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The single exponential kinetics (SEK) and parallel exponential kinetics (PEK) models were fitted to kinetic sorption data of welded and unwelded Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.). Furthermore, diffusion coefficients of water vapour in wood were determined using two different Fickian diffusion solutions. The objective was to identify how well these models could represent the moisture contents of the specimens and to characterize differences between the sorption behaviour of welded and unwelded wood. This knowledge can be used to enhance the moisture resistance of welded wood, develop drying schedules, and improve the quality of timbers. The PEK and SEK models provided the most precise and the second most precise fits to the sorption kinetic data, respectively. The two Fickian models are equivalent when both the infinite series are truncated at n = 10. The Fickian models also exhibited the highest discrepancy with the experimental data. Nevertheless, the Fickian models fit relatively better to the sorption data of the welded wood than to that of the unwelded wood. This behaviour may be due to the rigid and less-swelling structure of the welded bond line., Holzforschung, 77 (7), ISSN:0018-3830, ISSN:1437-434X

Fire-retardant (FR) treated wood-based panels, used commonly in furniture and construction, need to meet stringent fire safety regulations. This study presents a novel treatment for imparting fire resistance to wood composites by applying separate solutions of phytic acid and sodium silicate onto wood particles before the hot pressing at 160 °C. A scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analysis revealed that phytic acid and sodium silicate were uniformly distributed throughout the wood particles, and the formation of silica gel resulted in the aggregation of elemental silicon. Fourier-transform infrared spectroscopy (FTIR) displayed that phytic acid caused the thermal degradation of hemicelluloses, which led to a brownish outer appearance of the FR-treated composites. Fire performance was assessed using both limiting oxygen index (LOI) and a cone calorimeter. These techniques showed a higher LOI value and a significant reduction in heat-release rate (HRR), total heat release (THR), smoke-production rate (SPR), and total smoke production (TSP). In addition, cone calorimeter and thermogravimetric (TGA) analyses consistently showed increased char residue in treated wood composites. Moreover, internal bond strength (IB) and modulus of elasticity (MOE) of the wood composite were not significantly changed compared with those of the untreated composite. Surprisingly, in the FR-treated composite, the 24 h-thickness swelling, and the water uptake were slightly decreased. Consequently, this new treatment has the potential to increase the fire retardancy of wood composites, such as particleboard, without deteriorating the key mechanical properties. Validerad;2023;Nivå 2;2023-05-22 (hanlid);Funder: Slovak Research and Development Agency (APVV-16-0223); VEGA agency (VEGA 1/0678/22); KEGA agency (KEGA 016STU4/2021); Swedish wood industry; OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803) Biobased fire protection of wood panel for exterior conditions by using phosphorylated lignin from wheat straw Advanced research supporting the forestry and woodprocessing sector’s adaptation to global change and the 4th industrial revolution

Engineered wood products (EWPs) are being increasingly used as construction materials. EWPs are currently being made using synthetic adhesives or metal fasteners, which lead to poor recyclability and reusability. Therefore, this review paper focused on emerging adhesive- and metal-free assembling techniques including wood dowels, rotary-dowel welding, wooden nails, and dovetail joining as alternative ways of making prefabricated EWPs. This will contribute towards green construction and optimising the building process to minimise its negative impact on the environment and its inhabitants, while maximising the positive aspects of the finished structure. The respective advantages and shortcomings will be compared with those of equivalent EWPs. In general, the dowel-laminated timber (DLT) provides sufficient load-bearing capacity and even better ductility than EWPs of equivalent size, but its relatively low stiffness under a bending load limits its application as a structural element. Optimised manufacturing parameters such as dowel species, dowel spacing, dowel diameter, dowel insertion angle, dowel shape, etc. could be studied to improve the stiffness. The improved mechanical properties and tight fitting due to set-recovery of densified wood support its use as sustainable alternatives to hardwood dowels in DLT to overcome problems such as the loosening of connections over time and dimensional instability. The rotary welding technology could also enhance the strength and long-term performance of dowel-type joints, but its poor water resistance needs further investigation. The main obstacles to implementing DLT products in the market are missing technical information and design guidelines based on national codes. Validerad;2023;Nivå 2;2023-02-13 (hanlid);Funder: Republic of Slovenia; Slovenian Research Agency ARRS (J4-3087); CT WOOD, Luleå University of Technology

For manufacturers in the wood industry, an important way to make the produc-tion more effective is to automate the process of detecting defects and differentattributes on boards. One important attribute on most boards is heartwood andsapwood. This thesis project was conducted at the company MiCROTEC and aimsto investigate methods to classify heartwood and sapwood on boards. The datasetused in this project consisted of oak boards. In order to increase the amount ofinformation retrieved from the boards, hyperspectral imaging was used instead ofconventional RGB cameras. Based on this data, deep learning models in the form ofU-Net and U-within-U-Net architecture as well as different spectral dimensionalityreduction methods were developed to segment boards in heartwood and sapwood.The performance of these deep learning models was compared to PLS-DA and SVM.PLS-DA has already been used at MiCROTEC and has been used in this work forcomparison as a baseline model.The result of the thesis work showed that a deep learning approach could increasethe F1-Score from 0.730 for the baseline classifier PLS-DA to an F1-Score of 0.918,and that the different spectral reduction methods only had a small impact on theresult. The increase in F1-score was mainly due to an increase in precision, sincethe PLS-DA had a similar recall as the deep learning models.

Wood under thermo-mechanical densification behaves differently depending on the cross-sectional growth ring orientation (GRO) relative to the direction of compression. This influences the degree of cell damage, but also the shape-memory effects occurring when the compression load is released (spring-back) and when the timber is re-moistened (set-recovery). To study how the GRO influences the shape-memory effects, Scots pine specimens were separated into three distinct groups of GRO (Flat, Inclined, Hybrid) and then thermo-mechanically surface-densified. Spring-back and set-recovery were determined by thickness measurements and by digital image correlation. A GRO parallel to the densified surface, resulted in a low spring-back and a high set-recovery which were uniform over the width of the specimen. Specimens with a GRO between 15 and 45° to the densified surface showed high spring-back and low set-recovery, indicating cell-wall damage. Spring-back mainly occurred in the non-plasticised region immediately below the heated surface region and elasto-plastic rolling-shear deformation along individual growth rings occurred. The GRO of softwood subjected to thermo-mechanical densification determines if an applied load results in rolling shear-deformation or radial compression. This in turn determines where in the cross-section and when in the process the cells deform and if this deformation occurs below or above the glass-transition temperature.

Edge-sealing, which involves treating the edges of wood products, improves water resistance. This study investigated the feasibility of edge-sealed cross-laminated timber (CLT) panels to reduce capillary water uptake, thereby resisting mould formation. The water and vapour permeabilities of ten characteristically different single-layer sealant coating systems were systematically determined. Multi-modal assessment leveraged by computed tomography (CT) scanning methodology was used to enhance detection of material characteristics beyond the standard coating permeability assessment. Moisture content was observed to change during the specimens’ absorption and desorption depending on the sealant system applied. The results revealed different characteristics of coatings during the water absorption and desorption stages. Findings from this study were used to develop recommendations regarding the water resistance of coating systems, curing time, susceptibility to mould formation, and industrial applicability. Results suggest that edge-sealed CLT could minimise the risk of mould formation, which can occur at worksites with minimal weather protection. The method developed in this study provides a basis to evaluate new coating systems and determine which use case is the best for a particular coating type. This study also incorporates insights from industry to identify future research orientations, which may pave the way for new designs and assessment techniques. Validerad;2023;Nivå 2;2023-05-29 (joosat);Funder: TräCentrum Norr (TCN), [grant number 239268, 239278]; FORMAS project: Experimental Studies of Capillary Phenomena in Bio-based Materials [grant number 942-2016-64]Licens fulltext: CC BY License

