Effect of PEO on the network structure of PVA hydrogels prepared by freezing/thawing method

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Abstract
Poly(vinyl alcohol) (PVA)/poly(ethylene oxide) (PEO) hydrogels were prepared by freezing/thawing method for application as a wound dressing. The effect of PEO content on the network structure of PVA hydrogel was investigated in terms of crystalline and reological properties. It was found that a low amount of PVA crystallites were present in PVA/PEO hydrogels. With increasing content of PEO, the crstallinity of PVA hydrogel decreased, but the apparent dimensions of crystallites increased. The shear storage modulus (G′) decreased slightly with the increasing temperature within 30–50°C, probably resulting from the breaking of the hydrogen bonding; while it decreased sharply within 50–70°C, probably resulting from the melt of the crystallites of PVA hydrogel. The physical crosslinking density (Dpc) increased with decreasing PEO content, while decreased more dramatically with increasing temperature, indicating that hydrogen bonding was easier to be broken at high temperature. At very low strain amplitudes, the loss modulus (G″) of the hydrogel is lower than the storage modulus (G′) and G′ is independent of the strain amplitude, indicating that the deformation imposed on the network structure is entirely reversible. With increasing content of PEO, G′ at low frequency decreased, and the mesh size (Lc) increased, indicating of the decrease of the physical crosslinking density of PVA/PEO hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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