An investigation of the gasoline permeation resistance of the as-blowmolded and annealed polyethylene, polyethylene (PE)/polyamide (PA), and polyethylene/modified polyamide (MPA) bottles is reported. The gasoline permeation resistance improves dramatically after blending PA and MPA barrier resins in PE matrices during blow-molding, and the order of barrier improvement corresponds to the order of barrier improvement of the barrier resins added in PE. Somewhat unexpectedly, the gasoline permeation rates of the annealed PE and/or PE/PA bottles annealed at 90°C or higher temperatures increase significantly with the annealing temperature and time. On the contrary, the gasoline permeation resistance of the annealed PE/MPA bottles increase significantly as the annealing temperature and/or time increase. For instance, the gasoline permeation rate of the PE/MPA bottle annealed at 120°C for 32 h is about 190 times slower than that of the as-blow-molded PE bottle. Further investigations found that, after blending the MPA and PA barrier resins in PE matrices, the relatively nonpolar hydrocarbon components present in the gasoline fuels were significantly blocked, without permeation during the permeation tests, in which the as-blow-molded PE/MPA bottle inhibited the permeation of hydrocarbon components more successfully than did the as-blow-molded PE/PA bottle. In contrast, the amounts of polar components that permeated through the as-blow-molded PE/PA and PE/MPA bottles were very small and about the same as the amount that permeated through the as-blowmolded PE bottle. Possible mechanisms accounting for these interesting behaviors are proposed in this study.
Different modified polyamide (MPA) and modified polyethylene (MPE) resins were prepared by reactive extrusion of different contents of a compatibilizer precursor (CP) with either polyamide (PA) or polyethylene (PE). The MPE and MPA resins were then blow-molded with designed amounts of PA or PE resins to prepare four different sets of MPE/PA and PE/MPA bottles with the same CP, PA, and PE compositions. Somewhat surprisingly, the xylene permeation resistance of the MPE bottles is worse than that of the base PE bottle and decreases consistently as MPE contains more CP. In contrast, the MPE/PA and PE/MPA bottles exhibit much better xylene permeation resistance than that of the base PE bottle, wherein the PE/MPA bottles show significantly better permeation resistance than that of the corresponding MPE/PA bottles prepared at the same blow-molding conditions. On the other hand, it is worth noting that the xylene permeation rate of each of the MPE/PA and PE/MPA bottles prepared at a fixed extrusion temperature reaches a minimum when prepared with an optimum screw speed near 400 rpm. Similarly, at a fixed screw speed, the highest permeation resistance of each PE/MPA bottle is always obtained when prepared at an optimum extrusion temperature of about 230 o C. However, the xylene permeation resistance of each MPE/PA bottle improves consistently when prepared at the higher extrusion temperatures used in this study. These interesting phenomena were investigated in terms of the morphology, thermal analysis of the PE/MPA and MPE/PA blends, the compatibility between PE (or MPE) and MPA (or PA), and the viscosity ratios of MPA (or PA) to PE (or MPE) during the blow-molding process.
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