Nano-clays as rheology modifiers in intumescent coatings for steel building structures

The study focuses on evaluating the influence of bentonite nano-clays on the rheological profile of intumescent fire-retardant compositions and determining optimal structures and quantities of clay thixotropic additives to increase the single-layer thickness of intumescent paint during application.The influence of hydrophobic organomodified, and hydrophilic activated, nano-clays on the rheology of intumescent fire-retardant systems was investigated by determining dynamic viscosity using a Brookfield viscometer at shear rates 2.09 s-1 to 52.25 s-1 followed by mathematical modeling using Casson equation. Addition of hydrophobic organomodified bentonites with intercalated quaternary ammonium cations at 1 wt.% increases thixotropy of both solvent-based and water-based systems by 5–12 times. Hydrophilic clays positively effects the rheology of water-based systems (4–6 times increase in thixotropic effects) and have no effect on solvent-based systems (0,8–1,5 times). Based on extensive experimental data and theoretical calculations, the optimal approximate dynamic viscosity was determined for solvent-based systems (10–7 Pa × s, spindle N6, 20–50 rpm, 20 °С), and water-based systems (17–8 Pa × s, spindle N7, 20–50 rpm, 20 °С). They can be used as markers for industrially produced intumescent paints, to ensure the absence of sedimentation and provide adequate sag resistance when the paint is applied with 1.5 mm single-layer thickness.Laboratory fire tests, and the assessment of thermal expansion of intumescent systems with and without nano-clays, demonstrate that vinyl acetate polymers in intumescent coatings are more suitable for providing higher (60 min or more) levels of fire resistance to steel structures than styrene acrylates. When developing formulations of water-based fire-retardant coatings, capable of providing fire resistance of R120 and higher, the addition of 2–3 wt.% of nano-clays can ensure the formation of a strong and durable thermo-insulating charred layer.