RESUMO
The layer-by-layer (LbL) assembly of chitosan (CH) and phosphorylated cellulose nanofibrils (P-CNF) is presented as a novel, sustainable and efficient fire protection system for polyurethane foams. The assembly yields a linearly growing coating where P-CNF is the main component and is embedded in a continuous CH matrix. This CH/P-CNF system homogenously coats the complex 3D structure of the foam producing a nano-exoskeleton that displays excellent mechanical properties increasing the modulus of the foam while maintaining its ability of being cyclically deformed. During combustion the CH/P-CNF exoskeleton efficiently prevents foam collapse and suppresses melt dripping while reducing the heat release rate peak by 31% with only 8% of added weight. The coating behavior during combustion is investigated and correlated to the observed performances. Physical and chemical mechanisms are identified and related to the unique composition and structure of the coating imparted by the LbL assembly.
RESUMO
In this letter, we are presenting a novel approach for the deposition of layer-by-layer (LbL) coatings capable of conferring flame retardant properties to flexible polyurethane foams exploiting subsecond deposition times. The process yields nanoscale coatings able to reduce by 33% one of the main fire safety parameters, namely the heat release rate peak, with a total treatment time of only 2.5 s. This new approach turned out to be three to 4 orders of magnitude faster than conventional LbL treatments. Such results make it possible for the exploit of LbL as a competitive, efficient and ecofriendly technology at industrial scale.
RESUMO
Starch has been employed via layer by layer assembly for building an efficient and sustainable biobased coatings capable of protecting cotton from fire. In order to obtain a better understanding of the coating to substrate relationship, the coating efficiency has been tested on cotton fabrics having different densities (i.e., 100, 200, and 400 g/m(2)). The adopted deposition conditions allow for the buildup of a homogeneous coating even at a low number of deposition steps. The physical and chemical mechanisms are described and related to the achieved results. The coating can greatly enhance the char forming ability of cellulose, nearly doubling the amount of thermally stable organic residue produced by cotton at high temperatures, as assessed by thermogravimetric analyses. After only 2 bilayers deposited, this biobased system is capable of self-extinguishing a flame during flammability tests with less than 5% in weight deposited on cotton. This high efficiency is kept even when the coating is deposited on cotton with the highest density. By cone calorimetry, all treated cottons showed significant reductions (up to 40%) of the total heat released during combustion, thus demonstrating the high efficiency achieved.
RESUMO
The toxicity of the most efficient fire retardant additives is a major problem for polymeric materials. Cellulose nanofiber (CNF)/clay nanocomposites, with unique brick-and-mortar structure and prepared by simple filtration, are characterized from the morphological point of view by scanning electron microscopy and X-ray diffraction. These nanocomposites have superior fire protection properties to other clay nanocomposites and fiber composites. The corresponding mechanisms are evaluated in terms of flammability (reaction to a flame) and cone calorimetry (exposure to heat flux). These two tests provide a wide spectrum characterization of fire protection properties in CNF/montmorrilonite (MTM) materials. The morphology of the collected residues after flammability testing is investigated. In addition, thermal and thermo-oxidative stability are evaluated by thermogravimetric analyses performed in inert (nitrogen) and oxidative (air) atmospheres. Physical and chemical mechanisms are identified and related to the unique nanostructure and its low thermal conductivity, high gas barrier properties and CNF/MTM interactions for char formation.
