Effect of Log Soaking and the Temperature of Peeling on the Properties of Rotary-Cut Birch (Betula pendula Roth) Veneer Bonded with Phenol-Formaldehyde Adhesive

Abstract

Heating logs prior to peeling positively affects the surface properties of veneer as well as the wood-adhesive bond strength. However, the mechanism behind this increase in strength is not fully understood. The aim of the present study was to separate the influence of soaking temperature and peeling temperature on the physical surface properties and bonding quality. Rotary-cut birch (Betula pendula Roth) logs were soaked at 70 °C, and half of them were subsequently cooled to 20 °C prior to peeling. Surface roughness measurements, scanning electron microscopy (SEM), surface integrity testing, color measurements, and wood-adhesive bond testing were conducted with an automated bonding evaluation system. The results showed that logs soaked at 70 °C and peeled at 20 °C had roughness, color, integrity, bond strength, and wetting properties more similar to logs soaked and peeled at 70 °C than those soaked and peeled at 20 °C. In every test conducted, the effect of soaking temperature was greater than the effect of peeling temperature. Hightemperature soaking not only caused softening of the material during the peeling process, but it also caused irreversible changes in the wood material, which affected the veneer surface characteristics and bond strength development.

Lathe check development and properties: effect of log soaking temperature, compression rate, cutting radius and cutting speed during peeling process of European beech (Fagus sylvatica L.) veneer

“…Generally, at higher temperature during peeling the formation of deep lathe checks will be reduced (Meriluoto 1965;Dupleix et al2013) and the integrity of the veneer will be improved (Rohumaa et al 2016a). The depth of checks and integrity of veneer have been shown to be critical factors affecting the bonding process (Rohumaa et al 2013(Rohumaa et al , 2014(Rohumaa et al , 2016b, but also have effect on veneer based products shape stability and mechanical properties (Blomqvist et al 2014;Pot et al 2015).…”

Influence of Sessile Oak Log Characteristics on the Efficiency in Veneer Cutting

“…Moreover, the economic importance of this wood species is highlighted by the numerous publications that approached problems related to the wood structure and its quality, the specific defects that appeared, the efficiency in veneer cutting, the genetic variations, the genetic control of various characteristics, and the influence of the manufacturing features on the efficiency in veneer (Raczkowska and Fabisiak 1991;Savill et al 1993;Zhang et al 1994;Mosedale et al 1996;Feuillat and Keller 1997;Kremer and Zanetto 1997;Doussot et al 2002;Le Moguédec et al 2002;Mercker and Hopper 2004;Alberto et al 2011;Kruch 2011;Moldovan 2011;Moroşanu 2012;Dumitrascu et al 2013;Musat et al 2016;Rohumaa et al 2016;Denes et al 2017;Pangh and Doosthoseini 2017).…”

Characterisation, Recovery and Activity of Hydrophobic Compounds in Norway Spruce Log Soaking Pit Water: Could they be Used in Wood Preservative Formulations?

“…Log soaking is a standard pre-treatment in the plywood, laminated veneer lumber and veneer industries that facilitates the later debarking of the logs treated. For the bark and the wood beneath to soften, the logs are submerged in warm water for several hours or days, with the temperature varying depending on the wood species and properties [1]. Many factors affect the temperatures used in this process.…”

“…Many factors affect the temperatures used in this process. Nordic countries, such as Finland, use water between 20 and 70 °C, but outdoor conditions [1] and the specific practices performed by each company [2] will cause variations in these temperatures. Some wood and bark constituents, such as saccharides and several extractives [3] including phenolic compounds [4], leach into the water [5].…”