Synthesis and Properties of Moisture-Crosslinkable Poly(Urethane-Urea) With Intrinsic Flame Retardancy

Abstract

To improve the deteriorated performance caused by CO₂ release during the curing process of traditional moisture-crosslinked polyurethane or polyurea and poor flame retardancy, this work realized an effective in situ crosslinking technique triggered by moisture for poly(urethane-urea) with intrinsic flame retardancy, through the incorporation of trimethoxysilane and phosphorus groups via a continuous two-stage process. Moisture-triggered crosslinking reaction of trimethoxysilane groups resulted in the establishment of a robust Si─O─Si network, as confirmed by Fourier transform infrared spectroscopy (FTIR) test. The structure transformation considerably enhanced the material’s strength, with the stress at break increasing from 1.0 to 3.2 MPa and modulus from 32.9 to 46.9 MPa. The flame retardant properties of PUUS1 (poly(urethane-urea) sample) were investigated through limiting oxygen index (LOI) and cone calorimeter (CCT) analysis, demonstrating satisfactory flame resistance, as evidenced by high LOI value of 29%, high char yield of 46.2%, and controlled smoke production. Combining thermogravimetric analysis-infrared spectrometry (TG-IR), X-ray photoelectron spectroscopy (XPS), and flame retardant performance, it is speculated that the generation of phosphorus-free radical scavengers in gas phase from diethyl bis(2-hydroxyethyl) aminomethyl phosphonate (DBHAP), coupled with the barrier effects of charred layer and distinctive Si─O─Si framework in condensed phase inhibited combustion and toxic gas emission. The results highlight the successful synthesis of a moisture-crosslinkable poly(urethane-urea) with intrinsic flame retardancy, promising for applications necessitating moisture-crosslinkable materials with superior flame resistance.