Influence of an integral blend of silane coupling agents on the wet mechanical properties of epoxy particulate-filled composites for outdoor electrical insulation

In outdoor electrical applications the cast-resin epoxy formulations usually use fillers treated with silane coupling agents. These are intended to provide moisture resistance to the filler-matrix interface. In this work the silane integral blend method was compared with the pre-treatment of fillers. Diglycidyl-ester-type cycloaliphatic epoxy formulations, filled with mineral silica (with and without silane treatment) or wollastonite were additivated with silane Coupling agents - glycidoxypropyl (GPS), chloropropyl (CPS) and diamine (APS). The T-g and water absorption of cured materials were measured. The flexural strength and the fracture surface were studied in terms of the ageing behaviour in hot water. The additivation with silaries generally decreases the T-g and increases the water absorption. Wollastonite or APS formulations show the higher water absorption. GPS gives better flexural strength after hot water ageing. The non-aged materials show cohesive fracture surfaces. After ageing the materials, the non-additivated one shows filler-matrix adhesive fracture, while those additivated with GPS show mainly a cohesive type fracture. This fracture behaviour agrees with the flexural strength results.