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Article

Graphene-Enriched Acrylic Paint to Preserve Wood Substrates from Trametes versicolor

by
Hamid R. Taghiyari
1,*,
Elham Nadali
2,
Antonio Pizzi
3,
Roya Majidi
4,
Mohammad Taheri
1,
Mohammad Hassan Sowlat
5,
Olaf Schmidt
6,† and
Antonios N. Papadopoulos
7,*
1
Wood Science and Technology Department, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran 16788-15811, Iran
2
Natural Resources Faculty, Semnan University, Semnan 35131-19111, Iran
3
LERMAB-ENSTIB, University of Lorraine, 27 Rue Philippe Seguin, 88000 Epinal, France
4
Department of Physics, Faculty of Sciences, Shahid Rajaee Teacher Training University, Tehran 16788-15811, Iran
5
M.S. Graduate, Faculty of Law, Tarbiat Modares University, Tehran 1411713116, Iran
6
Wood Biology, Institute of Wood Science, University of Hamburg, Leuschnerstr. 91d, 21031 Hamburg, Germany
7
Department of Natural Environment and Climate Resilience, Democritus University of Thrace, 66100 Drama, Greece
*
Authors to whom correspondence should be addressed.
†
Deceased author.
Forests 2026, 17(8), 871; https://doi.org/10.3390/f17080871
Submission received: 15 June 2026 / Revised: 22 July 2026 / Accepted: 25 July 2026 / Published: 26 July 2026
(This article belongs to the Section Wood Science and Forest Products)
Browse Figures
Versions Notes

Abstract

Fungal decay poses a significant threat and causes substantial economic losses worldwide. Graphene is a nanomaterial with positive results in improving paints and finishes, eventually protecting the substrates from damages, including fire and wood-decay fungi. This study investigated the effectiveness of graphene in an acrylic paint to protect unheated and thermally modified wood substrates from Trametes versicolor. Three commercial wood species were coated with either plain or graphene-enriched paints; a separate set of specimens was prepared for thermal modification at 185 °C. Exposure to T. versicolor was carried out for four months, and the impact of fungal degradation was evaluated through mass loss and a mechanical property. Incorporation of graphene markedly reduced mass loss in both unheated and thermally modified specimens; it also improved the compression strength compared with the controls, demonstrating its dual protective and reinforcing effects. These results highlighted the potential of graphene as an efficient and practical additive in acrylic paints, offering a viable and easy-to-apply method for protection of hardwood and softwood substrates against fungal biodeterioration.

1. Introduction

Wood is a natural constructional material that offers multiple applications because of its strength and aesthetic appeal. The natural properties of wood make it vulnerable to both environmental damage and biological deterioration [1]. Wood-decay fungi make a major threat to wood structures as they degrade wood cell-wall polymers, resulting in a significant decrease in mechanical properties [2,3]. The vulnerability of wood to biodegradation and fire, along with its tendency to swell and shrink from moisture exposure, establishes main drawbacks that reduce the expected service life and limit its applications, thus requiring continuous development of effective preservation methods [4].
In the present study, the fungus Trametes versicolor was selected to work on, as it is considered a widely distributed white-rot fungus worldwide, causing great damage to wood and significantly reducing the structural integrity and strength of different wood species by degrading cell-wall polymers [1,5]. Moreover, similar to Coniophora puteana, T. versicolor is also considered a main criterion for assessment of biological resistance of wood species and their durability classification that are used in many studies [6]. Various studies report that exposure to this fungus can cause mass losses of 20%–30% and reductions in bending strength of up to 40% within a few months [5]. Decay to such extents results in considerable economic losses in timber structures and garden furniture worldwide. This highlights the practical significance of developing effective antifungal treatments and easy-to-apply preservative materials for protection of wood substrates against this wood-decay fungus species.
Thermal modification, which may also be called heat treatment, serves as one of the most effective techniques to improve wood durability [3,4]. Scientists use controlled heat treatment regimes on wood (including both the duration and the temperature) to achieve different temperature levels starting from mild temperatures below 190 °C and ending at high temperatures above 200 °C under three commonly used media, including air, nitrogen, and water steam [3,4,7,8,9]. Under the applied temperatures, cell-wall polymers in wood (including lignin and holocellulose) are modified, and therefore, the fungal enzymes cannot degrade and break them down to the initial sugar molecules; the biological resistance is improved in this way in solid wood [2,4,7,8]. The modified polymers also gain lower hygroscopicity, and therefore, higher dimensional stability is achieved [3,7]. However, there is a negative aspect involved: heat modification simultaneously decreases the mechanical properties as well, as the result of the above-mentioned chemical alterations and the breaking down of the cell-wall polymers [3,7,10,11]. Based on the above-mentioned facts, one of the objectives of researchers is to find an optimum temperature for thermal modification under which the biological resistance is increased as much as possible while the mechanical strengths decrease as little as possible.
Nanomaterials have gained significant attention because their distinctive characteristics demonstrate a great potential to provide effective solutions that complement the existing methods [12,13,14]. Different nanomaterials have also been used as additives in polymer coatings, as they improve mechanical strength, barrier performance, and the overall durability of the coatings [15,16,17,18]. Even a small amount of clay nanoparticles was reported to make better superficial behavior and a longer service life when incorporated into epoxy coatings [19]. However, adequate studies are not available on the influence of this nanomaterial, when mixed with an acrylic paint, on the biological protection of different substrates made of wood against various fungi. Graphene consists of a layer of carbon atoms connecting to each other and forming a two-dimensional lattice structure, which provides remarkable mechanical strength and thermal stability and barrier performance [15,20,21]. Graphene exhibits antimicrobial and antifungal properties through three distinct mechanisms which include (i) physical degradation of the attacking organisms, (ii) generation of reactive oxygen which causes damage by oxidation, and (iii) formation of a protective barrier which restricts nutrient, oxygen, and moisture entry [22,23]. The properties of graphene-enriched coatings enable them to function as an effective superficial solution that protects wood from decaying fungi while maintaining its structural strength [24]. However, it should be considered that from an economical point of view, the improved protection and the prolonged service life of the wood substrates should justify the production costs of the graphene-enriched paints and coatings. Despite the remarkable mechanical, thermal, and antimicrobial properties, graphene presents significant dispersion challenges when incorporated and dispersed into different polymer matrices [25,26,27].
In the present study, an acrylic paint was selected as the matrix material due to the widespread use of this kind of paint in both industrial and decorative woodwork, providing good adhesion, flexibility, and ease of application [28,29]. Compared to other standard coatings such as polyurethane and epoxy, acrylic coatings offer adequate protection against moisture and moderate biological attack while allowing easy incorporation of nanomaterials such as graphene [30]. The rapid drying time of acrylic paint at ambient conditions and its ability to maintain the surface aesthetics of wood further supported its selection as a practical and cost-effective coating for evaluating the antifungal performance of graphene [31,32].
The above-mentioned literature review and the studies briefly reviewed were duly considered to test the hypothesis in the present research, assuming that the incorporation of graphene into acrylic paint improves the biological resistance of wood substrates (either normal substrates or heat-treated at a mild temperature) exposed to T. versicolor as a troublesome wood-decay fungus worldwide.

