Study of fibre surface treatments for control of interphase properties in composites

Dynamic wetting measurements and micromechanical and macromechanical testing have been used to characterize the fibre/matrix interaction. Unsized glass fibres, glass fibres sized with gamma-APS, poly(vinyl alcohol), gamma-APS/polyurethane or gamma-APS/epoxy, and untreated/unsized or treated/sized carbon fibres have been tested in combination with DGEBA-based epoxy resins of both amine and anhydride curing type. The experimental results of dynamic wetting show that the shape of the tensiogram depends on both fibre surface and resin chemistry. The slope of the force versus stage position plots represents the fibre/matrix interaction as swelling or acid-base interaction and depends on stage speed and fibre roughness. Wilhelmy wetting tests can be used to study the fibre/matrix interaction but conclusions about the resulting interphase can be drawn only in conjunction with micromechanical and macromechanical testing. Interfacial shear strength and transverse tensile strength show evidence of the same ranking and reflect the expected interphase behaviour. (C) 1997 Elsevier Science Limited.