Effect of nanoclay concentration on the lap joint shear performance of nanoclay/epoxy adhesive at cryogenic condition

Nanoclay has been a popular kind of nanofiller for polymer-based nanocomposites in industries since adding a small amount of it can effectively enhance the mechanical properties of polymer. In the present study, a suitable sonication time was first found for manufacturing nanoclay/epoxy adhesive. Then, the lap joint shear strengths of nanoclay/epoxy adhesives with different nanoclay content (0, 1, 3, 5wt%) conditioned at both room temperature and cryogenic temperature environment were investigated. The main failure mechanism of all samples was interfacial failure between the first layer of glass fiber and adhesive due to peeling. Results showed that 1wt% was the optimal nanoclay concentration for cryogenic temperature. Scanning electron microcopy was used to examine the fracture surfaces of samples. Good exfoliation and dispersion were found in samples containing 1wt% of nanoclay. Adding nanoclay into epoxy did not greatly affect the lap joint shear strength at room temperature but significantly influence the strength at cryogenic temperature. This was due to a clamping force induced on nanoclay by negative thermal expansion during conditioning from room temperature to cryogenic temperature. With good exfoliation and dispersion, the clamping force can be evenly distributed. Hence, 1wt% nanoclay/epoxy adhesive is suitable for bonding composite lap joints, which will be servicing at low temperature environment.