Binder degradation in Metal Injection Molding feedstock recycling
Researchers from Hungarian institutions John Von Neumann University, Kecskemet; Eszterházy Károly Catholic University, Eger; and Széchenyi István University, Gyor, have published a paper in Scientific Reports focused on the impact of recycling on polymeric binders in Metal Injection Molding.
The study, ‘Impact of recycling on polymer binder integrity in metal injection molding’, analysed feedstock through multiple reprocessing cycles, revealing the evolving structural and thermal behaviour of polymer binders.
After the initial injection molding, the material underwent seven consecutive reprocessing steps, during which its mechanical, thermal, and rheological properties were systematically evaluated. Advanced characterisation techniques – including SEM analysis, MFI measurements, dimensional shrinkage evaluation, DSC, and TGA – provided insights into the material’s degradation pathways and processability limits.
The researchers confirmed the crucial role polymer binder degradation and wax precipitation play in determining the recyclability of MIM feedstocks. The study’s melt flow index measurements indicate that the most significant changes occur by the fourth recycling cycle, beyond which material viscosity and processability begin to decline. The crystallisation behaviour of the polymer matrix, as inferred from DSC and shrinkage analysis, suggests that progressive molecular fragmentation leads to increased crystallite size and altered viscosity. This effect is counterbalanced by the reduction in wax content, which influences the overall thermal stability and rheological performance of the feedstock.
TGA results identified distinct decomposition stages, with early-stage material loss attributed to slip agents and wax degradation, while polypropylene decomposition exhibited a relatively stable trend over multiple cycles. Scanning electron microscopy and EDS analysis further validated these observations, revealing a measurable decrease in carbon content, indicative of progressive wax loss. These microstructural changes directly impact the material’s flow characteristics, emphasising the importance of binder optimisation strategies for extended recyclability.
Opening the door to further research
From an engineering and sustainability perspective, the study notes that its findings highlight the potential for integrating multi-cycle polymer binder reuse into MIM manufacturing workflows. The ability to maintain thermal and flow properties over four recycling cycles demonstrates the viability of resource-efficient material design in Metal Injection Molding.
The researchers stated that their work underscores the need for further investigation into binder system modifications and strategies that could enhance long-term recyclability without compromising material integrity.
While this study did not include any changes to the binder formulation or processing parameters, findings suggest that such optimisation approaches – particularly in terms of component selection and thermal profile adjustments – may be beneficial. By addressing these challenges, MIM technology can contribute to circular economy initiatives, reducing raw material dependency while ensuring high-performance component manufacturing.
‘Impact of recycling on polymer binder integrity in Metal Injection Molding’ is available here.
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