The Effect of Inorganic Preservatives in the Norway Spruce Wood on Its Wettability and Adhesion with PUR Glue

oleh: Dávid Ciglian, Ladislav Reinprecht

Format: Article
Diterbitkan: MDPI AG 2022-06-01

Deskripsi

Recycled recovered wood, for example, from historic buildings, containing biocides, fire retardants or anti-weather paints is an attractive material for manufacturing composite wood panels which can be used for decoration as well as load-bearing walls with a typical patina. This paper investigates the effect of four inorganic wood preservatives—CuSO<sub>4</sub>·5H<sub>2</sub>O, ZnCl<sub>2</sub>, H<sub>3</sub>BO<sub>3</sub> and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>—commonly used in the past, with the focus on their effect on the quality of wood bonding. The milled surfaces of Norway spruce (<i>Picea abies</i> Karst L.) wood were treated with 0.5, 1 and 2% aqueous solutions of these preservatives. The effect of preservatives in spruce wood was evaluated: (1) by its wettability with the drops of redistilled water, measuring the contact angles; (2) by the shear strength of the “spruce wood—polyurethane (PUR) Kestopur 1030 glue” interphases according to the standard EN 205; (3) by microscopic analysis of the “wood—PUR” interphases. The wettability of spruce wood worsened when using ZnCl<sub>2</sub>, by a maximum of 28.2%, but on the contrary, it improved due to other preservatives mainly by using (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, at a maximum of 22.9%. In general, the shear strength of glued joints “wood—PUR” continually decreased with higher concentrations of all the preservatives. The most significant decrease of adhesion “wood—PUR”, by 19.8% from 10.66 MPa to 8.55 MPa, was caused by 2% ZnCl<sub>2</sub> used for the treatment of both spruce wood specimens in interphase with the PUR glue. On the contrary, the less significant decrease of adhesion “wood—PUR”, by 2.5%, was caused by 0.5% (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> applied only on one surface of the two inter-bonded spruce wood specimens. The effects of preservatives on the wood wettability and its adhesion with PUR glue were partly confirmed by microscopic analysis.