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With the advent of low evaporative emission requirements there has been the rapid adoption of multilayer extrusion technology into the production of Fuel and Vapour tubing used on Fuel systems on automobiles. Multilayer extrusion technology enables a manufacturer of Fuel and Vapour tubing to simultaneously co-extrude dissimilar thermoplastic materials in tubular form. This allows the manufacturer to combine expensive and brittle high performance evaporative emission ‘barrier’ polymers with lower cost engineering polymers. However, it is a well-known characteristic of these multilayer tube constructions that the joints between them and connector ‘barbs’ have lower joint integrity. Joint integrity is most often quantified by ‘Pull-off’ and leakage tests. Recent developments in LEV-II requirements for 2004 and beyond indicate that joint integrity will become a focus area for study and improvement.

The diffusion of methanol, ethanol and toluene in a Nylon 12 and a poly(vinylidene) fluoride (PVDF) was measured using Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, a technique which allows the quantification of the penetrant concentration diffusing in thin polymer films in situ. Furthermore, it is also possible to study multi-component diffusion using FTIR-ATR provided each component displays unique infrared absorbance peaks. Thin films of a Nylon 12 and PVDF were made by both solvent casting from either 1,1,1,3,3,3, hexafluoro-2-propanol or dimethylacetamide and by cast film extrusion. The films made by the cast film extrusion process had a more uniform thickness than those solvent cast. The diffusion coefficients of methanol, ethanol and toluene in Nylon 12 and PVDF were determined gravimetrically and by the FTIR-ATR technique. Both methods afforded comparable diffusion coefficients for similar solvent-polymer systems.

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.