Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Ping Liu


The mechanical properties of recycled high density polyethylene (HDPE) reinforced by short glass fibers were investigated. The composites formed by an injection molding process were examined in terms of tensile strength, percent elongation, and hardness. Recycled HDPE was compared to virgin HDPE regarding the effects of fiber concentrations, types, sizes, and treatments. The addition of three coupling agents at different concentrations was investigated.

The virgin HDPE composites slightly outperformed their recycled HDPE counterparts; having higher tensile strength and hardness, but were less ductile. Increase in fiber concentration generally increased the tensile strength and hardness, but the concentration of fibers was inversely related to the percent elongation. Owens Corning chopped fibers (20 wt.%) were the most beneficial, increasing the tensile strength by 30 % over the unreinforced plastic.

The addition of Owens Corning chopped fibers produced less ductile, but stronger tensile specimens than composites incorporating Fibre Glast fibers. It was noted ocularly that the Owens Corning chopped fibers dispersed better throughout the specimen than the Fibre Glast fibers. Fiber size was also significant on the tensile strength, and percent elongation of the composites. The test results suggested that the Owens Corning chopped fibers were more effective in increasing the tensile strength and reducing the ductility than the shorter Owens Corning milled fibers.

Two types of fiber treatment were examined. The first treatment involved drying Owens Corning chopped fibers at 80 °C (176 °F) for 10 hours. Similarly the second type of treatment was to soak Owens Corning chopped fibers in acetone for one hour and then dry at 80 °C (176 °F) for 10 hours. The treatments decreased the tensile strength, and percent elongation, but increased the hardness. Furthermore, an investigation of drying the recycled HDPE at 65.6 °C (150 °F) prior to processing the composites was conducted; but no significant changes were obtained in this study.

Fusabond brand coupling agent decreased the tensile strength and percent elongation for recycled HDPE reinforced with Owens Corning chopped fibers, but increased the strength and elongation for the composites incorporating Owens Corning milled fibers. The hardness of the composites with Owens Corning chopped and composites with Owens Corning milled fibers increased slightly. NZ 44 coupling agent was determined to significantly affect the tensile strength negatively, and LICA 38 coupling agent was determined to increase the ductility of the composites. NZ 44 and LICA 38 did not significantly affect the hardness of the composites.