PubMed · 13091440
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L J LEACH, R H WILSON, K E LAUTERBACH, C J SPIEGL, S LASKIN. 1953. Semiportable air-sampling system.. https://pubmed.ncbi.nlm.nih.gov/13091440/
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We studied the fracture surface evolution of ultra high molecular weight polyethylene (UHMWPE) specimens, manufactured from GUR 1050 compression moulded sheets, after gamma sterilisation in air followed by different aging times after thermal treatment at 120 degrees C. Degradation profiles were obtained by FTIR and DSC measurements after 0, 7, 14, 24 and 36h aging. We observed by SEM the morphology patterns at these aging times, in surface fractographies after uniaxial tensile test of standardised samples. The results pointed out clear differences between short and long aging times. At shorter times, 7h, the behaviour was similar to non-degraded UHMWPE, exhibiting ductile behaviour. At longer times, 24-36h, this thermal protocol provided a highly degraded zone in the subsurface, similar to the white band found after gamma irradiation in air followed by natural aging, although closer to the surface, at 150-200mum. The microstructure of this oxidation zone, similarly found in gamma irradiated samples shelf-aged for 6-7 years, although with different distribution of microvoids, was formed by fibrils, associated with embrittlement of the oxidised UHMWPE. In addition, the evolution of the oxidation index, the enthalpy content, the mechanical parameters, and the depth of the oxidation front deduced from the fractographies versus aging time showed that a changing behaviour in the degradation rate appeared at intermediate aging times.
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Partition coefficients of 28 volatile organic solvents (13 alkylbenzenes, 10 chlorinated hydrocarbons, and 5 ketones) in olive oil, saline, and rat brain tissue homogenates were measured by equilibration in a closed vial and subsequent gas-chromatographic analysis of headspace air. The values of oil and saline partition coefficients correlate well with previously reported data. Brain partition coefficients were fit to a bilinear equation of the form P(brain:air) = alpha(o)P(oil:air) + alpha(s)P(saline:air) + c. The regression coefficients accurately predicted previously reported rat brain partition coefficients of 19 solvents with distinct physicochemical properties within a factor of 2.5. The combined data set of presently determined and previously reported brain partition coefficients (n = 46) yields tissue-specific regression coefficients for solvent partitioning in rat brain of 0.028 for alpha(O'), 0.845 for alpha(S'), and 0.90 for the intercept, with coefficients of variation amounting to 11%, 4%, and 463%, respectively. The generalized empirical relationship predicts the brain partition coefficients within a factor of 2.5 accurately for 95% of the compounds. The ratios of rat brain concentrations calculated from predicted and measured P(brain:air) and P(blood:air) values were within a factor of 4 for 95% of the compounds. It was concluded that the enlargement of the empirical data set leads to more reliable predictions of rat brain partition coefficients, particularly for the lipophilic volatile organic compounds.