2. Materials and Methods

2.1. Production of Graphene Flakes

A production system was used in which a cathode electrode made of platinum alloy (Pt 0.5 × 10 cm2) along with a graphite foil electrode (2 × 10 cm2), which acted as an anode, carried out electrochemical exfoliation of graphite to produce graphene. The working distance between the electrodes is considered a critical variable, which was set at 2.7 cm in this study. A water suspension (0.05 M concentration) of NiCl2·6H2O (98.0%, produced by Merck, Germany) was prepared as the electrolyte. A 10 V voltage was applied for the exfoliation of graphite; the same voltage was further used for depositing Ni, too. Sometimes, accumulation of graphene occurs on the cathode; to prevent this, the platinum electrode was cleaned by washing it with an HCl solution in 20min intervals. In order to collect the produced graphene, a vacuum filtration method was used [15,20,21]. The collected graphene was characterized and validated in several ways, including X-ray diffraction radiation, X-ray photoelectron spectroscopy, tunneling electron microscopy, and dynamic light scattering, as the procedures described, and the data of graphene production was verified by Sheykhifard et al. [21]. In the present study, Ni-doped graphene flakes were used. In this atomic model of graphene, a carbon atom can be substituted quite randomly with an Ni atom, as shown in Figure 1. Based on the TEM and XRD reported by the collaborator and producer of the graphene flakes [21], the nanocrystals, with the chemical formulations Ni, Ni(OH)2, and Ni-oxides, were spread out in a random manner throughout the graphene nanosheets. The producer also reported that the size of Ni and Ni(OH)2 nanocrystals was30–40 nm, based on their TEM and XRD [21].

