Synthesis of polyacrylamide/mica superabsorbent nanocomposites with thermal stability and fire retardancy

Abstract

Superabsorbent polymers of poly[acrylamide-co-(2-acrylamido-2-methylpropane sulfonic acid sodium salt)], poly(AM-co-AMPS-Na+), poly[acrylamide-co-(2-acrylamido-2-methylpropane sulfonic acid), poly(AM-co-AMPS-H+)] and poly(AM-co-AMPS-Na+) superabsorbent nanocomposites were synthesized by free-radical crosslinking polymerization. Ammonium persulfate (APS), N, N, N’, N’-tetramethylethylenediamine (TEMED), and N, N’-methylenebisacrylamide (MBA) were used as an initiator, a co-initiator, and a crosslinker, respectively. The superabsorbent nanocomposites were produced by adding mica, zinc borate or melamine as fire retardant agents. The influences of ionic comonomer (both the sodium and acid forms) and crosslinker concentrations on the water absorbency of the prepared superabsorbents were investigated. The presence of main function groups of the synthesized copolymers was analyzed using FTIR technique. The thermal stability of superabsorbent nanocomposites was detected by TGA and cone calorimetric technique. The equilibrium water absorbency of poly(AM-co-AMPS-Na+) and poly(AM-co-AMPS-H+) was found to increase with the increase in ionic comonomer concentration, and decrease with the increase in the crosslinker and fire retardant agent loadings. The maximum water absorbency of 1212±54 g g-1 was obtained for poly(AM-co-AMPS-Na+) at 85% mol of AMPS-Na+, 0.6% mol each of APS and TEMED, and 0.05% mol of MBA. The superabsorbent nanocomposite/20% zinc borate/10% melamine coated on a wood board increased the ignition time to 258 s from only 13 s ignition time of the uncoated wood.