A novel natural adhesive from rice bran

Abstract

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.

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