Flame-retardant cyanate ester resin with suppressed toxic volatiles based on environmentally friendly halloysite nanotube/graphene oxide hybrid

Flame retardancy effects between expandable graphite and halloysite nanotubes in silicone rubber foam

The effect of expandable graphite (EG) and modified halloysite nanotubes (HNTs) on the flame retardant properties of silicone rubber foam (SiF) was studied in this paper. Modified HNTs were obtained by surface modification of the silane-coupling agent A-171. The flame retardancy of SiF was studied by limiting oxygen index (LOI), vertical combustion and cone calorimeter tests. The mechanical properties of SiF were analyzed by a universal mechanical testing machine. The LOI results showed that EG/HNTS@A-171 could enhance the LOI of SiF. The cone calorimeter test results showed that EG/HNTS@A-171 effectively reduced the peak heat release rate, the total heat release rate, the smoke production rate, the total smoke production rate, the CO production rate and the CO2 production rate and increased the carbon residue rate. TGA shows that main chain pyrolysis temperature of the SiF is delayed by 123 °C. The mechanical properties test results showed that EG/HNTS@A-171 improved the tensile strength of SiF. These results indicated that EG/HNTS@A-171 can significantly improve the flame retardant performance of SiF.

The Effect of Halloysite Nanotubes on the Fire Retardancy Properties of Partially Biobased Polyamide 610

The main objective of the work reported here was the analysis and evaluation of halloysite nanotubes (HNTs) as natural flame retardancy filler in partially biobased polyamide 610 (PA610), with 63% of carbon from natural sources. HNTs are naturally occurring clays with a nanotube-like shape. PA610 compounds containing 10%, 20%, and 30% HNT were obtained in a twin-screw co-rotating extruder. The resulting blends were injection molded to create standard samples for fire testing. The incorporation of the HNTs in the PA610 matrix leads to a reduction both in the optical density and a significant reduction in the number of toxic gases emitted during combustion. This improvement in fire properties is relevant in applications where fire safety is required. With regard to calorimetric cone results, the incorporation of 30% HNTs achieved a significant reduction in terms of the peak values obtained of the heat released rate (HRR), changing from 743 kW/m2 to about 580 kW/m2 and directly modifying the shape of the characteristic curve. This improvement in the heat released has produced a delay in the mass transfer of the volatile decomposition products, which are entrapped inside the HNTs' lumen, making it difficult for the sample to burn. However, in relation to the ignition time of the samples (TTI), the incorporation of HNTs reduces the ignition start time about 20 s. The results indicate that it is possible to obtain polymer formulations with a high renewable content such as PA610, and a natural occurring inorganic filler in the form of a nanotube, i.e., HNTs, with good flame retardancy properties in terms of toxicity, optical density and UL94 test.

Halloysite Nanotubes as an Additive to Ensure Enhanced Characteristics of Cold-Curing Epoxy Resins under Fire Conditions

At present, the most commonly used electrical insulating materials, including cold-curing epoxy resins, are well designed for normal operating conditions. However, new generations of materials should also be capable of withstanding extreme emergency conditions, e.g., in case of fire. For this reason, this study presents the possibilities of an improved cold-curing epoxy resin using halloysite nanotubes (HNTs) to increase its operational safety. The positive effect of HNT addition is indicated mainly in terms of the suppression of thermo-oxidation processes, which has been demonstrated by the decreases in the maximum heat flow peaks as well as the specific enthalpy values during the thermal decomposition of the epoxy resin. The observed dielectric parameters of the HNT-added materials differ only slightly from those without a filler, whereas their mechanical properties strongly depend on the amount of dispersed HNTs.