Impact of recycling on polymer binder integrity in metal injection molding

Metal Injection Molding (MIM) is a manufacturing process that integrates polymer binders with metal powders to produce high-precision components, offering both material efficiency and design flexibility. This study explores the recyclability of polymer-based feedstocks used in Metal Injection Molding, specifically evaluating how repeated recycling affects the structural integrity and thermal stability of polymer binders. Given the high cost of raw materials in MIM, optimizing recyclability is essential for reducing production costs and minimizing material waste, contributing to more sustainable manufacturing practices. To assess the feasibility of repeated material reuse, the study systematically subjected molded specimens to grinding and reinjection molding over eight consecutive cycles. The effects of reprocessing were analyzed using melt flow index (MFI) measurements, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) to track changes in polymer viscosity, thermal behavior, and degradation. The results indicate that wax precipitation during processing alters polymer viscosity and thermal stability, leading to gradual material property changes over successive recycling cycles. However, polymer degradation-induced viscosity reduction counterbalances these effects up to the fourth cycle, ensuring processability within standard injection molding conditions. The findings underscore the significance of analytical techniques in evaluating polymer binder integrity during multi-cycle reuse. Melt flow index (MFI) initially increased, peaking at the fourth recycling cycle, and then declined, while linear shrinkage rose by approximately 3% within the first three cycles before stabilizing. SEM-EDS analyses indicated around a 20% wax loss after multiple recycling cycles, significantly influencing binder rheology. Polymer binders can thus be successfully recycled up to four times while maintaining acceptable thermal and rheological properties, supporting resource-efficient and sustainable manufacturing strategies in MIM production.