2.2. Specimen Preparation

The number of wood species that were selected in this study was three, comprising two hardwood species (beech and poplar) and one softwood (spruce). Beech with a medium density (Fagus orientalis Lipsky) was selected due to its widespread availability in Iran, aesthetic grain design, and high mechanical performance, with a reported modulus of elasticity of 12–13 GPa and bending strength of approximately 100–110 MPa [10]. Poplar as a low-density hardwood (Populus nigra Lipsky) and spruce as a low-density softwood (Picea abies L.H.Karst.) were chosen based on their low cost and high availability in the local market (Tehran, Iran), making them widely used in construction and furniture manufacturing. By including these species, this study encompasses both high- and low-performance wood species commonly being utilized in many countries, allowing assessment of graphene’s protective impact across a range of wood species and properties.
Lumber from the above-mentioned three wood species were bought from Tehran Wood Market (Tehran, Iran). The cross-section size of the beech lumber was 55 mm × 350 mm, with a length of 2.5–3 m. The poplar lumbers were 40 mm × 250 mm, with a length of 2.5 m; and those of the spruce lumbers were 38 mm × 230 mm, with a length of 2 m. Identification of the species was done by both the visual identification of the wood grain, density, and part of the bark that remained on some of the lumbers as well as the selling documents issued by the seller. Based on the documents presented by the supplier of the wood, the beech trees were harvested from Hyrcanian forests at an altitude of 1800 to 2000 m with mixed brown and alluvial soils (Iran); the poplar lumbers were from Kurdistan Province at an altitude of 300 to 500 m and with a well-developed soil (Iran); and the spruce lumbers were purchased and transported from Tver Province (Russia). It is to be noted that the growth rate and the overall quality of wood can significantly be shaped by the local soil and environmental conditions [34]. Therefore, while the wood species should be taken into account while interpreting and generalizing the results obtained here, the significant effects of various soil traits, climate, and the surrounding vegetation should also be taken into consideration for comparison purposes, as they may significantly affect the grown wood.
For the mass loss experiment, a total of90 specimens were prepared from the three wood species and the six different treatments in each wood species (5 replicates for each treatment), the results of which are reported in Table 1 in the following section. In terms of the compression parallel to grain experiment, one specimen was spared for SEM imaging, leaving a total of72 specimens for the three wood species and the six different treatments (4 replicates for each treatment) (Table 2). The sizes were 20 × 20 × 50 mm; the maximum size (50 mm) was in the longitudinal direction. All specimens were visually inspected to ensure the absence of any pre-existing defects, including fungal or insect damage, checks, cracks, and knots. Only boards without visible discoloration, boreholes, or structural irregularities were selected for this study. Specimens were also examined under a 10× hand lens to detect any possible signs of fungal mycelium or insect infestation, ensuring that all samples were free from biological or structural defects prior to treatment. The average densities of the beech, poplar, and spruce wood species were measured to be 0.64, 0.43, and 0.44 (g.cm−3), respectively; the mean content of moisture was measured to be 9%, measuring the specimen weights before and after being kept in an oven for 24 h at 103 ± 3 °C. The densities of the wood species were determined according to the specifications detailed in the ASTM D2395-17 standard. Separate sets of rectangular specimens (25 mm × 25 mm × 25 mm) were prepared for density measurement, using a digital scale for their weight measurement, having a precision of milligrams. The dimensions of specimens were recorded with a digital caliper, having a precision of ten micrometers. Then, specimens of each species were categorized into two main treatments of “unheated” and “heat-treated” at random. The specimens to be heat treated for each wood species were arranged at random on the metal tray of a laboratory oven with gravity convection and 240 L capacity, produced by Fan Azma Gostar Co. (Tehran, Iran). The heat treatment was carried out at 185 ± 4 °C for four hours. This temperature was selected not to exceed the mild temperature limit for heat treatment as discussed in the Introduction section and in order to achieve the maximum chemical alterations in the wood cell-wall polymers while maintaining the mechanical strength [3,7,8]. The tolerance range (±4 °C) represents the inclusive temperature range read on the oven’s temperature indicator, which was based on the sensitivity of the built-in thermostat of the laboratory oven. Direct contact of the specimens with the metal tray should be avoided in heat treatment processes due to the overheating of the area in direct contact with the metal. Therefore, the specimens were placed on wood strips, arranged in rows on the tray. The thickness and width of the strips were 3 mm and 20 mm, respectively. Once the four-hour duration was complete, the specimens were slowly cooled off for 12 h. The heat-treated specimens were then conditioned (25 ± 2 °C and a relative humidity range of 45 ± 3) for a month together with all the control specimens of the three wood species; the mass stabilization was monitored every 24 h during the conditioning period.
From each of the initial treatments (that is, those that were unheated and those that were heat-treated) in each wood species, 5 specimens were randomly selected as the “control” (the unpainted) treatment, 5 others as the “painted” (to be painted with plain paint), and the last 5 as “graphene-painted” (to be painted with graphene-added paint). Because of the increasing popularity of water-based acrylic paints in the market [28], an acrylic paint (code number ALCO-6510) was selected to be purchased from a reputed chemical and resin producer (Alvan Paint and Resin Production Co., Tehran, Iran). Based on the producer’s report, the content of the polymer binder was 32% ± 1% (consisting mainly of methacrylic acid and methacrylate ester derivatives); additionally, it contained 5%–6% pigments. Moreover, there were about 3% different additives. The additives comprised Natrosol 250 and sodium bicarbonate. The paint contained polyoxyethylene 25 octyl phenol, too. Based on the producer’s data sheet and inquiry, the acrylic paint did not contain the following toxic chemicals: cobalt, cadmium, chromium, and manganese. A brush was used to apply the paint (either plain or graphene-enriched) on all specimens. Two runs of brushing with an average paint consumption of 280 g/m2 and 390 g/m2 were applied, based on the wet weight of the paints, for the plain and graphene-enriched acrylic paints, respectively. The dry film thickness was measured by a model 121/4 thickness gauge. It is a destructive type of gauge, produced by Elcometer Co. (Manchester, UK). As the thickness tests were destructive, four separate specimens were prepared for each treatment, and the film thickness was measured at multiple locations on each. An average thickness of 210 ± 10 μm indicated a satisfactory level of coating consistency among the specimens. There was an interval of 24 h between the two runs.
For the graphene-added paint, the amount of graphene was set at 12 wt% (based on the wet paint) and mixed by a magnetic stirrer for 20 min at room temperature (about 27–29 °C), based on the wet paint. An HS-860 model magnetic stirrer uniformly dispersed the nanomaterial with the polymer. The producer of the stirrer was an Iranian producer of laboratory equipment (Alfa Lab Co., Tehran, Iran). The content level of 12% was selected considering a previous study in which graphene was used as a fire retardant [33], assuming that positive results for fungal protection would provide a coating with double purposes (protection against both fire and fungal attack). Other graphene contents were not investigated in this study because the main objective of the present study was to evaluate the feasibility and protective performance of a graphene-enriched acrylic coating rather than to optimize graphene loading. Moreover, the present study was carried out with an aim to utilize the possible promising results at an industrial scale. Therefore, using high-tech devices for dispersing graphene was not economical at a commercial scale due to their high costs. However, using a mechanical and simple device for mixing graphene can be afforded at any factory. In this connection, graphene powder was slowly poured into the acrylic paint, during which the stirrer worked constantly to avoid the formation of visible agglomerates during mixing. The paint mixture exhibited a visually uniform appearance prior to application and remained sufficiently stable throughout the coating process, with no observable sedimentation. The dispersion of graphene caused an increase in the viscosity compared with the plain acrylic paint; however, it remained homogeneous during mixing and sufficiently workable for a paintbrush without noticeable sedimentation, phase separation, or coating defects. However, it is to be noted that no direct characterization of graphene dispersion within the acrylic matrix (e.g., Raman mapping, rheological analysis, or particle-size measurements) was checked here. Thus, the adopted mixing procedure should be considered a practical preparation method rather than a verification of homogeneous graphene dispersion.
After coating the specimens with either the plain or graphene-enriched paints, they were conditioned (25 ± 2 °C and a relative humidity range of 45% ± 2%) for two months. This long duration was used to make sure that the wood substrate beneath the graphene-enriched paint film definitely reached the mass stabilization and the equilibrium moisture content. In this connection, it will be further explained in the Discussion section that the addition of graphene to the paint makes the paint film a rather impregnable barrier towards transmission of water, vapor, and, to some extent, even oxygen. Specimens had an average moisture content of 9% ± 0.5% at the time of fungal exposure.

