Bio‐based flame‐retardant rigid polyurethane foam with high content of soybean oil polyols containing phosphorus

Abstract Rigid polyurethane foam (RPUF) is prepared from petroleum‐based polyols and isocyanate, which consumes a large amount of petroleum. To alleviate the consumption of petroleum, it is necessary to synthesize green and sustainable polyols. However, the greatest disadvantage of RPUF is its flammability. To reduce the risk of fire caused by RPUF, phosphorylated soybean oil polyol (Polyol‐P) and phenyl phospho‐soybean oil polyol (Polyol‐PPOA) were synthesized by ring‐opening reactions of epoxy soybean oil with phosphoric acid and phenylphosphonic acid, respectively. A flame‐retardant RPUF was prepared via polymeric 4,4‐diphenylmethane diisocyanate (p‐MDI), which reacted after mixing Polyol‐P and Polyol‐PPOA with polyether polyol‐330N in different proportions. Scanning electron microscopy (SEM) showed that the cell sizes of the RPUF‐P and RPUF‐PPOA increased first and then decreased and the cell number decreased first and then increased with the increase in the contents of Polyol‐P and Polyol‐PPOA. Mechanical property tests showed that the compressive strength of the RPUF‐P4 reached 0.1 MPa, and the compressive strength of the RPUF‐PPOA4 reached 0.07 MPa. The limiting oxygen index values of the RPUF‐P4 and RPUF‐PPOA4 were 20.9% and 24.3%, respectively. The UL 94 of the RPUFs indicated that the rating of the RPUF‐PPOA3 was improved to V‐1. The results showed that the flame‐retardancy mechanism of the Polyol‐P and Polyol‐PPOA in the RPUF was based on the charred surface as a physical barrier, which slowed down the decomposition of RPUF and prevented heat and mass transfer between the gas and the condensed phase.