Unveiling Polypropylene's Repetitive Recycling Potential at High Temperatures

Abstract

Polypropylene (PP) is renowned for its lightweight, chemical stability, hygienic properties, and low cost, making it a valuable material in many applications. However, improper disposal of PP presents significant environmental hazards. One of the efforts made to reduce plastic pollution is through recycling. The semi-crystalline behavior of PP is prone to degradation in its mechanical performance, especially when the plastic undergoes a high-temperature reheating process. This study investigated the degradation limits of recycled PP produced from injection molding from the 15^th to 19^th cycles at two different temperatures, namely 220 °C and 240 °C. A comparison of the tensile and bending properties of the recycled product was made for these two temperatures to determine the maximum limit of PP degradation. When recycling began at the 15^th cycle, there was a significant reduction in tensile and bending properties compared to the original PP. Subsequently, the degradation rate was relatively slow from the 15^th to the 19^th cycles. As the recycling temperature increased, it was found that the degradation of yield strength became more severe. The decrease in bending strength could be more pronounced with the effect of temperature. The color transformation of recycled PP, resulting from the chain scission effect, contributed to the deterioration of its mechanical properties. Thus, industrial users must consider the down-cycling resilience to extend PP recycling beyond 15 cycles.