2.3. Exposure to Wood-Decay Fungus Trametes Versicolor

Fungal exposure was carried out based on EN 113-1 (2020) standard specifications. The initial dry mass of each specimen was determined by keeping them in a laboratory oven for 24 h while heating at 103 ± 3 °C. All weight measurements were carried out by a digital balance with a milligram precision. Afterwards, the prepared specimens were put in a conditioned closed area at 25 ± 2 °C and a relative humidity of 45% ± 2% to get to a constant weight, that is, to their equilibrium moisture content. The mass stabilization was monitored every 24 h. Specimens were then exposed to the white-rot fungus, with the scientific name of Trametes versicolor (L.: Fr.) Pilát, isolate 325. Isolate 325 was provided by Olaf Schmidt, from the fungi collection at the Institute of Wood Science, University of Hamburg (Hamburg, Germany). This fungus species was selected since it is a well-characterized model organism for wood decay, efficiently degrading lignin and cellulose, and widely used in biodeterioration studies [5] . The isolate was purified following the standard procedures. Once purified, it was further cultivated on 2% malt extract agar (MEA) until the surface was overgrown with active mycelium. The temperature was 25 °C during cultivation. Agar plugs of about 5 mm in diameter with visually apparent mycelium were placed in the 500 mL glass jars. Once sterilized, the specimens were positioned in the jars. The sterilization of the wooden specimens was carried out by an HV-50 autoclave apparatus at 121 °C under 1.5 bars for 25 min; the autoclave was produced by HMC Europe (84577 Tüssling, Germany). To ensure uniform contact, the sterilized wood specimens were positioned directly onto the fungal mat when more than 70% of the top surface of the agar in the glass jars was overgrown with the mycelium from T. versicolor. Jars were sealed with Parafilm and maintained in a climate chamber with the conditions mentioned in Section 2.2.
Successful fungal colonization was confirmed both qualitatively and quantitatively. Periodic inspections verified active mycelial growth on specimen surfaces and edges, and after four months, colonization was further confirmed by characteristic surface mycelium and staining patterns. Following incubation, surface mycelium was gently removed using a sterile soft brush to avoid damaging the wood substrate or the coating. Then, the specimens were oven-dried, followed by weighing them all to further calculate the percentage of mass loss.

2.4. Measurement of the Mechanical Property

As the specimen dimensions for this mechanical property for solid wood species are rather small (20 × 20 × 50 mm), and the specimens can easily be exposed to the target fungus species in available dishes, this particular mechanical test was chosen. This way, the fungus-exposed specimens could be tested once their mass losses were weighed and calculated. Standard specifications of DIN 2-185 were used in this study to carry out the compression strength parallel-to-grain tests. A universal testing machine was used to test and record the values. The model of the machine was Zwick/Roell Z050. It was produced by ZwickRoell GmbH & Co. KG (located in Ulm, Germany)and was used at the Thünen Institute of Wood Research (Hamburg, Germany).

