One of the highest growth rates in demand among wood-based materials is projected for plywood until the year 2050 (Held et al., 2022). The projected increase is 102 % compared to 2020. Due to the trade restrictions resulting from the Ukraine War, significantly lower quantities of wood-based products are currently being supplied to the market (Bösch, 2022). The availability of plywood in global markets is affected by such trade restrictions as well as general raw material scarcity and the development of supply and demand for plywood is becoming increasingly in conflict. To sustainably meet the increasing demand for plywood, novel solutions must be developed for both the utilized hardwood species and adhesives. One approach is to expand the range of wood species used and the intensified utilization of renewable resources, such as lignin, in the production of adhesives. Lignin is extracted in large quantities as a natural resource through industrial processes, but its material utilization remains limited so far (Yoo and Ragauskas, 2021). The substitution of silver birch (Betula pendula) with alternative hardwood species and its consequent impact on the mechanical-technological properties of plywood have been previously discussed (Kallakas 2020, Akkurt 2022). In these studies, researchers utilized an aqueous phenol-formaldehyde adhesive to produce plywood. Currently, there is a lack of knowledge about the suitability of lignin-phenolic adhesives for application with hardwood species other than silver birch. Investigations regarding the suitability of lignin-phenolic adhesives with a lignin content of 50 % for other hardwood species have been conducted only to a limited extent, specifically with European beech (Fagus sylvatica) and okoumé (Aucoumea klaineana). The present work contributes to closing this knowledge gap by investigating the suitability of such an adhesive for bonding lay-ups of silver birch, black alder (Alnus glutinosa), lime (Tilia spp.), and black locust (Robinia pseudoacacia). Based on the mechanical-technological properties of the plywood produced, wood species-specific adaptation requirements for the adhesive can be determined and formulated. In the production of plywood, the term “lignin-phenolic adhesive” denotes a liquid condensation product of phenol, lignin, and formaldehyde, used in conjunction with a hardener. In the utilized product, 50 % of petroleum-based phenol is replaced by lignin (Prefere, 2015).
Keywords: plywood, hardwood, lignin-phenolic adhesive, sustainable substitution
Authors
Marcus Cordier
Gerorg-August-University of Goettingen, Wood Biology and Wood Products, Germany
Peter Meinlschmidt
Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institute WKI, Technology for Wood Research and Natural Fiber-Based Materials, Riedenkamp 3; 38108 Braunschweig Germany
Carsten Mai
Gerorg-August-University of Goettingen, Wood Biology and Wood Products, Germany
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