Anti‐drip flame retardant poly(urethane‐imide) thin films for high‐temperature applications

Abstract The present work deals with developing anti‐drip, flame‐retardant, poly(urethane‐imide) copolymer films for potential use in specialized applications. PUI formulations containing varying amounts of different flame retardants were prepared to achieve UL‐94 VTM‐0 rating without any melt‐drip. Thermogravimetric analysis revealed that PUI exhibits multi‐step degradation. The presence of flame‐retardant additives operating through a condensed phase mechanism was found to reduce the initial degradation temperature and increase char yield. SEM imaging of the char residue revealed the intumescent behavior of PUI with APP and PEPA additives. Both these additives were found to be effective flame retardants for PUI films. The addition of 25% APP and 25% PEPA led to VTM‐0 and VTM‐1 ratings, respectively, without melt drip. DOPO, a representative vapor phase flame retardant, was also found to be effective for PUIs, with 25% DOPO introduction resulting in a VTM‐0 rating. Conventional phosphate‐based flame retardants, such as triethyl phosphate, tricresyl phosphate, and triphenyl phosphate, were found to be relatively ineffective for PUI films. Interestingly, the mechanical properties of PUI improved significantly upon the introduction of flame‐retardant additives. High thermal stability, and anti‐drip flame retardant properties, bestows these formulated PUIs excellent candidature as materials for applications where flame retardancy with anti‐drip is mandatory.