2.5. SEM Imaging

An FEI Quanta 250 FESEM (field-emission) was used for scanning electron microscopy. The apparatus was produced by FEI Co. (Hillsboro, OR, USA). Cutting the specimens to the final size of 10 × 10 × 2 mm was first to be carried out. Before delicate cutting of the target surfaces, they were wetted with distilled water, using a sponge. The target surface was then cut to a final smooth surface by a razor blade. Once dried at room conditions for 24 h, the prepared specimens were mounted onto aluminum holders, using carbon paste to fix them in position. The final step was sputter-coating the target surfaces. A thin layer of gold was coated on them.

2.6. Statistical Analysis

Two-way analyses of variance (ANOVA) were separately used in this study to determine statistically significant differences between the treatments at a 95% level of confidence (p < 0.05) to find out the effects of the variables on the two properties measured. The analyses were carried out by SPSS software (version 18, 2010) to determine significant differences between treatments at a 95% level of confidence. It was followed by Duncan’s multiple range test to ascertain groupings among them. For the mass loss ANOVA and Duncan test, a total of90 specimens were analyzed and categorized into three wood species and size treatments (5 replicates). The total number of specimens for the compression strength statistical analyses was 72 (4 replicates). Using the same sets of data, fitted-line, contour, and surface plots were also designed by Minitab software (16.2.2, 2010) to provide a visual estimate of trends. Hierarchical cluster analysis was also performed for each wood species to show similarities (and dissimilarities as well) between the studied treatments. The statistical significance for the cluster analyses was set at p < 0.05, based on more than one property in a single run. The scaled indicator on each cluster analysis indicates the degree of similarity or dissimilarity between the treatments. Those treatments connected to each other with lower numbers on the scaled bar are assumed to have more similarities than those connected with larger numbers. The scale No. 25 indicates the maximum dissimilarity between the studied treatments.

