The process for the recycling of microcellular polyurethanes which comprises the steps of:

1.comminuting the microcellular polyurethanes

2.admixing a mixture which comprises the comminuted polyurethanes in an amount of from 0.1 to 40 percent by weight, based on the polyaddition mixture, with (a) polyisocyanates, (b) substances reactive toward isocyanates and containing active hydrogens, and optionally, (c) chain extenders and/or crosslinkers, catalysts, blowing agents and customary additives, to prepare a prepolymer.

3.reacting said prepolymer with water, and optionally, additional amounts of (c) to produce a recycled polyurethane.

Chemical processes such as hydrolysis, hydrogenation, pyrolysis and glycolysis are suitable for the recycling of polyurethanes. Furthermore, the polyurethanes can be dissolved in isocyanates and the resulting mixture can, after purification, be reused. Common to these processes is the fact that the polyurethanes can be reintroduced into their production process only at considerable expense and usually not without a loss of quality.

Further processes for recycling comprise the preparation of compact polyurethanes from comminuted elastomers ("flake bonding") or use as filler material in the preparation of new components.Introduction of comminuted polyurethanes into the polyol component for preparing polyisocyanate polyaddition products where air introduced with the polyurethanes caused considerable problems which became apparent in an undesired increase in the viscosity. This problem was solved by wetting the comminuted polyurethanes with volatile hydrocarbons. The addition of these substances may be disadvantageous for systems in which these materials are not used as blowing agents and is to be avoided. A loss in quality of the polyurethane which is prepared using recycled polyurethanes compared with the recycled elastomers can be avoided only with difficulty in the known processes, particularly in the case of microcellular polyurethane elastomers.