Selective laser sintering of polyamide 12/flame retardant compositions

Abstract

In this work, various flame retardants (FR) and clays were added to polyamide 12 (PA12). The processability by Selective Laser Sintering (SLS), thermal behaviour and flame retardancy of these compounds were evaluated. The observations show an important impact on powder flowability of some formulations containing melamine cyanurate and melamine polyphosphate leading to difficulties during SLS process. The incorporation of FRs also leads to changes in melting and crystallization temperatures of polyamide as a function of the FR type. Furthermore, in order to evaluate the influence of the process on thermal properties of samples, a comparison between thermocompression (TC) and SLS techniques was performed for the formulations containing the flame retardants alone. The addition of flame retardants impacts the porosity of the SLS samples as a function of the FR type. For the additives which are able to melt during SLS process, a lower porosity was observed. Samples made by TC containing 30 wt% of ammonium polyphosphate, zinc diethylphosphinate and a pentaerythritol ester of methane phosphonic acid showed a better thermal stability and flame retardancy compared to the ones made by SLS, probably due to the porosity of the SLS samples and some degradation of the flame retardant by the laser beam. For the formulation containing only zinc borate, no difference was observed between TC and SLS. In order to evaluate possibly synergistic effects between flame retardants, binary and ternary formulations were prepared by SLS. On the whole, these formulations led to an improvement of flame retardancy compared to neat PA12. Moreover, XRD results showed the formation of borophosphates for binary and ternary formulations, indicating interactions between flame retardants. EDX results showed that at least 95% of the phosphorus remained in the residue for the formulations containing zinc borate, thus corroborating the results obtained by XRD. The partial substitution of zinc borate by kaolinite led to a further improvement of flame retardancy at the expense of a porosity increase in the samples.

Effect of Additives and Print Orientation on the Properties of Laser Sintering-Printed Polyamide 12 Components

“…Combining PA 6 or PA 12 with various additives can increase material properties and enable wider application in the automotive, aerospace, and mechanical engineering industries. Popular additives include aluminum powder [ 39 ]; glass [ 40 , 41 , 42 , 43 ], and carbon fibers [ 44 , 45 , 46 , 47 , 48 , 49 ], as well as self-extinguishing particles (flame retardant) [ 50 , 51 ]; antistatic particles (electrostatic discharge) [ 52 ], and black carbon [ 53 ].…”

Fire Behavior of Polyamide 12/Rubber Formulations Made by Laser Sintering

“…The use of additives can significantly change the melting and crystallization temperatures of polyamides [ 6 ]. Generally, the addition of fillers can decrease the polymer chain mobility, which will lead to an increase in the melting temperature.…”

“…The use of additives or polymer blends in LS can lead to changes in the morphology of the printed parts because of the restriction of the polyamide chains mobility, the interface quality, and the polymer compatibility. One of the most common effects is an increase in the porosity, which would affect the mechanical properties and the fire behavior of the LS parts [ 6 ]. Thus, to evaluate the morphology of PA12/NBR blends, SEM observations of the cryofractured cross sections of blends containing 20 wt.% of each rubber were carried out and are presented in Figure 2 .…”

“…This printer uses a CO 2 laser beam and has a build platform of 1.3 L. The process parameters were identical for every composition: a layer thickness of 0.1 mm; a hatching distance of 0.1 mm; a laser power of 3.5 W; and a laser scan speed of 2700 mm/s. These process parameters were obtained in previous studies as the optimal process parameters for sintering PA2200 using the SnowWhite printer [ 6 ]. In order to evaluate the effect of the processing on the rheological behavior, disks of 25-mm and 1-mm thicknesses were also prepared by compression at 80 °C, and a pressure of 20 bar.…”

“…Moreover, because of the requirements of LS, only a few polymers and additives (e.g., flame retardants, glass beads) are currently available. In order to improve the range of additives that could be used in LS, various works have evaluated the addition of organomodified clays [ 2 , 3 ], multiwalled carbon nanotubes [ 4 , 5 ], and fire retardants [ 6 , 7 ]. The addition of these materials aims to improve the final properties of polyamide 12 (PA12), which is needed for most applications, such as in the aerospace industry.…”