Research On The Enhancement Mechanism Of Urea Pre-treatment And Low Molar Ratio MUF Resin Eucalyptus

Eucalyptus is the main timber tree species in China,and its timber yield is about 30% of hold country.It is difficult to be directly used as furniture and floor material because of its large growth stress,easy cracking and poor dimensional stability.In order to improve the application value of eucalyptus and alleviate the contradiction between supply and demand of high-quality timber,physical and chemical modification of eucalyptus is of great significance.However,eucalyptus has poor permeability,difficult functional improvement and high modification cost,which makes it difficult to realize industrial promotion.In this paper,weak alkaline urea solution etc.pre-treatment was used to improve the permeability of eucalyptus.Low molar ratio melamine modified urea formaldehyde(MUF)resin was used to improve the properties of eucalyptus.By analyzing and characterizing the structure and properties of eucalyptus before and after modified,the physical and chemical properties and enhancement mechanism of modified wood were studied,which would provide theoretical and technical support for expanding the use and realizing the high value utilization of eucalyptus.The main conclusions are as follows:(1)The main factors affecting the poor permeability of eucalyptus are dense structure,infiltrate in the catheter,rich gum in wood rays,and cribriform pit.(2)Three methods,was used to pre-treatment eucalyptus,could form new fluid channels and improve the permeability of eucalyptus.Permeability of organic solvent treated eucalyptus increased by 4 % due to dissolve the glue in the ray and the filler in the catheter to open blocked channels.The permeability of eucalyptus treated with vacuum-atmospheric pressure increased by 9% because formed pressure difference,destroys the weak part of cell wall(e.g.,thin-walled wood ray cells),formed circulation channels.Urea solution could hydrolyze part of hemicellulose,soften lignin,dissolve pectin.And the porosity and specific surface area of wood were increased.After treatment with 20 % urea solution,the gas permeability and water absorption of eucalyptus increased by 41.41 % and 189 %,respectively.(3)The dimensional stability,mechanical strength and durability of eucalyptus was effectively improved,because of low molar ratio and low molecular weight MUF resin could enter into the cell wall of eucalyptus.The low molar ratio and low molecular weight MUF resin was used for impregnation treatment of eucalyptus.The resin was mainly filled in the cell wall,cell cavity and intercellular layer of wood.The hydroxymethyl group on the molecular chain of the resin reacted with the hydroxyl group on the cellulose molecular chain to form a hydrophobic three-dimensional network polymer.At the same time,the curing resin in the cell cavity hindered the absorption of water by wood,so that the dimensional stability and mechanical properties of MUF resin modified eucalyptus were effectively improved.Compared with the untreated wood,the density of the modified wood(0.53 g/cm3),compressive strength(CS)(66.39 MPa)and flexural elastic modulus(MOR)(5.62 GPa)increased by 22.9%,32.67% and14.22%,respectively.And the equilibrium moisture content,the water absorption(WA),buried mass loss decreased by 23%,33%,47 %,respectively.When the WPG was 6.59%,ASE was 53.15 %.The formaldehyde emission of eucalyptus treated with MUF resin at mole 0.7was 0.06 mg/L(the desiccator test value).(4)Low molar ratio and low molecular weight MUF resin was used to modify eucalyptus pre-treated by urea.WPG and mechanical properties of the modified wood were effectively improved.The WPG of NM was 75 % higher than M.Compared with untreated wood,the MOE and CS of treated with NM was increased by 22.57 % and 43.92 %,respectively.