| Thermoplastic polyurethane (TPU) and BaSO4 filled TPU possess outstanding combinations of physical properties, blood compatibility, X-ray trace-ability and processability advantages in comparison to other commercial polymers. As a result, TPU is widely used in the medical devices industry, preferably without any additives. However, the selection of operating conditions and geometry for the processing of TPU and BaSO4 filled TPU is a complicated task. This complication arises from the thermal and oxidative degradation and curing of TPU under relatively high temperatures and residence times, its rapid hydrolysis when moisture is present and the continuing development and modification of the hard/soft block morphology upon processing at temperatures lower than the melting temperature. When compounded with the x-ray tracer BaSO4 additional complications involving development of viscoplasticity, dilatancy, wall slip, formation of surface irregularities and the entrainment of air occur. In this thesis an integrated investigation of the rheology, wall slip, single and twin screw extrusion, co-extrusion, structure development and the mechanical properties of a medical-grade TPU and its BaSO4 filled composites has been carried out. This investigation is anticipated to be very helpful to the medical devices industry in general and to the processing of thermoplastic urethanes in particular. |
