On the characterization of wetting and adhesion in glass fiber-PA12 composites

A variety of glass fibers (GF) and Polyamide 12 (PA12) resins were selected to study fiber-matrix wetting and adhesion in thermoplastic composites. Th e fibers differed in the nature of their surface treatment, the PA12 resins in their content of amine terminal groups and melt viscosity. The wetting behavior and the interfacial adhesion were investigated by conducting conta ct angle and interfacial shear strength measurements on fiber-droplet speci mens. Depending on the fiber surface finish, variations in contact angle of up to 60 degrees and differences in interfacial shear strength of up to 7 MPa were obtained. Slight variations in contact angle and interfacial shear strength were also observed as a function of the resin viscosity and the c hain termination chemistry. These results are of practical relevance for ta iloring the fiber-matrix interface, to minimize the fiber impregnation time during processing and optimize the mechanical performance of the composite during service. The results also allow a correlation to be established bet ween the contact angle and the interfacial shear strength, in agreement wit h an existing model. The validity of the experimental methods suggested for the determination of contact angle and interfacial shear strength in therm oplastic composites is thus confirmed.