New developments in additive manufacturing of polymers. Selective laser sintering of polyamide 12 / Flame Retardant Compositions.

3 December 2019
Versione stampabile

Venue: Polo Fabio Ferrari 2, via Sommarive 9 (Trento) - Seminar Room
Hour: 15:00 

  • José-Marie Lopez-Cuesta, IMT Mines Alès (EMA)

Additive manufacturing is a relatively new technology raising an increasing interest. Among the different techniques available, Selective Laser Sintering (SLS) is receiving much attention in literature due to its great flexibility. SLS has demonstrated substantial potential for the production of parts for various applications, especially aerospace and defense industries.

SLS is based on the selective heat and fuse of plastic micronic particles layer by layer using generally a CO2 laser. The process is performed in three main steps: powder spreading, energy input and material consolidation.

Despite SLS is able to process any polymer able to fuse when heat is applied, mainly a limited range of semi-crystalline polymers have been used until now: polyamide 11 and 12, polyaryl etherketones (PAEK) and more recently polyurethanes (PU) and polybutylene terephthalate (PBT).  In fact, polyamide based materials represent more than 90% of the SLS production. Polymer blends, (nano)composite materials and incorporation of additives are expected to increase the potential of SLS and the range of functional properties.

For some applications, parts should have specific properties with improved flame retardancy. To achieve the flame retardancy level required, additives must be incorporated into SLS powder formulations. Still, the addition of these particles could induce changes in polymer properties, especially melt and crystallization temperatures and powder rheology. All these variations in powder characteristics can lead to parts with mechanical properties and fire resistance which are not suitable for technical applications. Even though, only few studies concerns the addition of nanoparticles to SLS powder formulantions which are dedicated to evaluate their influence on the mechanical and electromagnetic properties of SLS parts .

Furthermore, it should be pointed out that, compared to thermocompression or  injection moulding SLS parts generally show a decrease in mechanical properties compared to traditional processes (extrusion/injection). Concerning flame retardancy, until now, there is no study in the literature that concerns the influence of flame retardants on sintering of powders.

Thus, to evaluate the potential properties of commercial polyamide 12 (PA12) used in the SLS process, different flame retardants and fillers were dispersed in the polyamide powder by mechanical mixing. Specimens of composite were manufactured by the SLS process and characterized by differential scanning calorimetry, termogravimetric analysis, cone calorimeter and microscope observations. Finally, 3D printed specimens are compared with similar compositions processed using thermocompression.