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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. Validerad;2023;Nivå 2;2023-04-21 (joosat);Funder: OP RDE (Grant no.CZ.02.1.01/0.0/0.0/16_019/0000803); CT WOOD, Luleå University of TechnologyLicens fulltext: CC BY License

Chemical modification of wood typically requires the impregnation of wood with reactive compounds capable of undergoing covalent bonding to functional groups present in the cell wall. Creating such reactive agents in situ, with the use of low-priced chemicals, would prove more attractive for commercial applications. In this study, Scots pine (Pinus sylvestris L.) sapwood was impregnated with an aqueous solution of urea (30%), dried at 40°C for 24 h, and subsequently heat treated in an oven at 150°C for 24 h to produce the reactive isocyanic acid. By using accelerated fungal tests under laboratory conditions, provisional tests demonstrated a high biological resistance against selected moulds and rots. Migration of urea into the wood structure and grafting to its polymers during subsequent heat treatment, led to a bulked cell wall and enhanced resistance to water swelling, even after cycling water treatments. The bending strength (MOR) of modified pine wood was reduced by the treatment applied, while its modulus of elasticity (MOE) remained unchanged. Validerad;2023;Nivå 2;2023-06-30 (joosat);Licens fulltext: CC BY-NC-ND License Biobased fire protection of wood panel for exterior conditions by using phosphorylated lignin from wheat straw

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

Wood composites are manufactured by joining wood fibres, strands, or particles together with an adhesive, but it is necessary for eliminate the use of formaldehyde-based adhesives in the manufacture of wood composites for the sake of indoor air quality and human health. This initial study has demonstrated the use of sorbitol and citric acid as a potential bio-based formaldehyde-free adhesive for wood-composite manufacture. A solution of citric acid and sorbitol in water was sprayed onto wood particles which were then pressed at 160°C, 180°C, or 200°C for 13 min, to produce boards with a target thickness of 8 mm. The FTIR spectra contained an absorption band at 1720cm−1, presumably due to the esters of citric acid and sorbitol. Pressing of a temperature of 200°C gave boards with the highest modulus of elasticity and the highest internal bond strength. The results reveal a new potential bio-adhesive for the manufacture of wood composites. Validerad;2022;Nivå 2;2022-11-25 (hanlid);Funder: OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803); Swedish wood industry CT WOOD

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. Validerad;2022;Nivå 2;2022-04-13 (sofila);Funder: CT WOOD; 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

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, the introduction of the fire-retardant additive guanyl-urea phosphate (GUP) into furfurylated wood is reported. The treatment improved both the thermal and fire stabilities of the modified wood, as supported by the results of thermal gravimetric analysis (TGA) and limiting oxygen index (LOI) before and after accelerated ageing testing (according to EN 84) to determine the water resistance of the treatment. The results indicated that the hydroscopic GUP remained within the wood structure and provided superior thermal and fire properties. The work suggests the idea of combining GUP and furfuryl alcohol (FA), which has the prospective to impart substantial fire-retardancy to the furfurylated wood, thus increasing the potential for exterior applications. Validerad;2021;Nivå 2;2021-11-30 (johcin);Funder: OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803); CT WOOD – a centre of excellence at Luleå University of Technology supported by the Swedish wood industry

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.

This study presents a novel application of the Wilhelmy plate method on welded joints of Scots pine sapwood and beech. Welding resulted in an increase in the contact angle (increased hydrophobicity) as well as a decrease in the water uptake and swelling of the welded pine-joint compared to non-welded pine. When the welding time was extended from 4 to 5 s, these properties were further pronounced. Welding of beech, on the other hand, led to an increase in the contact angle and a decrease in the water uptake, but an increase in the swelling. Fourier Transform Infrared spectroscopy showed that welding increased the aliphatic C–H and unsaturated C=C stretching absorption bands in pine and beech. Scanning electron microscopy showed a dense structure at the welded joints of the both species, giving evidence of a lower porosity that leads to a lower permeability as a result of the welding.

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 (HRR

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.

Scots pine (Pinus sylvestris L.) wood impregnated with guanyl-urea phosphate/boric acid and a melamine-formaldehyde resin exhibited considerably increased resistance to leaching, while sustaining superior fire retardancy as tested by the limiting oxygen index (LOI) method. It was found that guanyl-urea phosphate has been well trapped in the wood structure by the cured resin network as evidenced by FTIR spectroscopy. Markedly, weight percentage gain (WPG) losses of fire retardant as low as 7.4% were achieved after excessive leaching of treated wood (EN 84). This was attributed to the effect of melamine-formaldehyde resin. Overall, this type of treatment could be a reliable method for producing fire-resistant pine wood for exterior uses.

