Sorption and desorption of tetrachloroethylene in fluoropolymers : Effects of the chemical structure and crystallinity

• In 18 fluoropolymers with different repeating-unit structures and crystallinities, the solubility, diffusivity, and permeability at 70degreesC of a polarizable nonpolar solute (tetrachloroethylene) were studied. The transport properties were mostly controlled by the polarity of the polymer and to a lesser degree by the polymer crystallinity. The highest permeability was observed in the dipole-containing ethylene-chlorotrifluoroethylenes because of their high tetra chloroethylene solubility. The lowest permeability was observed in the hydrogen-bonding poly(vinylidene fluoride) polymers because of the combination of low solute solubility and solute diffusivity. The tetrachloroethylene diffusivity was solute-concentration-dependent, and sorption curves were S-shaped, indicating that the solute surface concentration was time-dependent. The rate at which the surface concentration approached the saturation level was proportional to the product of Young's modulus, the square of the thickness of the dry polymer, and the logarithm of the solute diffusivity. Data for the water-hyperbranched polymer and limonene-polyethylene conformed to the same relationship. Therefore, this provides a new tool for predicting the solute-surface-concentration time dependence from data obtained by independent measurements.

Nyckelord

diffusion

fluoropolymers

strength

small-molecule penetrants

diffusion

transport

polymers

polyethylene

permeation

kinetics

liquid

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