Preparation And Properties Of Modified Chitosan Wood Medium Density Fiberboard

As an important branch of wood-based board,fiberboard plays an important role in wood processing industry.The traditional medium density fiberboard(MDF)uses "third-aldehyde adhesives"(urea formaldehyde resin,phenolic aldehyde resin,Melamine formaldehyde resin)as the main binders.There are problems that free formaldehyde exceeds the standard and endangers health and environment.To solve the above problems,this study first used chitosan as binder,explored the effects of chitosan addition amount and hot-pressing process parameters on the physical and mechanical properties of MDF,and screened out a better MDF preparation process.Chitosan was modified with vanillin and citric acid respectively,and MDF was manufactured by optimal preparation technology.The influence of modification on the physical and mechanical properties of MDF was studied,and the mechanism of enhancing the physical and mechanical properties of MDF by modified chitosan was clarified.The main research contents and results are as follows:Chitosan was used as binder.By designing five-factor and four-level orthogonal experiment,and conducting significance analysis and range analysis on the experimental results,the influence law of chitosan addition amount and hot-pressing process parameters on the physical and mechanical properties of MDF was explored to optimize the MDF preparation process.The results showed that the optimum preparation process for medium density fiberboard(MDF): hot-pressing temperature under 220 °?,hot pressing time for 12 min,hot-pressing pressure for 3 MPa,chitosan addition amount of 4%.The physical and mechanical properties of MDF are better under this preparation process: the static bending strength(15.0 MPa),the elastic modulus(1 896 MPa),the internal bonding strength(0.64 MPa),and the expansion rate of water absorption thickness(15.52%).Medium density fiberboard with excellent mechanical properties was successfully prepared by using vanillin modified chitosan as binder.The modification mechanism was analyzed by Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD).Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)and thermogravimetric analysis(TG)were used to analyze the reinforcing mechanism of fiberboard.The results showed that the amino group of chitosan reacted with the aldehyde group of vanillin to form the Schiff base bond,and formed the three-dimensional network structure under the action of hydrogen bond.At the same time,when vanillin /chitosan was 2:1,the physics mechanical properties of MDF prepared are as follows: the static bending strength(20.6 MPa),the elastic modulus(3 005 MPa),the internal bonding strength(0.86 MPa)and the water absorption thickness expansion rate(14.72%).Medium density fiberboard with excellent mechanical properties was successfully prepared by using citric acid modified chitosan as binder.The modification mechanism was analyzed by FTIR and XRD.FTIR,XPS,SEM and TG were used to analyze the reinforcing mechanism of fiberboard.The results show that the amino group of chitosan is cross-linked with the carboxyl group of citric acid,and the bonding between ionic and hydrogen bonds can improve the mechanical properties of fiberboard to a great extent.The optimal mass ratio of citric acid to chitosan as binder was 0.25:1.At this time,the fiberboard obtains the best mechanical properties: elastic modulus(3 426 MPa),static bending strength(31.0 MPa),internal bonding strength(1.27 MPa),water absorption thickness expansion rate(15.63%),which meets the requirements of medium density fiberboard GB/T 11718-2021.