Synthesis and characterization of flame‐retardant polyurethane based on new chain extenders

Abstract A series of novel flame‐retardant waterborne polyurethanes (FWPU) were synthesized with tris(hydroxymethyl)phosphine (THPO) obtained from the reaction of tetrakis(hydroxymethyl)phosphonium sulfate and bis(2‐hydroxyethyl)terephthalate from the alcoholysis of waste poly(ethylene terephthalate) as flame‐retardant chain extenders. Influences of THPO on flame retardancy and bonding properties of FWPU were investigated using limiting oxygen index (LOI) measurement, vertical burning test, cone calorimeter test (CCT), thermogravimetric analysis and shear tensile test. The results of LOI, vertical burning test and CCT indicated that flame retardancy of FWPU was improved with the introduction of THPO. The peak of heat release rate of FWPU with 1.5 wt% THPO was 401 kW m −2 . After hard segment flame‐retardant modification, the initial bonding strength of FWPU adhesive increased by 150%, and the final bonding strength decreased slightly. A new way is provided for the design of novel reactive FWPU which maintained better flame retardancy and adhesive properties after hard segment flame‐retardant modification. © 2022 Society of Industrial Chemistry.