The synthesis of an adhesive composed of fructose, hydroxymethylfurfural (HMF), and bishexamethylene triamine was optimized. The intended application of the adhesive is the production of wood composites such as particleboard or medium-density fiberboard. Adhesives synthesized using HMF-rich precursors produced in continuous and batch systems were compared in regard to their tensile shear strength development; no significant differences could be found. The use of sodium dithionite for HMF stabilization during precursor production led to lower resin viscosities, whereas no significant influence on the adhesive strength development was measured. Variation of the critical synthesis parameters' reaction temperature and reaction atmosphere allowed the production of an adhesive with similar or even faster strength development than commercially used urea–formaldehyde adhesives. The ideal reaction temperature was found to be 60°C. Adhesive synthesis under nitrogen atmosphere shifts the curing reaction to lower temperatures, which was demonstrated by differential scanning calorimetry measurements, but did not improve the overall strength development of the adhesive system.Abstract
Soy flour can be substituted in polymeric diphenylmethane diisocyanate (pMDI) resin for bonding plywood. Resin bleed-through is avoided by prepressing at 95°C. The boards have greater wet and dry strength than do those prepared from melamine-urea-formaldehyde (MUF) resin. Soy flour can also be substituted in emulsion polymer isocyanates for cold-press applications. The soy increases dry strength but keeps the wet strength unchanged. The optimal level of soy flour substitution is about 20 percent in all cases as determined by infrared spectroscopy.Abstract
This paper addresses strengths, weaknesses, opportunities, and threats of the wood adhesives industry as discussed at the International Conference on Wood Adhesives in May 2022. The authors have organized the points made during the discussion and added further facts, assumptions, and conclusions to provide context and perspective, even surpassing the outcome of the discussion. The biggest themes of the discussion were the unprecedented opportunity for adhesives to enable forest products to supply society's surging demand for renewable materials and the challenges in meeting those demands. We see excellent opportunities for wood-based panels and with this, for wood adhesives. The abundant challenges to bio-based adhesives for wood products are highlighted by the large amount of research and commercial effort compared with the small volumes of bio-based adhesives in use. Other threats to the adhesive and bonded products industries include aversion to any chemicals (even stable adhesives), and lack of experienced work force. Wood adhesives underwent significant changes in the past decades, mainly focused on reducing emissions during panel use. Wood use in construction will be boosted by efforts to fulfil the European Green Deal, as implemented in the New European Bauhaus and European Renovation Wave.Abstract