Kalafat K. Development of polymer intumescent coating technology for steel structures with improved fire-retardant properties

One of the main methods for increasing the fire resistance of steel is the use of materials for passive fire protection that increase the time during which loadbearing capacity of building structures are retained during fire. The object of research is the process of formation of heat-insulating coke layer and the mechanism of influence of the polymer component of the intumescent system on fire-retardant and operational characteristics of intumescent-type coatings. The subject of research is the technology of production of polymeric intumescent coatings for steel structures with improved fire-retardant and operational characteristics. The main aim of current study is to create a technological scheme for production of a polymeric coating for steel structures, which would provide not less than R 120 fire resistance rate of steel structures and have a service life of over 10–15 years, by identifying the patterns of influence of polymeric component of the intumescent system on fire-retardant efficiency and performance properties of the coating. The main factors which can be used to regulate fire-retardant efficiency of intumescent coatings for steel in order to ensure a specific fire resistance rate R 120 were determined in the dissertation. It was shown that the use of styrene acrylate copolymers in combination with ammonium polyphosphate/melamine/ pentaerythritol mix with approximately 20:10:10 ratio (mass % in the intumescent composition), provides the R 30–45 fire resistance rate of steel structure. While intumescent systems with the ratio of ammonium polyphosphate/melamine/ pentaerythritol close to 35:10:15 (mass % in the intumescent composition) combined with vinyl and vinyl acetate polymers allow to achieve the R 120 fire resistance rate of steel structure. IR spectroscopy was used to investigate the mechanism of chemical transformations between the components of intumescent system in the presence of individual copolymers, as well as their nanocomposites with bentonite type nano-clays and nano-graphite. It was shown that the most optimal polymeric binders for intumescent systems are vinyl acetate polymers, and nanocomposites based on them, due to their complex and slow decomposition mechanism, capability to release reaction products that have a positive effect on the formation of heat-resistant protective char. The influence of fiber of different nature on the fire resistance of the intumescent coating of ammonium polyphosphate/melamine/ pentaerythritol/ melamine/ copolymer of ethylene with vinyl acetate was studied. The addition of a mixture of mineral fiber and fiberglass in the fire protection system allows obtaining the coating whose fire resistance class exceeds the same value for imported analogues. According to the results of accelerated ageing tests and studies of water resistance of the coating comprising of ammonium polyphosphate/melamine/ pentaerythritol/polymer (either ethylene vinyl acetate or styrene acrylate), it was found that the loss of fire-retardant efficiency of the system occurs due to leaching of pentaerythritol and ammonium polyphosphate, as well as polymer degradation via acid hydrolysis. Significant improvement of water resistance, service life and fire-retardant characteristics of obtained coating can be achieved by adding organomodified montmorillonite type nano-clays with a high degree of exfoliation into the studied system. The following was established for the first time: - influence of the mechanisms of thermal degradation of vinyl acetate and styrene acrylate polymers, as well as the ratio of main components of the intumescent system (ammonium polyphosphate: melamine: pentaerythritol), on the formation of heatresistant charred layer, which determines the value of fire resistance rate for steel structures; - an increase in fire-retardant efficiency of polymer intumescent coating when using a nanocomposite matrix of ethylene vinyl acetate with nano-clay, obtained by "in-situ" method, compared to conventional technology; - synergism of nano-clay and nano-graphite in a hybrid nanocomposite of ethylene vinyl acetate/nano-clay/nano-graphite, which manifests itself in increasing the fire retardant efficiency of the polymer intumescent coating in comparison with the coating containing the individual nanocomposites of ethylene vinyl acetate; - synergistic effect of a mixture of melamine with dicyandiamide in the polymer intumescent composition, which leads to a 1.5-fold increase in the mass of char residue of intumescent composition at 700 °C and a 15% increase in fire-retardant efficiency of the coating; - the effect of organo-modified nano-clays on the reduction of solubility constants of polymeric intumescent coatings, consisting of ammonium polyphosphate/melamine/ pentaerythritol/ethylene vinyl acetate (or styrene acrylate), which causes the increase in expected service life of fire-retardant coatings.