3. Results and Discussions

The statistical analysis indicated that the variances were equal across groups (p < 0.05). The control (neither coated nor heat-treated) beech wood specimens had the highest value (42.4%) for mass loss (ML) (Table 1). The control poplar and spruce specimens showed lower mass losses of 27.95% and 13.3%, respectively (Table 1). These differences reflected the inherent susceptibility of the wood species to Trametes versicolor, with beech being prone to fungal decay, as it is categorized in the “Not Durable” group based on the durability rating standard classification, according to CEN/TS 15083-2 [35]. SEM images demonstrated that the fungus’s mycelium could penetrate without any obstacle from a cell to the adjacent one through pits, openings, or any possible cracks (Figure 2). This illustrated the way fungal mycelium spreads throughout wood bodies.
Among the unheated wood species, the plain acrylic paint demonstrated the highest decreasing impact on ML in the poplar specimens; the mass loss was decreased by 83% (from 27.9% in the control specimens to 4.7% in the coated specimens with plain acrylic paint). The decreasing impacts of plain paint in the unheated specimens were followed by the spruce (76%) and beech specimens (29%) (Table 1). The highly significant difference in the mass losses between the uncoated and the coated (with either the plain or graphene-enriched paints) was attributed to the paint layer, blocking the openings through which mycelium could penetrate and acting as an effective physical barrier toward the penetration of the fungus’s mycelium.
In terms of the lower impact of the plain acrylic paint on the ML values in the control beech specimens (the above-mentioned 29%), some findings from previous studies should be first duly noted. Databases on wood properties indicate that swelling in beech wood is several times more than poplar wood. In this connection, visual examination of the specimens exposed to T. versicolor for four months revealed the deterioration of the paint layer in the beech specimens (Figure 3A). However, the paint layer was practically intact in the poplar and spruce specimens after four months of exposure to T. versicolor (Figure 3B). The effect of lower moisture sorption characteristics on fungal decay was also reported by Kim et al. [36] in wood–plastic composites (WPCs). The cited authors reported that wood fillers with lower moisture content caused lower fungal decay in WPCs. Based on the above, the comparatively lower influence of the plain paint in the control beech treatment is hypothesized to be related to its high moisture absorption and the high swelling coefficient thereof. However, the measurements of neither moisture content nor the swelling of the specimens were parts of the experiments here; therefore, further supplementary research should cover these properties before a final conclusion.
The graphene-enriched paint maintained the mass losses under 5% in absolutely all treatments and the two variables of wood species and heat treatment. In terms of the unheated specimens, the impact of the addition of graphene demonstrated the highest impact. The addition of graphene in the heat-treated specimens showed no statistically significant effects in poplar or spruce specimens but produced a 63% reduction in beech specimens. The improved protection provided by the graphene-enriched coating is attributed to several mechanisms that acted simultaneously. In this connection, it was reported that graphene had a reinforcing role in coating films by spreading the applied stresses over the whole film instead of letting them bunch up on one spot, significantly keeping the integrity of the coating films, even when a multi-axial stress was applied [25]. Katamipour et al. [16] showed that sonication together with magnetic stirring improved homogeneity in nanoparticle–polymer composite systems, achieving surfaces that were harder and more uniform. In the present study, the improved mechanical resilience and hardness of the coating film overcame the internal stresses in even beech specimens with a very high baseline swelling coefficient, eventually preserving its integrity against the penetration of the fungus’s mycelium. This improved integrity was observed in the increased values of the compression strength, too (Table 2).
Additional mechanisms were also brought up in the literature carried out by researchers to explain the improved protective performance of graphene-containing polymer coatings, including enhanced barrier properties that reduce the transport of moisture and oxygen through the coating, reinforcement of the polymer matrix, stress transfer, and the intrinsic antimicrobial activity of graphene arising from oxidative stress and physical interactions with microbial cell membranes [15,17,22,23].
The above-mentioned mechanisms are all consistent with the substantial reduction in fungal decay and, therefore, provide plausible explanations for the achieved results. In this connection, the improved strength and integrity of the graphene-enriched film can be considered as another corroborating evidence of the improving effects of graphene on the spread of stresses and keeping the resilience of the paint film (Figure 3C).
The uncoated specimens showed reduced mass losses caused by heat treatment. The highest improving impact was seen in poplar. The beech, poplar, and spruce experienced mass losses that decreased by 57%, 82% and 67%, respectively (Table 1). This demonstrated the impact of the modification on the durability against fungal decay even in the uncoated specimens of all three species (Table 1). Thermal degradation of wood polymers and the chemical changes thereof caused the improvement in the biological resistance to the fungus [7,8,11]. Heat treatment also affected the extractive content, thus reducing wood’s ability to absorb moisture and supply initial nutrients for the fungus [3,7,11]. Those poplar and spruce specimens that were both heat-treated and coated (with either of the paint types, with or without graphene) showed no statistical difference in their ML values (Table 1). This can also be caused as a result of the thermal degradation of lignin and holocellulose, altering the number of active hydroxyl groups and altering the hydroxyl groups of the polymers (mainly in cellulose and hemicellulose) in a way that eventually reduces the hygroscopicity. However, experiments with longer durations of fungal exposure are needed to come to a firm conclusion about whether graphene is always neutral in heat-treated poplar and spruce or only in durations shorter than four months.
In terms of the results of the mechanical property measured here, the highest compression strength was seen in the beech specimens, which were heat-treated and coated with the type of acrylic paint containing graphene but unexposed to the fungus (64.1 N·mm−2). On the other spectrum, the lowest compression strength was seen in the control specimens (uncoated and unheated, 13 N·mm−2) exposed to T. versicolor (Table 2). Among the unexposed specimens, beech specimens demonstrated generally higher values of compression strengths than poplar and spruce, whereas poplar and spruce exhibited relatively similar values under different treatments (Table 2). The higher compression strength in beech was attributed to its higher density, thus having higher woody mass that naturally caused higher strength. Poplar and spruce were in the same density category, and therefore, their compression strengths showed no statistical significance.
Exposure to Trametes versicolor caused significant reductions in the compression strength in the control specimens for all species, with decreases of 75% (beech), 55.1% (poplar), and 42.2% (spruce), compared to the unexposed controls (Table 2). Coating of the control (unheated) specimens with the acrylic paint that did not contain graphene significantly protected them from the fungal damage. Graphene demonstrated a generally higher protective and improving impact against T. versicolor decay damages; the compression strength values in all treatments that were coated with the acrylic paint containing graphene were higher compared with those uncoated treatments, either the control or heat-treated (Table 2).
