Preparation of a polyurethane/phenolic foam from a polyurethane prepolymer

A novel polyurethane/phenolic foam has been prepared by using a polyurethane prepolymer(PU) and a phenolic resin(PF) as the precursors.FT-IR spectroscopy showed that the reaction of PF and PU reached completion.The effect of the ratio of PU to PF,and the amount of the dimer of PU prepolymer present in the mixture on the preparation and properties of the PU/PF foam were studied.The experimental results showed that the foam has good size stability and low shrinkage rate when the mass ratio of —NCO groups to PF resin is 40/100.The content of dimer in the system had a significant influence on the foaming process and foam properties.With increasing content of dimer,the foaming process was characterized by a decrease in cream time,bubble time and tack-free time,and an increase in the density of the resultant foam.The water absorption,volume stability and toughness of the PU/PF foam also showed monotonic changes.In particular,the toughness of the new polyurethane/phenolic foam was much better than that of a pure phenolic foam,as shown by a comparison of the plots of bending stress and strain.