Gels and foams from ultrahigh-molecular-weight polyethylene

Ultrahigh molecular weight polyethylene (UHMW PE) foams with densities from 0.04 to 0.2 g/cm{sup 3} have routinely been made in our laboratory. First, an entangled solution of UHMW PE is made. Then, the solution is geled by cooling to crystallize the PE. The gel is later dried to a foam by critical point drying. Viscometry and cloud point measurements were used to determine the gelatin point and the critical gelatin concentrations. Polarized light microscopy and differential scanning calorimetry were used to investigate the effects of cooling rate on the gel, while the effects of cooling rate on the foam were investigated via x-ray diffraction and scanning electron microscopy. We found that rapid cooling of 5 wt % UHMW PE/tetralin solutions to {minus}10{degree}c yielded small, uniform structure at the expense of crystallinity and strength; cooling over three days yielded spherulitic structure with strength. 5 refs., 3 figs.