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 to reduce the greenhouse gases emissions from traditional materials and processes, there has been a shift to more environmental friendly alternatives. The conversion of biomass to bioenergy, including biofuels has been considered to contribute to the future of climate change mitigation, although there are concerns about carbon balance from forest utilization. Bioenergy accounts for more than one-third of all energy used in Sweden and biomass has provided about 60% of the fuel for district heating. Apart from heat and electricity supply, the transport sector, with about 30% of global energy use, has a significant role in a sustainable bioenergy system. This review presents the state of the art in the Swedish bioenergy sector based on literature and Swedish Energy Agency’s current statistics. The review also discusses the overall bioenergy production and utilization in different sectors in Sweden. The current potential, challenges, and environmental considerations of bioenergy production are also discussed.

To improve the resistance of wood to biological decay the Maillard reaction between introduced amines and wood cell-wall polymers can be utilised. However, initial studies in wood modification showed almost complete leaching of bicine and tricine from treated wood and the loss of beneficial effects. The objective of this study was to assess whether possible reactions of bicine or tricine with wood could be further enhanced and reaction products stabilised through the addition of glucose and/or citric acid. Thus, Scots pine sapwood specimens were impregnated with tricine or bicine, with or without glucose and citric acid, and then heated to a temperature of 160°C. The dimensional stability, degree of chemical leaching and mechanical properties were assessed. Overall, it was concluded that neither the presence of glucose nor citric acid did appear to enhance the reactivity of tricine or bicine. Anti-swelling efficiency (ASE) of 50% was observed for combined treatments of bicine/tricine and citric acid but the leaching resistance originated mainly from citric acid and glucose, with no indication for the retention of bicine or tricine. The presence of citric acid led to a strongly reduced modulus of rupture. 

In order to meet the needs for the developing bio-based economy, maintaining and expanding the market potential for wood raw materials and wood products in indoor and outdoor construction uses remains a key activity for industries in the biotechnological and forestry sector respectively. A major restraint in this respect is the drastically deviating views and expectations on quality and performance of the material. Such differences can be found between producers and consumers, between architects and engineers, between planners and approval bodies as well as between academia on the one hand and industry and traders on the other hand. The wood protection and wood preservation sector is located exactly within this area of deviating opinions. To overcome the barriers due to different perceptions and therewith strengthen the standing of wood as a desirable building material in the future, new strategies and methods for communication, knowledge transfer and education are needed. Networking and scientific exchange between different disciplines is needed, such as forest science, silviculture, applied forestry, material sciences, wood technology, building technology, architecture and engineering. Consumer demands and preferences, which might serve as limit states to develop service life prediction and performance models, need to consider aesthetical aspects as well as the functionality of timber building assemblies. Finally, teaching students, craftsmen, and salesmen is the key to enhance the acceptance of renewable and carbon-storing products, which are both biodegradable and highly variable in their properties. All these peculiarities require a deeper understanding of their nature and characteristics to improve their purpose-related usage.

The thermal modification of wood is recognized as the most commercialized wood modification process. The treatment of wood at temperatures usually greater than 180 ºC results in a product with some properties enhanced (dimensional stability, durability, aesthetical colour) and some diminished (mechanical properties). The loss of mechanical strength is recognized as a limitation to the use of thermally modified wood in certain products. The mechanical strength reduction is linked in varying degrees to the release of acidic volatile species, the acid-catalysed depolymerisation of the hemicelluloses present and the plasticization and redistribution of the lignin components present. Buffers, although been designed not to influence the reaction systems, may have some interactions when exposed to some conditions, potentially acting as promoters of biological changes on different systems. In this study, two zwitterionic buffers, bicine and tricine, were chosen to be tested regarding their volatilization reduction properties, as well as tricine due to offering the potential of forming Maillard-type products with fragmented hemicelluloses/volatiles. In order to determine if there were any resultant effects of the bicine and tricine treatments submitted or not to thermal modification, the efficacy against subterranean termites was conducted as well as an evaluation of the effect of the different combinations of treatments on the termite gut symbiotic protists. The durability of thermal modified wood is recognized as low and the results of the present work are in accordance with that perception. However, bicine and tricine treatments alone had a clear influence on the survival of the termites and the study of the protist symbionts (9 morphotypes) gave a better insight of the ability of termites to react to unfavorable diet changes.

