Search Results (129)

Growing demand for more sustainable packaging has increased interest in bio-based adhesives as alternatives to conventional fossil-derived systems. Among renewable raw materials, lignin is particularly attractive because of its aromatic structure, phenolic functionality, and availability as a side stream of pulp, paper, and biorefinery processes. This review critically examines the potential of lignin-based adhesives for packaging applications. Selected polysaccharide-, protein-, vegetable-oil-, and tannin-based systems are briefly discussed as comparative references, while the main focus is placed on the properties of kraft lignin, lignosulfonates, organosolv lignin, and soda lignin. Their structural differences, adhesive behaviour, and suitability for chemical modification through hydroxymethylation, phenolation, demethylation, depolymerization, oxidation, and epoxidation are evaluated. Because most lignin-adhesive research concerns wood bonding, the transferability of these findings to paper, paperboard, labels, coatings, films, and hot-melt packaging adhesives is critically assessed. Direct evidence for packaging applications remains limited, although existing studies demonstrate promising opportunities for paper bonding, pressure-sensitive systems, and paperboard hot-melt adhesives. Key challenges include lignin heterogeneity, processing complexity, moisture resistance, colour, food-contact safety, scalability, and compatibility with recycling. Full article

The diverse colour range of tropical woods is a highly valued commercial feature for specialized interior applications. This study evaluates the long-term indoor colour changes in 98 tropical wood species from Goa (India), Mozambique, and East Timor, stored in a xylarium for 45–50 years. Using the CIEL*a*b* system, surface colour changes ΔL*, Δa*, Δb* and ΔE were quantified by comparing unexposed reference surfaces, obtained through sanding, with the long-term exposed surfaces. Results showed that darkening occurred in 96% of the species, though visual assessments identified colour differences in only 58% of the samples. Pteleopsis myrtifolia (Lawson) Engl. and Diels and Bombax malabaricum DC. (both light yellowish-brown) exhibited almost no change, while Cedrela odorata (light pinkish-brown) and Pterocarpus antunesii (moderate orange-brown) showed slight lightening. The initial wood colour was not a significant predictor of the magnitude of chromatic change. Total colour difference (ΔE) was primarily driven by reductions in lightness (ΔL*), followed by hue change (Δh*). The chromatic components contributing to ΔE differed according to the initial lightness class: in lighter woods (L* > 50), redness change (Δa*) showed the strongest chromatic contribution to ΔE, whereas in darker woods (L* ≤ 50), yellowness change (Δb*) was the dominant chromatic contribution. With a mean total ΔE of only 5.76, the overall wood chromatic identity of most species was maintained over time. These findings indicate that indoor ageing of tropical woods is mainly characterized by progressive darkening rather than by drastic chromatic shifts, supporting their long-term aesthetic suitability for premium interior applications over several decades. Full article

This study presents a wood modification process using Fast Pyrolysis Bio-Oil (FPBO) as a fully biobased alternative to conventional, fossil-based and potentially toxic preservatives such as copper salts, organic biocides, and creosote. Standard FPBO was used in the development of 10 formulations, which were systematically characterized in terms of pot life, viscosity evolution, density, and pH. Radiata pine samples were subsequently impregnated using a bench-scale reactor, with specimens prepared in multiple geometries to assess treatment performance across different dimensions. The modified wood was comprehensively characterized with respect to moisture uptake, dimensional stability, density, mechanical strength, fixation efficiency, biological durability, and VOC emissions. Additional screening focused on properties relevant to outdoor applications, including aesthetic appearance and colour uniformity after UV exposure. The results enabled the identification of three top-performing formulations, treatments H, A, and E, which exhibited the most favourable balance between durability, environmental performance, and structural integrity. Overall, the findings demonstrate the strong potential of FPBO-based impregnation as a sustainable, multifunctional, and high-performance alternative for advanced wood protection systems. Full article

The durable enzyme functionalisation of cellulosic fibres is often limited by enzyme deactivation under alkaline processing and insufficient wash resistance. Here, a cold pad–batch (CPB)-compatible route integrates reactive dyeing and lysozyme anchoring by using the commercial bifunctional dye C.I. Reactive Red 195 (MCT/VS) as an interfacial mediator to build a cellulose–dye–lysozyme ternary layer. The dye is first fixed on cotton, and residual electrophilic motifs are proposed to facilitate subsequent coupling with nucleophilic residues in lysozyme. A nine-run, four-factor/three-level orthogonal design was used to identify a practical processing window; under the selected condition, an ELISA-equivalent releasable lysozyme level of 53.8 U/L was achieved together with moderate colour strength (K/S = 6.5). The treated fabrics exhibited 96.5% inhibition against Escherichia coli and >99.9% against Staphylococcus aureus and retained antibacterial functionality after five ISO 105-C06 laundering cycles. Textile-relevant properties were preserved, including colour fastness (Grade 4–5), tensile strength retention (~86%), and capillary wicking close to pristine cotton. This dye-mediated strategy offers a practical route to wash-resistant bioactive interfaces on cellulose fibres and is extendable to regenerated cellulose and wood-pulp-derived cellulosics. Full article

