ELASTIC PROPERTIES AND STRUCTURE OF POLYA CRYLATE STARCH-BASED HYDROGELS

Elastic properties of polyelectrolyte hydrogels based on acrylate poly mers and starch were examined over a wide range of hydrogel swelling d egrees. The plot of elastic modulus versus volume fraction of the poly mer in the gel is depicted by a characteristic curve with a minimum. T his curve may be described within the framework of the modified theory of rubber elasticity, which takes into account the fact that the netw ork chains have limited extension and are nonphantom. Quantitative com parison between calculated and experimental data resulted in the evalu ation of the network parameters, which were found to be controlled by the starch : acrylate ratio. The network is formed by the chains of sy nthetic polymer only, whereas the starch is not incorporated into the network but, by affecting the gelation kinetics, leads to a higher cro ss-linking density. Some aspects of the theoretical description of the elasticity of networks with nonideal structure are treated and a new approach to the evaluation of the fraction of side-chains in these net works is suggested.