Molding Characteristics and Impact Strength of Polypropylene with Different Numbers of Recycling Cycles

We analyzed the changes in the molding properties of polypropylene (PP) resin in the process of recycling after multiple plasticization, injection, and crushing processes. We also explored the changes in the material properties and characteristics with the ASTM-D256 impact test specimen and the number of recycling cycles. After the material is injected and crushed, it is recycled to produce the material required for re-injection, and a pressure sensor is installed at the nozzle position to observe the effects of material properties and impact characteristics in recycling. Injecting and pulverizing PP several times results in looser molecular spacing, increasing the fluidity of the material. After several recycling cycles, the fluidity of the material gradually decreased. Its crystallinity fluctuated depending on the crystallinity and crystallization rates. Recycled PP materials in various molding processes were influenced by melt temperature, screw speed, back pressure, and injection speed, which also affected nozzle pressure and strength. As the melt temperature increased, the effect on the nozzle pressure and impact strength became more evident.