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Endurance of Polyurethane Automotive Seating Foams under Varying Temperature and Humidity Conditions

The long-term comfort and durability properties of the flexible molded foams used in many forms of transportation seating are a subject of increasing interest to foam molders and seat producers. 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. In previous papers 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 molded seating foams all around the world. Our focus turns now to a more fundamental study of the mechano-sorptive properties of these alternative foams in order to understand the mechanisms by which temperature and moisture cause changes in the foamed polymers. It was postulated that by knowing the exact sites of the water attack on the polymer, new ideas for improving important performance characteristics like wet compression set and tropical fatigue would arise. To get to the details of how temperature and moisture affect the mechanical response of a polyurethane network, we studied compression sets over a wide range of conditions and correlated those data with 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. We are now able to present a more comprehensive picture of the mechanisms behind the phenomena of wet compression set and tropical fatigue. This knowledge will be helpful to those striving to develop new raw materials and formulations for the next generation of transportation seating foams.