Stergios Adamopoulos

• PhD
• Professor at Swedish University of Agricultural Sciences

The disposal of wood waste at facilities for incineration in Sweden is the only applied management practice today. Energy production from biomass has gained attention for its potential to recover energy and reduce greenhouse gas emissions. However, besides being a valuable source for energy generation, wood waste can be effectively recycled into ne...

Birch has long suffered from a lack of active forest management, leading many researchers to use material without a detailed management history. Data collected from three birch ( Betula pendula Roth, B. pubescens Ehrh.) sites in southern Sweden were analyzed using regression analysis to detect any trends or differences in wood properties that could...

Petrochemical-based phenol–formaldehyde (PF) adhesives are widely used in plywood production. To substitute phenol in the synthesis of PF adhesives, lignin can be added due to its structural similarity to phenol. Moreover, micro-fibrillated cellulose (MFC) can further enhance the bond performance, mechanical properties, and toughness of adhesive sy...

This study investigated whether improved downy birch could perform as well as improved silver birch, and whether there was sufficient genetic variation and control for non-destructive testing (NDT) values to include them as selection traits in breeding programs. NDT tools were applied to a 15-year-old downy birch family trial intermixed with improv...

Polystyrene (PS) is a synthetic polymer widely used as a packaging material and in thermal insulation of buildings. At end-of-life, there are not many recycling management options of PS because of the reduced incentive and high cost. PS is non-biodegradable, and consequently, the disposal of this product causes serious health and environmental conc...

In the search for alternative raw materials of agricultural origin and bio-based adhesives for wood panel manufacturing, the influence of production parameters has hardly been investigated. Therefore, this study examined the effect of press temperature on the properties of an oat husk particleboard bonded by a dialdehyde starch-based adhesive of 99...

Two types of geopolymer-bonded boards were produced using initial wetting of lignocellulosic aggregates followed by dry mixing and hot-pressing. Boards were prepared by incorporating large fractions of lignocellulosic material (up to 50 wt%). Geopolymer particleboards (GP) were produced using wood particles whereas geopolymer sandwich boards (GSB)...

Partial liquefaction of residual biomass shows good potential for developing new materials suitable for making bio-based composites. Three-layer particleboards were produced by replacing virgin wood particles with partially liquefied bark (PLB) in the core or surface layers. PLB was prepared by the acid-catalyzed liquefaction of industrial bark res...

Bio-based adhesives have gained considerable attention in the last years as more sustainable and healthier alternatives to the formaldehyde-based adhesives used today in wood-based panel manufacturing. In this study, dialdehyde starch (DAS) with various aldehyde contents was prepared by using sodium metaperiodate as an oxidizing agent. Characteriza...

Cellulosic fibrous mats were impregnated with various water-repellent formulations based on reclaimed polystyrene (5, 10, 15, and 20%), alkyd resin (5%), gum rosin (5%), and paraffin wax (0.5%). The mats were tested for their bursting strength and resistance to bending. They were also subjected to the ring crush test and short-span compression test...

The growing interest in timber construction and using more wood for civil engineering applications has given highlighted importance of developing non-destructive evaluation (NDE) methods for structural health monitoring and quality control of wooden construction. This study, critically reviews the acoustic emission (AE) method and its applications...

The growing demand for wood-based panels for buildings and furniture and the increasing worldwide concern for reducing the pressure on forest resources require alternatives to wood raw materials. The agricultural industry not only can provide raw materials from non-wood plants but also numerous residues and side streams. This review supplies an ove...

This paper presents electrical resistance characteristics of ThermoWood® Thermo-D Norway spruce for wood moisture content measurements below fibre saturation point. Electrical resistance along the grain of small clear wood specimens was measured at various moisture content levels of ~ 4–15% for thermally modified and ~ 5–25% for unmodified spruce....

This study investigated the performance of polyurethane adhesives prepared with various combinations of wheat starch that had been modified by isophorone diisocyanate (MS), two polyol types (1,3-propanediol (PD) and glycerol (Gly)), native wheat starch (NS), and 4,4′-diphenylmethane diisocyanate (pMDI) at a NCO:OH weight ratio of 1:1. Two more adhe...

Rattan cane is an important forest product with economic value. Its anatomical, physical, and biological properties vary with the cane height. This makes it difficult to select the appropriate cane diameter for harvesting. Understanding the material properties of rattan cane with different diameter sizes is important to enhance its utilization and...

