Environmental and Climate Technologies 2022, vol. 26, no. 1, pp. 1350–1360 https://doi.org/10.2478/rtuect-2022-0102 https://content.sciendo.com 1350 ©2022 Author(s). This is an open access article licensed under the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0). A Review of Bio-Based Adhesives from Primary and Secondary Biomass for Wood Composite Applications Ilze VAMZA 1* , Guntars KRIGERS 2 , Karlis VALTERS 3 1–3 Institute of Energy Systems and Environment, Riga Technical University, Azenes street 12/1, Riga LV-1048, Latvia Abstract – Today there is a great demand in the market of wood-based panels like medium density fibreboard (MDF), plywood and oriented strand board (OSB). These boards provide functionality in various industrial fields from building to furniture production. All are produced from timber and some type of binding resin, the most often used in Europe are phenol formaldehyde (FF), isocyanate (MDI) and melamine urea formaldehyde (MUF). These resins guarantee sturdiness of the material but are toxic to humans and makes recycling of the wood-based panels very difficult. There are attempts of wood-based panels industry to transition away from fossil-based adhesives. Various resins have been developed using lignin and tannin or protein. Soy based adhesive SOYAD™ has already reached the market, other soy protein-based adhesives are integrated into ultra-low formaldehyde emission particle boards like Nu green 2 ® and Transform™. This paper gives an overview on bio-based adhesives that are used or have the potential to be used for wood-based panel production. Keywords – Bioresources; plant-based; polyaddition; polycondensation; polymerization; urea-formaldehyde; wood composites 1. INTRODUCTION Adhesives are required for many fields of engineering, engineered wood products are no exception. Fibres in timber have great load bearing properties, but the strength of these fibres decreases dramatically when applied in any other way than perpendicular to the longitudinal axis [1]. Engineered wood products are created to even out the load bearing properties of timber by disrupting the natural timber structure and binding the biomass back together with adhesives. Wood-based panels (WP) can be used for construction and carpentry applications. The application of WP depends on their characteristics, such as hardness, surface properties, strength and composition. An important property of WP is moisture resistance; greater resistance can be acquired by the right adhesive or coating. One of the most popular WP are: particle boards (PB), fibreboards, oriented strand boards (OSB). Density of the boards ranges from 650 kg m 3 to 1000 kg m 3 [2]. Fibreboards are classified by density – low density fibreboards (LDF) with 400–600 kg/m 3 , medium density fibreboard (MDF) 600–750 kg/m 3 and high-density fibreboard (HDF) with up to 1000 kg/m 3 density [3]. For easier processing and for economic reasons, wood panels are mostly made of softwood. Fibreboards usually use synthetic adhesive such as urea-formaldehyde, melamine-formaldehyde or phenol- formaldehyde [4]. Hardening adhesives are easy to handle with woodworking tools, hence in * Corresponding author. E-mail address: Ilze.Vamza@rtu.lv