Structural and Material Features that Influence Emissions From Thermoplastic Multilayer Fuel Tanks

An analysis of permeation of hydrocarbon fuel in thermoplastic multilayer fuel tanks is presented. Measurements of permeability coefficients in indolene of high density polyethylene, HDPE, the ethylene-vinyl alcohol, EvOH, copolymer barrier layer and a maleated linear low density polyethylene, LLDPE, have been incorporated to provide an approximate description of the relative permeability of a fuel tank laminate. The effects of laminate thickness, barrier layer thickness, the incorporation of a regrind layer and laminate construction have been addressed using existing simple theoretical expressions. Particular attention has been focused on the overall permeability of the seam or “pinch off” and a simple description of seam geometry and structure has been applied to estimate the relative contribution to emissions. Results suggest that the seam may contribute considerably more to overall tank emissions than the body of the tank.