Microwave Enhanced Diffusion in Polymeric Materials

A process is described using microwave radiation (2.45 allz) which, for temperature equivalence, greatly accelerates the diffusion of ethylene oxide (EO) in polymeric materials compared to that using conventional heating. The mechanism of action was investigated in detail by examining the desorption of EO from polyvinylchloride (PVC). The diffusion coefficient was found to be dependent upon diffusant concentration.Values of activation energy for diffusion were obtained from Arrhenius plots of the logarithm of diffusion coefficient versus inverse temperature for both conventional and microwave-enhanced diffusion, and there was a significant reduction in activation energy for the latter. There is agreement, to within the range of experimental error, between this value and an energy value equal to the activation energy for conventional diffusion less the translational kinetic energy of the diffusant molecules. Therefore, it seems likely that the enhancement of the rate of diffusion of EO in PVC using microwaves is brought about by the active disruption of the EOIPVC hydrogen bonding resulting in a significant reduction in the proportion of immobilized diffusant molecules at any instant. This suggests that this process could be generally applicable for enhancing diffusion for polarIpolarizable materials when a proportion of the diffusant molecules are immobilized in the host material.