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

In the present work, the processability and fire behavior of parts made by the laser sintering (LS) of polyamide 12/rubber powder blends is studied. In order to evaluate some of the interactions that could take place during LS, three acrylonitrile butadiene rubbers (NBRs) were used, which included two that had different acrylonitrile (AN) contents, and one that had carboxylated rubber. The results show that the flowability of the powders is strongly dependent on the rubber used. For the carboxylated rubber, a good flowability of the blend was observed, whereas the use of rubbers with different AN contents led to significant changes in the powder flowability, with a heterogeneous powder bed, and differences in the porosity as a function of the AN content. Furthermore, the addition of rubbers to polyamide 12 (PA12) entails an increase in the sintering window and, in particular, a change in the melting temperature of PA12 is noticed. Even though some changes in the crystallization and melting temperatures are observed, formulations containing 10 and 20 wt.% of rubbers could be processed using the same process parameters as PA12. Furthermore, the formulations containing carboxylated rubber show improved fire behavior, which is measured by a cone calorimeter, with reductions of about 45 and 65% in the peak of the heat release rate, compared to the PA12. Moreover, almost all of the samples evaluated in this study are classed as “Good” by the Flame Retardancy Index. This result can be partially explained by the formation of an amide linkage between the polyamide and NBR during processing, which could result in increases in the melt viscosities of these samples.