Biorenewable Polyelectrolyte Nanocoating for Flame-Retardant Cotton-Based Paper.

Cotton-based raw paper, made of 100% cellulose, is used to make humidity-sensing, cottonid for bio-architecture applications. Despite its renewability and excellent mechanical properties, it is inherently flammable. In an effort to reduce its flammability, thin films of fully renewable and environmentally benign polyelectrolytes, chitosan (CH) and phytic acid (PA), were deposited on raw paper via layer-by-layer (LbL) assembly. Only four bilayers (BL) of the CH/PA coating are required to achieve self-extinguishing behavior, with a 69% reduction in peak heat release rate measured by microscale combustion calorimetry. These results demonstrate that this renewable intumescent LbL-assembled film provides an effective flame-retardant treatment for these environmentally friendly, climate-adaptive construction materials and could potentially be used to protect many cellulosic materials.

Clay-Filled Polyelectrolyte Complex Nanocoating for Flame-Retardant Polyurethane Foam.

Polyurethane foam (PUF) is a highly flammable material typically used for cushioning in furniture and automobiles. A polyelectrolyte complex coating containing polyethylenimine, ammonium polyphosphate, and halloysite clay was applied to PUF using a two-step deposition process in an attempt to reduce its flammability. Electron microscopy confirms that this conformal thin film preserves the porous morphology of the foam and adds 20% to the foam's weight. Directly exposing coated foam to a butane torch flame yields a 73% residue after burning while keeping the internal structure of the foam intact. Cone calorimetry reveals a 52.5% reduction in the peak heat release rate (pkHRR) of the clay-based coating compared to that of the uncoated foam. This significant reduction in pkHRR and preservation of the porous structure of the foam highlights the utility of this easy-to-deposit, environmentally benign treatment to reduce the foam's flammability.

Environmentally Benign and Self-Extinguishing Multilayer Nanocoating for Protection of Flammable Foam.

Most current flame-retardant nanocoatings for flexible polyurethane foam (PUF) consist of passive barriers, such as clay, graphene oxide, or metal hydroxide. In an effort to develop a polymeric and environmentally benign nanocoating for PUF, positively charged chitosan (CH) and anionic sodium hexametaphosphate (PSP) were deposited using layer-by-layer (LbL) assembly. Only six bilayers of CH/PSP film can withstand flame penetration during exposure to a butane torch (∼1400 °C) for 10 s and stop flame spread on the foam. Additionally, cone calorimetry reveals that the fire growth rate, peak heat release rate, and maximum average rate of heat emission are reduced by 55, 43, and 38%, respectively, compared with uncoated foam. This multilayer thin film quickly dehydrates to form an intumescent charred exoskeleton on the surface of the open-celled structure of polyurethane, inhibiting heat transfer and completely eliminating melt dripping. This entirely polymeric nanocoating provides a safe and effective alternative for reducing the fire hazard of polyurethane foam that is widely used for cushioning and insulation.