Multifunction for the high hardness ultra-thin fiberboard loaded with functional unit and by the in-situ synthesis of CaCO3 attached on the wood fiber

Ultra-thin fiberboard (UTF) is a biomass-based composite product exhibiting excellent decorative and processing performance. However, the problems such as flammability and insufficient hardness of UTF have limited further potential application. In this work, wood fiber as raw material, diphenylmethane diisocyanate (MDI) as adhesive, and ammonium polyphosphate (APP) as flame retardant were used to manufacture UTF with high hardness and excellent flame retardant performance. Before the hot-pressing process was carried out, CaCO 3 was synthesized in-situ on the surface layer of the ultra-thin fiberboard slab (UTFS) by spraying the Ca 2 + -CO 3 2- system to further improve its hardness and flame retardant performance. The surface of wood fiber in UTFS is rich in −OH groups, which can firstly adsorb a large amount of Ca 2+ on the fiber surface with coordination bond, then the in-situ synthesis of CaCO 3 on the surface layer of UTFS was realized after Na 2 CO 3 was introduced. The hot-pressing process can promote the combination of CaCO 3 to the adhesive, thus its hardness reaches as high as 83.4 HD. The UTF with 10 wt% APP (UTFCa-10APP) exhibits excellent mechanical properties and outstanding flame retardancy, and its total heat release (THR) and total smoke production (TSP) are reduced by 48.27 % and 81.00 %, respectively, compared with the control group. As it was used to manufacture electrothermal thin fiberboard (ETF), its temperature rise reach 25.1 ℃ on surface in 1000 s under 500 W·m −2 . The developed flame retardant UTF with high hardness will display more potential for use in floors, furniture, decoration and other application. • UTFCa was prepared by in-situ synthesis of CaCO 3 on surface layer of UTF. • The developed process can be directly applied to the industrial production. • The surface Shore hardness of UTFCa can reach 83.4 HD. • Flame retardancy of UTFCa was further improved by adding APP and synthesis of CaCO 3 . • UTFCa-10APP has advantage to manufacture electrothermal thin fiberboard.