Compressing the surface of sawn timber results in a substantial increase in hardness, and this opens up new market opportunities of using low-density timber species as the raw material for high-value wood products. Unfortunately, widespread commercialisation is hindered by the lack of an industrially viable surface densification process, the major obstacle being the set-recovery (SR) of the densified wood cells upon exposure to moisture. Our hypothesis is that partial dissolution of the crystalline cellulose during densification will largely prevent the SR of densified wood. We therefore evaluated the effect of ionic liquid (IL) or organic superbase pre-treatment on the elastic spring-back (SB), SR and Brinell hardness (HB) of surface-densified wood. Specimens of Scots pine were treated with solutions of ILs or superbases, and then densified in a hot press at temperatures between 200°C and 270°C. The SR was reduced from 90% for the control group to only about 10% for the treated materials. The treated and densified specimens exhibited a higher HB than their untreated and densified counterparts. The method presented in this study is a precursor to the development of a continuous densification process adapted for an open system. Further studies are needed to understand the underlying mechanisms of the pre-treatment.

A simple chemical solution-based synthesis route has been developed to prepare uniform and shape-controllable Ag3PO4 crystals. Tetrapod- and cube-shaped crystals having a size of about 9–10 μm were prepared from AgNO3 and NH4H2PO4 precursors, and pseudo-octahedral (equiaxial) crystals were prepared from AgNO3 and (NH4)2HPO4. TEM analysis revealed Ag3PO4 crystals to be electron beam sensitive materials, which under a voltage of 200 kV decompose to the metallic Ag, thereby demonstrating the difficulty in determining crystal facets and structural defects using conventional electron diffraction studies. UV–Vis diffuse reflectance spectroscopy was used to study the correlation between structural and optical properties of surfaces of Ag3PO4 crystals. Furthermore, a spatial 3-dimentional (3D) reconstruction of Ag3PO4 surface structures was performed from SEM images. The reconstruction produced realistic 3D mesh models, insomuch that the 3D reconstructed structures provided extra information about the examined crystals. Results suggested that the proposed synthesis route and performed spatial reconstruction of Ag3PO4 had the potential for simulating processing conditions to produce various microcrystals and explore material surface structures and reconstruction of microstructures.

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. Validerad;2019;Nivå 2;2019-09-18 (johcin);For correction, see: Garskaite, E., Karlsson, O., Stankeviciute, Z. et al. Correction: Surface hardness and flammability of Na2SiO3 and nano-TiO2 reinforced wood composites. RSC Advances 9, 34086-34087 (2019). https://doi.org/10.1039/C9RA90075F

This work aimed at finding ways to improve the leaching resistance of Scots pine (Pinus sylvestris L.) wood impregnated with water soluble fire retardant (FR). Sapwood specimens of Scots pine (10 × 10 × 50 mm) were impregnated with aqueous solution of guanyl-urea phosphate (GUP)/boric acid (BA). Limiting oxygen index (LOI) revealed that treatment could improve the fire performance. At the same time, thermogravimetric analysis (TGA) illustrated increased thermal stability after the treatment. However, since the FR itself was not fixed within the wood cell wall, it was extracted during water leaching (EN 84), and the wood lost its fire retarding property. The resistance to leaching of FR from the treated wood can be primarily improved while maintaining high fire retarding performance and thermal stability of treated wood by mixing melamine-formaldehyde (MF) resin with GUP/BA before impregnation to the wood. To mix GUP/BA to MF solution, due to the acidic nature of GUP/BA, the condensation/polymerisation reaction would be accelerated in an undesired way even if the solution was adjusted to non-acidic by NaOH. The resulting solution would not penetrate deeply into the wood structure, whilst it would be difficult to re-use the FR solution. In order to avoid the reaction proceeding in an undesired way, introducing 0.5 wt% of pentaerythritol to the GUP/BA/MF solution can decrease the reaction rate. Additionally, it improved the weight percentage gain (WPG) and fire retarding performance, without significantly influencing the leaching resistance and thermal stability. Overall, it is suggested that such a treatment could be a suitable methodology for producing exterior-use fire-retardant pine wood. ISBN för värdpublikation: 978-3-030-41234-0, 978-3-030-41235-7

Changes in both formaldehyde legislations and voluntary requirements (e.g. Germany RAL) are currently the driving factors behind research on alternatives to amino-based adhesives; moreover, consumer interest in healthy and sustainable products is increasing in bio-based adhesives. Sources of formaldehyde emissions in wood-based panels as well as different emission test methods have been discussed, and the main focus of this review is on the research conducted on sustainable bio-based adhesive systems for wood panels. Lignin, tannin, protein, and starch have been evaluated as both raw materials and adhesive alternatives to existing amino-based thermosetting adhesives. Adhesion improving modifications of these bio-based raw materials as well as the available and experimental crosslinkers have also been taken into account.

