Fire safe and sustainable lightweight materials based on Layer-by-Layer coated keratin fibers from tannery wastes

The increasing consciousness about the depletion of natural resources and the sustainability agenda are the major driving forces to try to reuse and recycle organic materials such as agri-food and industrial wastes. In this context, keratin fibers, as a waste from the tannery industry, represent a great opportunity for the development of green functional materials. In this paper, keratin fibers were surface functionalized using the Layer-by-Layer (LbL) deposition technique and then freeze-dried in order to obtain a lightweight, fire-resistant, and sustainable material. The LbL coating, made with chitosan and carboxymethylated cellulose nanofibers, is fundamental in enabling the formation of a self-sustained structure after freeze-drying. The prepared porous fiber networks (density 100 kg m–3) display a keratin fiber content greater than 95 wt% and can easily self-extinguish the flame during a flammability test in a vertical configuration. In addition, during forced combustion tests (50 kW m–2) the samples exhibited a reduction of 37% in heat release rate and a reduction of 75% in smoke production if compared with a commercial polyurethane foam. The results obtained represent an excellent opportunity for the development of fire-safe sustainable materials based on fiber wastes.