The increasing awareness of sustainability motivates the development of building materials from renewable resources. The requirements of wood-based products with improved durability, for example, enhanced liquid repellence and UV and biological resistance, are still a challenge. Surface modification of wood by a superhydrophobic layer is one approach for counteracting the challenge. In this thesis, wood veneers of untreated and acetylated birch were surface-modified with fluorinated or non-fluorinated silicone nanofilaments in gas phase. Results demonstrated that the fluorine surface-modified birch (F-SMB) samples showed superamphiphobicity, i.e. a surface that repelled water, ethylene glycol and hexadecane with contact angles (CAs) greater than 150° and roll-off angles (ROAs) of less than 10°. Fluorine-free surface-modified birch and acetylated birch (SMB and SMAB) showed superhydrophobicity with static CA greater than 160° towards water and low ROA even for samples prepared with the shortest reaction time of 1 h. The surface-modified wood showed good wetting resistance analyzed by the multicycle Wilhelmy plate method. The SMB showed a lower water uptake than the acetylated wood while the SMAB showed the lowest water uptake, i.e. a pronounced increased water resistance, due to a combined effect of acetylation and surface modification. The silicone nanofilaments were not degraded after UV irradiation. Both the UV-irradiated SMB and SMAB still showed good wetting resistance with high static CAs and low water uptake. The UV-irradiated SMAB showed the lowest water uptake. The SMB and F-SMB showed good mold resistance with mold appearing later or with less intensity than those on the untreated birch due to the improved water resistance. All acetylated birch showed an even better mold resistance since the acetylation reduces the moisture absorption in the wood substance; whereas the surface modifications on acetylated birch played a slightly negative effect due to side effects from the surface modifications. All birch samples showed high blue stain coverage but almost no blue stain fungi were observed on the acetylated birch. The preconditioned and UV-irradiated acetylated wood samples showed good mold resistance as well. However, more outdoor tests need to be performed to further understand the resistance to mold and blue stain fungal growth on acetylated wood. The surface modifications of both untreated and acetylated birch give excellent water repellence and resistance, which shows the potential of such surface-modified wood in outdoor applications. Den ökande medvetenheten om hållbarhet motiverar utvecklingen av byggmaterial från förnybara resurser. Kraven på träbaserade produkter med förbättrad beständighet, till exempel förbättrad vätskeavvisning och UV- och biologisk beständighet, är fortfarande en utmaning. Ytmodifiering av trä med ett superhydrofobt ytskikt är ett sätt att tackla utmaningen. I denna avhandling ytmodifierades träfanér av obehandlad och acetylerad björk med fluorerade eller icke-fluorerade silikon-nanofilament i gasfas. Resultat visade att björkproverna som ytmodifierats med de fluorerade silikon-nanofilamenten (F-SMB) uppvisade superamfifobicitet, alltså ytor som stötte bort vatten, etylenglykol och hexadekan med kontaktvinklar (CA) större än 150° och avrinningsvinkel (ROA) på mindre än 10°. Proverna av björk och acetylerad björk som modifierats med de icke-fluorerade silikon-nanofilamenten (SMB och SMAB) uppvisade superhydrofobicitet med statisk CA större än 160° för vatten och låg ROA även för prover preparerade med den kortaste reaktionstiden på 1 timme. Det ytmodifierade träet uppvisade god vätningsbeständighet, analyserat genom flercykelmätningar med Wilhelmy-metoden. SMB visade ett lägre vattenupptag än det acetylerade träet medan SMAB visade det lägsta vattenupptaget, det vill säga en markant ökad vattenresistens, tack vare en kombinerad effekt av acetylering och ytmodifiering. Silikon-nanofilamenten bröts inte ned efter UV-bestrålning. Både den UV-bestrålade SMB och SMAB visade fortfarande god vätningsbeständighet med höga statiska CA och lågt vattenupptag. Den UV-bestrålade SMAB visade lägst vattenupptagningsförmåga. SMB och F-SMB visade god resistens mot mögelpåväxt som uppträdde senare eller med mindre intensitet än påväxten på den obehandlade björken tack vare den förbättrade vattenavvisningen. All acetylerad björk visade en ännu bättre mögelresistens eftersom acetyleringen minskade fuktupptagningen i träsubstansen; medan ytmodifierad acetylerad björk uppvisade något sämre mögelbeständighet på grund av sidoeffekter från ytmodifieringarna. En kraftig blånad uppstod på alla obehandlade björkprover men nästan ingen blånad observerades på proverna av acetylerad och ytmodifierad acetylerad björk. De förkonditionerade och UV-bestrålade acetylerade träproverna visade också god mögelresistens. Fler utomhustester behöver dock genomföras för att ytterligare förstå resistensen mot mögel- och blånadspåväxt hos acetylerat trä. Ytmodifieringarna av både obehandlad och acetylerad björk ger utmärkt vattenavvisning och motstånd mot vattenupptag, vilket visar potentialen hos sådant ytmodifierat trä i utomhusapplikationer. QC 20230223

In the modern building industry wood as a building material has been looked on as one of the solutions to lower the environmentally impact of the building industry. Building types that normally have been reserved for concrete and steel are today being built with wood as main load bearing component. However, the structural robustness of high-rise wood building has been questioned. The concern relates to wood’s brittle failure-mode and therefore the capacity of wood buildings to withstand catastrophic events where a loadbearing structural part its removed from the construction. To counteract a brittle failure mode in wood and create a ductile failure mode that allows alternative load paths, ductile steel connectors are seen as a solution. With inspiration from the concrete and steel industry, catenary action is brought forward as the most efficient method to create an alternative load path in high-rise wood buildings. To create catenary action, a tube connector that allows excessive deformation with increasing strength was believed to have sufficient capacity. A test method for testing tube connector capacity in a catenary event was developed with a main focus on tube capacity and forces created on the surrounding structure in a catastrophic event. To achieve this, a long stroke reversed 4-point bending test was formed and testing of traditional fasteners and the tube connector was conducted. Test result from catenary capacity testing showed low to no capacity for traditional fastening methods, however, traditional fastening method created arcing action in the beginning of the test cycles. The traditional fasteners showed a consistency in failure mode with arching and wood crushing before connection failure in form of screw withdrawal. Tube connectors had low to no consistency in failure modes, but higher consistency in capacity. Failure mode regarding tubes consisted of steel failure in tube and wood failure in the test specimen. In general, the tubes connector showed promising capacity and ductility to create alternative load paths with the help of catenary action. The project has shown that some design development for the tube connector and lager scale testing are needed to completely understand tube connector capacity and failure mode.

The Old Wood in a New Light database project focuses on the digitization and accessibility of the results of dendrochronological samples analyzed and archived at four Swedish university-based tree-ring laboratories at Lund University, Stockholm University, University of Gothenburg, and the Swedish University of Agricultural Sciences. Collaboration with the Environmental Archaeology Laboratory and Humlab at Umeå University enables long-term open access to data, raw data, and metadata. In this project, we (1) systematically undertake large-scale entry and open access publication of results from wood samples scientifically analyzed and archived by Swedish laboratories and the associated metadata, into the Strategic Environmental Archaeology Database (SEAD; www.sead.se) research data infrastructure, and (2) actively promote the database as a resource for new and ongoing interdisciplinary research initiatives. Including dendrochronological data in SEAD infrastructure allows interdisciplinary studies that combine major scientific and societal questions. Building on a pilot study of construction timber from southern Sweden and adaptation of SEAD digitization workflows, more than 70 000 samples archived at the four dendrochronological laboratories are now being handled in the project. The broad coverage of research networks, stakeholder interaction, and strategic support from the cultural heritage community is guaranteed owing to the ongoing collaboration between laboratories and an established international and multidisciplinary reference group.

Most of the physical, mechanical, and esthetic properties of wood products are affected by the drying of sawn timber. A better understanding of moisture transport in wood during kiln drying is necessary to obtain better quality products, shorter drying schedules, lower energy consumption, and a more sustainable process. Four-dimensional X-ray computed tomography (4DCT) (three-dimensional in space and one in time) with image processing techniques can be used to study the moisture content (MC) of sawn timber during kiln drying. The development of the technique is however made difficult by computational complexity and a lack of accurate experimental validation. In this study, a method relying on 4DCT has been developed using state-of-the-art image processing techniques. The method was validated by a regression analysis of the predicted MC against gravimetric measurements for different timber cross sections and different initial MC distributions on a significantly smaller scale than has previously been investigated. It is concluded that the MC can be estimated with an average uncertainty of ±4.8 percentage points on a 10 mm scale. Sawmills could ultimately benefit from a better understanding of wood-water interactions and dry sawn timber more efficiently.