The majority of thermal modification processes are at temperatures greater than 180 °C, resulting in a product with some properties enhanced and some diminished (e.g., mechanical properties). However, the durability of thermally modified wood to termite attack is recognised as low. Recent attempts at combining thermal modification with chemical modification, either prior to or directly after the thermal process, are promising. Buffers, although not influencing the reaction systems, may interact on exposure to certain conditions, potentially acting as promoters of biological changes. In this study, two zwitterionic buffers, bicine and tricine, chosen for their potential to form Maillard-type products with fragmented hemicelluloses/volatiles, were assessed with and without thermal modification for two wood species (spruce and beech), with subsequent evaluation of their effect against subterranean termites (Reticulitermes grassei Clément) and their symbiotic protists. The effect of the wood treatments on termites and their symbionts was visible after four weeks, especially for spruce treated with tricine and bicine and heat treatment (bicine HT), and for beech treated with bicine and bicine and heat treatment (bicine HT). The chemical behaviour of these substances should be further investigated when in contact with wood and also after heat treatment. This is the first study evaluating the effect of potential Maillard reactions with zwitterionic buffers on subterranean termite symbiotic fauna.

This study determined the impact of undertaking an initial treatment of oak wood by sealing its surface pores with epoxy resin, focusing on the durability of transparent coating systems when exposed outdoors. Throughout the exposure period, various parameters including color, gloss, surface wettability, and both macroscopic and microscopic surface evaluation were continuously monitored. The study involved two sets of samples: one set underwent the pretreatment, while the other did not. Subsequently, four coating systems were applied to the samples, comprising two solvent-based and two water-based coatings. The experiment was conducted over a period of two years, utilizing natural weathering methods within the premises of the Czech University of Life Sciences in Prague. The pretreatment with epoxy resin exhibited enhanced durability for all paint systems. The analysis showed a significant difference in gloss and color after 12 months of weathering exposure without any significant effect on surface wettability and sealing. However, after 24 months of the weathering exposure, no significant differences between the sealed and unsealed surface were observed. The most significant change in properties was noted for the water-based coatings used in coating systems number 3 and 4, and these coatings were rated as the best.

The introduction of new species in forest management must be undertaken with a degree of care, to help prevent the spread of invasive species. However, new species with higher profitability are needed to increase forest products value and the resilience of rural populations. Paulownia tomentosa has an extremely fast growth. The objective and novelty of this work was to study the potential use of young Paulownia trees grown in Portugal by using heat treatment to improve its properties, thereby allowing higher value applications of the wood. The average chemical composition of untreated and heat-treated wood was determined. The extractive content was determined by successive Soxhlet extraction with dichloromethane (DCM), ethanol and water as solvents. The composition of lipophilic extracts was performed by injection in GC-MS with mass detection. Insoluble and soluble lignin, holocellulose and α-cellulose were also determined. Physical (density and water absorption and dimensional stability) and mechanical properties (bending strength and bending stiffness) and termite resistance was also determined. Results showed that extractive content increased in all solvents, lignin and α-cellulose also increased and hemicelluloses decreased. Compounds derived from the thermal degradation of lignin were found in heat-treated wood extractions. Dimensional stability improved but there was a decrease in mechanical properties. Resistance against termites was better for untreated wood than for heat-treated wood, possibly due to the thermal degradation of some toxic extractives.

Life Cycle Assessment has become one of the most recognized and internationally accepted method for examining the environmental performance of forest products and processes. The main aim of this study was to evaluate the potential environmental impact associated with different commercial outputs of maritime pine wood (round, industrial, and residual) produced in the Portuguese forest under natural regeneration. Identifying the hotspots in the life cycle (cradle-to-gate) of each sort of maritime pine was another objective of the study. SimaPro software was used for this study, whilst the CML-IA (baseline) method was chosen to assess the environmental impacts. The study showed that round wood presented the highest values in all impact categories and industrial wood presented the lowest values except in photochemical oxidation where residual wood was the best co-product when economic allocation is chosen. The major hot spots appeared to be the felling and hauling processes due to fossil fuel combustion in the chainsaw and forwarder, respectively. The co-product that should be more environmentally friendly considerably depends on the allocation procedure chosen.

