Eco-friendly flame retardant coating deposited on cotton fabrics from bio-based chitosan, phytic acid and divalent metal ions

With the increasing awareness of environmental protection, the greening of flame retardants has become an inevitable choice for flame retardant technology. Bio-based materials have the advantages of wide source, recyclability and green environmental protection, and have received extensive attention. In this work, chitosan and phytic acid as intumescent flame retardant system and metal ion as a synergist were built on cotton fabrics to achieve efficient flame retardancy by facile dip-pad-dry process. Microscale combustion calorimetry results manifested that the heat release rate values of coated samples were lower than that of uncoated samples. The peak heat release rate and total heat release of uncoated samples were 333.1 W/g and 13.1 kJ/g, while these values of samples coated CH/PA/Ba/PA were 129.1 W/g and 5.4 kJ/g respectively and char residues also were increased sharply owing to the phosphate groups promote the formation of char layer covering the surface of the cotton fabrics, which can prevent heat transfer. Scanning electron microscopy confirmed that there were much more bubbles on the surface of fibers for the coated CH/PA/Ba/PA after horizontal flame tests. The results indicated that the synergy of the intumescent flame retardant system was achieved by the addition of metal ions which could accelerate the produce of a large number of nonflammable gases. Horizontal flame test and limit oxygen index (LOI) test showed that the burning rate and LOI values of samples coated CH/PA/Ba/PA, CH/PA /CH/PA, PA/Ba/PA/Ba were 1.5 mm/s and 22.0, 2.0 mm/s and 20.2 and 2.5 mm/s and 18.0 respectively, compared to 3.3 mm/s and 16.2 of uncoated samples. The samples with intumescent flame retardant system and metal ions (CH/PA/Ba/PA) had best flame retardant performance. Moreover its weight gain (5.2%) was less than that (10.7%) of the sample only with intumescent flame retardant system (CH/PA /CH/PA). The less weight gain had less effect on the softness of cotton fabrics. As a result, the coating is expected to be applied in practice.