STRUCTURAL TUNABILITY OF POLYMER FIBRILLAR BLENDS USING SUPERCRITICAL CARBON DIOXIDE: CROSSOVER FROM CLOSE-CELL TO OPEN-CELL TO BICONTINUOUS MACROPOROUS MONOLITHS

摘要

Polymers with three dimensional (3D) structures are scientifically and commercially interesting. We have prepared three distinct morphologies, namely close-cell foams, hierarchically porous open-cell foams, and bicontinuous macroporous structures using batch foaming. Current methods to prepare these morphologies are solvent intensive, involve multiple-steps or require laboratory synthesized polymers. We accomplish the same morphologies by preparing fibrillar blends of PP/PTFE and expose the samples to supercritical carbon dioxide in a high-temperature, pressure regulated autoclave. Morphological transitions occur by controlling the autoclave temperature. We attribute the transitions to the differences in the degree of crystallinity at the instant when foaming initiates. The melt stiffness dictates whether the walls of the foams will remain intact to form close cells, rupture to produce open-cells or in extreme cases, yield a bicontinuous macroporous structure.