Dicalcium phosphate dihydrate (CaHPO4·2H2O, DCPD, brushite) crystals were synthesised within Scots pine sapwood via a wet-chemistry route from aqueous solutions of Ca(CH3COO)2 and NH4H2PO4 salts. SEM/EDS analysis was used to assess the saturation of the wood cell lumina and cell wall as well as morphological features and elemental composition of the co-precipitated mineral. Brushite mineral crystallization and crystallite growth within the wood matrix was studied by in situ XRD. The chemical composition of the mineral before and after the dissolution was evaluated using FTIR spectroscopy. The overall impact of brushite on the thermal behaviour of wood was studied by TGA/DSC and TGA/DTA/MS analysis under oxidative and pyrolytic conditions. Bending and compression strength perpendicular and parallel to the fibre directions as well as bending strengths in longitudinal and transverse directions of the mineralised wood were also evaluated. Results indicate the viability of the wet-chemistry processing route for wood reinforcement with crystalline calcium phosphate (CaP)-based minerals, and imply a potential in producing hybrid bio-based materials that could be attractive in the construction sector as an environmentally friendly building material. Validerad;2023;Nivå 2;2023-02-16 (hanlid);Funder: FCT/MEC (PIDDAC) (UIDB/50011/2020,UIDP/50011/2020, LA/P/0006/2020)

This paper investigated the bending moment of chair base joints. The ultimate bending moments (maximum moment), calculated on the base of the measured maximum applied loads (maximum force), were compared for the front leg and rear leg joints of a chair base. The joints had different angles between the stretcher and the leg (joint angle) as well different tenon lengths (30 mm and 32 mm). The results of the tests indicated that for different test specimen configurations but the same tenon-and-mortise geometry, the maximum force of joints with a smaller value of joint angle (front leg joints) was higher than the force values of joints with a larger angle (rear leg joints) for all tenon lengths. However, the results showed less difference among the calculated bending moments of the analysed sets of joints. A significant difference was not revealed between the bending moments of joints with a smaller value of joint angle and the bending moments of joints with a larger angle for all tenon lengths. A significant difference between the bending moments for the tenon length of 30 mm and tenon length of 32 mm was determined for rear leg joints but not for front leg joints. The presented approach of joint strength analysis through the testing of specimens with different shapes and dimensions are applicable to research and practice. U radu je proučavan moment savijanja spojeva na križnoj potkonstrukciji sjedala stolice. Krajnji momenti savijanja (najveći moment), izračunani na temelju izmjerenih najvećih opterećenja (najveća sila), uspoređeni su za spojeve prednjih i stražnjih nogu križne potkonstrukcije sjedala stolice. Spojevi su imali različite kutove između poveznika i noge (kut spoja), kao i različitu duljinu čepova (30 i 32 mm). Rezultati ispitivanja pokazali su da je za različitu konfiguraciju ispitnih uzoraka, ali za istu geometriju čepa i rupe, najveća sila bila veća za spojeve s manjim kutom (spojevi prednjih nogu) nego za spojeve s većim kutom (spojevi stražnjih nogu), i to za čepove obiju duljina. Rezultati su također pokazali manju razliku između izračunanih momenata savijanja analiziranih grupa spojeva. Nije utvrđena značajna razlika momenata savijanja spojeva s manjim i većim kutom za čepove obiju duljina. Značajna razlika između momenata savijanja za čepove dužine 30 i 32 mm utvrđena je za spojeve stražnjih nogu, ali ne i za spojeve prednjih nogu stolice. Prikazani pristup analize čvrstoće spojeva ispitivanjem uzoraka različitih oblika i dimenzija primjenjiv je u istraživanju i u praksi. Validerad;2023;Nivå 2;2023-04-17 (hanlid)

Building with cross laminated timber (CLT) has gain increased interest over the last years, but in common to other wood-based building systems, inadequate low-frequency sound insulation is seen as a problem. This paper deals with two methods to improve the sound insulation of CLT panels, normally made from spruce: 1) heavy CLT, introducing compressed, i.e. densified, spruce as well as alternative wood species, and 2) elastic layer based upon shear motion. In addition to a series of laboratory measurements, a full-scale CLT floor made of two 60 mm birch panels with a 12 mm elastic layer in between was tested in a two-room test mock-up. The results from the acoustical measurements showed that the floor has about 7 dB greater airborne and impact sound insulation for one-third octave bands, 50–3150 Hz, compared to a standard CLT floor of the same total height. Validerad;2023;Nivå 2;2023-02-03 (sofila)

The susceptibility of surface-modified wood, surface-modified acetylated wood and acetylated wood to mold and blue stain fungi was investigated. The surface modifications were based on fluorinated and non-fluorinated silicone nanofilaments for increased hydrophobicity. Results showed an increased mold resistance of the surface-modified superhydrophobic wood with mold appearing later or with less intensity on the modified surfaces than on the untreated wood in accelerated mold chamber tests due to the increased water resistance of the samples. All acetylated wood samples exhibited good mold resistance as the available water in acetylated wood was reduced. The surface modifications on acetylated wood had a slightly negative effect on mold resistance due to side effects from the modification. The surface-modified wood showed high blue stain fungi coverage, whereas almost no blue stain fungi were observed on the acetylated wood and surface-modified acetylated wood. The surface-modified superhydrophobic wood showed high mold coverage after conditioning in a high-humidity environment or after exposure to UV irradiation. Meanwhile, the acetylated wood and surface-modified superhydrophobic acetylated wood showed a small amount of mold coverage in these conditions.

Fast growing hardwoods are one of the major renewable resources available to produce bio-based materials, platform chemicals and biofuels. However, the industrial processing of lignocellulosic biomass is hindered by the complex molecular structure of the cell wall components and their supramolecular organization. This highlights the necessity of improving green processing strategies to enhance biomass conversion to valuable products from industrial wood production species. In the present study, we implemented a hydrothermal step by sequential subcritical water (SW) in aspen wood prior to saccharification and validated the process for trees grown in greenhouse and field conditions. Subcritical water enables extraction of non-cellulosic cell wall polysaccharides in native polymeric form. A major part of the pectic fraction was easily extracted within the first 10 min, while acetylated xylan was enriched in the subsequent extracts after 20- and 30-min rounds. Prolonged extraction (above 60 min) resulted in partial deacetylation and a reduction of the molar mass of xylan. The analysis of the residues enriched with cellulose and lignin showed several micromorphological changes caused by subcritical water treatment, such as an increased porosity, a loosening of the fibre matrix and a decrease in the macrofibrillar dimensions. These morphological and molecular changes in the organization of cell wall polymers after SW treatment significantly enhanced saccharification yields compared to those of non-treated aspen wood chips from both field and greenhouse conditions. Our study demonstrates that SW can be implemented as pretreatment prior to saccharification reducing the requirements for chemical acid pretreatments. This process enables the extraction of native non-cellulosic cell wall polymers for potential material applications and promotes the subsequent biochemical conversion of the residual biomass into fermentable sugars and platform chemicals in future biorefineries.

