Recent observations on the mechanical properties of polymer networks

Abstract

The influence of several factors (temperature, elongation, swelling or dilution ratio, cross-link density, nature of the polymers and cross-linking agents) on the dynamic properties, creep and relaxation of polymer networks is surveyed in the terminal region of the spectrum. Whereas the deformation does not change the relaxation kinetics in large ranges of extension, the cross-link density acts as a reduced variable apparently accelerating uniformly the viscoelastic processes beyond the glass transition. The other possible reductions ‘time—temperature’ and ' ‘time—swelling’ do not necessarily seem related to the variations of free volume. From the view point of the explanation of the relaxation mechanisms in the terminal zone, the fact that the equilibrium of loosely cross-linked elastomers would only virtually be reached after several years at room temperature seem in better agreement with chain entanglement effects, either trapped or not by the permanent network, than with the dissociation of secondary linkages. © 1970, Walter de Gruyter. All rights reserved.