Observations of Short- and Long-Term Mechanical Properties of Glass Fiber Reinforced Polypropylenes with Post-Consumer Recycled Materials

In this study, the change in the mechanical properties of glass fiber-reinforced thermoplastic (GFRTP) according to the recycled material content was evaluated. The recycled material was polypropylene, with short glass fiber reinforcement, dry blended with virgin polypropylene and additional glass fiber, and injected into its final shape. It is known that during the recycling process, the length of the glass fibers decreases, which leads to the deterioration of the mechanical properties. Therefore, to compensate for the fiber length shortening, long glass fibers were introduced, and changes of the length distribution of the glass fiber and mechanical properties were investigated. Variation of key short- and long-term mechanical properties by introducing long fibers was measured and investigated by performing tensile test, Izod impact test, essential work of fracture (EWF) test, and fatigue test. Most of the mechanical properties showed a linear relationship with the long glass fiber content, but the percent elongation at break and the resistance to the crack initiation were significantly improved immediately after the long fiber was introduced. In addition, the distribution of fiber length was measured and analyzed, and it was found that significant fiber breakage occurred during the injection process and the recycling process including the chopping of recycled material. Finally, through the observation of fracture surfaces, it was validated that the ductile-to-brittle fracture mechanism transition was mainly caused by the poor compatibility between virgin and recycled materials.