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Physically based models for predicting the source and sink behavior of homogeneous, diffusion-controlled polymer materials are described. The source model was initially developed to interpret emissions of volatile organic compounds (VOCs) from the polymer backing of new carpets measured in a chamber study. That work is extended here to include the equivalent sink model. Analogous models should be applicable to the uptake and release of volatile compounds by other homogeneous, diffusion controlled indoor materials. Key parameters for the models (the diffusion coefficient of the VOC in the polymer, and an equilibrium polymer/air partition coefficient) may be inferred from experimental chamber data. The use of more direct methods to measure these parameters is proposed. Possible analytical methods to quantify the concentration of VOC in the polymer are briefly discussed and the use of a microbalance to directly measure diffusion and partition coefficients is described using illustrative experimental data. These procedures can eliminate, to a large extent, the need for chamber studies, which are costly, time consuming, and may be subject to confounding sink effects. Results from the carpet study are presented showing that the diffusion coefficients generally decrease as the molecular weight of the VOCs increase, while the partition coefficients generally increase as the vapor pressure of the compounds decreases. Evidence suggests that correlations based solely on commonly available properties such as molecular weight, and vapor pressure can be developed. Ultimately, the prediction of the diffusion controlled source/sink behavior of indoor materials may be possible based solely on a knowledge of the properties of the relevant volatile compounds and the indoor material.
diffusion, microbalance, model, polymer, VOC
Virginia Polytechnic Institute & State University, Blacksburg, VA
Lawrence Berkeley Laboratory, University of California, Berkeley, CA