Green DNA-based flame retardant coatings assembled through Layer by Layer

For the first time, DNA and chitosan are employed using the Layer by Layer technique in order to build green coatings exhibiting efficient flame retardant properties. DNA by its chemical structure can be considered as an intrinsically intumescent compound, since it contains precursor of phosphoric-polyphosphoric acid, a polyhydric char source (deoxyribose) and the nitrogen-containing bases that may release ammonia, acting as a blowing agent. When combined with chitosan, DNA layers promote the char formation of the former, by releasing phosphoric and polyphosphoric acid. Such bioarchitectures show an exponential growth as assessed by infrared spectroscopy and scanning electron microscopy. Very interestingly, these LbL assemblies are capable of i) reaching the self-extinguishment of cotton during horizontal flammability tests, ii) increasing the limit oxygen index up to 24% and iii) reducing the heat release rate by 40% during cone calorimetry tests.