Aspects of surface characterization of polyurethane adhesives

Abstract

AbstractThe performances of adhesives is strongly dependent on the contributions to overall surface energies from dispersion and nondispersion forces. In this work, surface energies have been studied for polyurethanes representing the categories of aliphatic and aromatic polyethers and aliphatic polyesters. The surface energies of the polymers were measured by static and dynamic contact angle methods. In addition to determining the energy values for polymers as received, evaluations were also made on the polymers following modification by an aminopropyl silance (APS), present at concentrations ranging from 0.1 to 20 wt %. The dispersion surface energies of the three polymers were roughly equal; however, the nondispersive surface energies strongly differentiated among them. Organic liquids were used for calculations of energy parameters from static contact angles. Data for water failed to follow theoretical expectations and were used instead to compute a work of adhesion parameter for the polymer/water interface. This correlated with nondispersion surface energies of the polyurethanes. Somewhat different values of the nondispersion surface energy were obtained from static and dynamic contact angles, an effect attributed to the tendency of polyurethanes to restructure when their surfaces were in prolonged contact with water during dynamic analysis. This behavior may be important to the type of adhesive bond formed by the polymers and to variations in bond characterstics with time. The use of APS was found to influence both static and dynamic contact angle values, with primary changes occuring in nondispersion contributions. The effects of APS addition were fully developed at concentrations of 1 wt % or less, raising doubts about the efficiency of using this additive at higher concentrations. © 1994 John Wiley & Sons, Inc.