abstract |
OPEN-CELLED MICROPOROUS POLMER FILMS CHARACTERIZED BY HAVING A REDUCED BULK DENSITY AS COMPARED TO THE BULK DENSITY OF THE CORRESPONDING POLYMER FILMS HAVING NO OPEN-CELLED STRUCTURE, A CRYSTALLINITY OF ABOVE ABOUT 30 PERCENT, A PORE SIZE OF LESS THAN 5000 ANGSTROMS AND A NITROGEN FLUX OF GREATER THAN 35.4, ARE PREPARED BY THE CONSECUTIVE STEPS OF COLD STRETCHING, HOT STRETCHING AND HEAT SETTING A NON-POROUS, CRYSTALLINE, ELASTIC FILM. |