Facile construction of H3PO3-modified chitosan/montmorillonite coatings for highly efficient flame retardation of polyester–cotton fabrics

Chitosan (CS) has been used to form flame-retardant coatings containing clays and nanoparticles. However, further improving the flame-retardant efficiency of the system remains a challenge. In this work, we developed a type of polyelectrolyte complex coating (PCM) using H3PO3 protonated CS and montmorillonite for highly efficient flame retardation of polyester–cotton fabrics. The surface morphologies, chemical structure, flame retardancy, burning behavior, thermal decomposition behavior, laundering durability, mechanical properties, and hand assessment of the coating and coated fabrics were investigated. The PCM coatings were built on the fabric surface by blading coating, in which H3PO3 presented in the form of salts via ionic interactions with CS. With 13 wt% add-ons of the PCM, the coated fabrics (PCM-13) presented a limiting oxygen value reaching 64.3 %, and easily self-extinguished in the vertical flammability test. In the cone calorimetry test, PCM-13 presented reductions in peak heat release rate, total heat release, and total smoke production of 49 %, 65 %, and 59 %, respectively. PCM-13 exhibited good laundering durability and maintained superior flame retardancy even after 50 washing cycles. We found that PCM coatings showed both condensed and gaseous flame-retardant activity. PCM-13 had good mechanical properties but became more inflexible than the untreated fabrics. This study may offer possibilities for modifying CS via ionic bonds for functional polyelectrolyte complex coatings.