利用PEF及纖維素提升PET之阻氣性質

Abstract

聚對苯二甲酸乙二酯(PET)是目前在食品包裝中被廣泛使用的石化高分子之一，然而因為環保意識的抬頭，要如何減少PET的用量又可以維持﹑甚至提升其機械、阻氣性質成為重要的議題之一。本研究利用摻入具有高阻氣性及機械性質，但相對高成本的生質聚酯高分子聚2,5-呋喃二甲酸乙二酯(PEF)，以達成PET的減量及阻氣性的提升。然而PET及PEF因化學結構的不同，會在混摻後發生大規模的相分離，不僅提高加工上的困難度，性質亦大打折扣。因此，本研究透過將PET/PEF摻合物加熱至熔融態進行酯交換反應，由DSC觀察Tg的變化(兩個Tg變一個)證明成功使PET及PEF相容，並且能透過反應時間控制相容性及結晶度。在機械性質上，摻合物酯交換前後之楊氏模數及抗張強度並無明顯變化，斷裂伸長率則些微下降。在阻氧性上，摻入PEF可以有效降低氧氣透過率，PEF比例達30wt%時即可降至PET的0.6倍以下。 另外，本研究亦成功利用摻入少量纖維素奈米纖維(CNF)及纖維素微米結晶(MCC)，使PET的氧氣透過率降至原本的0.6倍以下。

Polyethylene terephthalate (PET) is a fossil-based polymer widely used as food and beverage packaging material. Nowadays, because environmental issue has been much more important, reducing the usage of PET and simultaneously enhancing gas barrier properties becomes a critical issue. We blend a 100% bio-based polyester which has superior gas properties and high mechanical properties, polyethylene furanoate (PEF), into PET for solving the issue we have mentioned. However, PET and PEF are naturally immiscible, which may cause the difficulty of processing and may even deteriorate the properties of PET after blending. We enhance the compatibility of PET and PEF by transesterification over their melting temperature. The compatibility between PET and PEF was observed from the change of their glass transition temperature which was measured by DSC. After the transesterification reaction, we find that the compatibility between PET and PEF is improved dramatically. Moreover, we can control the crystallinity of PET/PEF blending by different reaction time. When it comes to mechanical properties, we find that after transesterification, modulus and tensile strength do not change much but elongation at break decrease. We successfully reduce oxygen permeability of PET by blending with PEF. For blending 30 wt% of PEF, oxygen permeability is 0.6 times lower than that of PET. We also blend cellulose nanofiber (CNF) and cellulose microcrystalline (MCC), an eco-friendly material extracted from plants, into PET to improve gas barrier properties. Blending 1wt% of CNF and MCC into PET can dramatically decrease oxygen permeability to 0.6 times lower than that of PET.