The surge towards a sustainable future in the construction industry requires the use of bio-based insulation materials as an alternative to conventional ones for improving energy efficiency in structures. In this article, the features of bio-based insulation materials, including their thermal conductivities, moisture buffering value, fire performance, and life cycle evaluations are examined. It is clear from the review that pre- and post-treatment of the bio-based materials used for insulation materials optimize their properties. The life cycle analysis reveals a significant reduction in global warming potential (GWP) compared to conventional foams. In addition, it is envisaged that producing bio-based insulation materials on a larger scale will further decrease the net GWP. The article, therefore, proposes the implementation of policies that will promote the commercialization of bio-based insulation materials. Licens fulltext: CC BY License

Walnut (Juglans regia L.) is widely used in wood furnishings, and machinability is a key factor for improving product quality and enterprise benefits. This work focused on the influence of the rake angle, depth of cut, and cutting speed on the cutting force and machined surface roughness during the straight-tooth milling of walnut. On the basis of the experimental findings, a mathematical model was created using a response surface methodology to determine the relationship between the cutting force and the cutting conditions, as well as the relationship between the surface roughness and the cutting conditions. Variance analysis was used to study the significant contributions of the interactions of various factors and two-level interactions to the cutting force and surface roughness. The optimized combination of milling conditions, resulting in lowest cutting force and surface roughness, was determined to be a rake angle of 5°, a depth of cut of 0.6 mm, and a cutting speed of 45 m/s. Validerad;2023;Nivå 2;2023-01-01 (sofila);Funder: National Natural Science Foundation of China (grant no. 31971594); Natural Science Foundation of the Jiangsu Higher Education Institutions of China (grant no. 21KJB220009); Nanjing Forestry University (grant no. nlzzyq202101); Technology Innovation Alliance of Wood/Bamboo Industry (grant no. TIAWBI2021-08); The Qing Lan Project; International Cooperation Joint Laboratory for Production, Education, Research and Application of Ecological Health Care on Home Furnishing

This work presents a rapid and facile way to access the cell wall of wood with magnetic nanoparticles (NPs), providing insights into a method of wood modification to prepare hybrid bio-based functional materials. Diffusion-driven infiltration into Scots pine (Pinus sylvestris L.) sapwood was achieved using colloidal Fe3O4 nanoparticles. Optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray powder diffraction analyses were used to detect and assess the accessibility of the cell wall to Fe3O4. The structural changes, filling of tracheids (cell lumina), and NP infiltration depth were further evaluated by performing X-ray microcomputed tomography analysis. Fourier transform infrared spectroscopy was used to assess the chemical changes in Scots pine induced by the interaction of the wood with the solvent. The thermal stability of Fe3O4-modified wood was studied by thermogravimetric analysis. Successful infiltration of the Fe3O4 NPs was confirmed by measuring the magnetic properties of cross-sectioned layers of the modified wood. The results indicate the feasibility of creating multiple functionalities that may lead to many future applications, including structural nanomaterials with desirable thermal properties, magnetic devices, and sensors., The work has been supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) in the Project “Utilization of solid inorganic waste from the aquaculture industry as wood reinforcement material for flame retardancy” (Grant No. 2018-01198). Magnetic characterization at G.U. has been supported by the US NSF (ECCS-1933527). The acquisition of a Magnetic Property Measurement System (MPMS3, Quantum Design) at G.U. used here was supported by the US NSF (DMR-1828420). We acknowledge Dr. Agnieszka Ziolkowska at the Umeå Centre for Electron Microscopy (UCEM), Sweden, and the National Microscopy Infrastructure, NMI (VR-RFI 2019-00217) for providing assistance in TEM microscopy.

The aim of this study was to assess selected properties of coatings incorporating nanocellulose, with the potential of being applied as a surface modification for cellulosic and lignocellulosic materials, particularly for applications within biodegradable packaging. Cellulose nanocrystal (CNC) and cellulose nanofibril (CNF) coatings were produced and applied on both sides of pure cellulose samples in the form of filter paper with a Mayer bar. Selected organosilicon compounds, albumin, and the TEMPO reagent were used as additional modifying substances. Coating parameters were determined, such as water contact angle, water absorption, hygroscopicity, and tensile strength. The presence of the coatings resulted in a significant increase in water vapor absorption by the substrate. Nanocellulose coatings proved to be sensitive to the water vapor and showed no barrier properties against it. However, the samples coated with nanocellulose had a noticeably lower tendency to absorb liquid water. The samples coated with modifying substances had a contact angle of ≥90°, proving that such coatings were an additional barrier to the penetration of liquid water. In the case of cellulose material coated with nanocellulose (i.e., without the addition of silane), there was no barrier effect established, thereby allowing full wetting of the substrate. The nanocellulose coatings increased the tensile strength of the samples. This increase was observed for all tested coating variants. The results obtained offer several potential routes to the manufacture of more environmentally friendly coatings and packaging materials. Validerad;2022;Nivå 2;2022-09-21 (joosat);Funder: National Center for Research and Development, III edition of EEA and Norway grants, "Applied Research in the frame of Norway Grants 2014-2021/POLNOR 2019" (NOR POLNOR/CellMat4ever/0063/2019-00); “Advanced research supporting the forestry and wood-processing sector’s adaptation to global change and the 4th industrial revolution”, OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803)

The objective of the work was to improve the leaching resistance of fire-retardant (FR) modified wood by the incorporation of a thermoset resin. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with melamine formaldehyde (MF) resin and hydrophilic FRs guanyl-urea phosphate/boric acid by a vacuum-pressure treatment. Resistance to leaching of FR-modified wood was evaluated, after conducting an accelerated aging test according to European standard EN 84. Inductively coupled plasma analysis showed that the incorporation of MF resin significantly reduced the leachability of FRs. Scanning electron microscopy/energy-dispersive X-ray spectrometry revealed that the mechanism of water resistance was by doping the FRs into MF resin microspheres. Fourier transform infrared spectra showed the chemical functionality changes of FR-modified wood such as the formation of methylene bridges by drying the modified wood specimens. An increase in the thermal stability of FR-modified wood was confirmed by thermal gravimetric analysis. Excellent fire performance of FR-modified wood after leaching was affirmed by the limiting oxygen index and cone calorimeter tests. Validerad;2021;Nivå 2;2021-05-21 (alebob);Finansiär: Slovak Research and Development Agency (APVV-16-0223); Czech Republic’s funding office (CZ.02.1.01/0.0/0.0/16_019/0000803); Swedish wood industry

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 adhesives were also synthesized with NS, PD, or Gly and pMDI blends and served as controls. The thermal behavior of the adhesives before and after the curing process, as well as their rheological performance and lap shear strength, were analyzed. Differential scanning calorimetry (DSC) showed a reduction in curing temperature and heat by adding MS. The thermal stability of the cured adhesives was slightly increased by MS addition. The viscosity of the adhesives that contained MS substantially increased at a linear ascendant ramp of shear, while the controls exhibited relatively low viscosity during the whole shear rate spectrum from 0.1 to 100 s−1. The tensile shear strength of wood veneers was also significantly increased by the incorporation of MS under both dry and wet measuring conditions. The maximum dry shear strength was obtained for the adhesive with Gly polyol and a higher content of MS and was comparable to the control adhesive with pMDI This research was funded by Lantmännen Forskningsstiftelse (Grant No. 2017H011) and Formas, Swedish Research Council for Sustainable Development (Grant No. 2018-00637).

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 performance for different end uses. Thus, the present study was performed on two rattan species, Calamus zollingeri and Calamus ornatus, at two different cane heights (bottom/mature and top/juvenile). Calamus zollingeri was studied at diameter classes of 20 mm and 30 mm, while Calamus ornatus was analyzed at a diameter class of 15 mm. The anatomical properties, basic density, volumetric swelling, dynamic moisture sorption, and biological durability of rattan samples were studied. The results showed that C. zollingeri with a 20 mm diameter exhibited the highest basic density, hydrophobicity, dimensional stability, and durability against mold and white-rot (Trametes versicolor) fungi. As confirmed by anatomical studies, this could be due to the higher vascular bundle frequency and longer thick-walled fibers that led to a denser structure than in the other categories. In addition, the lignin content might have a positive effect on the mass loss of different rattan canes caused by white-rot decay.

