄膜之固形物含量以 70.48 g/m2製作，可完整成膜，大於 105.73 g/m2則會有破裂的情形；固定每片薄膜為 70.48 g/m2的固形物含量，在研磨時間 10、20、30分鐘之各濃度皆可形成完整的薄膜，但在 60分鐘的薄膜易破裂。在溫度25℃，相對濕度 85%與75%之乾燥條件，可得到完整的薄膜外觀，當相對濕度降低至60%時，薄膜則會破裂。相對濕度由 60% RH (至水分含量達 5 g water/g dry cellulose時)轉換成 85% RH，也可得到完整、平整性佳的薄膜，且可節省 47.79%之乾燥時間。減速乾燥期的乾燥速率為薄膜成膜性的影響關鍵。研磨時間 10分鐘之薄膜有較佳之機械性質，抗張強度與延展性分別為 55.31±5.46 MPa、1.98±0.41%，機械性質皆會隨研磨時間增加而降低；就濃度而言，3%之濃度有較佳之機械性質。纖維素薄膜屬於抗張強度高的生物性材料，但薄膜之延展性不佳，未來需改善延展性與增加薄膜之應用性。

Biodegradable polymers can be degraded to CO2, CH4, H2O, inorganic compounds or biomass predominantly through the enzymatic actions or microorganisms. Thus, the goals of waste management and sustainable environment can be achieved. Generally, cellulose or cellulose derivatives need to be dissolved or modified with chemical solvents before processing. However, the use of chemical solvents not only lead to the environmental issues but also increasing the cost for wastewater treatment. Therefore, in this study, an attempt has been made to fabricate the cellulose film through physical method (media milling) only by using cellulose and water. This study aimed to explore the effect of particle size, concentration of cellulose suspension and drying conditions on mechanical properties and integrity of film. The results showed that mean particle size decreased with the increase in milling time. Volume mean diameter decreased from 11.37±0.34 μm to 4.03±0.03 μm, and number mean diameter decreased from 3.72±0.50 μm to 0.14±0.02 μm with increase in milling time from 10 to 60 min. When solid content of film was 70.48 g/m2 film integrity was maintained but when the solid content was greater than 105.73 g/m2, the film was cracked. Moreover, the integrity of the film could be maintained using 70.48 g/m2 solid content, 1- 5% concentration of suspension and milling time 10, 20 and 30 min, but the film lost its integrity at milling time 60 min. The drying condition 25℃、85% RH and 75% RH favored the film integrity, while reducing the relative humidity to 60% resulted in a cracked film. By modifying the drying conditions to 60% RH (till 5 g water/g dry cellulose moisture content) and then increasing to 85% RH, an intact and flat film was obtained, which also saved 47.79% drying time. The drying during falling rate period is critical for film integrity. The film obtained after 10 minutes of milling showed good mechanical properties with tensile strength and percentage elongation as 55.31±5.46 MPa and 1.98±0.41%, respectively. Increase in milling time leads to reduction of these mechanical properties. In terms of concentration, the greatest mechanical properties of film were achieved at 3%. Hence, the cellulose film prepared in this study possess high tensile strength, but poor ductility. In the future, an improvement on film elongation could result in more applications of cellulose film.