The paper deals with the optical stability and biological resistance of solvent-based polyurethane and water-based polyurethane–acrylate finishes intended for interior use, applied on beech wood with mature wood and false heartwood. Optical stability was assessed through colour and gloss measurements. The surface finishes were applied in one (I), two (II), and three (III) layers. Natural ageing was carried out under indoor conditions with exposure to natural daylight behind a glass window. Colour and gloss measurements were performed after 30, 150, and 300 days of exposure. The development of mould growth activity (GAM) during 21-day exposure was assessed on untreated and coated beech wood with different coating thicknesses. A significant colour difference in the solvent-based polyurethane finish on both mature wood and false heartwood occurred after 30 days of natural ageing. The colour difference in the water-based polyurethane-acrylate finish on both mature wood and false heartwood increased with exposure time. The solvent-based polyurethane finish with three layers applied to false heartwood showed reduced colour difference (by 62.5%). Natural ageing under interior conditions did not significantly affect the gloss of the matte surface for either finish on both mature wood and false heartwood. The degree of mould growth decreased with an increasing number of coating layers for both polyurethane and polyurethane-acrylate finishes. Full article

The influence of growing site conditions on the chromatic properties of heartwood in black locust (Robinia pseudoacacia L.) cultivar ‘Nyírségi’ sampled from five regions of Hungary was investigated in this study. A total of 23 boards (average age of trees: 34.5 years) representing four site types were analyzed by instrumental colorimetry using the CIE Lab system. The overall average color coordinates were L* = 69.9 ± 4.0, a* = 4.0 ± 0.8, and b* = 27.4 ± 2.3. Significant chromatic differences were observed among site types proven by statistical analysis; however, no single site type consistently increased within-site color variability. Average total color differences (ΔE*) ranged from 3.94 to 6.31 across site types, corresponding to “noticeable” to “large” visual differences. Regionally, 89.1% of 55 specimen pairs exhibited clearly perceptible color variation (ΔE* > 2), with 61.8% classified as “large” (ΔE* > 5). Within-tree comparisons revealed ΔE* values of 3.72–3.75 under poor site conditions but <2.0 on good growing sites. The a* and b* components appear with measurable variations across all sites, while the characteristic yellow hue remains distinct and stable independent of site origin due to the high b* value. Full article

The aim of the study was to investigate the effect of hydrothermal treatment (different steaming process) conditions, specifically temperature, pressure, and steaming time on selected physical properties of beech wood (Fagus sylvatica L.), such as moisture content, density, colour, and longitudinal contraction. The research was conducted using two steaming modes: pressure steaming process (108 °C, 181 kPa, 7 h) and atmospheric steaming process (80 °C, 101 kPa, 15 h). The results showed that pressure steaming caused a more significant decrease in moisture content (by 16.9%) compared to atmospheric steaming (by 8.0%) and a smaller variation in values, which is favourable for subsequent drying. The differences in density after steaming were not statistically significant. On the contrary, longitudinal shortening was significantly greater with pressure steaming, which may indicate the release of tension reaction wood. The colour change was similar in both modes; lightness (L*) decreased and the wood acquired a redder hue without a significant effect of steaming conditions on the overall colour differentiation (ΔE). The results confirm that steaming temperature and pressure have a significant effect on the moisture change and longitudinal contraction of beech wood, while density and colour change remain relatively stable. The length of the steaming process has a major effect on the colour change of the wood. Full article

This study investigates the influence of thermal treatment and subsequent artificial irradiation on the colour stability of fir (Abies alba L.) wood extractives. Wood samples were heat-treated at temperatures ranging from 100 °C to 280 °C for varying durations, and their extractives were isolated using Soxhlet extraction with an ethanol–toluene solvent mixture. The extract solutions were subjected to accelerated ageing under xenon light irradiation for up to 400 h, and colour changes were systematically monitored using a spectrophotometer in transmission mode. The amount and colour of extractives varied with treatment temperature. The extractive yields decreased up to 150 °C, increased between 150 °C and 240 °C, and declined again above 250 °C. The initial colours of the extract solutions ranged from yellow to brown, depending on the treatment conditions. During irradiation, colour differences (ΔEab) progressively decreased, and after 400 h, the solutions became nearly colourless, with lightness values approaching 100. The decline in b* values indicated a loss of yellow hue, while a* values shifted from red or green towards neutrality. These results confirm that fir wood extractives are highly sensitive to both heat and UV exposure, leading to significant discolouration and reduced colour saturation. These findings enhance our understanding of the mechanisms underlying fir wood colour changes and contribute to the broader knowledge of wood ageing processes. Full article

