Influence of the hard-to-soft segment ratio on the adhesion of water-borne polyurethane adhesive

摘要

Three water-borne polyurethane dispersions were synthesised by the pre-polymer mixing process.Different hard segment contents in the polyurethanes were obtained by varying the diisocyanate/macroglycol(NCO/OH)molar ratio.A decrease in the NCO/OH ratio produced an increase in the mean particle size and in the pre-polymer viscosity,as well as a decrease in the molecular weight of the polyurethane.On the other hand,the lower the NCO/OH ratio,the more crystalline the polyurethane and the lower the resistance to flow at high temperature.Lower NCO/OH ratios improved the thermal degradation stability of the polyurethane.Finally,a high initial adhesion to PVC was obtained in all joints produced with the aqueous polyurethane dispersions and the final adhesion increased as the NCO/OH ratio in the water-borne polyurethane adhesive decreased.