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Quantitative influences of successive reuse on thermal decomposition, molecular evolution, and elemental composition of polyamide 12 residues in selective laser sintering

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Since its addition to additive manufacturing (AM), polyamide 12 has dominated the selective laser sintering (SLS) market, thanks to its stable thermal property and high mechanical quality. However, substantial un-sintered residue powders lead to economic losses and are burdensome to the environment. Though several works have reported the aging mechanism and reusability of the polyamide 12 residues in SLS, the quantitative degradation and decomposition changes of differently reused polyamide 12 are not available. This work experiments successive reuse of polyamide 12 residues and quantitatively monitors the thermal decomposition, molecular evolution, and compositional changes of the material in SLS AM. To understand the characteristics of such changes, we reused the same bucket of polyamide 12 powders up to 8 times, collected powder samples, and printed 3- and 32-layer part samples. Our tests revealed that the basic flowability energies per reuse are reduced by 9.90, 15.59, and 12.74 mJ in the 2-, 5-, and 8-time reused powders, respectively. These values are essential to control the flowability of polyamide 12. Laser and heat lower the material onset decomposition temperatures, making the material more labile at a decreased temperature after reuse. On the other hand, the nitrogen atmosphere delays the onset of thermal decomposition to a higher temperature. The 1H NMR spectra reveal the degradation of polyamide 12 with reuse: in polyamide 12 parts 3D-printed using 8-time reused powders, the relative area of the peak on C-H bonds adjacent to nitrogen has a 50% reduction compared to parts using new powders. The carbon deposit and degradation raise the atomic percentages of C and O by 72.49% and 7.13%, respectively, from new powders to the part printed using 8-time reused powders. This study further reveals the surface carbon deposit of polyamide 12 during successive reuse of SLS and explains the effect of laser in inducing polymer decomposition apart from high temperatures.
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ORIGINAL ARTICLE
Quantitative influences of successive reuse on thermal
decomposition, molecular evolution, and elemental composition
of polyamide 12 residues in selective laser sintering
Feifei Yang
1
&Angela Schnuerch
2
&Xu Chen
1
Received: 29 January 2021 /Accepted: 28 May 2021
#The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2021
Abstract
Since its addition to additive manufacturing (AM), polyamide 12 has dominated the selective laser sintering (SLS) market, thanks
to its stable thermal property and high mechanical quality. However, substantial un-sintered residue powders lead to economic
losses and are burdensome to the environment. Though several works have reported the aging mechanism and reusability of the
polyamide 12 residues in SLS, the quantitative degradation and decomposition changes of differently reused polyamide 12 are
not available. This work experiments successive reuse of polyamide 12 residues and quantitatively monitors the thermal decom-
position, molecular evolution, and compositional changes of the material in SLS AM. To understand the characteristics of such
changes, we reused the same bucket of polyamide 12 powders up to 8 times, collected powder samples, and printed 3- and 32-
layer part samples. Our tests revealed that the basic flowability energies per reuse are reduced by 9.90, 15.59, and 12.74 mJ in the
2-, 5-, and 8-time reused powders, respectively. These values are essential to control the flowability of polyamide 12. Laser and
heat lower the material onset decomposition temperatures, making the material more labile at a decreased temperature after reuse.
On the other hand, the nitrogen atmosphere delays the onset of thermal decomposition to a higher temperature. The
1
HNMR
spectra reveal the degradation of polyamide 12 with reuse: in polyamide 12 parts 3D-printed using 8-time reused powders, the
relative area of the peak on C-H bonds adjacent to nitrogen has a 50% reduction compared to parts using new powders. The
carbon deposit and degradation raise the atomic percentages of C and O by 72.49% and 7.13%, respectively, from new powders
to the part printed using 8-time reused powders. This study further reveals the surface carbon deposit of polyamide 12 during
successive reuse of SLS and explains the effect of laser in inducing polymer decomposition apart from high temperatures.
Keywords Polyamide 12 .Successive reuse .Thermal decomposition .Molecular evolution .Selective laser sintering
1 Introduction
Involving various materials, methods, and equipment, addi-
tive manufacturing (AM) translates directly three-dimensional
virtual models into physical objects layer by layer [13].
Selective laser sintering (SLS) AM is capable of producing
functional applications with complex geometries through fus-
ing materials and adjacent layers together by controlled laser-
material interactions [4,5]. Capable of processing a wide
range of materials (including polymers, metals, ceramics,
and composites), SLS has attracted increased industrial and
academic interests in recent years [6,7]. The semicrystalline
thermoplastic polymer, polyamide 12, appears to be the most
suitable material to date and dominates the SLS market thanks
to its good flowability, low processing temperature, stable
thermal property, and high mechanical strength [8,9].
Though extensive applications of polyamide 12 materials
exist in SLS, the average total volume of the sintered powders
during each batch of printing is small (515%) [10]. Most of
the loaded materials (between 85 and 95%) remain un-sintered
and can be reused for other practices [11,12]. However, the
elevated temperature, laser radiation, and repeated heating/
*Xu Chen
chx@uw.edu
Feifei Yang
yangff@uw.edu
Angela Schnuerch
Angela.Schnuerch@xerox.com
1
Department of Mechanical Engineering, University of Washington,
Seattle, WA 98195, USA
2
Xerox Corporation, 800 Phillips Road, Webster, NY 14580, USA
https://doi.org/10.1007/s00170-021-07368-w
/ Published online: 4 June 2021
The International Journal of Advanced Manufacturing Technology (2021) 115:3121–3138
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
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