Compression wood (CW) negatively affects the industrial quality of Pinus taeda by causing distortion in sawn boards and is visually characterized by a darker reddish colour. Thinning is considered a key factor influencing its formation, but the reported effects have been inconsistent. This study evaluated CW incidence at final rotation under five thinning regimes: 500-200, 500-325, 800-600-400, 700-450, and 1000-650 trees.ha⁻¹. The defect was assessed on log ends, basal discs, and sawn boards. Although overall CW severity was low, regimes differed significantly. The 500-325 trees.ha⁻¹ regime showed the highest stain and board defects, while the 500-200 trees.ha⁻¹ regime of similar intensity had lower values, indicating that intensity alone does not explain the occurrence of defects. After thinning, CW in growth rings increased and was positively associated with ring width and negatively with stand density index, indicating that reduced competition and accelerated radial growth are linked to higher formation levels. Visible CW staining on log ends was moderately correlated with board defects, indicating its potential as a practical, low-cost indicator of log quality. Thinning affects compression wood through its impact on growth and stand structure. In addition to intensity, timing and the effect of the wind must also be considered. Moderately intensive regimes help minimize defects, although their practical adoption may be limited by commercial priorities. Full article

The aim of this study was to investigate the potential of dyer’s woad (Isatis tinctoria L.) as a sustainable, plant-based colouring agent for enhancing the visual properties of wood surfaces. Veneers of oak (Quercus sp.) and poplar (Populus sp.) were used as materials and dyed with aqueous extracts derived from fresh and dried woad leaves. To facilitate dye uptake, the veneer surfaces were pretreated with various mordants: alum, citric acid, acetic acid, and distilled water (as a control). The aim was to assess the impact of both the form of the plant material and the type of mordant on the resulting colour change. Colour modifications were measured using spectrophotometry and subjected to statistical analysis. The results revealed distinct differences between untreated and dyed veneers, as well as among samples treated with different mordants. Furthermore, the effectiveness of the dye varied depending on whether fresh or dried leaves were used. These findings confirm the feasibility of employing Isatis tinctoria L. as a natural wood dye and highlight its potential as an eco-friendly alternative to synthetic surface treatments in decorative wood applications. Full article

Furniture surfaces are prone to the accumulation of bacteria, fungi and other micro-organisms, especially in humid environments such as kitchens and bathrooms. The antimicrobial treatment of coatings has been demonstrated to enhance the performance of wood, prolong its service life, and improve hygiene and safety. Consequently, by investigating the most effective preparation process for antimicrobial microcapsules and incorporating them into the coating, the coating can be endowed with antimicrobial properties, thereby expanding its application range. Microcapsules were prepared using a composite wall material consisting of chitosan (CS) and Arabic gum (AG), with tea tree essential oil (TTO) serving as the core material. The best CS-AG coated TTO microcapsules were prepared when the core–wall ratio was 1.2:1, the emulsifier concentration was 2%, the pH was 3, and the mass ratio of AG to CS (m_AG:m_CS) was 3:1. The m_AG:m_CS was identified as the most significant factor affecting the microcapsule yield and encapsulation rate. With the increase in m_AG:m_CS, the antimicrobial rate of the coating against Escherichia coli (E. coli) exhibited a trend of first rising and then falling, while the antimicrobial rate against Staphylococcus aureus (S. aureus) demonstrated a trend of first rising, then falling, and then rising again. The colour difference (ΔE) and gloss exhibited an overall downward trend, the light loss rate demonstrated a fluctuating upward trend, and the roughness exhibited a trend of first falling and then rising. The visible light band transmittance exhibited minimal variation, ranging from 86.43% to 92.76%. Microcapsule 14# (m_AG:m_CS = 3:1) demonstrated remarkable antimicrobial properties (E. coli 65.55%, S. aureus 73.29%), exceptional optical characteristics (light transmittance 92.12%, 60° gloss 24.0 GU), and notable flexibility (elongation at break 18.10%, modulus 0.10 GPa). The waterborne coating was modified by microcapsule technology, thus endowing the coating with antimicrobial properties and concomitantly broadening the scope of application of antimicrobial microcapsules. Full article

