Polymeric materials include polyethylene, polypropylene, polybutane, ethylene copolymers such as ethylene-vinyl acetate and ethylene-ethyl acrylate, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene (eg Teflon TFE), copolymers of tetrafluoroethylene and hexafluoropropylene (Teflon FEP), copolymers of tetrafluoroethylene and perfluoroalkoxy moieties (Teflon PFA) copolymers of eth