Effects of denaturisation of rice bran and route of synthesis of RB-modified UF adhesive system on eco-performance of agro-based composites

Abstract

Purpose The purpose of this paper is to examine the effects of denaturised rice bran (RB) and route of its incorporation during synthesis of urea-formaldehyde adhesive, on the performance of the resulting adhesive, especially viscosity, free-formaldehyde (HCHO) and quality of the produced bagasse-based composites, in comparison with those produced from commercial urea formaldehyde (UF) and RB-added UF. Design/methodology/approach The experiments were carried out using different denaturised RB at different percentages (1-5 per cent) and pH’s (9-11 per cent). These denaturised RB were incorporated at the last synthesis stage of UF synthesis process. The assessment was carried out on both the viscosity and environmental safety of the adhesive system, as well as the quality of the manufactured bagasse-based composites, of the particleboards (static bending, internal bond (IB) strength and water resistance properties), in comparison to commercial UF and RB added to UF. The performance of the adhesive system was evidenced by the thermogravimetric analysis and differential scanning calorimetry analyses. Findings The results showed that maximum static bending [modulus of rupture (MOR) and modulus of elasticity (MOE)], IB strength and water resistance properties of the resulted wood product accompanied the incorporating 5 per cent of the denaturised RB (pH = 9.0), at the last synthesised stage of UF synthesis process. Where, this synthesis process provided adhesive with viscosity nearly approaching to commercial UF adhesive, and reduced the free-HCHO of adhesive and board by approximately 56 and 49 per cent, respectively. For mechanical and water resistance properties, it provided board with 24.5 MPa MOR, 3,029 MPa MOE, 0.64 MPa IB, 11 per cent swelling (SW) and 20.5 per cent absorption. These properties fulfil the requirements of high grade particleboards American National Standard Institute (ANSI) A208.1, especially with respect to static bending values and water swelling property. Research limitations/implications Incorporating 5 per cent of pre-denaturised RB, at pH 9.0, in wet form, and in the last stage of synthesis UF, provided adhesive system with convenient viscosity together with lower free-HCHO and acceptable board properties, compared with that produced from commercial UF, or adding denaturised RB to already synthesised UF. For the mechanical (MOR, MOE and IB) and water resistance properties (SW per cent and absorption per cent) of the produced composite are complied the standard values of H-3 grade of particleboard. Practical implications Promising adhesive system is resulted from incorporating 5 per cent of pre-denaturised RB at pH 9.0, in wet form, during last stage of UF synthesis process. Social implications Incorporating the RB by-product of oil production to commercial UF or during synthesis of UF will be benefit for saving the healthy of wood co-workers, and motivating the wood mill to export its wood products. Originality/value The article provides a potential simple way to solve the drawback of increasing the viscosity of UF, as a result of adding RB, via incorporating the RB during synthesis process. The viscosity of the synthesised RB-modified UF approaches RB-free UF, and consequently the adhesive system easily penetrates through agro-fibres, and provides good bonding behaviour and high performance wood product (both quality and environmental by minimising formaldehyde emission or toxic gasses during board formation).