Performance of clays, carbon nanofibers, multi-walled carbon nanotubes, and nano-alumina in polyamide 11 nanocomposites

The objective of this research is to develop an improved polyamide 11 polymer with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering rapid manufacturing. In the present study, a nanophase was introduced into the polyamide 11 and combine with a conventional intumescent flame retardant (FR) additive via twin screw extrusion. Polyamide 11 polymer pellets were blended separately with chemically modified montmorillonite nanoclays (NCs), or carbon nanofibers (CNFs), or multi-walled carbon nanotubes (MWNTs), or nano-alumina (NA) and an intumescent FR additive to create a family of intumescent FR polyamide 11 nanocomposites. Transmission electron microscopy (TEM) analyses indicated good dispersion of individual nanoparticles and intumescent FR additives were achieved in the polymer matrix. Injection molded specimens were fabricated for physical, thermal, flammability, and mechanical properties characterization. Thermal stability of these polyamide 11 nanocomposites was examined by TGA. All systems of polyamide 11 containing nanoparticles and FR additive have higher decomposition temperatures than those compositions with solely nanoparticles or FR additive alone. None of the nanoparticles alone was able to pass UL 94 V-0 rating. Selective FR-PA11-nanoclay and FR-PA11-CNF nanocomposites passed the UL 94 V-0 requirement and suggest synergism between FR and selected nanoparticles. Some trends and relationships were observed between the results of TGA, UL 94, heat deflection temperature, and cone calorimetry.