No abstract

Polycarbonate absorbs water in two stages: in the initial period of absorption at an elevated temperature all of the water was found in an unassociated state when cooled to room temperature; and, in the second stage, most of the additional water absorbed by the polymer was identified in a separate liquid phase (clustered water). From water sorption studies on polycarbonate bars, we advance the following model for the formation of clusters. After the polymer is saturated with water at an elevated temperature and cooled, its solubility is lowered and water condenses in the form of microscopic water-filled cavities, providing the internal pressure which is generated by the excess water exceeds the strength of the polymer. Below Tg the clusters are formed only after the polycarbonate (Mw=26 600) has been hydrolytically degraded; whereas, above Tg, clusters can be formed without degradation. Cluster regions were found by SEM to be spherical cavities, usually measuring from 0.1 to 1.0 μ across. In addition, the glass temperature of polycarbonate was lowered as the molecular weight decreased due to hydrolysis and the amount of water in the polymer increased. Unassociated water was found to enhance the low-temperature dielectric loss of polycarbonate. Frozen clustered water produced an additional secondary loss peak about 40 °C below the β transition. In addition, the liquid clustered water produced a loss mechanism in the kHz region that was interpreted as a Maxwell-Wagner effect.

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Eight organochlorine pesticides may be quantitated routinely at levels below 10 parts per trillion (ng/L) in natural groundwaters. Analytes are extracted rapidly from 1 L groundwater samples by using conditioned Teflon filter disks impregnated with silica containing bonded octadecyl phase. Filter is dried briefly under vacuum, and pesticides are eluted with 10 mL ethyl acetate. The extract is dried with about 1 g anhydrous sodium sulfate and then concentrated to exactly 1 mL. Pesticides are separated in a gas chromatograph equipped with a capillary column, detected by a high-sensitivity electron capture detector, and quantitated by the method of external standards. Certified reporting limit (CRL) values for the 8 pesticides ranged between 2 and 7 ng/L. Preliminary data demonstrated that the organochlorine pesticides could be collected on the filter disks and stored up to 4 weeks in the dark at either refrigerated or ambient temperature without obvious degradation of the sample. Calculated CRL values are comparable (within a factor of 2) to method detection limit values defined by the U.S. Environmental Protection Agency.

Studies were conducted to evaluate lipophilicity as a predictor sorption for a mixture of organic compounds with high vapor pressures commonly present at hazardous waste sites. Sorption partition coefficients (Kp) for the mixture of 16 volatile and semivolatile organic compounds were measured on a Captina silt loam (Typic Fragiudult) and a McLaurin sandy loam (Typic Paleudults) using a zero headspace extractor. The experimental Kp was determined for acrylonitrile, furan, methyl ethyl ketone, tetrahydrofuran, benzene, toluene, p‐xylene, chlorobenzene, chloroform, nitrobenzene, 1,2‐dichlorobenzene, 1,2,3‐trichloropropane, carbon tetrachloride, ethylene dibromide, 1,2,4,5‐tetrachlorobenzene, and hexachlorobenzene on each of the two soils. The Kp values were generally lower in the McLaurin sandy loam, which had a lower organic C content (0.66 ± 0.04%) than the Captina silt loam (organic C content = 1.49 ± 0.06%). Sorption was normalized to soil organic C content of the soil by converting Kp for each compound and soil to Koc. Weighted regression analyses of Koc observed for the compounds in the mixture on Koc predicted from the n‐octanol/water partition coefficient (Kow) for individual compounds yielded a pooled, weighted regression of Koc observed = 1.084 + 0.457 Koc predicted, n = 29, r = 0.88. Statistical analysis indicated that the slope of 0.457 ± 0.046 (estimated standard error) was significantly less than 1.00, indicating that soil sorption of nonionic organic compounds differed from that predicted for the same individual compounds based on Kow. The results indicate that predictive equations for sorption of individual organic compounds can be applied to mixtures of volatile and semivolatile organic compounds in soils when log Kow are in a range from approximately 1 to 3; however, outside this range a correction factor may be needed.