Reactive blends of epoxy resin (DGEBA) cross-linked by anionically polymerized polycaprolactam: Adhesive property and chemical resistance

Different ratios of epoxy resin (i.e., diglycidyl ether of bisphenol-A [DGEBA] and caprolactam) have been used to synthesize DGEBA/polycaprolactam reactive blends by carrying out anionic polymerization of caprolactam at 140 degrees C. Anionic polymerization conducted by a strong base such as sodium hydride was used as a catalyst along with a cocatalyst such as N-acetyl caprolactam. The experiments were carried out to study the effect of composition on the adhesive property (i.e., lap shear strength and chemical resistance of the reactive blends). It was observed that the lap shear strength of the reactive blends increased with increasing DGEBA content from 50 to 70wt% and increased drastically above 70wt% DGEBA content with all metals (i.e., copper, aluminum, stainless steel, and mild steel). The lap shear strengths of all these reactive blends were observed to be maximum on mild steel. The study of chemical resistance indicates that the films of reactive blends Ep(75)Ca(25) and Ep(80)Ca(20) with 75 and 80wt% DGEBA content showed better resistance to acids, alkalies, and solvents than the reactive blends Ep(50)Ca(50) and Ep(70)Ca(30) with 50 and 70wt% DGEBA content. Among the solvents, methyl ethyl ketone, toluene, and methanol were found to be more attacking as compared to acetone, xylene, and ethanol.