Mechanical, Thermal and Rheological Properties of Polymers Used in Plastic Fuel Tanks 2006-01-0333

The materials used for making plastic fuel tanks are: virgin high-density polyethylene; fuel tank regrind; ethylene vinyl alcohol copolymer (EVOH) fuel barrier; and maleic anhydride modified linear low-density polyethylene adhesive. Impact strength measurements were conducted per ASTM D256 using Izod & Charpy machine configurations. All polymers were found to have superior impact resistance at room temperature. The polyethylene and fuel tank regrind maintain superior impact at −40 °C; however, a sharp drop in impact resistance is noted for EVOH. Dynamic mechanical analysis (DMA) of EVOH showed that in addition to the glass transition at about 70 °C, the polymer undergoes a second order transition around −35 °C, which is responsible for embrittlement.

All materials are sensitive to the presence of notches or sharp discontinuities. Notched Izod impact resistance is five to ten times lower for polyethylene matrices; and forty times lower for EVOH than unnotched samples.

Melt rheology measurements were conducted a capillary rheometer at temperatures of 210, 220, and 230 °C, and shear rates of 1 to 10000 per second. Results show that all polymers used have similar melt viscosities under normal extrusion conditions.

Physical and rheological properties results are explained in terms of polymer structures.