Network-structure of plasticized epoxy resins by dynamic measurements

Abstract

Viscoelastic parameters are strongly connected with the glass transition temperature and the degree of cross-linking of polymers. In this paper an attempt was undertaken to analyse the storage modulus in the rubbery plateau and the transition region of a series of plasticized epoxy polymers, in terms of their network structure, by means of dynamic measurements.

A series of dynamic tests was carried out at frequencies between 0.1 and 100 Hz and temperatures from 50 °C to 140 °C. By applying the time-temperature superposition principle, composite curves for the storage modulusE′ (ω) were derived over a wide frequency range.

The crosslink density, or the molecular weight, between crosslinks could be changed by adding different amounts of plasticizer in the epoxy polymer, and it was calculated by applying the theory of rubber elasticity. The glass transition temperatureT _g for each substance was found to be influenced by the amount of plasticizer and the molecular weight between crosslinks. This behaviour of the highly crosslinked epoxies was different from that of rubbers or analogous materials.

Finally, an estimation of the free volume of the materials tested was attempted by using the WLF-equation.