Gas transport in poly(vinylidene fluoride): Effects of uniaxial drawing and processing temperature

Abstract

SynopsisThis paper reports on the gas sorption and transport properties of poly(viny1idene fluoride) (PVF,) and on the effects uniaxial drawing and processing temperature have on these prop erties. Sorption and transport were first examined for "as-received" commercial Kynar PVF2 film at 35°C. This film was 54% crystalline by weight. Solubility, diffusion, and permeability coefficients were measured for He, H2, Ar, 0 2 , Nz, CH,, and COz. The solubility coefficient and the diffusion coefFicient D were correlated with the Lennard-Jones potential and mean molecular diameter of the gas, respectively. Uniaxial drawing of PVF, films was performed up to a draw ratio of 3.7 and over the temperature range 75-140°C. Transport properties were correlated with the extent of draw and drawing temperature. The permeability P and D were found to significantly decline with uniaxial drawing; the magnitude of this effect was dependent on both the drawing temperature and the molecular size of the penetrant considered. Reductions in P and D became progressively more pronounced with increasing molecular diameter and with decreasing drawing temperature (down to a limit of about 75"C), which reflects an increase in effectiveness of drawing at low temperatures. PVFz films annealed above 75°Cshowed a n increase in P and D as opposed to the effect of drawing. The solubility of various gases in PVF2 was not found to be sensitive to processing treatments such as drawing and annealing, in agreement with the relatively small changes observed in free volume. PVF2 films subjected to various treatments were characterized by DSC, density, birefringence, and dynamic mechanical measurements. Gas transport measurements appear to provide a more sensitive and hence more viable measure of the effectiveness of drawing than these other techniques. Drawing PVF2 in the melt state was found to increase P and D, in contrast with the effects observed for solid-state drawing. The results have been interpreted in terms of existing theories on morphology and microstructure in semicrystalline polymers. INTRODUCTIONIn an earlier paper' we reported a detailed study of the gas sorption and transport behavior of poly(viny1 chloride), a glassy and primarily amorphous material, and how these characteristics are influenced by uniaxial drawing and heat treatment. The latter processing steps were found to have substantial effects on the transport properties of PVC. In the present work, we focus on the effects of drawing and thermal treatments on gas transport in poly(viny1idene fluoride) (PVF,), which is a semicrystalline polymer whose amorphous fraction is rubbery at room temperature.PVF2 is a good barrier material, having gas permeabilities of the same order as those for PVC, and has excellent chemical resistance. PVFp is now finding some commercial uses in miscible blends with poly(methy1 methacrylate) for applications requiring good barrier performance and resistance to harsh chemical environments. These factors prompted us to examine the effects of uniaxially drawing...

Permeability, Diffusion and Solubility of Gases in Polyethylene, Polyamide 11 and Poly (Vinylidene Fluoride)

“…Few studies concerning this polymer are available in the literature. The values of the activation energies obtained during this work can only be compared to those determined in [20] on the same polymer at a pressure varying from 0.1 to 2.5 MPa: in the case of helium, their E Pe value is about of 36 kJ/mol, that is identical to the results of this study. In the case of methane, the values are also close: E Pe = 65 kJ/mol, E D = 67 kJ/mol and ∆Hs = -3.5 kJ/mol.…”

“…The lower temperature (97°C) at which the permeation tests were made on the extruded sample can be a good explanation of this variation. These observations are confirmed in one study whose authors noticed that the orientation of the polymer chains induced by the extrusion is not sufficient to modify in a significant way the values of gas transport coefficients in this PVF 2 [20]. Figure 12 shows the importance of the type of gas used.…”

Gas and Vapor Sorption, Permeation, and Diffusion in Glassy Amorphous Teflon AF1600

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CO₂ Capture Membrane Process for Power Plant Flue Gas

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