聚乙烯醇/氧化石墨片複合材料之製備、性質與其應用探討

Fabrication,properties and applications of Poly (vinyl alcohol)/graphite oxide composite

李淑娟(shu-Chuan Lee)

指導教授 ： 林金福

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01902

摘要

本研究將未改質過的石墨在硫酸與強氧化劑過錳酸鉀參與環境下，氧化形成氧化石墨片，再與聚乙烯醇水溶液混合形成均勻溶液後，直接倒入塑膠培養皿烘乾成膜，成功製備出聚乙烯醇與氧化石墨片的複合材料。由X光繞射圖譜中可以發現氧化石墨片以脫層結構的方式存在在高分子基材裡面。其玻璃轉移溫度會因加入氧化石墨片使得分子鏈段難移動而有所上升，但添加量變多反而又呈現下降的趨勢，可能是因為過量的氧化石墨片在高分子基材中分散性變差了。我們選用兩種不同分子量的聚乙烯醇，將試片置於20% RH、60% RH、80% RH三種不同的相對濕度下，藉由拉伸實驗來測定機械性質，比較分子量大小與不同相對濕度間結果的差異。加入氧化石墨片後，其楊式模數都有提升。其中高分子量的聚乙烯醇在相對濕度為80% RH下表現出優異的延展性，極限應變為1275.5%，添加1wt%的氧化石墨片下，其極限應變也可達968.2%。

我們更進一步將其應用在質子交換膜上，加入聚磺酸化苯乙烯於上述膜材中提供質子傳導途徑，選用戊二醇當交聯劑，對所製備的膜材進行質子傳導度、甲醇滲透率和吸水飽和率進行研究。本研究成功地利用氧化石墨片的添加大幅降低甲醇滲透率，結果交聯前的聚乙烯醇/3wt%的氧化石墨片下，選擇性為3.36×103 Ss/cm，比起Nafion117(2.55×103 Ss/cm)的表現還要優異。

關鍵字

聚乙烯醇 ； 氧化石墨片 ； 拉伸測試 ； 相對濕度 ； 質子交換膜

並列摘要

In this thesis, graphite oxide was prepared from the natural graphite powder through the Hummer’s method, by which the unmodified graphite was treated with sulfuric acid and potassium permanganate to prepare the water-soluble graphite oxide. 10 wt% of poly(vinyl alcohol) (PVA) in aqueous solution was then mixed with graphite oxide in various concentrations to form a homogeneous solution. The well-mixed solutions were cast onto plastic petri dishes and dried in an oven. The polymer membranes were successfully fabricated by solution casting method. The exfoliated morphology was confirmed by the X-ray diffraction patterns. For the PVA/graphite oxide membrane, the glassy transition temperature was increased with the content of graphite oxide and then decreased as the graphite oxide restacked due to the van der Waals attraction of the nanoplatelets. The mechanical properties of composite films have been investigated for the PVA/graphite oxide membranes with two different molecular weight (Mw=20,000∼30,000 and Mw=88,000), which have been conditioned at 20% RH(relative humidity),60% RH and 80% RH. It is obvious that the addition of graphite oxide into the polymer matrix has a significant influence on the mechanical behavior. The ultimate strain of PVA film of high molecular weight at 80%RH reached 1275.5%. It was only decreased to 968.2% for the nanocomposite containing 1 wt % graphite oxide, indicating that the nanocomposite membrane is still highly ductile.

Furthermore, we applied these PVA/graphite oxide nanocomposites for proton exchange membrane by mixing with poly(sodium 4-styrenesulfonate) and with glutaraldehyde(GA) acting as a cross-linking agent. The membrane properties such as methanol permeability, proton conductivity and water uptake were investigated. From the methanol permeability measurement, the methanol permeability could be decreased in the presence of graphite oxide. As the result, the selectivity of the nanocomposite with 3 wt% graphite oxide before cross-linking increased to 3.36×103 Ss/cm, higher than that of Nafion 117 (2.55×103 Ss/cm).

並列關鍵字

PVA ； graphite oxide ； tensile test ； relative humidity ； proton exchange membrane

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