This article deals with the effect of various temperatures of thermal modification and fire retardants on selected burning characteristics and chemical wood components of teak (Tectona grandis L. f.) wood. The thermal modification was carried out at temperatures 160 °C, 180 °C and 210 °C. Subsequently, thermally modified wood was treated by natural (arabinogalactan) and synthetic (ammonium phosphate) fire retardants. The effect of thermal modification as well as fire retardant was detected by burning characteristics such as weight loss, burning rate, maximum burning rate, ratio of the maximum burning rate and time to reach maximum burning rate. The chemical changes caused by the influence of these factors were determined by changing the content of cellulose, hemicelluloses, holocellulose, lignin and extractives. The relationship between burning characteristics and chemical changes in the thermally modified wood was analyzed using Spearman’s correlation. The results showed that the thermal modification of teak wood had a negative effect on its ignition and burning properties. Synthetic fire retardant had the highest retardation effect in all cases. The natural fire retardant caused a better retardation effect on thermally modified wood at temperature 180 and 210 °C. The relative content of lignin, extractives and cellulose increased, while the amount of holocellulose and particularly hemicelluloses decreased.

The objective of this study was to explore an effect of the combined inorganic materials on the wood hardness and flame-retardancy properties in a concept of sustainable material management. Herein, the reinforcement of Scots pine (Pinus sylvestris L.) sapwood with sodium silicate and TiO2 nanoparticles via vacuum-pressure technique is reported. Pyrolysis of modified wood was studied by TG-FTIR analysis; the results showed that maximum weight loss for the modified wood was obtained at 40–50 °C lower temperatures compared to the reference untreated wood. The Gram–Schmidt profiles and spectra extracted at maxima absorption from Gram–Schmidt plots indicated chemical changes in wood–inorganic composites. SEM/EDS analysis revealed the presence of Na–O–Si solid gel within the wood-cell lumen and showed that TiO2 was homogeneously distributed within the amorphous Na–O–Si glass-forming phase to form a thin surface coating. EDS mapping further revealed the higher diffusivity of sodium into the cell wall compared to the silicon compound. The presence of amorphous sodium silicate and nano-TiO2 was additionally confirmed by XRD analysis. FTIR spectra confirmed the chemical changes in Scots pine sapwood induced by alkalization. Brinell hardness test showed that the hardness of the modified wood increased with the highest value (44% increase in hardness) obtained for 10% Na2SiO3–nTiO2 modified wood. The results showed good correlation between TG and flammability test; limiting oxygen index (LOI) values for the wood–inorganic composites increased by 9–14% compared to the untreated wood.

Groynes have been part of the coastal appearance for centuries, helping prevent coastal erosion resulting from the littoral drift of material with prevailing sea currents. Whilst the use of rock groynes increased during the late 20th Century, the use of timber still remains the material of choice. Their performance depends upon the timber species used, and often sections are suitable for re-use. Assessment of the replacement of groyne fields in Bournemouth, United Kingdom appears to show the suitability of certain species to be re-used. Results indicated that ekki was the most suitable species for re-use, closely followed by greenheart.

COST Action FP 1303 (Performance of bio-based building materials) was established in 2013 with the main aim to improve the knowledge on the performance of bio-based materials used as building products and the assessment of factors influencing these, with the aim of increasing their service life. This Action has helped in understanding the interlinked relationships between durability, product aesthetics, fibre-moisture relationships, decay hazards and achieving a better understanding of the biology and mechanisms influencing the growth of fungi and other degrading organisms and the consequent damage in terms of discoloration and decay of wood and bio-based building materials with building design and maintenance. Within this COST Action performance is considered in its manifold meaning, i.e. optical, aesthetical, moisture and functional performance and durability. Numerous studies into the performance of modified wood was presented by researchers during the 4-year duration of the Action, and this paper aims to provide an overview of some of the work presented by the more than 260 scientists that took part in the Action activities.

The use of biobased building materials is an important factor in our modern Built Environment, particularly in meeting global environmental challenges linked to continued urbanization. This increase in use comes at a time when performance expectations continue to rise. This paper will review some of the activities from a recently completed COST Action, FP1303 “Performance of Biobased Building Materials”, with particular emphasis on moisture performance.

