Endurance of polyurethane automotive seating foams under varying temperature and humidity conditions

The long-term comfort and durability properties of the flexible moulded foams used in many forms of transportation seating are a subject of increasing interest to foam moulders and seat producers. In previous contributions we have demonstrated the broad range of performance that can be expected from the well established and finely tuned chemistries (Hot Cure, TDI HR, MDI HR and TM-20 HR) currently used to make moulded seating foams all around the world. Existing and proposed new specifications for load bearing and other fatigue losses have necessitated a new look at the fundamental understanding of why foam properties change with temperature and humidity: the mechano-sorptive properties. The polymer morphology of foam specimen representative for the commercially available types has been determined by a combination of spectroscopic techniques: DMS, FT-IR, SAXS and TEM. A rationale is presented for the formation of the observed morphologies during reactive processing based on the theory of spinodal decomposition and a morphological picture is proposed encompassing the measured morphological parameters. To get to the details of how temperature and moisture effect the mechanical response of a polyurethane network, we studied compression sets over a wide range of conditions and correlated those data with eventual morphology changes obtained from spectroscopic studies and with traditional dynamic fatigue tests conducted in similar conditions. Additional insight into the reorganization of the polymer networks was gained from detailed analysis of the foam's dynamic mechanical performance under the influence of transient moisture conditions. Specifically the energy loss associated with moisture induced network reorganization has been measured.