Application of Modified Starch @ Phenolic Resin Flame Retardant Coating on RPUF

In this study, sodium tripolyphosphate was used to modify starch, resulting in a novel starch-based flame retardant. The phenolic resin was employed as the matrix, with the starch-based flame retardant incorporated as a filler and applied to the surface of rigid polyurethane foam (RPUF) to prepare the composite material. Scanning electron microscopy revealed that the coating effectively penetrated the RPUF framework, forming a strong and tightly bonded layer with excellent coverage. The combustion and mechanical properties of the composite material were investigated. The results showed that, in vertical combustion tests, the composite material met the UL940-5VA standard. In thermogravimetric analysis, the composite exhibited a 42.71% increase in char residue compared with the RPUF. In three-point bending pulverization resistance tests, the composite demonstrated a 28.42% reduction in chalking compared with the RPUF coated solely with phenolic resin. This study paves a new path for the practical application of bio-based flame retardants.