Aging of poly(vinylidene fluoride) hollow fibers in light hydrocarbon environments

In this work, PVDF hollow fibers were aged in different light hydrocarbon solvents (e.g. paraffins, olefins, and aromatics with carbon number <9) and the thermal, mechanical, morphological, and structural properties of the resulting fibers were determined. While TGA, DSC, and DMA are used to probe the thermal and mechanical stability for the bulk samples, XRD and FTIR are used to probe the polymorphic crystalline phases on the sub-nanometer length scale. Combined with BET and SEM results on pore structure, the changes in polymorphic crystalline phases together with the changes in the morphology provide scientific insights on the interactions that the hydrocarbon solvents and aging have on the properties of the PVDF micro-porous hollow fibers. The results suggest that after a long-term exposure at ≤50 °C, the chemical and morphological structures of PVDF change more noticeably in solvents with the carbon number ≥6 than those with a lower carbon number. Furthermore, aromatic solvents produce greater changes than the paraffins of the same carbon number do. However, aging studies show that the PVDF hollow fibers preserve the thermal and mechanical properties in light hydrocarbon solvents for more than two years at the elevated temperature.

► PVDF hollow fiber preserves its thermal and mechanical properties in light hydrocarbon environments.
► Aging in organic solvents changes the morphological properties of PVDF microporous membrane.
► Long-term organic solvent exposure results in the crystalline phase transformation from α- to β- or even γ-phase.