Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Ping Liu

Thesis Committee Member


Thesis Committee Member



This study identified the mechanical properties and processibility of composite materials of recycled high density polyethylene (HDPE), recycled rubber tire particles, and/or ethyl co-vinyl acetate and poly (e-caprolactone). The composites were processed using a single screw extrusion system.

Three groups of experiments were conducted, on the composites in their extruded form to investigate the mechanical properties of ultimate tensile strength, percent elongation, and hardness. The first experiment investigated the effect of recycled rubber particle concentration in the composites up to 25 percent. The second experiment investigated the effect of recycled rubber particle size on the composites of recycled HDPE and 5 percent recycled rubber. The third experiment studied the effect of ethyl co-vinyl acetate and/or poly (e-caprolactone) as compatibilizers on composites of recycled HDPE with 5 percent recycled rubber. Ethyl co-vinyl acetate (EVA) was introduced to the recycled HDPE, individually with the recycled rubber, or together with the recycled rubber as a "pre-blend" material. The pre-blend consisted of 75 percent EVA and 25 percent recycled rubber and was extruded prior to the extrusion with the recycled HDPE. Poly (e-caprolactone) was extruded with the recycled HDPE/recycled rubber and the pre-blend.

The first experiment showed that the strength of composites of recycled HDPE and rubber particles decreased with increased rubber content. The ductility of recycled HDPE/recycled rubber composites decreased drastically at rubber concentration of 5 percent, then remained fairly constant as rubber content increased. The hardness of recycled HDPE/recycled rubber composites decreased with increased rubber particle content.

The second experiment, involving composites of recycled HDPE and 5 percent recycled rubber, showed that recycled rubber size in the studied range did not have any significant effect on tensile strength, while finer particles proved to increase percent elongation and decrease hardness.

The third experiment demonstrated that the addition of compatibilizers ethyl co-vinyl acetate and poly (e-caprolactone) affected the mechanical properties of the composites, but EVA improved the processibility of the recycled HDPE/recycled rubber.

Tensile strength and hardness decreased with the addition of EVA and/or poly (e-caprolactone) to the composites, while percent elongation decreased significantly only in the composites not containing "pre-blend" material. Further study is recommended in the processing of the composites.

Polarized contrast and differential interference contrast (DIC) were utilized to view the distribution of the recycled rubber particles and interfacial bonding within the recycled HDPE matrix. Significant interfacial bonding and uniform distribution between recycled rubber particles were found throughout the recycled HDPE matrix.