By Gary Thomas
A team of researchers from the National Institute of Standards and Technology (NIST) has created a novel clay-based coating, which may lead to a new generation of sustainable flame retardants for home furnishings.
Above, untreated polyurethane foam ?catches fire? from a nearby heat source. Below, foam treated with a novel clay-filled coating did not ignite when exposed to the same heat source. Instead, a fast-growing protective layer?called char?forms on the surface.
The thick coating includes a high quantity of flame-inhibiting clay particles. It sticks firmly to the surface of polyurethane foam that is used in children's car seats, carpet padding, furniture cushions and other products.
Till date, scientists have formulated coatings by stacking thin layers of polymer that are held together by electrical attraction. The process is fast and the resulting thick coating created contains only a pure polymer and clay is completely absent. However, the material is not fire retardant.
The NIST researchers designed trilayers: a positively charged layer at the bottom and two negatively charged layers at the top. The two negative layers will repulse each other under most situations; however hydrogen bonds created between the negative layers overcome this repulsive force. The trilayer finally produces a thick, fast-forming clay coating on the surface of polyurethane foam. When compared to the traditional bilayer coatings, this coating contains 6 times more clay, is 10 times thicker and uses at least 5 times lesser number of layers.
The NIST team reported that a clay brick wall developed by coating all internal and external surfaces of the polyurethane foam through the eight trilayer system decreased foam flammability by about 17%. The coating is transparent, just a few hundred nanometers thick and the foam possesses the same feel, support and softness.