Kinetics of the aeration of ethylene-oxide sterilized plastics.
The aeration of ethylene-oxide (EO) sterilized medical plastic materials is dealth with mathematically, and subsequently the model found is used for calculation of the EO diffusion coefficient in various plastics with the composition and temperature as variables. Absorption and dissolution of EO in various plastic materials are measured at varying concentrations of EO, temperatures and compositions of plastics. The mathematical model is used to evaluate the EO desorption from medical devices under different physico-chemical conditions as well as in vivo. EO analysis methods are evaluated on the basis of the model and are compared with experimental results.
Infrared spectroscopic study of polymers exposed to ethylene oxide.
Fourier transform infrared spectroscopy has been used to study thin polymer films exposed to ethylene oxide (EO). The i.r. technique represents a new way of studying this subject. The polymers studied were poly(vinyl chloride), polyethylene and polystyrene. They were exposed to EO, either in a small commercial EO-sterilizer which uses pure EO and operates at subatmospheric pressure, at a temperature of 37 or 55 degrees C, or under experimental laboratory conditions. The absorption and diffusion of EO in the polymers was studied. Potential reaction products, such as ethylene glycol and ethylene chlorohydrin, were looked for but could not be traced. The detection limit of the method was 1 ppm (microgram/g) EO. Typical spectra of the polymer films, before and after exposure to EO, are shown. Diffusion coefficients for poly(vinyl chloride) and polyethylene have been calculated.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.