Increasing environmental awareness and the carbon-storing capability of wood have amplified its relevance as a building material. The demand for high-quality wood species necessitates exploring alternative, underutilized wood sources due to limited forest areas and premium wood volume. Con-sequently, the veneer-based industry is considering lower-value hardwood species like grey alder (Alnus Incania), black alder (Alnus glutinosa), and aspen (Populus tremula) as substitutes for high-quality birch (Betula pendula). Initially less appealing due to their lower density and mechanical prop-erties, these species show promise through densification, which enhances their density, strength, and hardness.
Screws have become increasingly common in plywood applications when it is used as a construction material. However, low-density wood species do not have enough screw withdrawal capacity when used in construction or packaging. The withdrawal capacity of screws is affected by the wood spe-cies. Aytekin et al. (2008) showed that high-density wood species such as oak wood exhibited the highest screw withdrawal resistance, followed by Stone pine (Pinus pinea), black pine (Pinus thun-bergia), and fir (Abies). The withdrawal capacity of wood screws is positively correlated with wood density, as evidenced by Xu, J et al. (2021) study on Japanese larch cross laminated timber, which demonstrated that with a density increment of 0.05 g/cm³, the withdrawal capacity increased by an average of 9.4% . Similarly, it has been reported by Suhaily, S.S et al. (2019), that there is a positive linear relationship between the withdrawal capacity of the screw and the specific gravity.
This study aims to enhance plywood screw withdrawal capacity and surface hardness by densifying low-density wood species and using them in plywood face-veneer layers, or in all layers. The rela-tionship between the wood density, surface hardness, and screw withdrawal capacity of plywood made of low-value species like aspen and black alder is examined.
Keywords: veneer, plywood, densification, density, screws, surface hardness
Authors
Tolgay Akkurt
Laboratory of Wood Technology, Department of Material and Environmental Technology, Tallinn University of Technology, 19086 Tallinn, Estonia
Heikko Kallakas
Laboratory of Wood Technology, Department of Material and Environmental Technology, Tallinn University of Technology, 19086 Tallinn, Estonia
Alexander Scharf
Wood Science and Engineering, Department of Engineering Sci-ences and Mathematics, Luleå University of Technology, 93187 Skellefteå, Sweden
Fred Mühls
Laboratory of Wood Technology, Department of Material and Environmental Technology, Tallinn University of Technology, 19086 Tallinn, Estonia
Anti Rohumaa
Fiber Laboratory, South Eastern Finland University of Applied Sciences, Vipusenkatu 10, FI-57200 Savonlinna, Finland
Jaan Kers
Laboratory of Wood Technology, Department of Material and Environmental Technology, Tallinn University of Technology, 19086 Tallinn, Estonia
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