Purpose -The purpose of this paper is to investigate a new approach for making a bio-based adhesive from a new resource, rice bran (RB) adhesive. Design/methodology/approach -RB solution was prepared and its pHs were adjusted to either 8.5-9.0 or 10.0-10.5. The solid content of slurry was controlled at <18 per cent and then gelatinised in a water bath shaker at 608C for 2 h or at 1008C for 1 h. The bonding strength of RB adhesive was determined by testing the strength of three-layer plywood. A differential scanning calorimeter (DSC) was used for detecting the reaction energy and curing temperature. According to the DSC analysis, hot pressing at three temperatures was performed to select the best bonding conditions. Then, a two level split-plot design was used to determine the effects of gelatinisation and pH on the bonding strength of RB adhesive. Thus, the formulation of RB adhesive was optimised. In order to improve the water resistance of RB adhesive, toluene diisocyanate (TDI) was used as a cross linking agent. Findings -In the study reported here, a RB adhesive was developed by alkaline modification. Very high pH was not necessary, when RB adhesive with pH 10.0-10.5 was gelatinised at 1008C for 1 h, its bonding strength was significantly lower than pH 8.5-9.0 gelatinised at 608C for 2 h. Water resistance of RB adhesive improved significantly when TDI was added as a cross linking agent. Compared to pure RB adhesive, the RB-TDI mixed adhesive started curing at a higher temperature. For RB adhesive curing, 1308C was a suitable hot pressing temperature. Research limitations/implications -Though the RB adhesive developed had a good bonding strength, its water resistance and dark colour was not satisfactory, which risks discolour of light colour wood. Further study is needed to solve this problem. Practical implications -The approach provided a bio-adhesive with good bonding strength, reasonable working life, and without formaldehyde emission. Based on further study, RB adhesive could be considered a promising alternate adhesive in many applications such as paper board bonding and plywood. Originality/value -It provided a potential way to utilise by-product of agriculture, RB as industrial raw material. This will do farmers a great favour. Meanwhile, the modified RB adhesive is promising to partly or completely replace urea formaldehyde resin that mainly used in wood industry, avoiding formaldehyde emission and reducing the dependence on petroleum products.

Paper mill sludge (PMS) is a waste material from pulping. In this article it was used to replace part of a wood fiber (WF) filler to reinforce high‐density polyethylene (HDPE). The properties of the PMS/WF/HDPE composites were investigated. When half of WF was replaced with PMS, the bending strength and modulus of WF/HDPE composites decreased by 16.08% and 29.91%, respectively, but their impact strength increased by 11.31%. Dynamic mechanical analysis demonstrated that with PMS addition, the storage modulus decreased and the loss tangent increased. Although the flexural properties of the PMS/WF/HDPE composites decreased compared to WF/HDPE composite, they still had satisfactorily high strengths. The 30:30:36 PMS/WF/HDPE composite presented bending and impact strengths of 61.00 MPa and 12.11 kJ m−2, respectively. The 50:20:26 PMS/WF/HDPE composite presented bending and impact strengths of 55.02 MPa and 10.37 kJ m−2, respectively. Rheological test proved that substituting part of WF with PMS would not affectmanufacture processing. This study indicated that paper mill sludge could be used in wood plastic composites, which would reduce pollution from paper manufacturing. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Purpose -To investigate a new approach for making soy-based adhesive having appropriate properties for potential application in wood industry. Design/methodology/approach -Three chemicals were used for modifying protein contained in soy flour. According to orthogonal experiment design, nine soy-based adhesives were prepared. Shearing strength of plywood bonded with these adhesives was measured to evaluate the bonding strength of nine formulas. Based on statistic analysis, the main effect factor and an optimised formula were determined. Further investigation on the modification effect to protein molecule was conducted by Fourier Transform Infrared Spectroscopy. In order to facilitate practical application, the viscosity of optimum formula adhesive was measured to determine possible working life. Three additives were added to optimise formula for reducing mould growth. Findings -Based on soy-flour mass, the best combination of lime milk, sodium hydroxide (NaOH) and sodium silicate was 10, 2, and 20 per cent, respectively. NaOH was considered the main effect factor on bonding strength, and sodium silicate was of the second importance. The viscosity of the optimised adhesive changed lightly in 2 h, and significantly increased from 2 to 4 h. However, it still could spread on veneer, which indicated a reasonable working life for practical application. Based on soy flour mass, when 0.5 per cent sodium benzoate or 25 per cent phenol formaldehyde was added, mould growth could be restrained after early stage. Research limitations/implications -Though the studied soy-based adhesive had a good bonding strength and comparative water resistance, its pH was a little too high, which may cause risks of discolour of light coloured wood. Further study is needed to solve this problem. Practical implications -The approach provided a bio-adhesive with good bonding strength, comparative water resistance, reasonable working life, and without formaldehyde emission. Soy-based adhesive is considered a promising alternate adhesive in wood industry and other applications because of the above mentioned advantages. Originality/value -It provided a potential way to utilise by-product of agriculture, soy-flour, as industrial raw material. This will benefit farmers significantly. Meanwhile, the modified soy-based adhesive is promising to partly or completely replace urea formaldehyde resin that are mainly used in wood industry, avoiding formaldehyde emission and reducing the dependence on petroleum products.

PurposeTo investigate the effects of moisture and freeze‐thaw cycling on the absorption and flexural properties of rice‐hull‐polyethylene (PE) composite.Design/methodology/approachVarious rice‐hull‐PE composite specimens were submerged in water at various temperatures and subjected to various freeze‐thaw cycles. Various characterisations including water absorption, bending strength and stiffness, Fourier transform infrared spectroscopy and scanning electron microscope imaging were performed.FindingsHigh temperatures accelerated the water sorption of the rice‐hull‐PE composite and increased the equilibrium moisture content. The uncoated surface was not significantly more easily permeated than the coated surface, contrary to expectations. However, more water was absorbed from the cut surface than from the original extruded surface. This was attributed to the tiny checks left on the surface by the sawing action, which indicated the importance of protecting the original surface layer from scraping or other damage. Bending strength and stiffness of the rice‐hull‐PE composite decreased significantly after the freeze‐thaw cycling treatment. The modulus of elasticity decreased more than the modulus of rupture. Compared to the effect of water immersion alone, freeze‐thaw cycling treatment slightly accelerated this decrease.Research limitations/implicationsThe results of this study were obtained from accelerated laboratory experiments. Further research could be carried out to evaluate the properties of this rice‐hull‐PE composite in practical application.Practical implicationsThe research revealed a possible degradation in quality when the rice‐hull‐PE composite is used in moist or freezing conditions. The resin layer on the extruded surface provides an important protection.Originality/valueIn China, rice‐hull powder is widely used as a reinforcing component in plastic composite. However, the durability of rice‐hull/PE composites has rarely been investigated. Results from this study will help users apply rice‐hull‐PE composites correctly and encourage the development of other agro‐fibre/polymer materials.