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.