SEGMENTAL ORIENTATION BEHAVIOR OF FLEXIBLE WATER-BLOWN POLYURETHANE FOAMS

The ambient temperature structure-property orientation behavior in two different polyurea-urethane polymers (one cross-linked and one linear) was measured by using infrared dichroism along with mechanical response. Thin films (plaques) thermally compression-molded from TDI-polypropylene (PO) flexible water-blown polyurea-urethane foams and solution-cast TDI-PO polyurea-urethane elastomers were studied. Segmental orientation was measured as a function of elongation and relaxation, as well as of hysteresis behavior. The level of strain was 50-70% for the plaques and up to 240% for the elastomer. The soft segments for both materials exhibited a low state of orientation with elongation. Small changes in orientation with time and upon cyclic straining were also observed for the soft segments. Significant transverse orientation upon stretching was observed in the hard segments of the plaques and up to elongations of 100% for the elastomer. The transverse behavior of the hard segments in the plaques pressed from the foams was attributed to both the smaller hard domains as well as to the polyurea aggregates that have been reported to be present in flexible foams. This transverse behavior also suggested that the smaller hard domains and the polyurea aggregates possess a lamellarlike structure. At low strain levels (up to 50%), only small amounts of orientation hysteresis as well as mechanical hysteresis were observed for the hard segments of the plaques as well as for the elastomer. No significant relaxation in orientation was detected for the hard segments of both materials at a 30% strain level.