Performance of Bio-based Building Materials provides guidance on the use of bio-based building materials (BBBM) with respect to their performance. The book focuses on BBBM currently present on the European market. The state-of-the-art is presented regarding material properties, recommended uses, performance expectancies, testing methodology, and related standards.

Chapters cover both ‘old and traditional’ BBBM since quite a few of them are experiencing a comeback on the market. Promising developments that could become commercial in the near future are presented as well.

The book will be a valuable reference resource for those working in the bio-based materials research community, architects and agencies dealing with sustainable construction, and graduate students in civil engineering.

The effects of thermal modification of wood have been well established, particularly in terms of reductions in mechanical performance. In recent years, there has been an increase in studies related to the Maillard reaction. More commonly associated with food chemistry, it involves the reaction of amines and reducing sugars during cooking procedures. This study has attempted to combine the use of amines and thermal modification, with subsequent properties investigated for the treatment of spruce (Picea abies (L.) H. Karst) and beech (Fagus sylvatica L.). In this initial study, the combined effects of chemical treatments by tricine and bicine were investigated with thermal modification. Along with some preliminary data on mechanical properties, the modifications which appeared in the wood structure were evaluated by infrared spectroscopy and biological studies according to EN113 and EN117 methodologies. The hierarchal study interpretation of FTIR suggested interactions between the bicine or tricine and the wood, which was partly supported by the analysis of volatile organic compounds (VOC), though other tests were not as conclusive. The potential of the method warrants further consideration, which will be described.

The desire to incorporate wood in modern construction has led to a considerable increase in the use of wood modification techniques, and especially thermal modification. However, thermally modified wood has poor performance against termites. The concept of using a combined chemical and thermal modification has been undertaken through the impregnation with either bicine or tricine prior to modification. This paper considers the effects of these chemicals on the activity of termites and considers their mode of action in terms of termite survival and on their effects on the symbiotic protists present within the termite gut. 

The effects of thermal modification have been well established, particularly in terms of reductions in mechanical performance. In recent years, there has been an increase in studies related to the Maillard reaction. More commonly associated with food chemistry, it involves the reaction of amines and reducing sugars during cooking procedures. This paper has attempted to combine the use of amines and thermal modification, with subsequent properties investigated for the treatment of beech (Fagus sylvatica). In this initial study, the combined effects of chemical treatments by tricine and bicine were investigated with thermal modification. Along with some preliminary data on mechanical properties, the modifications which appeared in the wood structure were evaluated by infrared spectroscopy. After the treatment about 6-7 % of WPG was identified in treated samples, but further thermal treatment decreased the WPG to about 5%. The modifications appearing in the spectra were mostly related to increase of the intensities of the bands assigned to C=O groups but also to N-H and C-N groups, with shifting of some bands to higher wavenumber values.

Wood modification (chemical, thermal, impregnation) represents an assortment of innovative processes continually being adopted in the wood protection sector. COST Action FP1407 (Understanding wood modification through an integrated scientific and environmental impact approach - ModWoodLife) was initiated in 2015, with its 4-year programme aiming to investigate modification processing and products design with emphasis on their environmental impacts. As was reported at Timber 2018, a recent task within COST FP1407 was to re-evaluate the current status of wood modification across the member countries, which resulted in a meeting in Florence, Italy, where the national status of wood modifications in 18 different European countries was presented.

However, it became clear that activities in other European countries needed to be addressed, and as a result, a more extensive evaluation of wood modification processes across Europe was undertaken. As a result, it became clear that the original figures quoted at Timber 2018 were considerably lower than actual production levels, which are reported herein. These figures suggest that wood modification is undergoing a significant increase in production due to demand, with levels of recent growth seemingly suggesting this will continue for the coming years.

