Abstract:

Objective: Taking poplar wood fiber as material, enhance the reactive sites on the fiber surface by oxidative modification, establish the multi-site network structure of hydroxyl and aldehyde groups on the fiber surface, and prepare high-strength, low-absorbent thickness expansion rate of self-bonding fiberboard, so as to achieve the whole biomass low-carbon and recyclable production and utilization. Method: The surface groups of wood fiber were oxidatively modified by sodium periodate to establish highly reactive aldehyde group network sites, and the aldehyde group content was determined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analyze (TG), and differential scanning calorimetry (DSC), which analyzed the microstructure and chemical structure of wood fiber before and after the reaction, as well as the content of different aldehyde groups. Using chemical bond cross-linking in low temperature hot pressing conditions to prepare self-glued fiberboard, to explore the mechanical properties of dialdehyde wood fibers to prepare self-bonding fiberboards and absorbent thickness expansion rate. Result: The quantitative modification of dialdehyde wood fibers can be realized by controlling the conditions of reaction time, temperature, and concentration of oxidizing agent; comparing with the original fibers, the surface roughness of dialdehyde wood fibers increased, the fiber size became shorter, and the degree of cellulose polymerization decreased, the cellulose-hemicellulose-lignin encapsulation structure was loosened, and a large number of pores were produced on the surface of wood fibers. The cellulose crystallization zone was gradually destroyed with the increase of reaction strength, and the thermal stability of dialdehyde wood fibers increased with the increase of reaction strength. The thermal stability of dialdehyde wood fibers gradually decreases with the increase of aldehyde content, which is conducive to the low-temperature hot compression molding of glueless fiberboard. Dialdehyde wood fibers can realize self-gluing through chemical bond cross-linking in the hot pressing process, the hot pressing temperature and aldehyde content of aldehyde-based wood fibers have a significant effect on the performance of the glueless fiberboards, and the self-bonding fiberboards prepared through the optimization of raw materials and process conditions have excellent mechanical properties and water resistance. Conclusion: Different aldehyde content of dialdehyde wood fibers can be obtained by controlling the reaction conditions, and the controlled modification of aldehyde groups on the surface of wood fibers can be realized; too low a temperature (50 ℃) in the self-gluing process is likely to lead to poor water resistance of dialdehyde wood fibers, and too high a temperature (125 ℃) is likely to cause the degradation of dialdehyde wood fibers, which will lead to blistering, swelling, carbonization, and decrease the mechanical properties of the fiberboards. When the concentration of sodium periodate was 0.07 mol·L^?1, the reaction temperature was 30 ℃, and the reaction time was 6 h, the aldehyde content of the wood fiber was 1.86 mmol·g^?1; at a hot pressing temperature of 100 ℃, a pressure of 20 MPa, and a hot pressing time of 5 min, the mechanical properties of the self-glued dialdehyde wood fiber boards and the water resistance of the fiber boards reached the optimum: the bending strength of 78.36 MPa, the modulus of elasticity of 10.88 GPa, the internal bonding strength of 3.88 GPa, and the water resistance of the fiber boards. The mechanical properties and water resistance of the prepared self-glued dialdehyde wood fiber boards were optimal: flexural strength of 78.36 MPa, modulus of elasticity of 10.88 GPa, internal bonding strength of 3.04 MPa, and the expansion rate of the water-absorbing thickness of 24 h was only 8.01%.

Key words: dialdehyde wood fibers, self-bonding, mechanical properties