Fire‐Retardant Polyurethane Adhesive for Laminating Metallized <scp>PET</scp> Films for Use in Fire Proximity Clothing

ABSTRACT A fire‐retardant polyester‐based polyurethane adhesive was synthesized for laminating dual‐metallized PET films with both glass as well as aramid substrates. The resin, synthesized through chain extension of an MDI‐based prepolymer with butanediol and crosslinked using trimethylol propane (0.5 wt%), exhibited high thermal stability ( T onset &gt; 260°C) and flexibility ( T g = −37°C). The laminates prepared using the developed polyurethane adhesive met the adhesion and flexing requirements, however, they failed during vertical flammability tests. Incorporation of melamine‐coated ammonium polyphosphate (APP, 10% w/w) increased the char yield and enabled the laminates to pass key fire‐resistance tests, including heat resistance, thermal shrinkage, and flammability. The developed laminates demonstrated high flexibility and adhesion under dry/wet conditions and withstand 1000 flexing cycles even after immersion in hot water. Flexural rigidity was measured in both directions, and protection against radiative heat (84 kW/m 2 ) was quantified in terms of time to second degree burns (), yielding 21.5 s for aramid and 24 s for glass laminates. When assembled into a multilayer fire proximity suit configuration, both the laminates met the standard requirement (TPP = 35 cal/cm 2 ). The results demonstrate the viability of the adhesive system for fire proximity applications, with aramid substrates offering a practical alternative to glass fabrics.