The Effective Parameters of Adhesion Strength in Polyurethane Systems

Polyurethane adhesives have wide applications in various industries. These adhesives are made of two major components, including isocyanate and polyol. In their synthesis, in accordance with their usage, other materials such as chain extenders, solvents, catalysts and additives are used. Despite all their advantages such as appropriate flexibility, high abrasion resistance, excellent mechanical properties and good adhesion to various surfaces, the adhesion strength of polyurethane adhesives highly depend on process parameters such as ratio of components, molecular weight of polyols, type of isocyanates and polyols, their surface quality and the process temperature. In this study, polyurethane adhesives and the effects of three variablessuch as, reactive component ratio, molecular weight of polyols and surface quality on polyurethane adhesive strength and properties are evaluated. Two variables of crystallization and the ratio of NCO/OH affect the hardness values of polyurethane adhesives, so that by increasing crystallinity and NCO/OH ratiothe stiffnessshows an ascending trend. By increasing of chain extender content (decreasing polyol content)the adhesive young's modulus is significantly increased. This is while the elongation-at-break shows a gradual decline. Also, higher polyol molecular weight increases the storage modulus of polyurethane adhesive. Different ways of surface treatment shows different results of surface roughness. In this fashion, the wettability of resin/substrate is also affected. It is worth mentioning thatapolyurethane-stainless steel system without proper preliminary cleaning process exhibits poor adhesion and polyurethane-SBS rubber system without surface modification has low adhesion strength.