This study investigates the effect of thermal modification, ThermoWood Thermo-D treatment versus no treatment , on the embedment properties of Norway spruce timber (Picea abies [L.] Karst.) with dowel-type fasteners. The test specimens were reinforced to prevent splitting of the wood. The influence of density, load direction, test specimen configur...

Machine learning (ML)-based models, decision tree and ANFIS, were used to predict the degree of surface checking and bending properties of 30-month weathered thermally modified timber. The results showed that the investigated initial board properties did not allow accurate predictions of surface checks. ML regression and clustering analysis confirm...

This study reports the fabrication and performance of sustainable polyurethane (PU) films based on wheat starch (native NS, modified MS), bio-polyols (1,3-propanediol PD, glycerol Gly), and polymeric diphenylmethane diisocyanate (pMDI). NS was successfully modified with isophorone diisocyanate, confirmed by Fourier transform infrared spectroscopy (...

Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzed polyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate (pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained from the liquefaction process with a high yield of 99.7%. PU adhesives, namely CLW...

This study investigated the properties and sustainability of cement-bonded composites containing industrial residues such as wood chips, tyre fibres and biomass combustion residues, i.e. bottom ash (BA) and fly ash (FA). The effect of cement-to-raw material (wood/tyre fibre) ratio (C/RM) and the aggregate content (BA and FA) on thermal and mechanic...

This paper presents a novel method of partially liquefying bark sawmilling waste for use in making particleboards. Maritime pine (Pinus pinaster Ait.) bark of different particle sizes (fine, medium, coarse, and mixed) was partially liquefied in the presence of ethylene glycol as a solvent and sulphuric acid as a catalyst at 180°C for 30 minutes. Si...

This study investigated possibilities to predict the presence of internal checks in thermally modified Norway spruce timber after 2.5 years of weathering based on the initial properties of the boards. Machine-learning classification enabled sorting the input parameters based on their relative importance for accurate predictions. The parameters of t...

This study investigated heritability of stem and wood traits to improve Swedish silver birch (Betula pendula Roth.) through breeding. Birch is 12% of Sweden’s forest area but mainly used for low value pulp or firewood. This paper applied non-destructive test (NDT) methods, and estimated traits’ heritability (h²), to help breed birch for high value...

In recent years, there has been a growing interest in many parts of the world for more effective biomass utilization due to legislative and public interest in sustainable development. Whilst much of the effort has been on energy generation from biomass, there is considerable interest on biomass availability and utilization for other end uses. With...

Scots pine sapwood was pretreated with two levels of propanetriol (20% and 40% w/w glycerol), and then subjected to vacuum-heat treatment (VHT) at 180°C and 200°C. The treated samples were examined with respect to their weight and volumetric changes, mechanical properties, colour changes, and dynamic water vapour sorption. The weight of the samples...

Change of relative humidity (RH) in surrounding environment can greatly affect the physical and mechanical properties of wood-based panels. Commercially produced acetylated medium density fiberboard (MDF), Medite Tricoya®, was used in this study to predict strength and stiffness under varying humid conditions by separating samples in parallel (//)...

Understanding the properties of any particular biorefinery or pulping residue lignin is crucial when choosing the right lignin for the right end use. In this paper, three different residual lignin types [supercritical water hydrolysis lignin (SCWH), ammonium lignosulfonate (A-LS), and sodium lignosulfonate (S-LS)] were evaluated for their chemical...

In the continual desire to reduce the environmental footprints of human activities, research efforts to provide cleaner energy is increasingly becoming vital. The effect of climate change on present and future existence, sustainable processes, and utilizations of renewable resources have been active topics within international discourse. In order t...

This study investigates the effect of renewable formulations based on tall oil bio-refinery products on the water vapor sorption and interfiber strength of cellulosic fibers as well as on the properties of high-density fiberboard (HDF) panels. The results obtained for HDF prepared using renewable formulations were compared to the results for HDF ob...

Bark as a sawmilling residue can be used for producing value-added chemicals and materials. This study investigated the use of partially liquefied bark (PLB) for producing particleboard with or without synthetic adhesives. Maritime pine (Pinus pinaster Ait.) bark was partially liquefied in the presence of ethylene glycol and sulfuric acid. Four typ...

The effect of thermal modification (TM) on the chemistry, anatomy and mechanical properties of wood is often investigated using small clear samples. Little is known on the effect of growth-related and processing defects, such as knots and checks, on the bending strength and stiffness of thermally modified timber (TMT). Nine boards of Norway spruce...

