Abstract
Increasing demand pressures on the fibre supply are forcing manufacturers to explore using new species in plywood. Here we investigated aspen and black alder, alone and in combination with birch faces, and with different veneer thicknesses in plywood production. The aim of this study was to evaluate the effect of different veneer thicknesses, lay-up systems, and hardwood veneer combinations on plywood mechanical properties. Impacts on modulus of rupture (MOR), modulus of elasticity (MOE), glue consumption, and density properties were observed. All process parameters were the same as for pure birch plywood. Not surprisingly, birch plywood had the highest MOR and MOE, followed by aspen and black alder. Aspen had the highest glue consumption and birch the lowest, when applied with a spreader roll, but the common practice of using relatively thick 2.6 mm aspen veneers resulted in the lowest glue consumption per mm of product. The effects of wood species and veneer thickness on MOR, density, and glue consumption were analysed for panel thicknesses from 6.5 to 18 mm to guide manufacturers in choosing their species and construction to optimize cost, MOR and stiffness, weight, and glue consumption. In conclusion, birch gave the best strength properties while aspen gave the best price and weight combination.
Highlights
Plywood is the second highest volume wood panel product in the world [1]
Veneers from three different wood species were used for plywood production: birch (Betula pendula Roth), black alder (Alnus glutinosa L.), and aspen (Populus tremula L.)
Glue consumption followed the pattern of core veneers, where adhesive was applied
Summary
Plywood is the second highest volume wood panel product in the world [1]. In Estonia, timber and wood-based products are one of the biggest contributors to the economy, accounting for 10% of gross domestic product (GDP) and 5% of the workforce. The main wood species utilised by plywood manufacturers in Northern Europe are spruce, pine, and birch. These species have been used for many decades due to the availability and high quality of the wood material. Aspen and black alder are not commonly used in the production of plywood, either as sole-species or mixed-species products In the past, their relatively lower availability and quality compared to birch made their utilisation not feasible. Their relatively lower availability and quality compared to birch made their utilisation not feasible These species have commonly lower density [3], and lower density has been shown to decrease the mechanical properties of wood [4]. These species have lower log prices, and especially for aspen, lower density provides the possibility of lower cost and lower weight products
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