Utilization of sweet sorghum bagasse and citric acid for manufacturing of particleboard I: Effects of pre-drying treatment and citric acid content on the board properties

Recently, the investigation of wood-based composites produced using agricultural waste and natural adhesives has become very important due to the decreased wood resources and fossil resource reserves. In this study, sweet sorghum bagasse and citric acid were used as the raw material and natural adhesive, respectively, for the experimental manufacture of particleboards. A pre-drying treatment of sprayed particles was performed to observe the effect of the pre-pressing moisture content of sprayed particles on the physical properties of the particleboards. In addition, the effect of the citric acid content on the physical properties of the particleboards was investigated. The boards were manufactured under the pressing conditions of 200°C for 10min. The citric acid content was varied in the range of 0–30wt%. The board size and target density were 300×300×9mm and 0.8g/cm3, respectively. Particleboards manufactured using phenol formaldehyde (PF) resin and polymeric 4,4′-methylenediphenyl isocyanate (pMDI) were used as references. The physical properties of boards prepared using pre-dried particles were superior to those of the boards prepared using non-dried particles. The physical properties of boards improved with increasing citric acid content up to 20wt%. The physical properties of boards bonded with 20wt% citric acid satisfied the requirement of the JIS A 5908 (2003) 18 type. In addition, the properties of these boards were comparable to those of boards bonded using PF resin and pMDI. Infrared (IR) spectral analysis suggested the presence of ester linkages, indicating that the carboxyl groups of citric acid had reacted with the hydroxyl groups of the sorghum bagasse to give the boards good physical properties. Consequently, it was concluded that pre-drying treatment of the particles and a citric acid content of 20wt% were effective in manufacturing particleboards composed of sweet sorghum bagasse and citric acid.