The effect of physical aging and degradation on the re-use of Polyamide 12 in powder bed fusion

Ben Sanders, Edward Cant, Hoda Amel, Michael Jenkins*

*Corresponding author for this work

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Abstract

Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) powder. Limited understanding of these phenomena can result in discarding re-usable powder unnecessarily, or the production of parts with insufficient properties, both of which lead to significant amounts of waste. This paper examines the thermal, chemical, and mechanical characteristics of PA-12 via an oven storage experiment that simulates multi jet fusion (MJF) conditions. Changes in the properties of PA-12 powder during oven storage showed two separate, time-dependent trends. Initially, differential scanning calorimetry showed a 4.2 C increase in melting temperature (T m) and a rise in crystallinity (X c). This suggests that secondary crystallisation is occurring instead of, or in addition to, the more commonly reported further polycondensation process. However, with extended storage time, there were substantial reductions in T m and X c, whilst an 11.6 C decrease in crystallisation temperature was observed. Fourier transform infrared spectroscopy, a technique rarely used in PBF literature, shows an increased presence of imide bonds—a key marker of thermo-oxidative degradation. Discolouration of samples, an 81% reduction in strength and severe material embrittlement provided further evidence that thermo-oxidative degradation becomes the dominant process following extended storage times beyond 100 h. An additional pre-drying experiment showed how moisture present within PA-12 can also accelerate degradation via hydrolysis.

Original languageEnglish
Article number2682
Number of pages20
JournalPolymers
Volume14
Issue number13
DOIs
Publication statusPublished - 30 Jun 2022

Bibliographical note

Publisher Copyright:
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • DSC
  • polyamide 12
  • powder bed fusion
  • recyclability
  • secondary crystallisation
  • thermo-oxidation

ASJC Scopus subject areas

  • Chemistry(all)
  • Polymers and Plastics

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