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 types of particleboard panels were prepared with a PLB content of 4.7%, 9.1%, 20%, and 33.3%, respectively. Another five types of particleboard panels were manufactured by using similar amounts of PLB and 10 wt.% of melamine&ndash, urea&ndash, formaldehyde (MUF) adhesives. Characterization of bark and solid residues of PLB was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and automated vapor sorption (AVS). Mechanical and physical properties of the particleboard were tested according to the European standards EN 310 for determining modulus of elasticity and bending strength, EN 317 for determining thickness swelling after immersion in water, and EN 319 for determining internal bond strength. The results showed that the increase in PLB content improved the mechanical strength for the non-MUF boards, and the MUF-bonded boards with up to 20% of PLB met the requirements for interior uses in dry conditions according to EN 312. The non-MUF boards containing 33.3% of PLB and the MUF-bonded boards showed comparable thickness swelling and water absorption levels compared to the reference board.

Big quantities of residues and side-streams are generated annually from forest-based and agricultural industries all around the world and present a relatively unexplored renewable resource. Due to the absence of a regularly updated and systematic database of supply, industrial residues and side-streams usually end up in landfill disposal, are used for energy generation, or remain at the production sites. These renewable side-streams are mainly lignocellulosic materials that can be used for fuels, chemicals, and other value-added materials. However, the difficulty in recovering useful components from industrial wastes from a techno-economic point of view is hindering the use of these materials. There are different methods for converting biomass into fuels, chemicals, and materials, including thermochemical, biochemical, and physical conversion. Negative environmental impacts from direct incineration of waste materials and increasing interest in reducing the dependency on fossil-based sources have increased the need for the valorization of the industrial side-streams for material and chemical applications. Among the different thermochemical conversion methods, liquefaction of lignocellulosic materials is an efficient way to convert solid biomass into liquids. Liquefaction including hydrothermal liquefaction (HTL) and moderate acid-catalyzed liquefaction (MACL), is often carried out in an aqueous environment by employing organic solvents with or without catalyst under pressure or ambient conditions. A liquefaction process is influenced by many factors such as material type, solvent, catalyst, time, and temperature. All the parameters of the liquefaction are related to each other, and they affect the yields and the properties of the final products. Studies on the utilization of industrial waste and side-streams as feedstock for liquefaction have increased in recent years, generating significant interest from both academia and industry. This PhD study included a literature review on liquefaction technologies that provide liquefied products for wood adhesives, followed by experimental work on MACL and its optimization for different industrial side-streams, such as wood sawdust, bark, and oat husks. Liquefaction of those materials led to different liquefaction yields (LY) due to their different chemical compositions. When the same liquefaction conditions were applied, liquefied wood sawdust had the highest LY while liquefied bark had the lowest. This was mainly attributed to wood sawdust having a higher cellulose and lower lignin content, when compared to bark and oat husks. After optimizing the liquefaction of wood sawdust, obtained products were applied in wood adhesive formulations successfully. Crude liquefied wood (CLW) and purified liquefied wood (PLW) polyols were obtained from the liquefaction of wood sawdust with the highest LY of 99.7% and used for the synthesis of polyurethane (PU) adhesives by reacting them with polymeric diphenylmethane diisocyanate (pMDI). The bonding strength and penetration to wood adherends of the PU adhesives were affected by the molar ratios between the isocyanate groups (NCO) in pMDI and the hydroxyl groups (OH) in the CLW and PLW. The highest bonding strength of PU adhesives was achieved at an NCO:OH molar ratio of 1.5:1. The thermal stability of the PU adhesives was improved by increasing the NCO:OH molar ratio. PU adhesives based on CLW and PLW with the same adhesive formulation did not show significant differences in their properties while CLW polyol contained more water and alcohols than PLW. A novel method called partial liquefaction of lignocellulosic biomass was also proposed. Partially liquefied bark (PLB) was prepared and used to replace wood particles for producing particleboards (PB) with or without the presence of a commercial synthetic adhesive, i.e. melamine-urea-formaldehyde (MUF). PLB was shown to provide single-layer PBs with good adhesion, mechanical strength, and water repellency. The overall mechanical properties of non-MUF single-layer PBs were inferior to those of MUF-bonded PBs. Increasing the PLB content up to 9.5% led to enhanced mechanical properties for MUF-bonded PBs. PLB prepared from bark with a particle size less than 2 mm ensured good mechanical behavior of single-layer PBs. Moreover, three-layer particleboards prepared from PLB and wood particles had comparable mechanical properties to the reference PBs made solely from wood particles, and PLB had less influence on the mechanical properties of the PBs when used in the surface layer than in the core layer. Formaldehyde emissions from the three-layer PBs were below the limits required by European Standard EN 13986:2004 and major volatile organic compounds (VOCs) were carboxylic acids. This research provided a comprehensive understanding of converting different lignocellulosic materials by a MACL process into valuable polymers and raw materials, which are suitable for the synthesis of wood adhesives and for the manufacturing of particleboards. Due to time constraints related to conducting the PhD, it was not possible to conduct a full characterization of the liquefied products from the selected materials. Such studies should be part of future research in order to supplement our knowledge of MACL mechanisms. Formas project 942-2016-2 (2017-21) - Utilization of renewable biomass and waste materials for production of environmental-friendly, bio-based composites

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. Funder: Northern European network for wood science and engineering (WSE); Advanced research supporting the forestry and wood-processing sector’s adaptation to global change and the 4th industrial revolution, OP RDE, (CZ.02.1.01/0.0/0.0/16_019/0000803)

Funding Information: Funding: M.K. is funded by a postdoctoral researcher grant from the Academy of Finland issued to project CHARFACE. J.D. is funded by the Czech Science Foundation (GACˇ R), Project No. 19-25171Y “Multi-scale Hygro-thermo-mechanical Behavior of Modified Wood-based Materials”. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. A relevant issue with charred exteriors is the inconsistency of the result, which makes service life predictions complicated. Contact charring enables the creation of a very evenly modified surface with accurate control of temperature and modification time, but the weathering properties are questionable. This paper evaluated the effect of the modification time relative to char layer and transition zone thickness, wood species and material density in an artificial weathering test. The results revealed higher color stability in connection to longer modification time, but also an increase in the cracked surface area. Cracking was heavily dependent on the modification regime and increased with increasing char and transition zone thicknesses. Dense spruce had the highest color stability with the most severe modification regime, but char layer thickness varied more than on other wood types. Furthermore, species-dependent cracking patterns affected the final result as the small-scale flaking experienced by birch increased the washing off of char. It is likely an even higher modification temperature with a shorter modification time is needed to produce sufficient weathering resistance suitable for exterior uses.

Swedish tree species of birch (silver: Betula pendula and downy: B. pubescens) are often neglected during forest management activities, resulting in low value logs. This thesis investigated birch stem characteristics and wood properties important for solid wood products, in genetics and management trials in southern Sweden. As well as visual stem size and form measurements, non-destructive testing and evaluation (NDT) tools were used to indirectly estimate wood density (hardness), wood stiffness, and grain angle. The results of this work suggest that for the 19-year-old silver birch and 15-year-old downy birch sites, important solid wood traits were under a reasonable degree of genetic control. It seems possible to breed birch to improve grain angle since heritability and genetic variation was high for this trait. Silver birch genotypes are expected to perform similarly across sites. At a site with both birch species, silver birch was larger with denser wood than downy birch. Few genetic correlations between measurements means selection for one trait will not inadvertently affect another trait. The radial density profiles showed density was continuing to increase. Acoustic velocity (AV) and fibre length were highly correlated, hardness and density were related, and ring width was related to ring density. In a 35-year-old planted Norway spruce stand, naturally regenerated birch AV was not different between treatments (20% or 50% of plot trees were birch by number). However, a correlation was observed between DBH and AV. This older site may reflect common Swedish conditions since planting birch is rare, and likely had more mature birch wood than the genetics trials. Although meeting an immediate need for studies of birch wood properties from managed stands, this work covered few sites. To meet this limitation the tools and techniques applied in this thesis could be used in further studies. The results of this thesis work will be of interest to forest managers who want to breed birch, or select birch stands, for solid wood products. FRAS- Framtidens skogsskötsel i södra Sverige

