Flame-Retardant Synergism through Chemical Intercalation for Rigid Polyurethane Foam by Using Intrinsic/inorganic Combination

Rigid polyurethane foam (RPUF) is a versatile thermal and acoustic barrier material with high flammability, which raises severe safety concerns and necessitates an effective flame retardant (FR). Compared to the single FR system, organic/inorganic flame-retardant composites with the synergistic effect show better performance in both flame retardancy. While the synergistic effect is always considered among FRs and does not include the polymer matrix, it obtains limited effectiveness. Our work prepared an extender for PU foam, which contains accessible phenyl side groups that can interact with modified expandable graphite through intercalation to construct a synergistic effect between the polymer matrix and the inorganic FR. With a total additive content of 21.9%, the LOI and UL-94 ratings increased to 37% and V-0 level, respectively, which shows the greatest improvement compared to other expandable graphite systems and only induces small fluctuations in physicochemical performances. The designed FRs fulfill the major requirements of current standards on RPUF, and they also show a great practicality for future large-scale production.