Gamma-irradiation effects on polypropylene-based composites with and without an internal lubricant

Polypropylene (PP) based materials for nonreusable syringe applications have been investigated, some of them containing an internal liquid lubricant. Hardness, tensile properties, and friction measured by two distinct procedures have been determined. We report three series of results: for nonirradiated samples; for samples directly after stopping the irradiation; and also for samples after accelerated aging equivalent to 2 years of shelf life. We find that effects of irradiation and aging on Shore A and Shore D hardness are small. Tensile strength at break, elongation at yield, and elongation at break all decrease after irradiation and then decrease still more after aging; these results are quantified but expected. By contrast, results from pin-on-disk tribometry are quite varied. In some cases gamma irradiation and aging both increase friction, in other cases both decrease friction. We also have a case when irradiation increases friction while aging decreases it-as well as vice versa. Possible mechanisms of all these types of behavior are advanced. POLYM. ENG. SCI., 49:1035-1041, 2009. (C) 2009 Society of Plastics Engineers