The heat treatment demonstrated an increasing impact on compression strengths of all three wood species (Table 2). The increased compression strength was attributed to two phenomena called “glass transition of lignin” [3,8,36,37,38,39] and “irreversible hydrogen bonding” [11,40,41,42,43,44]. The results of the phenomena were repolymerization and condensation of lignin fragments during which extra and irreversible cross-linking bonds are formed, strengthening the existing bonds between lignin and hemicellulose, ultimately increasing the compression strength.
The effect of the addition of graphene on the compatibility of the coating with the heat-treated substrates can also be discussed here. Graphene-enriched coatings were reported to demonstrate advanced “smart” capabilities [18]. This implies that graphene-enriched acrylic paint in the present study could have positively synergized with the heat-treated wood substrates, providing a multifunctional solution for high-value wood products that require long-term protection under fluctuating environmental conditions (mostly temperature and humidity). Moreover, decorated graphene oxide was reported to improve char yield and to shift the thermal decomposition pathways and mechanisms in epoxy systems [45]. However, further studies are needed to clarify the extent of the synergistic compatibility under various thermal modification regimes.
High and statistically significant correlations (R-squared values of more than 90%) were calculated between mass losses versus compression strengths (after fungal exposure) in the beech and spruce specimens. In the poplar specimens, the R-squared value was 62%. The strong correlations between the mass loss and the residual compression strength values indicated a close association between fungal degradation and mechanical performance. However, these statistical relationships should not be interpreted as direct evidence of the sole causal mechanisms. Instead, they supported the overall trend that the increased fungal deterioration was accompanied by reduced mechanical strength under the experimental conditions of the present study.
In this connection, smooth trends were found (between ML and compression strengths) in contour and surface plots that were designed for beech treatments, before and after the exposure to T. versicolor (Figure 4A,B). This indicated the significant relationship between these properties.
Cluster analyses of the six treatments in each species (beech, poplar, and spruce) based on the two measured properties demonstrated that control treatments (the unpainted specimens that were not heated) were remotely connected in the cluster to the uncoated specimens that were heat-treated (Figure 5A–C). This showed the highly significant impact of thermal modification on decay resistance against this wood decay fungus. In terms of the coated specimens, all the coated specimens were grouped quite remotely in comparison to the control treatments in poplar and spruce species; only the unheated beech specimens with the plain paint were clustered rather closely to the control beech treatment (the uncoated and unheated). This different clustering implied that the acrylic paint acted differently on specimens with low and medium densities; that is, in poplar and spruce specimens (both with rather low densities), even a simple layer of paint had a significant impact on protection of the specimens against T. versicolor. However, in beech specimens with higher density, the protection was not as much. This can be observed from the values of the two properties studied in the coated beech versus the painted poplar and spruce specimens (Table 1 and Table 2). From a general point of view, application of the graphene-enriched acrylic paint illustrated a statistically significant impact of the clustering of the treatments: those treatments coated with the paint that contained graphene were quite similarly connected, regardless of the wood species and substrate wood being either unheated or heated.
Based on the results obtained in the present study and the reviewed literature, the enhanced performance of the graphene-enriched acrylic coating was attributed to the following mechanisms, acting simultaneously:
  • An improved mechanical strength and stability of the coating, reported to promote more effective stress redistribution within graphene-containing polymer matrices [25];
  • Enhanced barrier properties that reduced the passing of moisture and oxygen through the coating [15,22];
  • Reinforcement of the coating matrix, potentially improving its resistance to cracking under dimensional changes of the wood substrate and the internal stresses thereof [16,25];
  • Antifungal property of graphene [22,23];
  • A potential synergistic interaction between the graphene-enriched coating and thermally modified wood substrates [18,45].
The extent of contribution of each of these mechanisms was not experimentally determined in this study. Therefore, they should be regarded as literature-supported. In this connection, future studies can investigate detailed coating characterization, including adhesion strength, surface roughness and hardness, wettability, Raman mapping, rheological measurements, and water and oxygen permeability and barrier performance, in order to establish a firm conclusion and a more comprehensive understanding of the mechanisms involved.
Only one graphene content (12 wt%) was investigated here. However, with the promising results achieved in this study, further research studies should be especially designed to find out optimum content. In this regard, it is to be noted that the polymer (paint) type and the content level of graphene may affect the dispersion quality, viscosity, film formation, and ultimately the protective performance of the coating. Moreover, different paint consumptions were measured for the plain and the graphene-enriched acrylic paints. The difference could not be avoided, as the viscosity of the paint was altered by the addition of graphene. In this connection, further studies should investigate the extent of impact of paints with different graphene contents while having the same consumption levels.
Although the present study demonstrated promising and effective protective performance against Trametes versicolor, the results cannot be generalized to all wood-decay fungi. Different fungal species employ different degradation mechanisms and may respond differently to graphene-containing coatings. Future investigations should cover the performance of graphene-enriched coatings against a broader spectrum of wood-decay organisms, including representative brown-rot fungi, including Coniophora puteana and possibly Gloeophyllum trabeum (and even some soft-rot fungi as well);wood-boring insects and termites; accelerated weathering; and ultraviolet (UV) exposure in order to determine whether the protective effects observed in the present study can also be true for all. Moreover, long-term durability tests of the coating under natural service conditions would provide reliable criteria for the commercial sector.
In addition to the above, some practical aspects should be considered before the large-scale commercial implementation, among which a cost/benefit analysis and environmental and occupational safety considerations would be essential. Furthermore, uniform dispersion of graphene would be a challenge at an industrial scale as a result of its powerful interactions (like van der Waals), as would the consequent agglomeration [25,26,27]. The above-mentioned areas can provide the commercial sector with reliable information to comply with the national and international regulations and provisions. It is to be noted that the promising results on the addition of graphene to polymer matrices achieved so far in this and other studies provide the logical basis for the industry to consider further practical surveys on the utilization of graphene.

