The use of nitrile butadiene rubber in the composition of intumescent fire-retardant materials based on plasticized polyvinyl chloride

Objectives. To investigate the properties of intumescent fire-retardant materials based on plasticized polyvinyl chloride and oxidized graphite as functions of their content of nitrile butadiene rubber. Methods. Intumescent fire-retardant materials with different contents of nitrile butadiene rubber (from 0 to 20 wt %) were obtained. The materials were prepared in the form of a sheet 38–52 mm wide and 1.5–1.9 mm thick by means of flat-die extrusion using a twin-screw compounding extruder. The raw materials used were plasticized polyvinyl chloride with a K-value of 71, nitrile butadiene rubber with a bound acrylonitrile content of 31–35%, oxidized graphite, and ultrafine aluminium hydroxide. The properties of the raw materials and the resulting fire-retardant materials were investigated using infrared spectroscopy, thermal analysis, scanning electron microscopy, as well as mechanical tests, flammability tests, and thermal shock foaming tests. Results. The mechanical, thermal, and fire-retardant properties of the obtained materials were studied as functions of their contents of nitrile butadiene rubber. The dynamics of foaming in the temperature range from 300 to 800°C were also explored. The flammability rating was determined. The dependence of fire-retardant properties on the melt viscosity of fire-retardant materials was described. The thermal properties were found to be in the temperature range of 40 to 900°C. Conclusions. The study found that the introduction of nitrile butadiene rubber into fire-retardant materials leads to a change in a number of properties: a decrease in density and hardness; a decrease in tensile strength; an increase in relative elongation; an increase in melt viscosity by 16 times; and, accordingly, a decrease in foaming rate by a factor of 1.43–1.65. It was established that the foaming rate has a linear dependence on the viscosity of the melt of fire-retardant materials. The introduction of rubber leads to an increase in the strength of foamed char by a factor of 4.8. Thermal analysis showed that increasing the rubber content leads to an increase in heat resistance from 222 to 236°C, and resistance to oxidation of foamed graphite in the composition of foamed char from 601 to 659°C. The presence of rubber does not have a noticeable effect on flammability. The established flammability rating for all compositions is V-0.