Polypropylene (PP) is a thermoplastic polymer and is one of the most widely used polyolefin polymer, which is a well-known semi crystalline polymer. Plastics such as polypropylene are commonly used for different applications and purposes due to their versatility;​ however, it should be noted that our current approaches in plastic product production, consumption and disposal are not sustainable and causes concerns for environment and human health. Hence, appropriate use and disposal, especially recycling has an essential role. There are several studies investigating the chemical and mechanical properties of polypropylene;​ and also there are a few studies on the effects of multiple recycling on chemical and mechanical behavior of polypropylene;​ however, there are relatively few investigations involving combination of virgin and recycled polypropylene. To more accurately investigate the effects of the addition of different percentage of recycled polypropylene on tensile properties of polypropylene this study was conducted. Also the effects of annealing and glass fiber additive on recycled content polypropylene are investigated in this study. Cold temperature effect on polypropylene properties also investigated (due to environmental conditions in Edmonton). Hence, using design of experiment (DOE) methods, the effects of all these factors on tensile behavior of polypropylene is carried out in detail. Also a wide angle X-ray diffraction (WAXD) system is used to investigate on crystalline structure of the recycled content polypropylene samples to better explain their tensile behavior. Furthermore, drop test simulations are performed on a sample box, using the measured tensile properties at room temperature as a case study. Based on the current experimental study, and combination with the literature reviews, it is concluded that recycled material could be use without detrimental effect on the material properties of polypropylene.

Guidelines of this study could be useful for further studies on different materials or more combinations. The comprehensive tensile results obtained through this study are valuable for plastic industries and designers, which could be helpful to reduce industries, cost of material and also recycling is one of the most environmental friendly ways to dispose plastics. Combination of DOE methods and statistical analysis with tensile experiments and FEA simulations makes a powerful method which could be used as a guideline for further studies, other researchers, industries and designers to reduce cost and plastic production.