No abstract

A batch reaction system (volume 1 L) for scaled-up production of 5-HMF-based adhesive precursor solutions from industrially available fructose syrup was developed. The stabilizing effect of sodium dithionite addition was demonstrated. With this system, no concentration steps are needed in the production of adhesive precursors for wood composite board production. The reaction system was optimized in a design of experiment approach to achieve good reaction conditions and to produce reaction solutions with 5-HMF concentrations appropriate for adhesive synthesis. Only three runs in the adjusted system are required to produce enough precursor for the synthesis of 10 kg of adhesive, thereby enabling the testing of the adhesive systems in particle board trials.Furthermore, the structure of humin side products from different reaction stages, formed from 5-HMF and byproducts by condensation, aldol-like reactions and attack on furan ring systems, was investigated. The data were compared to information from literature and possible elements of humin structures are proposed.

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.