ABSTRACT:We analyze an example of the application of polymer tribology to create a safety medical device, namely a retractable syringe. In service at various stages either low-or high-dynamic friction is needed. Our work focuses on a VanishPoint ® nonreusable safety syringe manufactured by Retractable Technologies, Inc., Little Elm, TX. Different medical-grade materials strongly affect the performance of this product. Extant tribological testing methods developed for flat surfaces are of little use. A functionality test that provides static and dynamic friction between rounded and cylindrical parts moving one inside the other gives us data not obtainable from the earlier techniques. These results combined with the liquid blowout force results (also for cylindrical surfaces) tell us that a polyolefin elastomer imparts better properties to a polypropylenecontaining resin than does silica as an additive. Data-based selection of appropriate polymeric materials for components of the syringe thus becomes possible.

Abstract:We have studied nine thermoplastic vulcanizate elastomers (TPVs) in four series: as made, after accelerated aging, after γ irradiation, after both irradiation and aging. The materials exhibit two glass transitions, one seen in crosslinked regions and the other in un-crosslinked amorphous regions. Three techniques of determination of glass transitions have been used and the results compared, all three based on dynamic mechanical analysis (DMA): as a peak in the loss modulus E''; as a peak in tan δ; and as the midpoint of the rapid decrease in the storage modulus E'. We recommend the last method for both fundamental and practical reasons.