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

Abstract

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—CuSO4·5H2O, ZnCl2, H3BO3 and (NH4)2SO4—commonly used in the past, with the focus on their effect on the quality of wood bonding. The milled surfaces of Norway spruce (Picea abies 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 ZnCl2, by a maximum of 28.2%, but on the contrary, it improved due to other preservatives mainly by using (NH4)2SO4, 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% ZnCl2 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% (NH4)2SO4 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.

Effect of Primary Spruce Lamella Aging on the Bending Characteristics of Glulam Beams

“…PUR glue was applied using coating technology on the interconnected surfaces of spruce lamellas at the recommended rate of 180 g/m 2 ± 10 g/m 2 . The three-layer glulam beams (Figure 2), as well as the double-bonded sets (see figure in [12]), were prepared by pressing spruce lamellas coated with PUR glue. Pressing was performed in steel bolts at a pressure of 1.2 MPa, a temperature of 20 • C ± 2 • C and an RH of 65% ± 5% for 2 h (Figure 2a).…”

“…The final quality of glulam beams is influenced by many factors: (1) the wood species, whether it is used in its natural state or after chemical, thermal, mechanical or biological modifications, and what are its typical structural characteristics and properties, e.g., the density and porosity, the type and amount of extractives, the pH value, roughness, free surface energy, moisture content at bonding, tension and compression strengths, elasticity, and resistance to pests, fire and weathering; (2) the glue type and its physical-chemical characteristics, e.g., the molecular weight, viscosity, surface tension, chemical reactivity, resistance to water and total durability; and (3) the technology of gluing, e.g., the spread rate of glue and its open time and the pressing diagram used [7][8][9][10][11][12][13][14]. The applicability of structural glulam beams depends mainly on their mechanical properties and resistance to biological damage, fire and weathering.…”

“…Finally, the mechanical properties of glulam from thermally modified wood lamellas are usually lowered [48]. In many cases, chemical preservatives-many of which are aggressive chemical substances or such substances can be formed over time in a wet environment-negatively affect the wettability of wood lamellas with polar glues [12] and deteriorate the lignin-saccharide matrix of wood cells in lamellas [39]. So, such chemicals can worsen the adhesion of glues to wood lamellas and/or decrease the strength of wood lamellas and finally degrade the mechanical properties of glulam beams [49].…”

Adhesive Bonding of Scots Pine Wood from the Szczecinek Forest District for the Production of Garden Equipment: An Experimental Investigation

“…Glued laminated wood, suitably protected with biocidal substances, offers Materials 2022, 15, 8994 2 of 13 high functionality and durability. For glued wooden elements exposed to atmospheric conditions, they should be held together with bonding substances that ensure the highest strength against various static and dynamic loads, resistance to the effects of water and temperature, and while it's used to fasten wood to protected surfaces-non-sensitivity to the protection agents [6][7][8]. In the woodworking industry, wood production for gardens is a fairly wide field and is very popular in Poland and Western European countries.…”

“…The results of these studies indicate a varied influence of protection agents on the strength of joints. In most cases, the comparisons show that such substances cause deterioration in the physico-mechanical properties of the wood and the strength and resistance of joints [3,7,[31][32][33][34][35][36][37][38][39]. However, some investigations have found that protection agents do not have an adverse impact on the gluing process and may even allow for a slightly higher strength to be obtained [40,41].…”