Highly loaded nanocomposite films as fire protective coating for polymeric substrates

The main fire retardancy mechanism of polymer–clay nanocomposites involves the progressive build-up of an inorganic-rich layer at the sample surface during combustion, by a combination of ablative reassembling and migration of the nanoparticles, reducing heat and mass transfer between gas and condensed phases. In this process, a non-negligible amount of polymer needs to be sacrificed before the entire surface of the residual material is shielded. This study aims to improve the fire behaviour of polymer–clay nanocomposites by accelerating the physical barrier formation through the development of new hybrid structures. For that purpose, a system based on polyamide 12 and halloysite nanotubes is chosen as reference and highly loaded nanocomposite films are coated on a virgin PA12 substrate. Both the influence of clay fraction in the nanocomposite film and its thickness on the flammability performance of the coated samples are evaluated by mass loss calorimetry and compared to that of homogeneous ‘bulk’ nanocomposites. Results show unambiguously that hybrid materials are more effective than conventional nanocomposites to flame retard polymers while substantially reducing the total filler loading, and so the cost of the final product. Moreover, a small amount of carbon nanotubes can be incorporated in the polymer substrate and/or in the nanocomposite film to suppress the vigorous bubbling of evolved degradation products as well as to reduce the flexibility of the thin protective skin, which can cause detrimental effects on its barrier properties