engleski

Influence of surface pretreatment to bonding quality of thermally modified wood

This paper presents the influence of natural surface ageing in indoor conditions to bonding quality of thermally modified wood for outdoor applications. Two unmodified and thermally modified wood species were used for the experiment: oak and beech. Samples 1000 x 100 x 20 mm (L x T x R) were planed and glued with MUF adhesive 2 hours, 1, 2, 6, 10, and 18 days after planing. Properties of laminated beech and oak beams, namely shear strength, delamination and contact angle were measured in order to detect 1) the suitability of species for laminations and 2) the influence of extended storage time after planing to properties of laminated wood. Generally, both native and thermally modified beech exhibited better results compared to oak and thermally modified oak. Results of the delamination test (total delamination) indicate a time dependence of surface ageing. Both unmodified and thermally modified beech may be successfully laminated at least up to 2 days after planing, whereas neither oak nor thermally modified oak are suitable for lamination process under here presented conditions. Shear strength of glue lines did not show any influence of natural surface ageing. Average shear strength of glue lines (in dry conditions) indicates that both native and thermally modified beech and oak may be successfully laminated no matter the duration of natural surface ageing. However, whereas beech and thermally modified beech samples exhibited almost the same values regardless the duration of surface ageing (~20 N/mm2), there is an obvious difference in shear strength of oak (~15 N/mm2) and thermally modified oak samples (~11 N/mm2). Results of delamination may be related with contact angle measurements which indicated that freshly prepared surface is easier to wet compared to naturally aged surface, but also that contact angle is lowest on beech (50 °, 2 hours after planing) and highest on thermally modified oak surface (~64 °, 2 hours after planing).

bonding, delamination, modified wood, shear strength, surface ageing

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