Fabrication,properties and applications of Poly (vinyl alcohol)/graphite oxide composite
Date Issued
2010
Date
2010
Author(s)
Lee, shu-Chuan
Abstract
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).
Subjects
PVA
graphite oxide
tensile test
relative humidity
proton exchange membrane
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