Wood modification (chemical, thermal, impregnation) represents an assortment of innovative processes continually being adoptedin the wood protection sector. COST Action FP1407 “Understanding wood modification through an integrated scientific andenvironmental impact approach — ModWoodLife” was initiated in 2015, with its 4-year programme aiming to investigate modificationprocessing and products design with emphasis on their environmental impacts. Among the final tasks within COST FP1407 wasto re-evaluate the current status of wood modification across the member countries. However, it became clear that activities in otherEuropean countries needed to be addressed, and as a result, a more extensive evaluation of wood modification processes across Europewas undertaken, as well as determining the activities globally. This paper outlines some of the recent updates in wood modification,along with summarising data collected by the authors from international colleagues and online sources, so providing an evaluationof the overall global position. These figures suggest that wood modification is undergoing a significant increase in production due todemand, with levels of recent growth seemingly suggesting this will continue for the coming years. Based on data gathered, the globalcommercial production of modified wood is dominated by thermal modification processes, which produce 1,110,000 m3/year. Amongthe other commercialised processes, acetylation accounts for 120,000 m3/year and furfurylation 45,000 m3/year. A further globalproduction of around 330,000 m3/year is estimated for other processes, predominantly based on resin-based systems (e.g., Impreg- andCompreg-based processes).

This report is a result of a questionnaire and subsequent collation of data, which outlines the current status of wood modification across Europe in terms of national inventories and groups that have reported current activity in the respective research areas covered in this report.

Wood modification (chemical, thermal, impregnation) represents an assortment of innovative processes currently being adopted in the wood protection sector. Though many aspects of these treatments are known, the fundamental influence of the process on product performance, the environment, and end of life scenarios remain relatively unknown. It is essential to integrate interactive assessment of process parameters, developed product properties, and environmental impacts. To optimise modification processing to minimise environmental impacts, much more information must be gathered about all process related factors affecting the environment (VOC, energy use, end of life use, etc.). To this end, COST Action FP1407 (Understanding wood modification through an integrated scientific and environmental impact approach - ModWoodLife) was initiated in 2015, with its 4-year programme aiming to investigate modification processing and products design with emphasis on their environmental impacts. This will require analysis of the whole value chain, from forest through processing, installation, in service, end of life, second/third life (cascading) and ultimately incineration with energy recovery.A recent task within COST FP1407 was to re-evaluate the current status of wood modification across the member countries, tasks previously undertaken within COST Actions E22 and E37 respectively and reported in several papers within several of the previous European Conferences on Wood Modification (ECWM). Whilst the early projected advances anticipated for various types of modified wood has not been as previously reported. During a COST FP1407 meeting in Florence, Italy, the national status of wood modifications in 18 different European countries was presented, and the findings will be presented herein.

Wood, a fundamental material in construction, confronts durability and weathering challenges, notably UV-induced degradation leading to colour changes. This study investigated a novel treatment using citric acid and urea to enhance the UV stability of wood. The reaction between these compounds generates water-soluble fluorescent species and insoluble particles upon thermal treatment which may provide wood with UV protection. Specimens were treated with two different treatment methods and then exposed to 2016 h of accelerated weathering, during which colour was measured regularly. Citric acid and urea were either pressure impregnated into the wood and thermally reacted in situ during heat treatment or pre-reacted in the absence of wood with subsequent implementation into melamine formaldehyde (MF) and water-based surface coatings. The results showed that water-soluble fluorophore compounds were formed with both treatment methods. Accelerated weathering tests revealed significant colour changes over time, where specimens coated with a mixture of MF and fluorescent particles from the reaction between citric acid and urea, exhibiting the least alteration. The lowest colour change ΔE of 5.9 was observed for specimens coated with a MF-based coating containing 1 wt% of citric acid and urea thermally pre-reacted at a temperature of 180 °C, showcasing potential wood protection applications.

Brown discolouration caused by resin exudation from knots is a problem for a range of light-coloured painted pines, and will negatively affect the appearance of the finish. To solve this problem, a hot-and-cold bath impregnation process of wood prior to painting was tested. Sawn timber, 18 × 120 mm in cross-section dimension, were heated in an oven and then immediately immersed in a cold liquid containing a phenol-formaldehyde-based solution, filling a 1–5 mm thick layer beneath the surface with phenol-formaldehyde. After curing, the timbers were painted with a white coloured coating system intended for exterior use, and tested in artificial weathering test (QUV). The phenol-formaldehyde treatment greatly reduced the discolouration of the coating compared to non-impregnated wood.

