An approach for estimating the permeability of agricultural films

Plastic tarps currently used during soil fumigation to control emissions ha ve been shown to be permeable to fumigant vapors, resulting in appreciable losses to the atmosphere. New low-permeability films are being developed to reduce fumigant emissions and increase efficacy. A rapid, reliable, and se nsitive method is required to measure the permeability of various films tha t may be used in new management practices. This manuscript presents an appr oach for estimating the mass transfer coefficient (h) of fumigant compounds across agricultural films. The h is a measure of the resistance to diffusi on which, unlike other measures of permeability, is a property of the film- chemical combination and independent of the concentration gradient across t he film. This method uses static sealed cells; fumigant vapor is spiked to one side of the film and the concentrations on both sides of the film are m onitored until equilibrium. An analytical model is fitted to the data to ob tain h. This model relies on a mass balance approach and includes sorption to and diffusion across the film membrane. The method was tested using two polyethylene films and a very low-permeability film and showed that the met hod produces a sensitive and reproducible measure of film permeability.