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Purging is a fundamental process in the injection molding sector, aiding in color transition, material shifts, and the removal of contaminants. The purging compounds can be classified according to physical or chemical mechanisms and are affected by processing parameters, such as temperature, pressure, or soaking period. Despite some studies on the effect of processing parameters in purging action, an analysis of the rheological behavior and physico-chemical changes is still required for a deeper understanding of this type of system. This study explored shear viscosity, activation energy behavior in the torque rheometer, injection molding process, and energy consumption for two polyolefin-based purging compounds: one on polypropylene (PP) and another on polyethylene (PE). The results showed that the PP-based compound is a highly viscous material with low thermal sensibility and low energy consumption. The PE-based chemical compound, which includes an expanding and scrubbing agent, presented higher thermal sensitivity. Lower purging times and specific energy consumption were observed for the mechanical purge regardless of the processing temperature in the injection molding machine. However, torque and specific total mechanical energy differed due to viscosity and possible filler particle agglomeration. These findings demonstrated the influence of processing temperature on rheology and performance. Nonetheless, further studies regarding pressure, soaking time, and rheological modeling are recommended.

The circular economy promotes plastic recycling, waste minimization, and sustainable materials. Hence, the use of agricultural waste and recycled plastics is an eco-friendly and economic outlook for developing eco-designed products. Moreover, new alternatives to reinforce recycled polyolefins and add value to agroindustrial byproducts are emerging to develop processable materials with reliable performance for industrial applications. In this study, post-consumer recycled high-density polyethylene (rHDPE) and ground rice husk (RH) of 20% w/w were blended in a torque rheometer with or without the following coupling agents: (i) maleic anhydride grafted polymer (MAEO) 5% w/w, (ii) neoalkoxy titanate (NAT) 1.5% w/w, and (iii) ethylene–glycidyl methacrylate copolymer (EGMA) 5% w/w. In terms of processability, the addition of RH decreased the specific energy consumption in the torque experiments with or without additives compared to neat rHDPE. Furthermore, the time to reach thermal stability in the extrusion process was improved with EGMA and MAEO compatibilizers. Tensile and impact test results showed that using coupling agents enhanced the properties of the RH composites. On the other hand, thermal properties analyzed through differential scanning calorimetry and thermogravimetric analysis showed no significant variation for all composites. The morphology of the tensile fracture surfaces was observed via scanning electron microscopy. The results show that these recycled composites are feasible for manufacturing products when an appropriate compatibilizer is used.

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