Conditions for phosphorylation of softwood kraft lignin was studied. Heating lignin at 150°C with ammonium dihydrogen phosphate water solution in the presence of urea gave a phosphor content in the worked-up product of ca. 2%. The intumescent behaviour during heating could also add to the fire stability of a potential product. In order to use lignin that has been treated with phosphoric acid as fire retardant in wood, acid removal or neutralisation is needed to obtain a final sustainable product. Water washing of phosphoric acid treated lignin led, however, to significant mass losses and a material that under suitable phosphorylation conditions (low temperature and shorter periods) could be efficiently solubilised in alkaline water.

Thermally modified timber (TMT)from Scots pine sapwood similar to Thermo-D quality was impregnated with methacrylate resin by the hot-and-cold method and subsequently cured at elevated temperatures. The results showedthat methacrylate resin could be used to reduce colouring of painted TMT wood during accelerated weathering probably by hindering the migration of extractives. The resin itself did not reduce greying of the unpainted wood. Hardness was only slightly improved by treatment with the resin probably due to a higher density of the material. Formation of blisters occurred but wasreduced by treatment with the resin. Resistance to mould growth by a mixture of Aureobasidium pullulans, Cladosporium cladosporioides, Aspergillus versicolor, Penicillium purpurogenumwas performed by applying EN-15457:2014. Treatment with methacrylic resin hindered the colonisation of the three last mouldfungi.

The reaction of wood with maleic anhydride (MA) and sodium hypophosphite (SHP) has been identified as a viable modification method, with macroscopical properties indicating formation of cross-linking to explain the results. However, the chemical reaction between wood and the modification reagents has not been studied yet. To resolve this, the reaction was studied with solid-state 13C cross-polarization magic-angle-spinning (CP-MAS) and 31P MAS nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) to reveal the formation of bonds between wood components, MA and SHP during the treatments to explain the formation of cross-linking and the possible fixation of phosphorus in wood. XPS, solid state 13C and 31P MAS NMR revealed the maleation of wood in the absence of SHP, whilst its presence led to forming a succinic adduct observed through the C-P bond formation, as evidenced by the loss of the maleate C=C bonds at around 130 ppm and the upfield shift of the peak at 165–175 ppm, which was also significantly smoothed, as well as the increase in a peak at 26 ppm due to the reaction between the maleate group and SHP; however, the C-P-C bond could not be unambiguously rationalized from the obtained data. On the other hand, a resonance line at 16 ppm in 31P MAS NMR and the peaks in the XPS P 2p spectrum suggested the formation of a cross-linked structure at low concentrations of SHP, which was more likely to be phosphonate (C-P-O) than organophosphinic acid (C-P-C). The results herein provide a greater fundamental understanding of the mechanisms involved in the reaction of wood, MA and SHP, providing further scope for improved treatment systems in the future.

The formation of crosslinked bonds between wood constituents is believed to be an effective way to stabilize wood against wet conditions. The possibility to use maleic anhydride (MA) combined with sodium hypophosphite (SHP) as crosslinking agents was studied, using Scots pine sapwood and a model compound. The modified wood showed weight gain and bulking effect after treatment and subsequent Soxhlet extractions, which indicated penetration into the wood cell wall and reaction of the chemicals with the wood constituents. The FTIR spectra confirmed the formation of an ester bond between the wood and MA. Furthermore, a decrease of intensity of band at 1635 cm-1 indicated a reduction of the double bond between carbons in MA after further treatment with SHP, especially at 170 ̊C. Such reactions were studied using monomethyl maleate (MMM) and SHP. The 13C NMR spectra of the reaction product confirmed a reduction of the double bond between carbons. This paper outlines studies undertaken to date, along with outlining aims of ongoing and future work.

