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.
General solution of the diffusion equation: application to formaldehyde sterilization and desorption of polymers.
A general solution of the diffusion equation for gas in polymers is developed by a numerical method. This solution allows diffusion to be calculated in all cases, by gas desorption after an incomplete adsorption, which is not the case for analytical solutions. When the analytical solutions are valid, both types of solution give identical results. The effect of equivalent sterilization treatment at different temperatures and gas concentrations on formaldehyde residuals in 9 polymers is calculated. High temperature gives lower residual content. Short sterilization times at high gas concentration produce a higher residual content at the end of the adsorption and a lower residual content during desorption than longer sterilization times with lower gas concentration. This is due to sharper gradients of diffusant in the polymer.
Intensification of Bubble Disintegration and Dispersion by Mechanical Stirring in Gas Injection Refining
Water model experiments were performed for establishing highly efficient gas injection refining processes. Mechanical stirring was applied to disintegrate the injected bubbles and to disperse them widely in the bath. The bubble disintegration and dispersion were investigated by changing rotation mode (direction of rotation), rotation speed, blade size of the impeller and gas flow rate. Forward rotation of the impeller induced a stable tangential flow and could not disperse bubbles in the bath due to formation of a vortex around the impeller shaft. The tangential flow could be suppressed by forward–interrupt rotation, which could reduce the vortex formation to some degree. However, forward–interrupt rotation could not disperse the bubbles widely in the bath. Forward–reverse rotation could prevent the vortex formation completely and create a strong shear stress field, which intensified the bubble disintegration and dispersion in the bath. Higher impeller rotation speed and larger blade length in forward–reverse rotation could enhance the bubble disintegration and make the dispersed bubbles smaller. The bubble dispersion zone became wider with larger blade length. The bubble size tended to be larger at higher gas flow rates. However, its dependence on the gas flow rate became smaller at higher impeller rotation speed.