Previous studies have shown that thermally modified wood (TMW) performs well in outdoor, above-ground conditions in terms of resistance to wood-decaying fungi. Yet, little is known about the development of defects such as checks and the corresponding mechanical properties of TMW in this condition. This experiment focused on the effect of 30 months...

This study investigated the shear strength of heat-treated solid wood of three species (beech, poplar, and fir) bonded with polyvinyl-acetate (PVA) adhesive reinforced by nanowollastonite (NW). Wood specimens were heat-treated at 165°C and 185°C, and then bonded using PVA reinforced by 5% and 10% of NW. Shear strength tests parallel to the grain of...

An adhesive for particleboards based on natural materials was prepared. Soy flour (38.9 wt%), magnesium oxide (MgO) (2.8 wt%), and a hydrolysate from an agricultural crop (13.9 wt%) were mixed with water and ground in a ball mill at 44% solids. The solubility and interaction of the soy flour proteins and the proteins contained in the plant hydrolys...

The incorporation of recycled papers, paperboards and Tetra Pak as filling materials in brittle matrices presents an interesting approach in the utilization of waste materials for building construction. This paper examines the compressive strength and microstructure of gypsum-bonded wastepaper-based composites. Recycled wastepaper of various types...

Tightening formaldehyde emission limits and the need for more sustainable materials have boosted research towards alternatives to urea-formaldehyde adhesives for wood-based panels. Lignin residues from biorefineries consist of a growing raw material source but lack reactivity. Two crosslinkers were tested for ammonium lignosulfonate (ALS)—bio-based...

Recently, there has been focus on lowering emission levels of wood-based boards. However, the accuracy and correlation between EN 717-1 and ASTM D 6007 chamber methods at emission levels below 0.05 ppm are not well investigated, and information about their correlation to the EN 16516 method is limited. In this paper, the low emission level of inter...

Wheat starch polymer was modified through the unequal reactivity of isocyanate groups in isophorone diisocyanate (IPDI) monomer. Fourier transform infrared spectroscopy (FTIR) and 13 C nuclear magnetic resonance (13 C NMR) confirmed the presence of both urethane and isocyanate functionalities in the modified polymer. Thermal stability and water vap...

This study focuses on manufacturing of medium density fibreboard (MDF) panels bonded with dextrin-based wood adhesive and crosslinked in situ with various weight ratios of synthetic (e.g., polymeric-methane diphenyl-diisocyanate, pMDI) or bio-based (e.g., glyoxal) crosslinkers. The physical and mechanical properties of the panels were evaluated and...

The market share of thermally modified wood (TMW) has increased in Europe during the past few years as an environmentally friendly and durable building product. However, TMW products of today are not permitted for use in structural applications, because the reduction in strength that is caused by thermal treatment cannot be accounted for. The purpo...

Wood modification is a well-known technology to enhance the dimensional stability of wood and the resistance to abiotic and biotic degradation. Impregnation modification of wood with thermosetting resins, such as melamine formaldehyde (MF) or phenol formaldehyde (PF), alters the material properties of wood through formation of a three-dimensional n...

Poly(vinyl alcohol) (PVA) is a water-soluble, semi-ionic and biocompatible polymer with excellent chemical and thermal stability. The chemical crosslinking of PVA membrane improve its stability towards humidity and water. In the present work, PVA nanofibrous membranes were fabricated using roller electrospinning techniques. The prepared membranes w...

This study was conducted to assess the effect of the pulping by‐products crude tall oil (CTO), distilled tall oil (DTO), and tall oil fatty acid (TOFA) on dynamic water vapor sorption behavior, interfiber strength, and thermal stability of cellulosic paper‐sheets. The results were compared against those obtained in cellulose papers treated with the...

In musical instrument making, there is a strong need to find alternatives to the traditional endangered and expensive tropical wood species used today. The present study examined whether different commercial and experimental modified wood materials have the necessary acoustic qualities under different humid conditions (dry, standard and wet) to con...

Pea starch and dextrin polymers were modified through the unequal reactivity of isocyanate groups in isophorone diisocyanate (IPDI) monomer. The presence of both urethane and isocyanate functionalities in starch and dextrin after modification were confirmed by Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C NM...

Thermally modified wood is available through a number of manufacturers in Europe on today’s market for interior and exterior building products. Thermal modification of wood allows for improvement of dimensional stability and durability, but a considerable decrease in strength properties occurs. Despite this loss in strength, thermally modified woo...

