Enhancing the Mechanical Performance of Fused Deposition Modeling-Printed Recycled Polypropylene through Annealing Temperature, Duration, and Cooling Method

This study examines the effects of annealing temperature, duration, and cooling method on the mechanical properties of FDM-printed recycled polypropylene (PP) parts. The Taguchi experimental design was applied to optimize process conditions, and tensile and impact tests were conducted to evaluate mechanical performance. Results show that impact strength was maximized at 155 °C, 1/2 h, and room-temperature cooling, while tensile strength was highest at 55 °C, 4 h, and slow cooling. ANOVA and regression analysis confirmed the statistical significance of these parameters, with annealing temperature and duration having the most pronounced effects. SEM analysis revealed that higher temperatures enhanced interlayer bonding, while slow cooling and longer durations improved fracture resistance. Unlike prior studies that examined only individual annealing parameters or used virgin PP, this work systematically explores the combined effects of annealing factors specifically for recycled PP, offering a comprehensive evaluation rarely addressed in the literature. These findings demonstrate that annealing significantly enhances the structural and mechanical performance of recycled PP, offering a sustainable approach to improving FDM-printed components. The results suggest that an intermediate condition (115 °C, 2 h, and room cooling) may balance impact and tensile properties, making annealing a viable post-processing technique for high-performance and sustainable polymer applications.