Elaboration of epoxy/silica composites by cationic photopolymerization: Kinetic study, optical and mechanical characterization

Abstract

Thick epoxy composite materials (>1 mm) have been elaborated by a room temperature process involving photopolymerization through a cationic pathway. Two epoxy resins (glycidyl ether and cycloaliphatic) were chosen as model organic matrix whereas microspherical silica particles (until 50 wt-%) were used as reinforcement. The monitoring of the photopolymerization kinetics by FTIR spectroscopy has first shown the existence of a conversion gradient in the material thickness, which resulted either from light absorption by the matrix and/or from light scattering induced by the presence of filler. More especially, the light scattering was found to be all the more important as the refractive index gap between filler and matrix was high. However, this conversion heterogeneity has then been able to be compensated by ageing involving a postpolymerization reaction at room temperature. The analysis of the mechanical properties of the obtained materials has confirmed that it was possible to obtain thick photocomposite materials homogeneously crosslinked. This homogeneity was even enhanced by using a radiation in the 300−440 nm wavelength range.