Suitability of sorghum stalk fibers for production of particleboard.

The aim of this study was to investigate the suitability of sorghum (Sorghum bicolor) stalk (SS) as a promising raw material for particleboard manufacturing. The SS particles and industrial hardwood particles in various proportions were used as the raw materials for the surface and core layers of the three-layer particleboards. Commercial urea formaldehyde (UF) adhesive was used as a binder. Morphological and chemical characteristics of the SS were evaluated. Effects of five variable parameters on the physical (thickness swelling (TS), water absorption (WA)), and mechanical (modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB)) properties of the particleboards were determined. Other parameters such as type of resin (UF), hardener content (1%), type of hardener (NH4Cl), press closing time (5 mm/s), board density (0.70 g/cm(3)), and press pressure (30 kg/m(2)) were held constant. Fractional factorial was used to find the optimum condition for the studied variable parameters. The morphological results showed that SS had comparable fiber length with softwoods and fiber width and wall thickness values greater than the hardwood of common forest species. They had higher hot-water solubility values, lignin and ash contents than those of the other woody materials. The experimental results showed that increasing of SS particles usage in the surface layer significantly affects the board properties. Containing 50 wt% SS particles in the surface, the MOE and MOR values exceed the minimum requirements of the European norms (EN) standards, for general purposes. All of the particleboards produced from SS had IB higher than the EN standard requirement. The presence of SS in the particleboards resulted in higher WA and TS values. All the mechanical properties of the boards decreased when the press temperature was increased from 160 to 180°C. Finally, it can be stated that SS has enough potential as a supplement fibrous material, in combination with industrial hardwood particles, for particleboard manufacturing and indoor applications.