Sterilization of organic sheet by plasma-based ion implantation

Summary form only given. Polyethylene terephthalate (PET) bottles are widely used as beverage containers due to the easy handling as well as the low cost. They have taken the place of glass bottles in most market. However, PET has something inferior to glass for industrial application. The bottles in a traditional bottling system are sprayed with hydrogen peroxide water or dipped in a basin filled with the toxic water for sterilization prior to being filled with beverages. Then they are rinsed with pure water and dried with hot air. PET bottles take much more time to fulfil this rinsing process than glass ones, since organic material like PET tends to absorb some of liquid or gas molecules into its bulk structure. In order to reduce the amount of toxic hydrogen peroxide in the sterilization process Jacobs and Lin developed a plasma sterilization using hydrogen peroxide vapour, in which the chemical reactivity of the toxic molecules is enhanced by particle collision in plasma. However, their method has not sufficiently resolved the problem of residual toxic molecules in organic material, yet. We are developing a new plasma sterilization for solid organic material without toxic residues. The plasma-based ion implantation (PBΠ) is utilized, since it can be applicable even to insulated materials like organic material without electrical charging problems. This research is for obtaining fundamental data for the sterilization. Microwave plasma in magnetic field is generated with nitrogen gas. A piece of PET sheet to which spores of Bacillus subtilis are attached are bombarded by ions with the energy of up to 10 keV. Since the ion bombardment is carried out with pulse mode of 0.5 % in duty cycle, the sheet temperature is kept too low to damage the organic material with heat3. The sterilization in this research occurs due to physical reaction of high energy ions with the spores, although the sterilization in most traditional "plasma sterilizations" occurs due to plasma-enhanced chemical reaction. The sterilization rate which is measured by aceptic test is obtained as a function of spore density on the PET sheet. The minimum ion fluence needed for sterilization is found to depend roughly proportionally on the spore density.