Structure and properties of waterborne polyurethane adhesives obtained by different methods

The structure and properties of two aqueous polyurethane dispersions prepared by two different methods (acetone method and prepolymer mixing method) were compared. The aqueous polyurethane dispersion obtained by the acetone method (PU-AP) showed a narrower particle size distribution than that of the sample obtained by the prepolymer mixing method (PU-PMP), because the use of an organic solvent in the synthesis produced a lower prepolymer viscosity. thus facilitating dispersion in water. PU-PMP showed more crosslinked structure than PU-AP. and, consequently, PU-PMP had higher elastic (G ') and viscous (G '') moduli and also a higher cross-over temperature between these moduli in the rheological curves. On the other hand, the lower degree of crosslinking in PU-AP facilitated polyurethane crystallinity. Thermal degradation resistance was similar and both polyurethanes showed similar decomposition patterns. Immediate adhesion of the aqueous polyurethane dispersions to PVC was low, although it was somewhat higher for the joint produced with PU-AP. The adhesive strength increased by increasing the time after joint formation. and after 72 h was similar for the two adhesives.