Development of bonding methods for thermoplastic advanced composites

Given high strength-to-weight and stiffness-to-weight ratios, sandwich composite materials are continually being considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased ease of manufacture and are recyclable making them even more attractive than thermoset composites. This investigation evaluates the adhesion of 13 adhesives with 8 surface treatments on both nylon and polypropylene thermoplastic adherends made from Towflex® preimpregnated fabric. A method of manufacture of these plates without contaminating the bonding surface while establishing an acceptable surface finish was developed. Adhesives and surface treatments were investigated and the candidates with the greatest likelihood of success without overlap were chosen. Initial testing was performed using the qualitative spot adhesion test (ASTM D3808) to identify the most likely adhesive and surface treatment parameter groups with each thermoplastic. From these results, 10 parameter groups were identified and tested quantitatively using the lap shear test (ASTM D 3163). Comparative bond strengths are calculated from the peak load and bonded area of each specimen. The results for the nylon were similar between the two tests, but the polypropylene was generally inconsistent. The results indicate that further testing to completely develop joining methods with nylon thermoplastic treated at least with an acid wash and bonded with Lord 320/322 could result in a method of adhesively joining thermoplastic sandwich composites.