The most common formaldehyde control method for wood panels in Europe, the perforator method, measures formaldehyde content, while most of the legal requirements in the world are based on emissions. Chamber methods typically used for emission measurements require too much time to reach steady state for factory quality control. The aim of this study...

Bamboo scrimber is one of the most emerging structural materials for future building applications and it possesses comparable properties to other natural wood-based engineered materials such as glulam, laminated veneer lumber and cross-laminated timber. The goal of this work was to study the decay resistance of bamboo scrimber against white-rot (Tr...

Scots pine sapwood samples were pre-treated with a Lewis acid (AlCl3) and a combination of Lewis and protonic acids (AlCl3 and H2SO4), and were subsequently exposed to respective temperatures of 180 °C and 120 °C for establishing a comparable mass loss with those impregnated with demineralized water and solely thermally modified at 220 °C. Water im...

Dimensional stability of wood-based panels is generally improved with application of suitable additives. Most of these additives, such as paraffin wax, are petroleum-based and with relatively high cost, and therefore, it is desirable to develop low-cost and effective substitutes from renewable resources. This work studied the potential of using a r...

Epoxy resins are mostly pro­duced from pe­tro­leum-based bisphe­nol A and epi­cholorhy­drin. Bisphe­nol A is syn­the­sized from non-re­new­able pe­tro­leum-based phe­nol and ace­tone. Bio­mass de­rived epoxy-based poly­mers (EBPs) are be­com­ing the most promis­ing al­ter­na­tive for pe­tro­leum-based coun­ter­parts, but still these bio­mass-based...

Changes in both formaldehyde legislations and voluntary requirements (e.g. Germany RAL) are currently the driving factors behind research on alternatives to amino-based adhesives; moreover, consumer interest in healthy and sustainable products is increasing in bio-based adhesives. Sources of formaldehyde emissions in wood-based panels as well as di...

The present research deals with a simple dipping method to insert octadecyltrichlorosilane (OTS) into cell walls of spruce wood and to deposit OTS layers on its inner and outer surfaces. Distribution and chemical interactions of OTS with wood polymers has been investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-ED...

The effects of nano-wollastonite (NW) suspension impregnation on the fire-retarding properties of heat-treated solid wood of three species (beech, poplar, fir) were studied. Heat treatment was performed at two temperatures of 180 °C and 200 °C. Impregnation was carried out at a pressure of 3 bars for 30 min. The fire properties included ignition ti...

This study investigates the effect of proton acid pre-treatment and subsequent thermal modification at relatively low temperatures (up to 180 °C) on wood with respect to dimensional stability and water vapour sorption properties. The effects are compared to those of solely thermally-modified wood at higher temperatures (up to 250 °C). Scots pine sa...

This research investigates wood defects, particularly the formation of surface cracks, during the production of thermally modified wood and its exposure to cyclic moisture changes. Boards of Norway spruce and Scots pine originating from different steps within the production of ThermoWood® were collected and wood defects were investigated at macrosc...

The difficulty in predicting the properties and behaviour of paper products produced using heterogeneous raw materials with high percentages of recovered fibres poses restrictions on their efficient and effective use as corrugated packaging materials. This work presents predictive models for the mechanical properties of corrugated base papers (line...

The effects of nano-wollastonite (NW) suspension impregnation on the fire-retarding properties of heat-treated solid wood of three species (beech, poplar, fir) were studied. Heat treatment was performed at two temperatures of 180 °C and 200 °C. Impregnation was carried out at a pressure of 3 bars for 30 min. The fire properties included ignition ti...

The quantitative penetration of three coldset wood adhesives [one-component polyurethane (PU), emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc)] under hydraulic pressure into different types of modified wood was studied using fluorescence microscopy and the results were compared to these of a previous study without pressure on adjacen...

The shear strength of furfurylated, N-methylol melamine (NMM) and thermally modified wood bonded with emulsion polymer isocyanate, polyvinyl acetate (PVAc), and polyurethane (PU) adhesives was examined. Furfurylation and NMM modification of Scots pine had a significant negative effect on the bonding strength with all adhesives irrespective of the t...

Micro-veneers of wood and holocellulose (HC) were modified with the thermosetting resins phenol formaldehyde and melamine formaldehyde. The dynamic water vapour sorption of the modified and untreated veneers was studied in a dynamic vapour sorption apparatus to assess the effects of resin modification. The adsorption of wood and HC as well as the d...

