Structure Control of polymeric porous Membranes by Mechanical Operations

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A porous structure was shown to be formed by a stretching operation on the assembled PTFE microparticles into a sheet at a high pressure. The porous structure was well characterized by a periodical cycle, which was varied along several typical parameters of the mechanical operations. The porosity was greatly enhanced by the two-step stretching operation done in two directions perpendicular to each other. The porous structure was provided as a slit-like void between two adjoining fibril structures yielded in parallel with the first stretching operation. The physical process of the stretching operation was simplified into a rheological model and the formation of the fibril structure was discussed in a close relation with the molecular structure of the starting PTFE material. The stretching operation was also attempted to a general-purpose polymer (PE) and an accurate temperature control in the stretching operation was revealed to be indispensable.