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Sorption ability of polymeric materials for medical purposes was studied with respect to the sterilizing gas - ethylene oxide - at 23, 35 and 55 degrees C. Sorption coefficients of ethylene oxide (EO) for the materials under study were calculated on the basis of results. Investigation of the kinetics of desorption of EO from the polymeric materials for medical purposes has shown that its content changes exponentially depending on the time of degassing. However, the lines in the 1g Q/Q0 - tau coordinates show a sharp break which testifies to a change in the mechanism of the process determining the character of the mentioned dependence. In the first region, corresponding to high concentrations and short periods of time, the determining process is diffusion while in the second region (low concentrations, long time intervals) - it is desorption of EO molecules most firmly bound to the polymer. Diffusion coefficients were calculated for the first region. The possibility of predicting the time periods of removing ethylene oxide from the polymeric materials was demonstrated for both stages on the basis of calculated diffusion coefficients and kinetic curves of degassing. Recommendations were given for the use of polymers for medical appliances and apparatuses.

The balanced sorption of a sterilizing gas--ethylene oxide (EO)--by medical polymers most commonly used in medical industry is studied. These polymers are compositions on the base of polyvinylchloride (PVC), polyethylene (PE), natural and silicone rubbers. The absorption coefficients for EO and the above materials are calculated. The most sorption capacity is inherent in the PVC-based compositions and the least one--in the PE-based materials. The latters as well as silicone rubber materials are recommended for medical engineering products subjected to gaseous sterilization.

Kinetics of ethylene oxide desorption from medical polymers at temperatures of 25, 35 and 55 degrees C over the wide range of concentration values is studied. The content of ethylene oxide in the material has been shown to vary exponentially depending on decontaminating time. However, (formula; see text) plots have a sharp inflection which indicates the change in the mechanism of the process determining the nature of the above relationship. At the first part of the plot with great concentration values and small decontaminating time the diffusion process dominates, but at the second part (small concentrations, great time) the main process is the desorption of EO molecules the most strongly bound with polymer. Diffusion coefficients for the first degassing area are computed. The methods to predict decontaminating time are described.

Some of the drawbacks are discussed associated with hygienic norms for gaseous sterilizing agents in polymeric products for medical applications. A new approach is proposed for regulating ethylene oxide (EO) in such products. To this end, limiting types of biological effect and its pathways have been determined and substantiated as well as the reliability factor for establishing hygienic norms for EO in medical products. Daily threshold EO limit values were calculated for momentary and repeated exposure of humans. The duration of long-term and short-term exposure of the patient to sterilized products was evaluated on the basis of EO extraction kinetics from a variety of materials. Using daily threshold limit values, threshold residual values (TRV) of EO were calculated for different groups of polymeric products for medical applications.