Effect of stoichiometry violation and UV- and γ-irradiation on the viscoelastic properties of an epoxy binder

In this paper, the effect of quantitative composition violations (stoichiometry) and UV- and gamma irradiation on the viscoelastic mechanical properties of an epoxy material (ED-20 resin and TETA hardener) during curing has been considered. The relevance of this study is justified by the development of technologies for manufacturing composite structures by curing under space conditions. Experimental studies have shown that reducing the hardener ratio to 0.8 of the calculated value does not significantly affect the material properties. With a greater violation of stoichiometry, the dynamic material constants decrease significantly, whereas the viscosity increases. UV-irradiation of the epoxy resin during curing leads to increased material rigidity and a shear relaxation kernel r(t) near t=0. The dynamic shear modulus of the samples exposed to gamma irradiation for curing is higher than that of the fully cured but not irradiated samples. For the samples that are pre-cured before irradiation and those that are cured during irradiation, the dynamic shear moduli are almost the same. The viscosity of samples with violated stoichiometry increases with decreasing hardener ratio. This fact is typical for both gamma-irradiated and non-irradiated samples, although the viscosity of the gamma-irradiated samples is lower than that of the non-irradiated ones.