Caramelization-inspired bio-based waterborne fire-resistant coating for various substrates

Inspired by the caramelization of sugar, which forms a viscous, nonflammable substance at around 150 °C, we developed a bio-based, intumescent fire-resistant coating. Comprising hydroxypropyltrimethyl ammonium chloride chitosan (HACC), phytic acid (PA), and magnesium gluconate (MgG), this coating underwent rapid dehydration and charring expansion upon exposure to fire at ca. 180 °C, expanding ∼137 times to create a protective honeycomb char layer that shields substrates from oxygen and heat. Importantly, this coating enhanced fire resistance for polypropylene (PP), rubber, polyurethane foam (PUF), wallpaper, and wood, while maintaining transparency and strong adhesion. Typically, the coating (200 μm) reduced the heat release rate of PP by 63.7 %, extending the time to ignition from 34 s to 525 s. Furthermore, the 1200 μm thick coating slowed the slow rise of backside temperature on the   steel plate, keeping it beneath 229 °C after being exposed to a butane torch flame at 1100 °C for 60 min. This eco-friendly innovation promises advanced fire protection and opens new avenues for sustainable, high-performance fire-resistance coatings.