Viscoelastic behaviour of self-assembling polyurethane and poly(vinyl alcohol)

The rheological behaviour of polyurethane (PU) and poly(vinyl alcohol) (PVA) was investigated in aqueous solution and the hydrogel state. The dependence of viscosity on polymer concentration is discussed. The formation of supramolecular structures induced by temperature increase or shear conditions was evidenced. In PU solutions, as temperature increases, a self-assembling process occurs due to hydrogen bonding and hydrophobic interactions determining a thermoreversible hydrogel formation. In creep and recovery tests, the weak PU network presents high elasticity only at low shear stress (below 10 Pa); it recovers only 15%-20% of strain above 40 Pa and the hydrogel structure fails at high shear stress (above 150 Pa). Also, PU hydrogel is not able to recover its structure after being submitted to successive low and high deformations. In PVA solutions, a shear induced aggregation was observed at 37 degrees C. PVA hydrogels obtained by the freezing-thawing method present high elasticity and stability due to the strong polymer-polymer interactions established between the polymer chains. Physical networks based on PU/PVA mixtures synergistically combine the characteristics of the two polymers, showing high elasticity when a shear stress up to 3000 Pa is applied during the creep test followed by a fast recovery of the hydrogel structure after exhibiting successive levels of deformation (self-healing ability). Therefore, these hydrogels are suitable materials for tissue engineering applications. (c) 2019 Society of Chemical Industry