Markers of quality in self-bonded beech boards

IRG/WP 17-40820

C Cristescu, D Sandberg, O Karlsson

A self-bonding phenomenon takes place when five layers of beech (Fagus Sylvatica L.) veneers are pressed at temperatures higher than 200ºC. If the pressing temperature between veneer surfaces reaches at least 225ºC during pressing and if the pressure applied is optimal, water-resistant bonds are formed between veneers. This study investigates the relation of thickness reduction (marker of compression) and mass loss (marker of heat treatment intensity) to boards quality. The effect of water and water vapour on the bondings between veneer in boards pressed at 200, 225 and 250ºC is studied. The conclusion is that pressing 5 layers of 2 mm rotary-cut beech veneer parallel-fibered at 225ºC, 5 MPa and 300 s leads to a thickness reduction of 33.4 % and mass loss of 1.23 %; in such boards bondings are not resistant to liquid water but are resistant to vapour after one adsorption-desorption cycle. When pressing at 250ºC, 5 MPa and 300 seconds, the thickness reduction is 50% and the mass loss 4%; in such boards no delamination was observed when soaked in water. Boards pressed at higher temperature show lower hygroscopicity. Their equilibrium moisture content (EMC) ranged between 3.6 and 7%. Based on the results of this study it is hypothesised that the decay resistance of self-bonded boards will increase when increasing the severity of the hot-pressing.

Keywords: self-bonding, thermo-mechanical treatment, mass loss, densification, veneer, beech, dimensional stability

Conference: 17-06-04/08 Ghent, Belgium

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