A New Era for MDI: Flexible Polyurethane Slabstock Foam

In the past few years, much effort was put into developing new technologies for high resilience (HR) slabstock foam applications involving the use of MDI-based prepolymers. The main advantages claimed were better feel of the foam and enhanced physical properties over standard HR foams. However, those HR technologies have been developed to be used in the high quality HR market segment at densities generally ranging from 2 to 4 lb/ft3. Little work has been reported so far in the area of conventional slabstock foams produced with MDI, i.e., using high potency surfactants and polyols with secondary hydroxyls. By carefully selecting the MDI component, it has been possible to manufacture slabstock foams at densities ranging from 3 to 1.5 lb/ft3 with acceptable processing latitude. The main advantage of those foams over TDI based ones are: (1) the possibility to make very firm foams without the need for any filler, (2) the use of low vapor pressure MDI, (3) very fine cell structure and resulting good feel of the foam, (4) very fast skin curing and final curing and (5) the possibility to manufacture non-shrinking low breathability foams. The challenges for these MDI-based foams include the lower NCO% of MDI, poorer blowing efficiency relative to TDI, compromised mechanical properties and narrow processing latitude, which may be a concern at the lowest densities especially on trough-like machines. This paper will discuss the influence of the nature of the isocyanate upon the formulation parameters and the final properties of the foam. A more fundamental look towards key parameters such as compatibility of the ternary (polyol/water/isocyanate) system, reactivity and viscosity, build-up of the reactive mixture, as well as polymer structure-foam properties relation characterized by means of DSC, DMS and FTIR will be presented.