Orientation Phenomena at Polyurethane Surfaces

The surface energies of soft-segment polyurethanes (SPU) have been evaluated by contact angle measurements. These showed that when solidified in air, the surface energies of the polymers were due almost entirely to dispersion forces. When immersed in liquids including formamide, water and saline solutions, surface rearrangements took place, gradually elevating the non-dispersive surface energy component. Equilibrium values varied with the corresponding non-dispersive surface energy of the contacting liquid. XPS analyses confirmed that compositional variations were responsible for changes in the surface energy. The surface restructuring was shown to affect the bond strengths of SPU/adhesive tape joints. The observations are relevant to property control in this important group of macromolecules.