(689b) Thermally Aged Poly(phenylene sulfide) Powder As a Feedstock for Powder Bed Fusion

Many new polymers are becoming commercially available for powder bed fusion (PBF) additive manufacturing (AM), including several regarded as high-performance polymers, like poly(phenylene sulfide) (PPS). PPS suits the needs of AM early-adopter industries, like aerospace, due to its high wear resistance, high specific strength, radiation resistance, and chemical resistance. Recent work has highlighted the process parameter selection considerations needed for processing PPS using PBF¹. While there are many benefits to polymer PBF (e.g., no additional support material needed and batch-style production), one drawback is thermal ageing of powder that is not incorporated into a printed part. Ideally, the unfused powder can be reused as part of future builds; however, it is unlikely that printability properties of the thermally aged powder will match those of fresh powder. This change in properties leads to either limited reuse through a practice of mixing used and new powder, or elimination of all powder after each build. The more often the powder can be re-used, the more sustainable and cost-effective PBF is.

In this work, the authors report how thermal ageing in simulated printing conditions affects the properties of PPS that are critical to PBF processing. PBF-grade PPS powder was aged for up to 300 h at three process relevant temperatures: 200 , 230, and 278°C under nitrogen. The aged powders were then evaluated for properties relevant to the three PBF manufacturing process sub-functions: powder recoating, energy input, and coalescence and cooling. While there are no observable changes for recoating related properties, significant and systematic deviations from the as-received state of the powder are observed for energy input and coalescence and cooling related properties with increasing ageing time and temperature. These changes are most pronounced for properties pertaining to the coalescence and cooling sub-function (e.g., melt flow rate). These changes are interpreted both in terms of physical and chemical changes in PPS and in terms of how these changes may impact the PBF printing process.

References

(1) Chatham, C. A.; Long, T. E.; Williams, C. B. Powder Bed Fusion of Poly(Phenylene Sulfide) at Bed Temperatures Significantly below Melting. Additive Manufacturing 2019, 28, 506–516.