Modified Flexible Urethane Foams

These foams include isocyanurate-modified rigid urethane foams, isocyanurate-modified flexible urethane foams, urethane-oxazolidone foams, urethane-based IPN foams, and urethane-based hybrid foams. 

Preparation of Integral-Skin Flexible Foams. The major polyisocyanates for use in making integral-skin flexible urethane foams are liquid MDl and TDl prepolymers. In order to make light-stable integral-skin foams, aliphatic diisocyanates, e.g., HDl (hexamethylene diisocyanate) and IPDl (isophorone diisocyanate) in modified forms are used. 

As opposed to flexible urethane foams, rigid urethane foams have a highly cross-linked chemical structure and a high percent of closed cells, e.g., over 90%. Rigid urethane foams can be classified as follows unmodified (or pure) rigid urethane foams and modified rigid urethane foams, which include isocyanurate-modified, epoxy-modified, amide-modified and oxazolidone-modified rigid urethane foams. 

Not only are these reactions of importance in the development of the cross-linked polyurethane networks which are involved in the manufacture of most polyurethane products but many are now also being used to produce modified isocycuiates. For example, modified TDI types containing allophanate, urethane and urea groups are now being used in flexible foam manufacture. For flexible integral foams and for reaction injection moulding, modified MDIs and carbodi-imide MDI modifications cU"e employed. 

Polyurethanes and Isocyanurate-Modified Polyurethanes. Phosphorus flame retardants, both additive and reactive, are used in large quantities in Polyurethanes. Rigid urethane foams employed in thermal insulation must adhere to stringent fire regulations. Flexible foams used in automotive seating must pass the MVSS-302 fire standard in furniture foam, they must pass the California state standard and other local fire codes. 

The polyisocyanates which can be used for preparing isocyanate-based foams are mainly aromatic compounds and some aliphatic or aralkyl polyisocyanates. TDI (toluene diisocyanate) is widely used for flexible foams. Pure MDI (diphenylmethane diisocyanate) is used for elastomers and coatings. Modified TDI and modified MDI are used for high-resilience flexible foams. Polymeric isocyanates (polymeric MDI or oligomeric MDI) are mostly used for preparing rigid urethane and isocyanurate foams, and in part, for preparing flexible and semi-flexible foams. 

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