Effect of moisture content and carbon fiber surface treatments on the interfacial shear strength of a thermoplastic-modified epoxy resin composites

Summary The effect of moisture absorption on the fiber-matrix interfacial shear strength (IFSS) between a polysulfone-modified epoxy matrix and silane surface-treated carbon fiber using a factorial experimental design was studied. Also, two conditions of relative humidity, 25%, and 95%, and likewise six combinations of interfacial adhesion level between the IM7 carbon fiber and the epoxy resin (diglycidyl ether of bisphenol A), modified with polysulfone (PSF) (8.75 wt.%), were studied. The results show that IFSS of the composites increased with both the carbon fiber surface treatments and the epoxy resin modification with PSF. Again, it was found the moisture content had a substantially detrimental effect on the IFSS. However, both the silane treatment and the (PSF) modification of the epoxy resin enhanced the composite's resistance to moisture attack. The ANOVA results showed that the three variables, matrix modification, fiber's surface treatment, and moisture content, were statistically significant. Furthermore, interactions fiber surface treatment–moisture content and fiber surface treatment–epoxy matrix were statistically significant and the interaction between fiber surface treatment and moisture content is as crucial as the polysulfone epoxy modification. It was also found that the silane-treated carbon fibers play a major role in preventing moisture attack to the composite.