Bonding of spruce wood with wheat flour glue—Effect of press temperature on the adhesive bond strength

The main objective of this research was to study the potential of renewable polymers based on wheat corn for wood-to-wood bonding and wood composites. Commercial wheat flour containing mainly starch and proteins was used as biobased glue. To evaluate the strength on wood joints under different curing temperatures tensile shear strength of spruce wood specimen was tested according EN 302-1. Thermal properties of the wheat flour glue were studied by means of differential scanning calorimetry (DSC). Pasting profiles of the wheat flour slurry were investigated by using a Micro Visco-Amylograph (MVA).With rising pressing temperature an increase of bond strength was observed up to a temperature of 105 °C. Under these conditions excellent bonding strength was reached and mainly wood failure was detected. At higher temperature a slight reduction of bond strength was observed, which can be related to beginning thermal modification of wood, especially changes in character of the wood surface. Best adhesive performance was not reached until the granular order was disrupted and thus starch molecules were separated. Changes in the molecular structure of starch during heating are described by means of analytical methods helping to explain the effects on the bond strength.