Wood has the ability to absorb and desorb moisture, which can affect its dimensional size when in use. Limiting this can provide products with greater shape stability and less stresses on external coatings. One method that has been investigated for achieving this has been through chemical modification. In this work, the dimensional stabilisation imparted to Scots pine sapwood by chemical modification with maleic anhydride (MA) combined with sodium hypophosphite (SHP) was investigated. The influence of concentration of MA, treatment temperature and treatment period on weight percent gain (WPG) and bulking coefficient (BC) during treatment with MA and SHP of wood was studied. Furthermore, dimensional stability was determined by the water soak/oven dry method (wet-dry cycle) through five cycles in order to determine the hydrolytic stability of the ester bond and any potential cross-linking reactions. Wood blocks (20 × 20 × 10 mm) modified with MA combined with SHP exhibited lower weight loss following water soaking than unmodified blocks or MA-treated blocks. Wood blocks modified with MA and SHP showed the best anti-swelling efficiency and minimum wet-volume (water-saturated). However, as the concentration of SHP increased, dimensional stability was diminished without any increase in weight percentage gain after water soaking. When combined with FTIR results, it appeared that the modification with MA and SHP seemed to form cross-linking between wood constituents, though high concentration of SHP did not seem to result in additional cross-linking.

The discoloration of uncoated wood surfaces in both outdoor and indoor use in non-heated spaces has become an increasing problem in European timber constructions due to the use of less toxic substances for protection and also changes in outdoor climate conditions, necessitating the use of protective coatings. To investigate the effect of methyl methacrylic (MMA) resin for the protection of wood from discoloration and mould growth, resin-treated wood surfaces were studied in a laboratory-scale mould test, as well as in an outdoor weathering test. Non-modified Scots pine and Norway spruce were used, and some of the test materials were also thermally modified. The resin suppressed mould growth for the laboratory-scale experiments. The protective effect was considerably reduced for outdoor tests. The MA resin did not effectively prevent the wood from greying from ultraviolet (UV) radiation exposure; there was some protective effect detected on the pine. The Fourier transform infrared (FTIR) spectra of weathered specimens showed a reduction of lignin-associated absorption bands for all treatments, which corresponded to the UV degradation and greying of the wood surface. It is suggested that MMA resin may provide adequate protection against mould growth on wood without direct exposure to rain and sunshine (e.g., attics, basements, etc).

Maleic anhydride (MA) is a cyclic anhydride capable of forming an ester bond with wood constituents, providing enhanced dimensional stability and fungal resistance of wood. However, the weight gain through treatment was lost during wet-dry cycle, which indicates that the ester bonds in maleated wood is susceptible to hydrolysis. This study focuses on improving the stability of the maleated product through the use of sodium hypophosphite. Studies have shown the combined treatment resulted in improved anti-swelling efficiency (ASE), lower weight loss and smaller saturated volumes than untreated or specimens treated with maleic anhydride along. In order to better understand the relationship between the modified wood and water, low-field nuclear magnetic resonance (LFNMR) spectroscopy was used to determine the influence of moisture in wood. The modification process resulted in a weak wood–water interaction using LFNMR, suggesting an increased T₂ relaxation time of capillary water. However, the weak wood–water interaction did not seem to be related to the accessible hydroxyl groups because the modification reaction resulted in a similar number of hydroxyl groups as present in unmodified wood. This finding would appear to agree with the concept of MA modification resulting in the “ring opening” of the anhydride, creating a carboxylic acid group for each hydroxyl group modified within the wood.

In this study, the wood–water interactions in Scots pine sapwood modified with maleic anhydride (MA) and sodium hypophosphite (SHP) was studied in the water-saturated state. The water in wood was studied with low field nuclear magnetic resonance (LFNMR) and the hydrophilicity of cell walls was studied by infrared spectroscopy after deuteration using liquid D₂O. The results of LFNMR showed that the spin–spin relaxation (T₂) time of cell wall water decreased by modification, while T₂ of capillary water increased. Furthermore, the moisture content and the amount of water in cell walls of modified wood were lower than for unmodified samples at the water-saturated state. Although the amount of accessible hydroxyl groups in modified wood did not show any significant difference compared with unmodified wood, the increase in T₂ of capillary water indicates a decreased affinity of the wood cell wall to water. However, for the cell wall water, the physical confinement within the cell walls seemed to overrule the weaker wood–water interactions.

