Non-monotonic degradation and strength recovery in mechanically recycled ABS for fused granule fabrication

This work systematically correlates the chemical degradation, microstructural evolution, and macroscopic mechanical performance for the sustainable and the reliable use of recycled acrylonitrile butadiene styrene (ABS). Through detailed multi-scale characterization of the virgin and the recycled ABS, the results showed that the virgin and recycled ABS at all stages exhibited core-shell and graft-like microstructure. While the recycling process reduced the uniformity of particle sizes and blurred interfacial regions due to thermo-oxidative chain breaking, the X-ray diffraction showed non-monotonic inter-chain spacing of the virgin and the three stages of recycling (4.392, 4.519, 4.478, and 4.477 Å) and a steady increase in full width at half maximum (7.03°-7.31°). Interestingly, a partial molecular weight recovery was observed in the third cycle (R3), which was attributed to partial volatilization of small oligomeric particles during printing. The Fourier-transform infrared spectroscopy also showed a clear isomerization process: the vinyl 1,2-butadiene units converted to trans 1,4 configurations during early degradation, which explained the simultaneous decrease in BDI₁,₂ and increase in BDI₁,₄ indices with recycling. Most notably, R3 demonstrated mechanical recovery, with elongation at break reaching 6.8%, surpassing the virgin material’s (6.5%). Meanwhile, it maintained a tensile strength of 23 ± 1 MPa, and the fracture position, which initially shifted during the first and second stages, returned towards the mid-gauge position. These results showed a non-monotonic degradation-related recycling pattern, which means that the degradation from recycling is manageable. Based on the results, the recycled ABS up to three cycles might be suitable for non-critical engineering applications, which still need some additives, while high-performance applications require blending with virgin material or targeted additives.