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Multilayer co-extrusion of plastics is fast becoming a very cost effective method of improving the barrier properties of plastic products. In this process individual polymers are melted and conveyed by separate extrusion systems, into a common distribution block and through a forming die where the polymer melts merge to form an integral multilayer structure. However, these multilayer structures are proving difficult to extrude because of their widely different temperature profiles required during extrusion, and the fact that all the melts enter a common die which can only be maintained at one particular temperature. The melt rheological characteristics of a range of commercially available barrier materials, polyvinylidene fluoride (PVDF), a terpolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), plasticised Nylons and tie layer materials have been studied using Dual Capillary Rheometric techniques.

With the advent of more stringent legislation for fuel and fuel vapor emissions from vehicles, it has been necessary to introduce a barrier polymer into the fuel line as a means of reducing emissions. This paper examines tensile dumbbell samples (ASTM D 638M) of a range of plasticised Nylons, tie layer polymers and fluoropolymers which were immersed in methanol, ethanol and toluene at 25°C. The percentage mass uptake and extent of swelling were determined. The mechanical properties and changes in glass transition were measured at different immersion times for up to 21 weeks.