The products with the highest return and longest life cycle in the sawmill industry are boards and planks. Unfortunately, a large part of the log becomes bi-products during the cutting process. One way to reduce the amount of bi-products in a sawline is to saw with as thin kerfs as possible. That is the cut of the blade. It is made possible by using as thin tools as possible. A thinner tool means using a tool with a thinner construction, which can be more sensitive to forces and vibrations. Thus it is important to know the performance of a bandsaw blade and the wear during a working cycle. This is to optimise how often the blade needs changing, but also to ensure that a blade does not break during the cutting process. This project is about analysing the forces on a tool during a working cycle. Can the already installed measuring systems help predict when a bandsaw blade will lose performance ? Data was extracted from the variable frequency drive connected to the motor driving the bandsaw, when cutting spruce and pine. The experiment was designed to test high and low values for several sawing parameters e.g., tool speed, feed rate, gullet fill ratio and bite per tooth, using bandsaw blades used for eight hours and newly serviced blades. A partial least squares regression model was fitted to the data to explain force per tooth. The linear model shows a similar behaviour in comparison with laboratory experiments. Although the values indicate larger forces, which may be due to various energy losses in the process and the instruments. It is shown that it is possible to explain force per tooth, with a value of determination R2 = 0.84, using bite per tooth, feed rate and gullet fill ratio as explanatory variables. The result of the analysis points at the working cycle of 8 hours being to short to be a significant factor in explaining the forces on a blade. Hence further work would be to design an experiment with a longer working cycle, but also with more extreme values of the sawing parameters.

Comprehensive work is in progress to preserve wood cultural assets in, for example, museums. Numerical simulation, namely finite element method (FEM), is performed to model the impact of climate change to avoid unnecessary damage in the objects. Material parameters for adhesives and coating materials, and mechanical properties along the three main axes (longitudinal, radial and tangential) of wood are then required for the modelling. In the present work, the modulus of elasticity, shear modulus, Poisson’s ratio and ultimate strengths, in the three main directions and in various moisture conditions were experimentally estimated for cherry (Prunus avium L.) and walnut (Juglans regia L.) wood, which are common species used in cultural assets and furniture. Characteristic values for Norway spruce (Picea abies L.) were also listed for comparison. Based on these data, orthotropic elastic deformation bodies were calculated. Furthermore, the sorption behaviour, the swelling and the diffusion resistance (dry and wet cup method) were also determined. Funder: Swiss National Science Foundation (SNF);ISBN för värdpublikation: 978-963-334-446-0

Plastic pollution is one of the most pressing environmental issues in today’s world. Addressing this problem calls for the development of environmentally friendly alternatives that would reduce the amount of persistent plastic waste. Wood-based cellulose is an excellent candidate as a renewable and biodegradable alternative to oil-based plastics in a variety of applications. However, for their widespread adoption, cellulosic materials need to perform comparably to their oil-based counterparts, while simultaneously attaining similarly high processing efficiencies. A major challenge today is to produce high-performance cellulosic materials at industrially feasible rates using scalable methods. This thesis demonstrates that with a fundamental understanding of fiber chemistry and behavior, cellulose fibers can be tuned to develop sustainable material streams and advanced functional materials at high process rates. First, a new stimuli-responsive cellulosic fiber material called self-fibrillating fibers (SFFs) was developed, where the mechanisms governing the swelling of the fiber wall were thoroughly investigated. The knowledge and understanding obtained from these fundamental studies were utilized to prepare pH-responsive filters. Secondly, the preparation of SFF papers and nanopapers using conventional papermaking methods and equipment was demonstrated within the context of rapid transparent paper preparation. It was shown that SFFs can be rapidly dewatered to obtain papers, where the constituting fibers can be nanofibrillated in situ, resulting in strong, transparent and gas barrier nanopapers without sacrificing processing speed. Thirdly, the use of SFFs was extended to functional nanocomposites. A new and scalable materials processing platform for the rapid preparation of functional cellulose hybrids was developed. The stimuli-responsive self-assembly of chemically nanofibrillated SFFs was studied and utilized to prepare nanopapers and hybrid materials. Finally, SFFs were used as bio-based binders in the fabrication of graphitic Li-ion battery electrodes with improved processing and electrochemistry. Taking advantage of their facile nanofibrillation and favorable chemistry, SFFs were nanofibrillated during slurry mixing then blade-coated on copper supports to create strong electrodes with excellent performance. The novel materials and methodologies presented herein combine an aqueous fiber modification strategy with excellent processing properties for the preparation of high-performance cellulosic materials that can compete with oil-based plastics in various applications. Plastföroreningar är en av de mest akuta miljöfrågorna i dagens värld. För att ta itu med problemet krävs en utveckling av miljövänliga alternativ som skulle kunna begränsa mängden icke nedbrytbart plastavfall. I träbaserade, cellulosarika fibrer utgör i detta avseende en utmärkt råvara som kan användas som ett förnyelsebart och biologiskt nedbrytbart alternativ till oljebaserade plaster i en rad olika tillämpningar. Cellulosamaterialen måste naturligtvis ha egenskaper som är i paritet med, eller bättre än, de oljebaserade materialen för att klara konkurrensen och samtidigt ha en konkurrenskraftig tillverkningsekonomi. En stor utmaning idag är därför att producera högpresterande cellulosamaterial med effektiva och skalbara processer. Föreliggande avhandling visar att det mha grundläggande förståelse för fiberkemi och fibrernas fysikaliska beteende under olika kemiska betingelser att det är möjligt att skräddarsy vedbaserade fibrer så att det är möjligt att utveckla hållbara, avancerade funktionella material tom vid höga tillverkningshastigheter. Initialt utvecklades ett stimuli-känsligt cellulosafibermaterial, sk självfibrillerande fibrer (SFFs), som tillåter att fibrerna kan användas i konventionella arkformningsmetoder för att sedan sönderdelas till fibriller i det tillverkade arket som förvandlar det tillverkade arket till en genomskinlig film. Det visade sig att det var möjligt att snabbt avvattna de självfibrillerande fibrerna och mha en pH-höjning var det sedan möjligt attfibrillera de modifierade fibrerna in-situ vilket resulterade i starka, transparenta nanopapper med goda barriäregenskaper. Med hjälp av avancerade karakteriseringsmetoder var det också möjligt att klarlägga de mekanismer som styr fibrillfriläggningen och svällningen hos fiberväggen i de modifierade fibrerna. Denna insikt, om hur de modifierade fibrerna sväller under olika betingelser, användes vidare för att tillverka pH-känsliga filter där avskiljningsförmåga och filtreringshastighet enkelt kan styras med enkla pH justeringar. De skräddarsydda, självfibrillerande fibrerna är naturligtvis mycket lämpade för användning i olika typer av kompositer och i avhandlingen visas hur SFF kan användas i olika typer av nanokompositer där de frilagda fibrillernas utmärkta mekaniska egenskaper kan utnyttjas i kombination med tex oorganiska, anisotropa material för att skapa kompositer med mycket goda barriäregenskaper och tex brandsäkra material. Genom att kombinera SFF med energilagrande aktiverat kol visade det sig också vara möjligt att tillverka batterielektroder för användning i Li-jon batterier där konventionella bindemedel kunde ersättas för att skapa elektroder med bättre egenskaper än det som idag finns i kommersiella Li-jon batterier. Alla dessa exempel visar att det nya SFF-materialet gör det möjligt att använda konventionella arkformningsmetoder för att skapa nya högpresterande material där det är möjligt att bibehålla en rimlig tillverkningshastighet och att framställa komponenter eller slutgiltiga anordningar som har egenskaper som kan konkurrera med högpresterande material som baseras på fossila råvaror. QC 2022-04-06

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. Funder: Advanced research supporting the forestry and wood-processing sector’s adaptation to global change and the 4th industrial revolution, OP RDE, (CZ.02.1.01/0.0/0.0/16_019/0000803)

ISBN för värdpublikation: 978-963-334-446-0

Furfurylated wood has been used widely for exterior purposes due to its superior dimensional stability and biological durability, though its fire resistance is not enhanced. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with a hygroscopic fire-retardant guanyl-urea phosphate (GUP) and furfuryl alcohol (FA) by a vacuum-pressure impregnation followed by curing in elevated temperature. The water-resistance of such treated material was evaluated according to European standard EN 84. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) revealed the penetration of GUP into the cell wall. The hydrophobic FA polymerised in-situ within the wood structure, and this enhanced the water-resistance of GUP. Fourier-transform infrared spectroscopy (FTIR) showed that the chemical functionalities changed such as formation of methylene bridges attributed to the polymerised FA and ketone groups attributed to GUP. Thermal gravimetric analysis (TGA) showed that GUP enhanced thermal stability at elevated temperature by promoting char formation. Fire stability test examined by limiting oxygen index (LOI) showed the improvement of fire-retardancy by the incorporation of GUP. Mechanical properties examined by Brinell hardness and three-point bending test indicated that GUP has a low impact on the properties of surface hardness, modulus of elasticity (MOE) and modulus of rupture (MOR) of the furfurylated wood. The work suggests that GUP/FA treatment has the prospective to impart substantial fire-retardancy to the furfurylated wood with small reduction in other properties, thus increasing the potential for exterior applications.

