Objective Impregnated paper, as a surface decorative material, is flammable, and in order to reduce its fire hazard, this study explored the impact of microencapsulated ammonium polyphosphate (MFAPP) on the thermal stability and flame-retardant properties of impregnated paper. Additionally, the study investigated the influence of flame-retardant impregnated paper on the performance of high-density fiberboard (HDF).

Method Using melamine-formaldehyde resin (MF) as the shell material and ammonium polyphosphate (APP) as the core material, microencapsulated ammonium polyphosphate was prepared by in-situ polymerization to study the effects of reaction time, reaction temperature, core-to-wall ratio, and pH on the encapsulation rate. The influence of MFAPP on the physicochemical properties of impregnating resin was analyzed. The flame-retardant performance of MFAPP-impregnated paper on HDF was investigated, and the morphology of residual char after combustion was analyzed to explore the flame-retardant mechanism of MFAPP.

Result (1) Microencapsulated ammonium polyphosphate with a coating rate of 17.48% can be prepared when the reaction time was 2 h, the reaction temperature was 70 ℃, the core-to-wall ratio was 2∶1, and the pH value was 5. The results of the SEM-EDS, FTIR and TG tests showed that the MF resin was successfully coated on the surface of APP, and the thermal stability had been improved. (2) Results of resin physicochemical property tests showed that MFAPP had minimal impact on the curing time and viscosity of the impregnating resin, meeting industrial requirements. (3) The water absorption thickness expansion rate and surface bonding strength of MFAPP impregnated paper veneered HDF were 6.9% and 1.21 MPa, respectively, which comply with the relevant national standards. (4) Compared with HDF, 60% MFAPP impregnated paper HDF had good flame retardant and smoke suppression performance, and the total heat release and smoke release were reduced by 13.19% and 17.62%, respectively. MFAPP impregnated paper showed good flame retardancy in gas phase and condensed phase.

Conclusion MFAPP prepared by in-situ polymerization can be used to prepare flame retardant impregnated paper to improve the flame retardant and smoke suppression properties of HDF.