Research Highlights: In this study, the Generally Recognised as Safe (GRAS) compounds were applied in order to study mould-fungi growth on dried Scots pine sapwood. Background and Objectives: The transition to the use of more sustainable wood-material may be possible by applying GRAS compounds that can control and prevent contamination by primary colonising mould fungi. Materials and Methods: Kiln-dried sawn timber was treated with three different GRAS compounds, and different fungal inoculation methods applied in order to investigate differences in the development of fungal communities. Results: Substances based on potassium silicate significantly reduced fungal growth and mould contamination on the studied wood surfaces. By combining wood-surface treatments with GRAS compounds, fungal-area size as predictors and mould grade as response, a partial least squares (PLS) model that makes it possible to predict mould grade on wood surfaces was developed. The PLS model is a key component in the development of a smart grading-systems equipped by e.g. high-speed digital cameras for the early detection of fungal attack on wood surfaces in different applications. However, the measurements based on chemical characterisation should be the next step to take in order significantly to enhance the model and increase the range of robust applications. In the current study, a multivariate model describing the influence of each fungal-covering area on mould grade was presented for the first time. Validerad;2019;Nivå 2;2019-08-27 (johcin)

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 (

Response surface methodology was used to optimize the refining conditions of Pinus massoniana cellulose fiber and to improve the mechanical properties of ultra-low density plant fiber composite (ULD_PFC). The effects and interactions of the pulp consistency (X1), the number of passes (X2), and the beating gap (X3) on the internal bond strength of ULD_PFC were investigated. The results showed that the optimum internal bond strength (91.72 ± 2.28 kPa) was obtained under the conditions of 8.0% pulp consistency, two passes through the refiner, and a 30.0 μm beating gap. Analysis of the physical properties of the fibers and handsheets showed that the fibrillation of fibers with optimum refining conditions was improved. Also, the tear index of the optimal specimen was 13.9% and 24.5% higher than specimen-1 with a lowest beating degree of 24 oSR and specimen-6 with a highest beating degree of 73 oSR, respectively. Consequently, the optimal refining conditions of the fibers are valid for preparing ULD_PFCs.

To obtain a suitable refining process for Pinus massoniana cellulose fibers (PMCF) and China fir cellulose fibers (CFCF), the effects of the beating gap and the pulp consistency on the physical properties and the morphology of the two cellulose fibers were investigated. The results showed that the physical properties of the PMCF and the CFCF were well affected by the beating gap and the pulp consistency. The CFCF showed a smaller weight-average length and width than that of the PMCF. The CFCF exhibited smaller weight-average length, width, and kink index than the PMCF. It is easy to get the high beating degree, indicating it is more easily to be refined. Additionally, the tensile index and burst index of PMCFP and CFCFP increased with increasing beating degree, while the tear index decreased. Compared to the CFCF, the paper made from PMCF had superior strength properties. Consequently, the PMCF was suitable for refining with a high pulp consistency and a medium beating gap, whereas the CFCF had a medium pulp consistency and a big beating gap.

Background The genus Pleurotus is most exploitable xylotrophic fungi, with valuable biotechnological, medical, and nutritional properties. The relevant features of the representatives of this genus to provide attractive low-cost industrial tools have been reported in numerous studies to resolve the pressure of ecological issues. Additionally, a number of Pleurotus species are highly adaptive, do not require any special conditions for growth, and possess specific resistance to contaminating diseases and pests. The unique properties of Pleurotus species widely used in many environmental technologies, such as organic solid waste recycling, chemical pollutant degradation, and bioethanol production. Methodology The literature study encompasses peer-reviewed journals identified by systematic searches of electronic databases such as Google Scholar, NCBI, Springer, ResearchGate, ScienceDirect, and ISI Web of Knowledge. The search scheme was divided into several steps, as described below. Results In this review, we describe studies examining the biotechnological feasibility of Pleurotus spp. to elucidate the importance of this genus for use in green technology. Here, we review areas of application of the genus Pleurotus as a prospective biotechnological tool. Conclusion The incomplete description of some fungal biochemical pathways emphasises the future research goals for this fungal culture.