Adhesion of epoxy and polyurethane adhesives in pultruded composite material

Abstract

An increase in applications of pultruded composite material has been noted in the last decades. The material is usually employed in sectors that require high mechanical properties as well as chemical and corrosion resistance. The pultruded profiles can be joined by mechanical fasteners (i.e. bolts) or adhesive bonding. Bonded joints present many advantages, such as low weight, design flexibility and corrosion resistance. However, an inherent property of the polymers is the low superficial energy, which tends to be detrimental to the adhesion quality of the structure. In this sense, is important to perform a proper surface treatment and select an adequate adhesive.The present work investigates the influence of the adhesive type and surface treatment on the adhesion of pultruded composites. Three polyurethane adhesives and an epoxy adhesive were evaluated using tensile tests in bulk specimens. Then, the composite bonded joint was tested using single lap joints (SLJs). Two methods of mechanical abrasion were applied as surface treatment: unidirectional abrasion (UA) and bidirectional abrasion (BA). The treated samples presented rougher and more homogeneous surface profiles. Results revealed that the surface treatments improved the adhesion quality of the bonded materials compared to untreated samples. The high surface roughness produced by the BA together with a ductile adhesive resulted in the best improvement of the joint strength.