Flexible water-resistant intumescent coatings: Fabrication, characterization, and fire protective performance

A flexible water-resistant intumescent coating imparting fire protection to PP. [Display omitted] •A novel intumescent fire-protective coating was obtained.•The coating is of water-resistance, high adhesion, and flexibility.•A 180 μm-thick coating reduces the peak of heat release rate of PP by 79.5%.•The char residue contains POC, POSi and POΦ cross-linked structures.•No harmful solvents were contained in coating formulations. In this study, a flexible water-resistant fire protective coating was fabricated by dip-coating with hyperbranched polyester (HBPE), polyvinyl formal-acetal (PVFA) and HBPE-modified ammonium polyphosphate (APP). HBPE with terminal carboxyl groups, generally being toughening additive, now was used as the surface modifier, film-forming agent and charring agent in this article. The slippery polypropylene (PP) was taken as the substrate to investigate the adhesion and fire protection performance of the coating. The plasma treatment enhanced the surface energy of PP, the hydrogen bonds between the coating and the substrate improved the adhesion, and the cooperation of HBPE and PVFA achieved the flexibility of the flame-retardant coating. Covered with a coating in an average thickness of 180 μm, the limiting oxygen index (LOI) of PP reached 32.2%, with an increase of 78.9%, and the vertical burning test (UL-94) passed V-0 rating. Cone calorimeter test (CCT) showed that peaks of heat release rate (HRR) and smoke production rate (SPR) were reduced by 79.5% and 60.4%, respectively. The structures of POC, POSi and POΦ formed during the thermal decomposition, leading to a stable char layer. All these results show that intumescent coating is of high efficiency in flame retardant and smoke suppression performance.