Special Features of Water-Dispersed Polyurethane Elastomers

SPECIAL FEATURES OF WATER-DISPERSED POLYURETHANE ELASTOMERS 

Liquid-NCO terminated prepolymers, which are primarily based on low-viscosity polyoxypropylene glycols and TDI require only a small amount of solvent (5-10%). However, the solvent remains in the finished dispersion. In addition the reaction of the primary emulsion with water or diamines, which results in the formation of poly urea, is dependent upon diffusion and difficult to control. 

Starting from the dispersed droplets of water, further water is incorporated into the polymer matrix by high-shear mixing the matrix becomes restricted and finally disintegrates into spherical dispersed particles, each individually enclosed by a continuous aqueous phase. A typical dispersed particle consists of a hydrophobic interior of polyether or polyester segments and an outer hydrophilic layer of hydrated salt, methylolbiuret and urethane groups. 

Phase inversion is particularly dramatic if water at c. 110-120°C is added to the ionomer in solvent, as rapid effervescence results. 

This sequence of events in the formation of a water-dispersed 

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