EVOH/黏土奈米複合材料之形態學與結晶行為研究

Morphology and Crystallization Behavior of EVOH/Clay Nanocomposite

江秉謙(Jiang, Bing Qian)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/碩士(2016年)

摘要

聚乙烯乙烯醇(EVOH) 是一種乙烯與乙烯醇單元隨機排列的高分子材料，由乙烯與乙烯醇兩種單體共聚合而成。由於其對氧氣和大多數有機溶劑優異的阻隔性質，EVOH在食品包裝工業上有著廣泛且大量的運用。本研究著重在於提高EVOH薄膜的阻隔性質、機械性質以及熱性質。利用界面活性劑改質後的奈米蒙脫土(Montmorillonite)添加於EVOH高分子薄膜當中，成為一高分子奈米複合材料，觀察其形態、結晶行為和阻隔性質造成。
　　研究中發現到，EVOH高分子鍵會插入或者是鑲嵌到奈米黏土的層間距離當中，使得其層間距離由原本的1.9nm增加至3.4nm，稱之為層間插入。而層間距離增大的現象，是目前EVOH/奈米黏土複合材料的研究中，達到最佳的效果。由EVOH高分子與奈米黏土所形成之層間插入的構造會再進一步的堆疊成較大的盤形結構，此一盤形結構會再進一步聚集而形成較大大尺度之不規則的碎形結構，故，在添加奈米黏土於EVOH高分子中所製備而得的複合材料係形成一階層性結構，形態上可以分為三個部分：由發生層間插入的EVOH與奈米黏土構成小型板狀體(第一階層)，此一小型板狀體進一步堆疊成較大的盤形結構(第二階層)，最後的部分係由許多盤形結構聚集而成所產生之大型碎形結構體。
　　另外也發現到，在添加少量(~1wt%)的奈米蒙脫土於EVOH高分子基質當中，能夠提升EVOH高分子的結晶速率，顯示奈米黏土作為晶核劑的效果。但是，當添加了過多(~5wt%)的奈米黏土時，卻又會出現結晶速率大幅降低的現象。在增加結晶性質的同時，熱穩定性也一並得到提升。

關鍵字

聚乙烯乙烯醇 ； 蒙脫土 ； 層間插入 ； 階層性結構 ； 結晶動力學

並列摘要

Ethylene vinyl alcohol (EVOH) is a random copolymer of ethylene and vinyl alcohol, which has been widely used for food package due to its excellent barrier property against oxygen, moisture and organic solvents. With the objective of further enhancing the barrier, mechanical and thermal properties of EVOH, here we investigate the nanocomposite of EVOH with surfactant-modified montmorillonite nanoclay.
A fraction of the EVOH chains were found to be intercalated between the clay galleries, leading to a swelling of the interlamellar distance of clay platelets from 1.9 nm to 3.4 nm. This is the best degree of intercalation having been achieved in this type of nanocomposite with EVOH. The EVOH-intercalated platelets stacked coherently over a limited length (ca. 10 nm), forming the dislike clusters which further aggregated to construct a fractal superstructure with the mass fractal dimension of ca. 2.8. Consequently, the morphology of the nanocomposite was characterized by a hierarchical structure with three distinct levels, i.e., the EVOH-intercalated clay platelets (level one) stacked to form disklike clusters (level two) which further constructed a fractal network.
The addition of a small amount of clay ( ~ 1 wt%) accelerated the crystallization of EVOH slightly, showing the effect of nucleating agent. However, EVOH crystallization was slowed down drastically upon the addition of 5 wt% of clay. The thermal stability of EVOH was significantly enhanced by forming the composite with clay.

並列關鍵字

EVOH ； momtmorillonite clay ； intercalation ； hierarchical structure ； crystallization kinetics

參考文獻

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