Guanyl-urea phosphate (GUP) was introduced into furfurylated wood in order to improve fire retardancy. Modified wood was produced via vacuum-pressure impregnation of the GUP–furfuryl alcohol (FA) aqueous solution, which was then polymerized at elevated temperature. The water leaching resistance of the treated wood was tested according to European standard EN 84, while the leached water was analyzed using ultra-performance liquid chromatography (UPLC) and inductively coupled plasma–sector field mass spectrometry (ICP-SFMS). This new type of furfurylated wood was further characterized in the laboratory by evaluating its morphology and elemental composition using optical microscopy and electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX). The chemical functionality was detected using infrared spectroscopy (FTIR), and the fire resistance was tested using cone calorimetry. The dimensional stability was evaluated in wet–dry soaking cycle tests, along with the mechanical properties, such as the Brinell hardness and bending strength. The fire retardancy of the modified furfurylated wood indicated that the flammability of wood can be depressed to some extent by introducing GUP. This was reflected in an observed reduction in heat release rate (HRR2) from 454.8 to 264.9 kW/m2, without a reduction in the material properties. In addition, this leaching-resistant furfurylated wood exhibited higher fire retardancy compared to conventional furfurylated wood. A potential method for producing fire-retardant treated furfurylated wood stable to water exposure has been suggested. Validerad;2022;Nivå 2;2022-05-02 (hanlid);Funder: CT WOOD, Luleå University of Technology; European Structural and Investment Fund, OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803);Part of special issue: Performance and Application of Novel Biocomposites II Advanced Research Supporting the Forestry and Wood Processing Sector’s Adaptation to Global Change and the 4th Industrial Revolution

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. Godkänd;2022;Nivå 0;2022-03-29 (sofila);Konferensartikel i tidskrift;Funder: Portuguese Foundation for Science and Technology (SFRH/BD/84920/2012); COST Action FP1407 ConstBio

The densification, i.e., transverse compression of solid wood can lead to improvements in the mechanical properties, and this can expand the areas of application for low-density wood species. For the past one hundred years, many efforts have been made to mass-produce densified wood products, but despite being available on the market, they remain niche products with low annual production volumes. One of the main reasons for this is that all available densified wood products are produced in a batch-type process, which limits the achievable process speed and integration into the continuous wood processing chain. For this reason, we propose a continuous surface densification process using a bespoke belt press – similar in principle to those used to produce MDF panels. The belt-press is capable of densifying full-sized wood boards at processing speeds of up to 60 m min-1. The primary belt for densification can be heated to temperatures above 160°C, while a subsequent belt functions as a cooling stage. During the densification process, the belt press can log the pressing forces, moments, and temperature. Preliminary tests with Scots pine specimens of 120 mm in width and 38 mm in thickness resulted in a twofold increase in peak density, after a pressing time of two minutes at 120°C. The resulting density profiles were similar to those obtained in studies using a static hot press. As the belt press can be fed with a continuous stream of boards, it has a higher net throughput than a static hot press. Further studies continue with the aim to evaluate different aspects relevant to the large-scale industrial production of densified wood products. Funder: Luleå University of Technology, CT Wood

Funder: Republic of Slovenia; Slovenian Research Agency ARRS (J4-3087); CT WOOD

Engineered wood products of today's construction industry require predictable mechanical properties of the used structural timber. At sawmills, automated strength grading is used to assess the stiffness and strength of sawn and dried timber boards. This process can be based on various technologies, e.g. surface scanning, dynamic excitation, flat-wise bending, which are used to derive so-called indicating properties, i.e. simplified numerical values. Heuristically derived statistical models can then be used to predict the stiffness and strength based on indicating properties. However, statistical strength grading can only exploit a small fraction of the potential strength of a single board, since it assesses the properties of a board in relation to its population. A growing number of sawmills in Sweden use computed tomography (CT) scanners to assess the incoming logs to optimise their positioning prior to sawing. CT scans provide high-quality data of the cross-sectional density distribution along the length of a log, which could also be used to derive continuum mechanical models of the yet unsawn boards and with that assess their mechanical properties. If the stiffness and strength of a virtual board can be predicted before it is sawn, then it could be pre-classified into a strength class or its specific use as a specific construction part could be predetermined already at the log stage, which would lead to a more efficient material usage. Additionally, the predictive power of the existing statistical strength grading processes could be improved for the final boards. The goals of this study were to i) derive 3D quasi-continuum and finite element (FE) models of CT scanned timber boards using different material laws for local stiffness based on measured density and ii) compare their capabilities for predicting stiffness and strength of the boards. The experimental material consisted of dried softwood boards (12% moisture content) of nominal cross-sectional dimensions 50x100mm with different lengths, scanned with a medical high-resolution CT scanner. The boards underwent an eigenfrequency measurement by dynamic excitation and were tested until failure in a four-point bending test, where both the local and global displacement were recorded. A previously developed algorithm was used to derive 3D quasi-continuum reconstructions from the CT scans and subsequently finite element (FE) models. The algorithm reconstructed the board geometry, pith, knots and local fibre directions (material coordinate system) on a volume grid of material points spaced 0.68mm apart. The stiffness tensor in each material point was made locally dependent on the measured density by different mathematical laws, e.g. constant, linear or power laws. Furthermore, material laws which scaled the stiffness tensor based on the ratio between the simulated and measured eigenfrequency were tested for comparison. The bending stiffness profile was calculated for each board along its length and different indicating properties for predicting stiffness and strength were derived and compared with respect to the experimental results. With the FE model, strain distributions in the cross-sections were studied and local stress states around the experimentally observed points of initial failure were investigated to determine whether similar dominant failure stress states existed among boards. The results showed high coefficients of determination between predicted stiffness and strength for material laws based on power laws and low values for linear laws. Nevertheless, the four-point bending tests only provided point-wise data (mid points) that could be used to validate the numerical model. It is therefore recommended to use field-based evaluations in the future, e.g. the surface strain obtained with DIC under four-point testing. ReadIStrength

A procedure is presented to generate 3D FE models of timber boards based on CT scans. Theboards were tested in four-point bending tests until failure and the local displacement in the pure bendingzone was recorded. The CT scans were treated as 3D images and image processing methods were usedto reconstruct the board, the knots and the pith. A new procedure to reconstruct the fibre deviationsaround knots by accounting for image gradient information was used. A quadratic tetrahedral mesh wasgenerated for the region of the board which was under pure bending in the tests. The fibre directions andthe stiffness tensor, scaled by the local density, were transferred into each integration point of the meshand the bending test was replicated. Preliminary results show that the procedure is able to realisticallypredict the observed local stiffness of the boards. Further development of the procedure is required toaccount for dead knots and to extend the procedure for indicating strength and predicting failure. ReadiStrength

