Effects of Inorganic Fillers on the Performance of the Water-Based Intumescent Fire-Retardant Coating

Evaluating the influences of filler type and its content on the performance of a water-based intumescent fire-retardant coating was the purpose of this research. three types of fillers (vermiculite, celite, and aluminum hydroxide) were added into intumescent paint formulation. in a conventional intumescent coating, there are specific components. these are an acid source like ammonium polyphosphate (app), a char producing source such as pentaerythritol (per), a blowing agent, e.g., melamine (mel), and a polymeric binder to hold all the components together1. upon heating, a sequence of events occurs in an intumescent fire-retardant system. the inorganic acid releases due to the decomposition of app, which then esterifies carbonaceous species like per. while the mixture melts, dehydration causes ester groups to form char (inorganic carbon residue), meanwhile released gases from mel decompose the viscose char layer to form a foam 1. the result is a multicellular char structure1. each component of the coating formulation plays a vital role in fire retardancy. the thermal and fire protective properties were studied with thermogravimetric analysis (tga), torch test, electrical furnace, scanning electron microscopy (sem), and fourier transform infrared analysis (ftir). torch test was used to evaluate each coating's fire retardancy and heat-shielding properties. natural gas was used as fuel, accompanied by pure oxygen for better combustion and higher flame temperatures. the purge of gas and oxygen was adjusted at a specific ratio. thermogravimetric analysis was conducted to evaluate the weight loss and degradation of the coatings with synergistic fillers. the weight of each sample was approximately 5-10 mg. scanning electron microscopy was used to study the morphology and inner structure of the char layers. char sections were selected from samples that were heated in the electric furnace. the results showed that fillers addition into the coatings up to 5 % could improve the intumescent coating's behavior, like increased endurance against flames. after approximately three minutes, all the samples had a slight temperature rise, and the coatings' expansion began. the back-plate temperatures then reached a steady value. the difference between coated and uncoated back-plate temperatures proves that the application of an intumescent coating will protect the steel substrate by playing an insulator's role. all the samples showed a somewhat similar thermal behavior in tga analysis. after an initial slight weight loss (which was at 100 °c and related to water evaporation that remained in the paint), the first main step in the curves occurred around 250 to 350 °c. the app starts to decompose and releases ammonia and water vapor 2. the weight loss in this stage is around 20 %, comparable to the amount of app used in the formulations (approximately 18 wt. %). this decomposition is the initiation of the coating intumescence. also, in this temperature range, the binder begins to soften, and the blowing agent will release gasses, which help to foam alongside the charring of the intumescent coating 2. the other main step in the curves happens after 500 °c. in this area, the polyphosphate groups from the reaction between app and per will deteriorate 2. after 650 °c, most of the organic groups in the char layer will decompose, which can be observed with the 40 – 45 % weight loss from the beginning of the intumescent reactions (250 – 300 °c) until 800 °c. the amount of resin in the dried coating is 45 wt.% for all the samples, which justifies the weight loss due to organic substances. titanium dioxide could form a ceramic-like residue (titanium pyrophosphate) in this temperature range 3,4. it is important to note that there is not much difference between different fillers in this test. of the three fillers used, vermiculite showed a better performance in the torch test, which can be attributed to its chemical and physical structure. vermiculite has a flake-like shape with high surface reflectivity against incident thermal radiations, which attributes to its low thermal capacity. the final back-plate temperatures in the torch test for the vermiculite-containing samples were around 100 – 150 °c lower than that of other samples. moreover, vermiculite's addition improved the coating's expansion by 10 percent compared to that of the control sample. the vermiculite sample's char layer morphology showed a uniform cell size distribution, indicating structural robustness. the coating samples successfully transformed polypropylene flammability from highly flammable to v0 level in the ul 94 vertical burning test standard. the results showed that vermiculite could improve intumescent paint's fire resistance and be used as an enhancer in intumescent coating formulations.