TEMPO氧化纖維素奈米纖維/水性聚氨酯複合透明包裝薄膜之製程及應用

Abstract

隨著人類文明的發展，聚丙烯(Polypropylene, PP)、聚乙烯(Polyethylene, PE)以及 聚氯乙烯(Polyvinyl Chloride, PVC)一類常見石化塑膠廢棄物日益堆積，這類高分子不具備可降解之特性，長此以往將對於生態環境造成持續且不可逆的負面影響，為此，生物可降解塑膠成為了近代廣受關注的新興材料。有別於傳統塑膠，生物可降解塑膠即使不回收，仍可在特定的自然條件下自行降解為二氧化碳、水以及小分子，此可有效降低環境負擔，故將日常及工業中常見之塑膠轉換為可降解高分子將對永續經營起到相當大作用。而在諸多塑膠類別中，以包裝膜作為應用目的者佔據了相當大的比例，若是可將生物可降解塑膠取代現今生活常見之不可降解塑膠袋、塑膠蓋等等，將大幅減少永久廢棄物之堆積。然而，要替代如今已存在完整產業鏈之石化塑膠包裝，仍存在許多問題需要克服，主要可分為製程以及應用性方面，欲汰換現今之石化塑膠包裝，首先必須在製程方面滿足市場的需求供給，這意味著可降解塑膠需要能開發出一套具備大規模生產之生產方式，除此之外，包裝薄膜本身諸如阻隔性、穩定性等方面若要滿足市場期望，也需要達到與目前石化塑膠接近的性能表現才有被大量採用的機會。 在本文中，我們首先將TEMPO氧化纖維素奈米纖維(TEMPO-oxidized cellulose nanofiber, TOTOCNF)進行超音波震盪以提升其分散性與填補性以便進行刮刀塗佈製程，而後添加同樣具備懸浮性之水性聚氨酯(Waterborne polyurethane, WPU)以增強塗佈成膜之延展性，而後為了提升兩者之混合性，TOTOCNF/WPU混合液隨後添加非離子型界面活性劑曲拉通X-100(TritonX-100)以提升水性聚氨酯於混合液中之分散性，添加後之混合溶液不但可有效增加成膜之透明度，且TritonX-100的添加也同時對乾燥速率以及咖啡還效應抑制方面都有明顯增益效果，此改善使該混合液在大規模刮刀塗佈下之薄膜製程更加穩定且快速。除此之外，完成乾燥後之薄膜可以透過二次酯化反應達到親水性官能基的大量去除，此可有效克服TEMPO氧化纖維素奈米纖維薄膜低阻水性之問題，最終可製程一適用於大規模連續塗佈製程之高透明(T: 89.4%, Haze: 97.8%)、高熱穩定(-50~278oC)、高阻隔性之生質包裝薄膜，其可廣泛應用於食品包裝中，本研究以香蕉之包裝作為實驗成果之展示。

With the development of human civilization, common petrochemical plastic wastes such as polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC) accumulate over time. These polymers are non-degradable, which will cause continuous and irreversible negative impacts on the ecological environment in the long run. Therefore, biodegradable plastics have become an emerging material that has attracted wide attention in recent studies. Unlike traditional plastics, biodegradable plastics can be decomposed into carbon dioxide, water and small molecules by themselves under specific natural conditions without recycling, which can effectively reduce the burden on the environment, so the conversion of common plastics in daily and industry into degradable polymers will be a significant step in sustainable development. In plastic industries, packaging films account for a considerable proportion of the application purpose. If biodegradable plastics can be used to replace non-degradable plastic bags, plastic covers, etc., which are common in today's life, it will greatly reduce the amount of permanent waste accumulation. However, in order to be the alternative for petrochemical plastic packaging that has a well-developed industrial chain, there are still many problems that remain. The main problems are manufacturing and application. To replace today's petrochemical plastic packaging, it is necessary to meet the market demand and supply in terms of process, which means that degradable plastic needs to develop a production method with mass production. In addition, for the purpose of meeting market expectations in terms of package barrier properties and package stabilities, etc., it is also necessary to achieve performance close if not better to the current petrochemical plastics to have the opportunity to be widely applied. In this paper, we first improve the dispersibility and film-filling ability of TEMPO-oxidized cellulose nanofiber (TOTOCNF) for the blade coating process by ultrasonication. The solution is then added with waterborne polyurethane (WPU) which also suspense in water to enhance the ductility of the dried film. To improve mixing, the TOTOCNF/WPU mixture was then added with a non-ionic surfactant TritonX-100 for dispersibility increase of WPU. After the addition, the mixture not only shows an effective increase in transparency of the casted film, but also the addition of TritonX-100 shows significant enhancement in drying rate and the inhibition of coffee ring effect. The improvement makes the film process of the mixed solution more stable and fast under large-scale doctor blade coating. Moreover, the film after drying can achieve a large number of hydrophilic functional group removal through the two-time esterification reactions, which can effectively overcome the problem of low water resistance of the nanocellulose film. The final Biomass packaging film with high transparency (T: 89.4%, Haze: 97.8%), high thermal stability (-50~278oC), and high barrier properties that can be applied to large-scale coating is fabricated. The film can be widely used in the food packaging industry. In this study, the packaging of the banana is demonstrated as the application of the product.