[Life expectancy indicator for re-sterilizable plastic materials]

Semi-disposable products in which only part of the product is disposable while another part made of plastic is designed to be reusable, are an effective counter to the increasing masses of plastic waste generated by hospitals. The major problem with such products has been the fact that the resterilizable parts could withstand only a limited number of resterilizations and the user had no means of seeing when this number had been reached. To resolve this problem, the Life-Span Indicator was developed in cooperation with Beiersdorf AG. This indicator changes colour from blue to orange after about 100 sterilizations. It is based on an azo pigment diffused into a carrier polymer, POM. Repeated heating of the slow colour change of the pigment. Not all the details of the mechanisms involved are clear, but the indicator functions reliably and reproducibly. Since the pigment is inside the polymer, the colour-change reaction is not affected by mechanical pre-cleaning or disinfection. The user can thus readily see how long he can use such products without risking malfunction. The number of resterilizations can be varied to suit the product, and the indicator can be shaped as required, for example as a nonseparable snap-in plug or a capable binder.