Molecular sieve loading phytic acid and ammonium polyphosphate: A novel approach for enhancing flame retardancy and smoke toxicity suppression of plywood

As a bio-based wood product, plywood is widely used in furniture, flooring, packaging, architectural decoration, etc. However, the flammability of plywood limits its application. Using flame-retardant adhesives to prepare plywood is the simplest way to improve its flame-retardant properties. However, a challenge in flame-retardant adhesives arose from the negative effect of flame retardants on the curing and bonding properties of adhesives. Herein, we developed a method to prepare a flame-retardant adhesive modified by using Z-3A molecular sieves as carriers to load flame retardants such as phytic acid and ammonium polyphosphate. The flame-retardant performance of obtained plywood bonded by this flame-retardant adhesive was significantly improved with robust bonding strength under extraordinarily low loading of flame retardants. Even if the loading rate of ZPA flame retardant for 2-ZPA-5 plywood was as low as 2.2 %, the total smoke production and the maximal peak value of the heat release rate were reduced by 79 % and 14 %, respectively, with the limiting oxygen index being 33.6 %, the time to ignition delaying by 14 s, robust wet bonding strength being 1.79 MPa, anti-loss rate as 1.06 ± 0.18 %, and moisture absorption rate as 4.45 ± 0.14 %. The whole process needs neither tedious work or equipment nor high loading of flame retardants. This judicious design strategy offers a versatile and scalable approach to preparing flame retardant plywood.