Permeation of water vapor through polymeric films

The use of gloves made of rubber or synthetically produced copolymers in protective atmosphere enclosures has focused attention upon the permeability of the film as a suspect area for the diffusion of water vapor as a contaminant into the protective gas system. This investigation was carried out to determine the role of the conditions affecting the permeability of glove materials. Particular attention was placed upon the system governing the permeation of water vapor through vinyl, Hycar, and milled and latex neoprene films. The investigation was carried out by a constant pressure technique conforming to Procedure B, ASTM Designation E96‐53T. The rate at which water vapor permeates a film was studied in the light of two independent variables: film thickness and water vapor pressure differential across the film. Permeation rate was found to be inversely proportional to thickness to a constant exponent. The variation of permeation rate with vapor pressure drop across a membrane is not as sharply defined as the variation with thickness, but does vary semilogarithmically. It was found that water vapor permeation rate may be mathematically defined in terms of the controlling variables and three constants. The relationship between permeation rate and the independent variables influencing this rate can be expressed as W/tA = KenΔp/xm where W is the weight of water permeating a film of area A area in time t. The film thickness is x, Δp is the difference in partial pressure of water vapor across the film, K is defined as the permeability constant, n is the partial pressure coefficient, and m is a thickness coefficient dependent upon the solution system employed for film manufacture. Characterization of a particular film with respect to its permeability is possible through the use of the permeability constants. The value of the thickness coefficient appears to be dependent upon the solution system empolyed in the manufacture of the film. The exponents of thickness are offered as 1.1 for an organic solvent dispersion system and 0.8 for an aqueous dispersion system. The value of the exponential constant dependent upon the vapor pressure differential and the value of the permeability constant are suggested as dependent upon the schedule of “compounding” and not readily predicable. They appear, however, to be well defined functions and, once determined for a particular composition, may be used to predict the permeability of that material as a function of the water vapor