The combination of different wood-modification technologies to obtain improved performance is increasingly receiving attention in research. In this study, Scots pine (Pinus sylvestris) sapwood was impregnated with furfuryl alcohol (FFA) in pure aqueous 20, 40, and 60% solution strength without adding any catalyst. In a second step, the FFA was polymerized while simultaneously performing thermal modification in a closed system at 130, 150, or 180 °C. After leaching and ageing tests, the nine different combinations were tested in use class 4 applications (in contact with or very close to the ground and frequently wet) according to CEN/TS 15083-2 (2005) decay laboratory test. It was noted that even the minimum-intensity combination of 20% FFA at 130 °C resulted in maximum durability class (DC) 1 performance. On the contrary, DC 4 was assigned to thermally modified control samples, even at the maximum intensity of thermal modification. Similarly, for FFA modifications, previous research has suggested that an uptake of 35% solution strength is required to obtain an adequate durability performance in use class 4 applications. High levels of resistance against termites were also noted by corresponding termite lab tests. Moisture studies showed the combined treatments resulted in improved stability and reduced moisture uptakes. Thus, the results obtained by this study revealed synergistic performance effects, which originate from the combined thermo-chemical modification approach, and which were higher than simple accumulation of the individual performance of purely thermally or chemically modified wood. Thus, the presented findings have provided positive implications for industrial applications of thermo-chemical modification techniques and offers an array of new research opportunities.

The sawmill industry generates substantial waste in the form of wood chips, shavings, and sawdust, which can be repurposed to manufacture particleboards. Conventional particleboards rely on formaldehyde-based adhesives, posing health risks due to formaldehyde emissions. Seeking alternatives, this study explored a bio-based adhesive system composed of citric acid and sorbitol (10 wt%) combined with 0–20 wt% fire retardants (imidazolium-based ionic liquid or ammonium dihydrogen phosphate) for particleboards made from residual sawmill processing. The objective was to assess the efficacy of the adhesive system in enhancing fire retardancy, moisture resistance, and mechanical properties of particleboards. Results indicate that incorporating ammonium dihydrogen phosphate significantly improves fire retardancy, evidenced by limiting oxygen index values of 50–78% and a thickness swelling after water immersion of 9.7%. However, with an internal bonding strength of max 0.24 MPa and modulus of rupture of max 4.3 MPa, the bio-based boards fell short of meeting standard requirements. Future research should focus on optimising the general citric acid and sorbitol-based adhesive formulations to overcome this limitation. Achieving sustainability and safety standards in particleboard production remains a critical objective for future research and industry implementation.

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 about 1% of the world’s commercial forest areas, Sweden provides about 10% of the sawnwood, and pulp and paper that is traded on the global market. The Swedish agricultural sector also contributes to biomass availability, not only by production of sustainable food crops, but also by utilizing side streams and underutilized land for biomaterial purposes. To meet the challenges that climate change presents, there has to be a shift to sustainable biomass production and increased interest in promoting a circular bioeconomy. This review presents a systematic assessment on the availability of biomass and its utilization potential in Sweden. The review also focuses on biomass production and trade in the Swedish forest industry. In addition, the environmental impact of biomass utilization is discussed.

The exterior application of fire-retardant (FR) timber necessitates it to have high durability because of the possibility to be exposed to rainfall. In this study, water-leaching resistance of FR wood has been imparted by grafting phosphate and carbamate groups of the water-soluble FR additives ammonium dihydrogen phosphate (ADP)/urea onto the hydroxyl groups of wood polymers via vacuum-pressure impregnation, followed by drying/heating in hot air. A darker and more reddish wood surface was observed after the modification. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state 13C cross-polarization magic-angle-spinning nuclear magnetic resonance (13C CP-MAS NMR), and direct-excitation 31P MAS NMR suggested the formation of C–O–P covalent bonds and urethane chemical bridges. Scanning electron microscopy/energy-dispersive X-ray spectrometry suggested the diffusion of ADP/urea into the cell wall. The gas evolution analyzed by thermogravimetric analysis coupled with quadrupole mass spectrometry revealed a potential grafting reaction mechanism starting with the thermal decomposition of urea. Thermal behavior showed that the FR-modified wood lowered the main decomposition temperature and promoted the formation of char residues at elevated temperatures. The FR activity was preserved even after an extensive water-leaching test, confirmed by the limiting oxygen index (LOI) and cone calorimetry. The reduction of fire hazards was achieved through the increase of the LOI to above 80%, reduction of 30% of the peak heat release rate (pHRR2), reduction of smoke production, and a longer ignition time. The modulus of elasticity of FR-modified wood increased by 40% without significantly decreasing the modulus of rupture.