The objective of this study is to develop improved polyamide (nylon) 11 (PA11) and 12 (PA12) polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering rapid manufacturing. PA11 and PA12 were melt-blended, dispersing low concentrations of nanoparticles, namely nanoclays (NCs), carbon nanofibers (CNFs), and nanosilicas (NSs) via twin-screw extrusion. To enhance their thermal and flammability properties, an intumescent flame retardant (FR) was added to the mechanically superior NC and CNF PA11 formulations. NC or CNF additions to either PA11 or PA12 generally increased its tensile strength and modulus, but sharply reduced its elongation at rupture. FR additives reduced PA11’s properties considerably. This substitution, however, only exacerbated the already steep drop in elongation at rupture due to FR additives alone; while elongation dropped 58% with the addition of 30 wt% FR, it dropped 98% with the addition of 25 wt% FR/5 wt% CNF.

The thermal insulation properties of thermoplastic polyurethane elastomer nanocomposites were characterized at different heat fluxes. Thermoplastic polyurethane elastomer was modified with different loadings of montmorillonite nanoclays and carbon nanofibers (CNFs) via twin screw extrusion processing. The addition of nanoparticle into thermoplastic polyurethane elastomer resulted in the formation of a char layer and modified the thermal insulative properties of the material. It was found that thermoplastic polyurethane elastomer with 10 wt% CNFs and with 5 wt% nanoclays gave the best thermal performance with respect to protecting a substrate. The surface temperature of the thermoplastic polyurethane elastomer-clay nanocomposites did not vary much with addition of clay particles while the surface temperature of the thermoplastic polyurethane elastomer-CNF nanocomposites varied more substantially. Some of the trends in surface and substrate temperature measurements with nanomodification can be described using a simple energy balance model that takes into account the basic heat transfer mechanisms.

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for fabricated parts that are required for performance driven applications. The introduction of selected nanoparticles such as carbon nanofibers (CNFs), combined with a conventional intumescent flame retardant (FR) additive into the polyamide 11/polyamide 12 (PA11/PA12) by melt processing conditions has resulted in a family of intumescent polyamide nanocomposites. These intumescent PA11 and PA12 nanocomposites exhibit enhanced polymer performance characteristics, i.e., fire retardancy, high strength, and high heat resistance and are expected to expand the market opportunities for resin manufacturers. The overall objective of this research is to develop improved PA11 and PA12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing. Arkema RILSAN® PA11 polymer was examined with CNFs and Clairant Exolit® OP 1230 intumescent FR additive. They were used to create a family of FR intumescent PA11-CNF nanocomposites. Transmission electron microscopy (TEM) was used to determine the degree of CNFs and intumescent FR additive dispersion in PA11. Injection molded specimens were fabricated for material properties measurements. Thermal stability of these polymer nanocomposites (PNs) was examined by TGA. Flammability and thermal properties of these PNs were obtained using the cone calorimeter, UL 94 test method, and heat deflection temperature.

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Cardiovascular manifestations of COVID-19 infection remain an ongoing study. We present a case of significant bradycardia in the patient with COVID-19 sepsis. We discuss about the possible mechanism, pathophysiology, and management in this pathology.