Towards the Reuse of Fire Retarded Polyamide 12 for Laser Sintering

Area of Science:

• Materials Science
• Additive Manufacturing
• Polymer Processing

Background:

• Powder aging is a challenge for serial production using Selective Laser Sintering (SLS).
• Reusing polymer powders necessitates understanding aging effects on material properties and performance.
• Flame retardants (FR) are incorporated into Polyamide 12 (PA 12) for enhanced safety in SLS parts.

Purpose of the Study:

• To investigate the influence of successive reuse on PA 12 blends with ammonium polyphosphate (APP) and zinc borate (ZB).
• To evaluate the impact of aging on the thermal and fire performance of these PA 12/FR blends.

Main Methods:

• Differential Scanning Calorimetry (DSC) to assess thermal properties.
• Thermogravimetric Analysis (TGA) for thermal stability.
• Pyrolysis Combustion Flow Calorimetry (PCFC) and Cone Calorimeter (CC) for fire behavior analysis.
• Fourier-Transform Infrared Spectroscopy (FTIR) to identify chemical changes.

Main Results:

• FR incorporation reduced the processing window, but aging did not further decrease it.
• Aging showed minimal impact on thermal stability (TGA) and crystallinity compared to initial processing.
• Reuse significantly reduced ignition time, indicating polymer chain scission; zinc borate reuse detrimentally increased peak heat release rate (pHRR).

Conclusions:

• Successive reuse of PA 12/FR powders leads to polymer degradation and altered fire retardancy.
• Zinc borate-containing PA 12 shows compromised fire performance upon reuse.
• Understanding aging effects is crucial for optimizing SLS serial production with recycled polymer powders.