Degree Name

Master of Science (MS)

Semester of Degree Completion

1997

Thesis Director

Ping Liu

Abstract

This thesis presents a study on the mechanical and tribological properties of composite materials of recycled high density polyethylene (HDPE) and recycled rubber tire particles. The materials were compounded by extrusion and formed into test specimens by injection molding.

The first experiment studied the effect of recycled rubber percentage on mechanical properties of composites of recycled HDPE and recycled rubber. The mechanical properties included tensile strength, percent elongation, hardness, and impact resistance. Recycled rubber concentrations of 0, 5, 10, 15, 20, 25, and 30 percent were tested. The second experiment investigated the tribological properties of recycled HDPE and recycled rubber composites. Tests were performed on the composite specimens to determine the effects of normal pressure, sliding speed, and recycled rubber percentage on coefficient of friction and wear rate. Normal pressure in the range in the range between 9.87 and 24.60 MPa was applied on specimens containing five percent recycled rubber at a sliding speed of 5.10 m s-1. Sliding speed between 2.55 and 5.95 m s-1 was studied on specimens containing five percent recycled rubber at a normal pressure of 16.46 MPa. Rubber percentages of 0, 5, 10, 15, 20, 25, and 30 percent were tested at a normal pressure of 16.46 MPa and a sliding speed of 5.10 m s-1.

Tensile strength decreased as recycled rubber percentage increased for the composites of recycled high density polyethylene and recycled rubber particles. The ductility of the composites decreased drastically as recycled rubber content increased to five percent, and further decreased gradually from five to 30 percent. The hardness decreased as recycled rubber content increased. The impact strength decreased drastically at five percent recycled rubber. It remained fairly constant from five to 25 percent of recycled rubber, and then decreased as rubber content increased to 30 percent.

The tribological experiments showed that coefficient of friction and wear rate increased as the normal pressure increased for the composite of recycled HDPE with five percent recycled rubber. Coefficient of friction and wear rate increased as the sliding speed increased for composites of recycled HDPE with five percent recycled rubber. Coefficient of friction and wear rate increased as the recycled rubber percentage increased in composites of recycled HDPE with recycled rubber.

Microscopic analysis of the friction and wear test specimens was performed to determine structural changes due to sliding. The sliding surface and cross section of the tested specimen were examined. The results of this analysis showed that surface damage increased as normal pressure, sliding speed, or percentage of recycled rubber increased. The depth of deformation decreased as the sliding speed increased, while the depth increased with increasing normal pressure and rubber percentage.

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