Acrylamide/2-acrylamido-2-methylpropane sulfonic acid and associated sodium salt superabsorbent copolymer nanocomposites with mica as fire retardants

Acrylamide (AM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS-H⁺) or its sodium salt (AMPS-Na⁺) were copolymerised by free-radical crosslinking polymerization to obtain poly(AM-co-AMPS-H⁺) and poly(AM-co-AMPS-Na⁺) superabsorbent polymers (SAPs). A maximum water absorbency in deionised water of 1200 g g⁻¹ was achieved for poly(AM-co-AMPS-Na⁺) at a 85% mol of AMPS-Na⁺. The inclusion of mica at 5-30% (w w⁻¹) into the preparation of poly(AM-co-AMPS-Na⁺) SAP leads to an intercalated structure, as detected by XRD and TEM analyses. Poly(AM-co-AMPS-Na⁺)/30% (w w⁻¹) mica SAP nanocomposite showed a tap water absorbency of 593 g g⁻¹ with a better thermal stability, compared to the pure SAP. Cone calorimetric analyses revealed that the wood specimens coated with the prepared poly(AM-co-AMPS-Na⁺) SAP or its 30% (w w⁻¹) mica nanocomposite provided excellent protection in delaying the ignition time after exposure to an open flame when compared to that observed with the uncoated specimen. The maximum reduction in the peak heat release rate and the greatest extension of time at peak heat release rate were observed with the nanocomposite-coated surface, but the total heat release rate was increased. The delayed burning mechanism is brought by the intercalating structure of mica in the SAP nanocomposites, which provided a better shielding effect against external heat sources, and the capability of the SAP nanocomposite in holding a large amount of water.