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The use of additives for resins modification is common practice in wood-based panel industry and wheat flour has been one of the most widely used extenders for decades. The amount of wheat flour to be added is determined through a sense of proportion, mainly based on experience, as systematic scientific studies on the effect of its individual components are limited. In this study, we added wheat flour, wheat starch and wheat protein as extenders in various quantities to urea (UF) and phenol formaldehyde (PF) resins and analysed their structure, pH value and buffer capacity through closely examining their interaction with the resins as well as their effect on viscosity and bonding strength development. As a result, wheat protein proved to be the most effective on both resins. Despite influencing adhesive properties in uncured state, no effect on the curing behaviour of the resins could be observed. [ABSTRACT FROM AUTHOR]

Wheat flour is used as an extender for urea (UF) and phenol formaldehyde (PF) resins in plywood production. The addition of wheat flour is usually based on operational experience. Whereas flour quality parameters are important predictors for the bread production, fundamental scientific knowledge is hardly available for adhesive applications. Therefore, this work focusses on the separate investigation of the main components of wheat flour: starch and protein, as additives to UF and PF resins in different amounts. The resin batches produced were used for manufacturing 9-layered birch plywood panels. While part I focused on physico-chemical properties of the adhesives, in this present part panel performance was tested in accordance with EN 314-1 (2005) and by evaluating formaldehyde emissions using micro-chamber/thermal extractor. The UF-based panels were tested for class 2 covered exterior use and the PF panels for class 3 non-covered exterior use according to EN 314-2 (1997). Wheat protein showed the most promising wet shear strength results for both resins, the resulting high viscosity limits its addition to 30%. An addition up to 100% wheat flour and wheat starch to UF resins provided sufficient wet shear strengths. None of the extenders had an effect on formaldehyde emissions. [ABSTRACT FROM AUTHOR]

Ammonium pentaborate (APB) was used to modify urea formaldehyde (UF) resins, in which the formaldehyde to urea molar ratio was set at 1.80, 1.50, 1.25, and 1.05. Some specific properties, including gel time, free formaldehyde content in UF, bond strength, and formaldehyde emission levels from plywood were evaluated. The result showed that APB increased the gel time length, but also decreased free formaldehyde content and emission levels, which was reduced mostly by 79.0% and 81.4%, respectively. The result of bond strength indicated that APB was proper to modify high F/U molar ratio of UF resin regardless of the loading level, but a recommended loading level should be considered to relevantly lower the F/U molar ratio of UF. The suggested loading level of APB to UF is 8.0% to 6.0%, 6.0%, and 4.0% to UF resin with F/U molar ratio of 1.8, 1.5, and 1.25 separately. [ABSTRACT FROM PUBLISHER]

The influence of glutaraldehyde blend on the properties of a commercially available resin in moist conditions was investigated. A UF resin with very low water resistance was blended with glutaraldehyde prior to the thermosetting step and the adhesive performance of the modified adhesive systems was studied. Experiments were performed on birch two-layer co-oriented plywood. It was shown that blending a commercial glue-mix as sold with glutaraldehyde can be an effective way to improve water resistance of the glue without introducing additional –NH 2 moiety. It was also found that glutaraldehyde does not deteriorate properties of the glue in the dry state, while glue susceptibility to boiling water is markedly reduced. [ABSTRACT FROM AUTHOR]