The Experimental Investigation of The Recycling Effect on The Low Strain Rate Behavior of HDPE and PP Materials Under Tensile Loading

Thermoplastics are widely used as engineering materials due to their advantages such as lightweight, corrosion resistance, and low cost. However, thermoplastic waste stands out as one of the major contributors to environmental pollution. This situation not only presents an economic disadvantage but also reduces the quality of life. The recyclability of thermoplastic materials is a crucial feature to address these disadvantages. Recycling not only conserves raw materials but also reduces environmental pollution. However, changes in the molecular structure of thermoplastics during the recycling process can lead to degradation in their rheological and mechanical properties. In this project, The impact of recycling via extrusion on tensile strength and the elasticity modulus of High-Density Polyethylene (HDPE) and Polypropylene (PP) materials at different strain rates was investigated. The raw HDPE material was recycled once and thrice, while the raw PP material was recycled once. The results indicated that the mechanical properties of HDPE material remain largely unaffected even after three recycling processes, while the PP material shows a slight reduction in elasticity after one recycling process. Additionally, an increase in mechanical properties was observed for all material types at high strain rates. While this increase was nearly the same for both raw and recycled HDPE materials, recycled PP materials exhibited a higher increase in mechanical properties compared to raw PP material. The results suggest that HDPE and PP materials subjected to a limited number of recycling processes can still be used as engineering materials.