Activation Of Wood Fiber Based On The Alkali Solution System Under Freezing

The mixed wood fiber was activated by sodium hydroxide/urea,sodium hydroxide/Diethanolamine and sodium hydroxide/Polyethylene systems under freezing treatment.The freezing activation effect of wood fiber was characterized by fourier tansform infrared spectroscopy(FTIR),Thermo gravimetry(TGA),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS),and the mechanical performance test of hot-pressed self-bonding fiberboard with activated wood fiber.The activation process of wood fiber was discussed.The optimize activation process was picked up through orthogonal experiments of the wood fiber activated by sodium hydroxide/urea mixed aqueous solution.The experimental results show that a mass ratio of NaOH/urea system(NaOH:urea=7:12)and wood fiber of 1:12,the freeze temperature is 15 ?,freezing temperature of-15 ??freezing time of 1.0 h,and wood fiber moisture content of 20%is the optimize process.The static bending strength and internal bonding strength of fiberboard prepared with wood fiber freezing-activated by sodium hydroxide/urea,sodium hydroxide/Diethanolamine and sodium hydroxide/Polyethylene glycol systems were significantly increased,and the water absorption rate and the thickness swelling rate was significantly decreased.The experimental results show that,compared with unactivated wood fiber,the static bending strength and internal bonding strength of fibreboard prepared with wood fiber freezing-activated by sodium hydroxide/urea system increased from 32.16 MPa and 0.35 MPa to 46.53 MPa and 1.85 MPa,and the water absorption rate and the thickness swelling rate decreased from 47.12%and 19.73%to 42.27%and 14.86%respectively.Compared with unactivated wood fiber,the static bending strength and internal bonding strength of fibreboard prepared with wood fiber freezing-activated by sodium hydroxide/Diethanolamine system increased from 32.16 MPa and 0.35 MPa to 45.68 MPa and 2.19 MPa,and the water absorption rate and the thickness swelling rate decreased from 47.12%and 19.73%to 38.78%and 15.34%respectively.The static bending strength and internal bonding strength of fibreboard prepared with wood fiber freezing-activated by sodium hydroxide/Polyethylene glycol mixed aqueous solution increased to 43.33 MPa and 1.71 MPa,and the water absorption rate and the thickness swelling rate decreased to 41.94%and 15.66%respectively.The mechanical properties of these fiberboard activated by above three systems have reached GB/T11718-2009 in the dry state of the use of ordinary medium density fiberboard performance requirements.The results of FTIR,TGA,XRD and XPS show that the hydrogen bonding structure of cellulose in the wood fiber was destroyed by the freezing activation treatment with above three systems,leading to the expansion of cellulose I lattice a new crystalline,a lower degree of molecular association and thermal stability,which consequently enhanced hydroxyl activity of the wood fiber surface.