SYNTHESIS AND CHARACTERIZATION OF WATERBORNE POLYURETHANE ADHESIVES: INFLUENCE OF THE METHOD OF SYNTHESIS AND THE HARD SEGMENT CONTENT ON PROPERTIES

摘要

Solvent-based adhesives are still the most currently used in the footwear industry to produce upper to sole bonding. Although their effectiveness has been widely proved, due to legislative and safety issues nowadays a great interest has come out in the use of waterborne polyurethane adhesives. The properties of aqueous polyurethane dispersions synthesised by two different methods, the acetone process and the prepolymer mixing process, were studied. The use of acetone during the synthesis allowed low prepolymer viscosity and polyurethane dispersion with narrow particle size distribution was obtained. Furthermore, this polyurethane showed a more linear structure facilitating the crystallinization of soft the segments, although the kinetic of crystallization was slow. The decrease in hard segment content by decreasing the DMPA content and the NCO/OH ratio produced an increase in mean particle size and an increase in polyurethane molecular weight. The lower the hard segment content the lower the resistance to flow under temperature but higher resistance to thermal degradation. The crystallization temperature moved toward lower temperature and the crystallization enthalpy increased. Immediate adhesion of the polyurethanes to PVC was mainly determined by their rheological properties and not by their crystallinity.