Development Of Binderless Particleboard From Cotton Stalk Using Steam-injenction Pressing

China is a country lacking of forest resource, the contradiction between wood supply and demand is getting more and more acuted, which highly restricts China's wood industry. Thus, utilizing agricultural residues is a new approach which will settle the severe shortage of wood material supply effectivly for the moment.China is the largest cotton producer in the world, cotton stalk is especially rich in natural resources. Under the severe shortage of wood supply and demand situation, as a substitute for the production of wood based panels, cotton stalk will show a considerable economic benefits, economic benefits and ecological benefits. Not only can make full use of idle resources of cotton stalk, ease the wood supply and demand, solve the the problems of environmental pollution caused by burnning it, but also the panels have no emissions of formaldehyde, which can meet the demand of environmental protection.In this paper, the analyses of the structure,fiber morphology and chemical composition of cotton stalk are used to investigate cotton stalks'feasibility of developing wood-based panels. The xylem of cotton stalk is the main composition of raw materials used for manufacturing. The fiber morphology of cotton stalk is all close to hardwoods. The chemical compositions of cotton stalks are as followed:hot-water extractive content is 5.23%, alcohol-benzene extractive content 2.53%, lignin content is 21.77%, hemicellulose content is 39.59%, a-cellulose is 41.00%, these are close to part hardwoods. Therefore, it is feasible to use cotton stalks as the raw materials to manufacture wood-based panels.Using hot pressing to develop cotton stalk binderless particleboard to investigate the effect of board density on the physical and mechanical properties of binderless particleboard. The results showed, under the conditions of particle moisture content(MC) 25%, hot-pressing temperature 190℃, hot pressure 5 MPa and hot-pressing time 7 minutes, the cotton stalk binderless particleboards with density of 0.9g/cm3 and thickness of 8mm have certain intensity and can meet the requirements of JIS A 5908 standards at the aspects of modulus of rupture(MOR), modulus of elasticity(MOE), internal bonding strength(IB). Binderless particleboard was developed from cotton stalk using steam-injection pressing. The effect of board density,steam pressure and steam-injection time on the physical and mechanical properties (modulus of rupture, modulus of elasticity, internal bond strength and thickness swelling) of binderless particleboard were investigated. And then compared the properties with the proterties of the cotton stalk binderless particleboard developed from hot pressing under the same density. The results showed:The optimum manufacturing parameters of cotton stalk binderless particleboard were as follows:steam pressure 1.0MPa and steam-injection time 7 minutes. Produced under the conditions, the cotton stalk binderless particleboard with density of 0.8g/cm3 and thickness of 7mm can meet the requirements of GB/T 4897.2-2003 standards and JIS A 5908-2003 standards at the aspects of modulus of rupture(MOR), modulus of elasticity(MOE), internal bonding strength(IB). However, the thickness swelling (TS) was a little high, which need optimize. Under the same density of 0.8g/cm3 or 0.85g/cm3, the properties of binderless particleboard using steam-injection pressing were superior to that of binderless particleboard using hot pressing.With the analysis of chemical components and infrared spectroscopy, the self-bonding mechanism of cotton stalk bindless particleboard was explored. After hot pressing and steam-injection pressing, the chemical components of cotton stalks,the positions and relative absorb intensity of major peaks changed. During the steam-injection pressing and hot pressing process, a few hemicelluloses and celluloses degradated to furfural compounds under high temperatures, and then occurred condensative reactions with lignins having the structure of phenolic hydroxyl, finally, them formed adhesive compounds which are similar to phenolic resins.Heated under high temperatures, ligins could also occur condensative reactions between themselves to form compounds similar to phenolic resin in a short time, played the role of adhesive.The rupture of glucoside bond among cellulose based ring increased the number of active hydroxyls, improved the combination of hydrogens between fibers, enhaced the bonding between particles, conducing to the bonding between particles.While the number of free hydroxyls reduced, the number of hydrophobic carbonyls increased, making the particleboard with good intension and water resistance; part of the hydroxyls dehydrated to C-O-C, enhanced the molecular bond force, which was conducive to the self-bonding.