This study investigated the bonding strength development of furfurylated, N-methylol melamine (NMM) modified and thermally treated birch veneers glued with hot curing phenol formaldehyde (PF) adhesive in different pressing (20, 160 s) and open assembly times (20 s, 10 min). For testing, the automated bonding evaluation system ABES was used with 2 N...

The effect of wood moisture content and open assembly time on penetration of polyurethane (PU) adhesive into thermally treated Scots pine (195 and 210°C) was investigated according to effective (EP) and maximum penetration (MP) measurements using fluorescence microscopy. For samples treated at 195°C, a higher EP was noted at 8.6% equilibrium moistu...

This study was conducted to explain the tensile strength loss of wood due to the modification with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and glutaraldehyde (GA). Modified and control wood blocks were macerated to deliberate fibres, and handsheets were produced thereof. The nitrogen content of the fibres indicated that maceration removed...

The experimental production of gypsum-based products (cylindrical samples, solid bricks) using different fractions of wood chips and rubber particles was studied. Recovered rubber and wood materials were mixed with gypsum and water in various proportions to fabricate gypsum-wood and gypsum-rubber cylindrical samples and standard solid bricks with s...

The presented research is about the use of a new type of a functional inorganic additive in particleboards, for the purpose of reducing free formaldehyde releases. One-layered particleboards were prepared in the laboratory by mixing industrial wood particles and urea-formaldehyde resin. Natural, abundantly and cheaply available nano-mesoporous diat...

This study investigated the radial penetration of three conventional cold-set wood adhesives [emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc), one-component polyurethane (PU)] into various degrees of furfurylated and N-methylol melamine-modified (NMM) Scots pine, and heat-treated Scots pine and beech based on measurements of effectiv...

This study reports on the water uptake (WU) and wetting properties of different modified wood materials; furfurylated and N-methylol melamine (NMM) modified Scots pine, and heat-treated (Vacu3 method) Scots pine and beech. All modifications caused a substantial reduction in WU in the longitudinal, tangential and radial directions both after short (...

The main objective of this study was to assess the effect of two amino resins, N-methylol melamine (NMM) and 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), on the intrafiber and interfiber strengths and water absorption of two types of waste paper categories, office paper (OP), and old corrugated containers (OCCs). The tensile strength of indiv...

In this work, the application of a laser drilling technique on fir (Abies borisii regis) and spruce (Picea excelsa) wood and a new approach of improvement the wood permeability is investigated. This technique is focusing on increasing the permeability of wood after surface drilling by a high power laser source. The research was involving the establ...

Fir (Abies borisii regis) and spruce (Picea excelsa) wood specimens, 2 × 2 cm in cross section and 34 cm long, were prepared with true radial and tangential surfaces. All lateral surfaces of the specimens were drilled by laser to a depth of 4 mm (1/5 of specimen thickness) with two drilling patterns (distance between holes 1 × 1 cm and 1 × 2 cm). )...

The modification of wood with methylolated melamine formaldehyde resin belongs to the group of impregnation modifications. In the course of this study, Koto sapwood samples were impregnated with methylolated melamine formaldehyde resin solutions in a full cell vacuum pressure process. The samples were cured at a maximum temperature of 120°C for 24...

Fir and spruce wood specimens, 20 × 20 mm in cross section and 340 mm long, were prepared with true radial and tangential surfaces. All lateral surfaces of the specimens were drilled by laser beams to a depth of 0.4 cm (1/5 of specimen thickness) with two drilling patterns (distance between holes 1 × 1 cm and 1 × 2 cm). After drilling, MOE and MOR...

This study evaluated the decay resistance of ash (Fraxinus excelsior L.), beech (Fagus sylvatica L.), and maple (Acer platanoides L.) wood impregnated by a full cell process with N-methylol melamine (NMM) and combined NMM-metal complex dye (NMM-BS) in aqueous solutions. Basidiomycete decay testing involved incubation with Coniophora puteana (brown...

Corrugated packaging production is currently facing the challenge to ensure a satisfactory strength of packaging despite the continuous increase in recycled paper as the main fibrous component. This research addresses a very common technical problem for the corrugated board industry - the difficulty of predicting the properties of paper products pr...

This study evaluated the combined modification and staining of ash, beech and maple wood with a low molecular weight N-methylol melamine compound (NMM) and a metal-complex dye. Wood samples were treated with aqueous solutions of 10, 20 and 30 wt% NMM and 5 wt% of the dye. The treatment caused the fixation of the water-soluble dye by the NMM resin....