ISBN för värdpublikation: 978-952-94-4383-3

An increasing number of multi-storey buildings are being constructed with engineered wood products, such as glulam or cross-laminated timber (CLT). Multi-storey timber buildings can be safely designed for foreseeable loads, but knowledge is limited concerning their ability to survive unforeseeable events, e.g. accidents, natural disasters or terrorism. Multi-storey buildings with many occupants are required to be able to resist a disproportionate collapse due to an unexpected event. Collapse resistance consists of three lines of defence: I) decreasing the probability of the event, II) decreasing the structural vulnerability and III) increasing the structural robustness. The focus of the present thesis is on defence lines II and III, since they can be affected by engineering considerations. Robustness requires the availability of alternative load paths (ALPs) after an initial structural damage, e.g. the removal of an element. The activation of an ALP, e.g. catenary action, usually happens as the result of a larger displacement than that for which the components are designed, and with the participation of the surrounding structure. Physical tests of removal scenarios are expensive and they are often unable to represent realistic building situations. Numerical models can replace physical tests, e.g. by introducing parameter variations or changed boundary conditions, and can deliver an insight into the underlying mechanisms. Vulnerability depends on the ability of individual components of the structure to withstand loads greater than their intended design loads. To reduce vulnerability, so-called key elements can be be made overly strong. If the uncertainty concerning the material properties is high, e.g. for timber, both nominally stronger and larger amounts of material are required, resulting in inefficient material utilisation. Automated strength grading of sawn timber can narrow the uncertainty, but, even with the current technologies, the variations in the graded material remain large. The predictive power of computerised models for sawn timber offers a great potential for integration with traditional strength grading based on testing combined with statistical models. So far, surface data of sawn timber has been used for numerical models, but X-ray computed tomography (CT) scanning equipment now being installed in sawmills has made it possible to measure the inner structure of logs. Using CT data could make it possible to develop high-fidelity numerical models for predicting the mechanical properties of sawn timber, possibly even before sawing, and this could reduce the uncertainty for structural components and enable the production of high-strength timber. However, attempts to develop CT-based models for timber have been scarce. The objective of the work presented herein was to advance the research front regarding the prevention of disproportionate collapse in multi-storey timber buildings. The work has focused on numerical modelling aspects and on subsystems and components, rather than on entire buildings. The goals were: 1) to describe the state of the art regarding the prevention of disproportionate collapse and its application in timber buildings, 2) to develop models to identify and quantify the ALPs in subsystems and components of CLT buildings, and 3) to develop models of sawn timber based on X-ray CT scanning data, to reduce the uncertainty regarding the mechanical properties of the timber. For goal 1, the literature was reviewed and a survey was conducted among practitioners and researchers in the field. The results provided an extensive overview of the topic and the status quo in the industry, and identified a scarcity of guidelines for multi-storey CLT buildings. For goal 2, non-linear finite element (FE) models were developed for quasi-static pushdown analyses. A study of a platform joint first validated some modelling assumptions. The ALPs in single storeys in a corner bay of an 8-storey CLT building were then studied after the removal of bottom-storey walls. In subsequent parameter variations, the full bay was studied in dynamic analyses. The results identified six different ALPs, which were dependent on the connection capacities and the shear capacity of the floor panels, and indicated that collapse was likely after a double wall removal, but unlikely after a single wall removal. Furthermore, the ALPs in a platform-type CLT floor system were studied in parameter variations of calibrated FE models. The results showed how three different ALPs can develop, depending on the storey, the floor geometry and the connectors. For goal 3, a method was developed for the generation of continuum and FE models from CT scanning data of sawn timber, in which the knots, pith and local fibre orientations were reconstructed. The models gave realistic impressions and they could predict the bending stiffness, strength and initial failure location for Norway spruce sawn timber. The predictions improved, if the eigenfrequency of the sawn timber was also considered for modelling.

ISBN för värdpublikation: 978-609-02-1762-7

ISBN för värdpublikation: 978-609-02-1762-7

Abstract Wood is an increasingly important material in the sustainable transition of societies worldwide. The performance of wood in structures is intimately tied to the presence of moisture in the material, which directly affects important characteristics such as dimensions and mechanical properties, and indirectly its susceptibility to fungal decomposition. By chemical modification, the durability of wood in outdoor environments can be improved by reducing the amount of moisture present. In this study, we refined a well-known chemical modification with acetic anhydride and showed how the spatial distribution of the modification of Norway spruce (Picea abies (L.) Karst.) could be controlled with the aim of altering the wood-water interactions differently in different parts of the wood structure. By controlling the reaction conditions of the acetylation it was possible to acetylate only the cell wall-lumen interface, or uniformly modify the whole cell wall to different degrees. The spatial distribution of the acetylation was visualised by confocal Raman microspectroscopy. The results showed that by this targeted acetylation procedure it was possible to independently alter the wood-water interactions in and outside of cell walls. The cell wall-lumen interface modification altered the interaction between the wood and the water in cell lumina without affecting the interaction with water in cell walls while the uniform modification affected both. This opens up a novel path for studying wood-water interactions in very moist environments and how moisture distribution within the wood affects its susceptibility towards fungal decomposition. Graphic abstract

The objective of the work presented in this doctoral thesis has been to correlate the commercial output of ThermoWood® process with a pre-defined, quantifiable, non-destructive measurable parameter - colour, and to show the feasibility of measurements to be the essential part of the internal and external quality-control system. Colour is the most evident property changed of thermally-modified timber (TMT). Colour can be thought of as describing the intensity of the process and as such is a sign of repeatability when working with same treatment methodology and materials. Intensity is usually related to the temperature and time, but elements like water or moisture, steam and pressure present on their own or when combined, have their own influence on the final properties of wood. There are several processes using these above-mentioned components as a modification method for wood. In addition, processes using oil as a heat-transferring element are included in this same modification category. Some of the methods are closely interrelated, with only subtle differences noted. Most of these methods are patented, introduced and processed in Europe, but the market and potential increase for these methods is worldwide. TMT is a new product, with a relatively short industrial scale history (approx. 25 years). During this time huge technical improvements have been made. Processes that are computer aided, remote controlled, and containing recordable systems have replaced the traditional manual processes. Building materials and technical parts regarding air circulation, ventilation, heating and measuring technology with much better thermal endurance has been introduced. All these, combined with several variety of wood species becoming commercially available, have set the frames for a successful enabling of the technology. TMT dominates modified wood. Nevertheless, it is only fraction of treated wood available when looking at preservative treated wood produced globally. Respective comparisons between thermally-modification processes ThermoWood® and WTT® have been undertaken. Due to different treatment atmospheres and wood moisture content, significant chemical changes of water-soluble compounds and degradation products, colour, acidity and strength properties were reported. All the material used in these studies was based on typical dimensions and lengths and they were industrially produced. There were several options for ThermoWood® sources, because the products are classified, and processes are certified. WTT® treatment process was lately presented and the initial experience and knowledge about process was minor. As a consequence. some unexpected reactions and observations were experienced. ThermoWood® represents the major part of TMT commercially produced in Europe. It has two treatment classes Thermo-D and Thermo-S, where the D describes “durability” and S “stability”, respectively. Thermo-D products are usually exposed to external applications and wood species such as Norway spruce and Scots pine are used. Most of the ThermoWood® producers have been audited by certification body since 2006. At present there are several producers from Finland, Iran, Latvia, Poland, Sweden, Turkey and latest Canada which are under continuous control system and certified. New treatment kilns have been supplied to several new countries and as a consequence more potential customers are expected to apply membership and certification. The importance of required treatment parameters in each class, repeatability and internal quality control is highlighted. Non-destructive colour measurements (CIELab) system from wood surface has been applied as one quality control method and extensive colour data has been collected during external audits and even much more in continuous internal quality control. Colour measurements have been entrenched as a daily routine in the production plants. Much of this data has been used in this study and a correlation between L* and b* has been observed in both treatment classes. There have not been a lot of studies published dealing with Norway spruce and Scots pine colour measurements, produced with a dry process under superheated steam, but all the studies found regarding these two wood species suggested that colour might be a reliable quality control tool and the studies done in this thesis strengthened this opinion.