The novelty of this study lies in the first comparative characterisation of five carbonaceous materials: three monophase carbons (wood charcoal, carbon, graphite) and two ore-derived CM samples from polymetallic sulphide and oxidised lithium ores. The methodology included IR spectroscopy, XPS, acid–base adsorption centres identified by colour indicators, chemical composition analysis, and kinetic flotation tests. Bulk and surface compositions differed significantly: although the ash content of ore-derived CM reached 84.4%, XPS revealed carbon-enriched surfaces with thin films of about 1–2 nm. IR spectra confirmed multiphase structures with carbonate, silica, and aluminosilicate bands, and showed an identical composition of CM from different industrial ore types. Flotation kinetics confirmed high floatability (recoveries 80%–99%, k up to 1.95 min⁻¹). Even with sodium lignosulphonate at 500 mg/L, recovery only decreased from 83.02% to 52.54%, showing the limited efficiency of depressants. These results provide a basis for the preliminary removal of CM prior to rough (bulk) flotation in the processing of different ore types, improving concentrate quality, reducing reagent consumption, and lowering metallurgical losses. Full article

While most efforts are aimed at preventing the surface roughening and colour change of wood due to weathering, some customers, mainly for decorative reasons, want wooden objects and elements to give the impression that they have been weathered for a long time. In this study, the simulated weathering of numerous softwoods as well as ring-porous and diffuse-porous woods by sandblasting and greying with iron sulphate was investigated. Calculations of the correlations between wood density, orientation, mass loss and thickness reduction by sandblasting were performed, and the difference between the hardness of late and early wood and the surface profile parameter P_t showed that the surface profiles correlate strongly with mass loss, especially in the tangential orientation. Softwoods appeared to be the most promising for simulated profiling, especially spruce and larch with tangential surfaces. Among the ring-porous woods, oak and sweet chestnut also delivered good results. Full article

Pine wood has a natural, rustic, and environmentally friendly style and is used in a large number of applications in the furniture industry. However, its soft and porous texture makes it susceptible to bacteria, mould, and other micro-organisms. Pine wood was selected as the test substrate, and tea tree essential oil@chitosan (TTO@CS) microcapsules with emulsifier concentrations of 4%, 5%, and 6% were added to the waterborne topcoat at a content of 1%–9% (in 2% intervals) to investigate their effect on the surface coating properties of pine wood. With the increase in microcapsule content, there was an overall increase in colour difference and light loss rate of pine wood surface coating, and the reflectance showed an increase and then decrease. The overall performance of the pine wood surface coatings containing 7% of 13# microcapsules was found to be excellent: the antimicrobial activity of the coatings was 62.58% for Escherichia coli and 61.29% for Staphylococcus aureus after 48 h, and the antimicrobial activity of the coatings was 40.14% for Escherichia coli and 38.89% for Staphylococcus aureus after 4 months. The colour difference in the coating was 2.37, and the light loss was 63.71%. The reflectance value was found to be 0.6860, while the hardness was determined to be 2H and the adhesion class was categorised as one. The impact resistance class was determined to be three, while the roughness was measured at 1.320 μm. The waterborne coating on the surface of pine wood was modified by microencapsulation technology with the objective of enhancing the antimicrobial properties of pine wood and expanding its scope of application. Full article

The sapwood and heartwood of European larch (Larix decidua Mill.) are both used in industrial applications, but they differ in structure and composition, which may lead to surface property differences. This study compared their surface characteristics (on radial and tangential sections) after sanding with aluminium oxide papers of four grit sizes (P60, P120, P180, P240). Surface roughness (Ra, Rz), wettability (contact angle with two reference liquids: water and diiodomethane, 3 and 30 s after droplet deposition), surface free energy, and colour parameters (L*, a*, b*) were analysed. Microscopic measurements were also performed to assess anatomical differences between sapwood and heartwood. The results showed no significant differences in roughness (Ra, Rz) between sapwood and heartwood. Measurement direction and sandpaper grit accounted for about 80% of variability in roughness parameters. Wettability was mainly influenced by wood area, with its effect ranging from 55% to 89% depending on measurement time. The sapwood was characterised by the lower wettability on the tangential section, while the heartwood was characterised by the lower wettability on the radial section. This was examined for the contact angle tests performed 3 s after the water droplet had been applied to the wood surface. Such dependencies were not observed after 30 s. Sapwood exhibited higher surface free energy (SFE) values than heartwood. The greatest colour change ΔE, at level 2.59, was noted for the heartwood on the radial section after sanding with P240 sandpaper. Full article