The formation of network structures in polyepoxides with various filler contents (γ-iron oxide)

Abstract

The effect of the polymer-filler contact area S on the parameters of the network structure of a polymeric matrix and the thermomechanical and strength properties of films has been studied. The films were prepared using an epoxide oligomer ( M n = 3200 ), cured at 200°C with a phenolformaldehyde oligomer and hexamethoxymethylmelamine, from a solvent whose solubility parameter was practically the same as that of the epoxide oligomer. The filler (γ-iron oxide) with a specific surface area, S N2, of 17 m 2/g was introduced into the composition at a rate of from 4 to 6 wt% (a value of S from 0.68 to 10.2 m 2/g). The degree of network formation in the films, determined from CHCl 3 absorption isotherms, and their strength remains practically unchanged for values of S up to 3.4 m 2/g, as compared with the unfilled film. An increase in the density of the network of the polymeric matrix is observed with an increase in S, together with a reduction in the rupture strength of the films. The critical value for the system investigated is 60% filling ( S = 10.2 m 2/g), which leads to an increase in the density of the network by a factor of more than 2, as compared with the initial film; relaxation processes do not go the completion and there is a practically complete loss of strength.