PET/PEF摻合物混煉條件優化與結構性質分析

Abstract

聚對苯二甲酸乙二酯（PET）是一種石化材料，被大量的應用生活中，其中以食品包裝材料佔了多數。隨著大量的生產伴隨產生的廢棄物，對於地球的環境造成了傷害，且近年來環保意識抬頭，如何減少石化材料的生產及尋找可替代的生質材料尤為重要。聚呋喃二甲酸乙二酯（PEF）其優越的機械性質及阻氣性等被視為可取代PET的生質高分子材料，但目前生產PEF的成本高完全取代PET仍然有難度，因此結合PET及PEF進行混摻作為PEF尚未完全取代PET過渡期的方法。因PET及PEF結構上的不同，兩者單純進行混摻時，兩者會產生嚴重的相分離，不利於後續的加工處理。本實驗室先前利用共沉澱的方式使PET及PEF達最佳混合狀態，利用熱壓機在高溫中進行酯交換反應產生共聚物成功提高PET/PEF彼此的相容性。但共沉澱的方式使用大量的有機溶劑，不利於工業界的應用，因此本研究利用微型混煉機進行混摻，同時進行酯交換反應。 本研究由DSC結果顯示隨著混煉時間增加，玻璃轉移溫度由兩個變成一個，代表摻合物達相容，當摻合物相容時成功利用1H-NMR推算摻合物的最高酯交換程度可達14%。利用奧士瓦黏度計量測混煉不同時間摻合物的極限黏度的變化，進一步證明分子量降低與機械性質延伸率的變化的關係。利用DSC及小角X光散射技術分析混煉後摻合物的晶體厚度的變化。以流變動態頻率掃描觀察混煉初期摻合物的鬆弛時間。發現在280℃氮氣中混煉10至15分鐘的條件下， 具有一定的酯交換程度，提高摻合物的相容性，其氧氣透過率可下降至PET的1/2，而且在機械性質維持一定的延伸率。

Polyethylene terephthalate (PET) is one of the mostly used fossil-based material in our daily life, especially in food packing usage. However, it accompanies lots of pollution for mass manufacturing and the production and end of life causes damage to our environment. With the rise of environmental awareness, it is important to reduce the production of petrochemicals and find an alternative material from biomass. Polyethylene 2,5-furandicarboxylate (PEF) is considered as bio-based substitute for PET because of its exceptional mechanical and gas barrier properties, but the high manufacturing cost hinders it from mass production. Thus, blending PET with PEF is a temporary solution before PEF could fully replace PET. However, PET and PEF are intrinsically immiscible due to structure difference, which may cause phase separation and the difficulty of processing. Previously, we had used co-precipitation method to prepare PET/PEF blends and the compatibility of the blends was enhanced by the transesterification of PET and PEF under high temperature. Nevertheless, this method requires a great amount of organic solvents and this might not be suitable for industry. In this study, instead of co-precipitation method, we blended PET and PEF by compounding during which the transesterification was simultaneously achieved. With sufficient compounding time, the compatibility between PET and PEF could be improved, as revealed by the changes of the glass transition temperatures. We estimated the degree of transesterification by 1H-NMR and it reached 14% when PET and PEF became compatible. However, the fracture strains of the blends declined dramatically with compounding time due to the decrease of molecular weight, as inferred from the decrease in intrinsic viscosity of PET/PEF blends. By optimizing the compounding parameters, we found that the blends compounded at 280 ℃ in nitrogen atmosphere for 10 to 15 minutes showed good compatibility and balanced properties, with an acceptable fracture strain up to 400% and a low oxygen transmission rate below half that of pure PET. Additionally, we used small angle X-ray scattering to study the crystal structures and used the rheometer to study the rheological properties of PET/PEF blends with different compounding time.