4. Conclusions

Incorporation of graphene into acrylic paint significantly reduced mass losses caused by exposure to Trametes versicolor in all three wood species (namely beech, poplar, and spruce wood). Graphene-enriched acrylic paint also helped maintain the compression strength values in the specimens that were exposed to T. versicolor. The potential of graphene-enriched acrylic paint can provide further improvements in the biological protection of heat-treated wood substrates at a mild temperature against wood-decay fungi.

Author Contributions

Conceptualization, H.R.T., O.S. and A.P.; methodology, H.R.T., E.N., R.M. and M.H.S.; software, H.R.T., E.N., M.T. and M.H.S.; formal analysis, H.R.T., E.N., A.P. and R.M.; investigation, H.R.T., E.N., A.P., M.H.S. and M.T.; resources, H.R.T., E.N. and M.H.S.; data curation, H.R.T., E.N. and R.M.; writing—original draft preparation, H.R.T., A.P. and A.N.P.; writing—review and editing, H.R.T., A.P. and A.N.P.; visualization, H.R.T., E.N. and R.M.; supervision, H.R.T., A.P. and A.N.P.; project administration, H.R.T., E.N. and R.M., funding acquisition, H.R.T., E.N. and M.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained and presented within the article.

Acknowledgments

The first author is grateful to the Alexander von Humboldt Stiftung (Germany) for providing the opportunity for him to do the tests at Hamburg University. He also appreciates the departed Olaf Schmidt for providing the necessary facilities for fungal culture at his laboratory.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 17 00871 g001
Figure 1. Atomic structure of the Ni-doped graphene flakes (reproduced from [33], with permission from the authors).
Figure 1. Atomic structure of the Ni-doped graphene flakes (reproduced from [33], with permission from the authors).
Forests 17 00871 g001
Forests 17 00871 g002aForests 17 00871 g002b
Figure 2. SEM micro-images showing Trametes versicolor mycelium ((A,B) ↓) proceeding its way from the cavity of one wood cell to the cavity of the neighboring cell through pits and openings that existed between them.
Figure 2. SEM micro-images showing Trametes versicolor mycelium ((A,B) ↓) proceeding its way from the cavity of one wood cell to the cavity of the neighboring cell through pits and openings that existed between them.
Forests 17 00871 g002aForests 17 00871 g002b
Forests 17 00871 g003
Figure 3. (A) A beech specimen coated with plain acrylic paint showing deteriorated and wiped-out paint layers (↓); (B) a poplar specimen with plain acrylic paint showing an intact paint film after four months of exposure; and (C) a beech specimen painted with graphene-added acrylic paint demonstrating the integrity of the paint layer after being exposed to Trametes versicolor for four months, though some scattered cracks can be observed on the paint layer (↓). [The scaled bars are in millimeters].
Figure 3. (A) A beech specimen coated with plain acrylic paint showing deteriorated and wiped-out paint layers (↓); (B) a poplar specimen with plain acrylic paint showing an intact paint film after four months of exposure; and (C) a beech specimen painted with graphene-added acrylic paint demonstrating the integrity of the paint layer after being exposed to Trametes versicolor for four months, though some scattered cracks can be observed on the paint layer (↓). [The scaled bars are in millimeters].
Forests 17 00871 g003
Forests 17 00871 g004
Figure 4. Contour (A) and surface (B) plots between the two studied properties (including fungal mass loss caused by being exposed for four months to T. versicolor and the values for compression strength parallel to grain in two separate specimens that were and were not exposed to the fungus) in beech specimens.
Figure 4. Contour (A) and surface (B) plots between the two studied properties (including fungal mass loss caused by being exposed for four months to T. versicolor and the values for compression strength parallel to grain in two separate specimens that were and were not exposed to the fungus) in beech specimens.
Forests 17 00871 g004
Forests 17 00871 g005
Figure 5. Cluster analyses separately designed for each of the wood species and their six treatments ((A) beech; (B) poplar; (C) spruce), based on their mass losses and also the compression strengths parallel to grain for the treatments that passed a four-month exposure period to Trametes versicolor (Gr = coated treatments with the acrylic paint containing graphene; HT = treatments that were heat-treated).
Figure 5. Cluster analyses separately designed for each of the wood species and their six treatments ((A) beech; (B) poplar; (C) spruce), based on their mass losses and also the compression strengths parallel to grain for the treatments that passed a four-month exposure period to Trametes versicolor (Gr = coated treatments with the acrylic paint containing graphene; HT = treatments that were heat-treated).
Forests 17 00871 g005
Table 1. Mass losses (%) in beech, poplar, and spruce wood specimens, caused by being exposed to the white-rot wood-decay fungus Trametes versicolor (Painted = coated specimens with acrylic paint that contained no additive; Graphene-Painted = coated specimens with acrylic paint that were enriched with graphene).
Table 1. Mass losses (%) in beech, poplar, and spruce wood specimens, caused by being exposed to the white-rot wood-decay fungus Trametes versicolor (Painted = coated specimens with acrylic paint that contained no additive; Graphene-Painted = coated specimens with acrylic paint that were enriched with graphene).
TreatmentsMass Loss (%)
UnheatedHeat-Treated at 185 °C
Wood SpeciesControl (Unpainted)PaintedGraphene-PaintedUnpaintedPaintedGraphene-Painted
Beech42.4
[3.20] 1
(A) 2		29.9
[2.01]
(B)		4.5
[0.51]
(D)		17.9
[0.93]
(C)		4.2
[0.41]
(D)		1.6
[0.49]
(E)
Poplar27.9
[4.74]
(A)		4.7
[0.58]
(BC)		1.9
[0.34]
(C)		4.9
[0.64]
(B)		2.4
[0.49]
(BC)		2.6
[0.34]
(BC)
Spruce13.3
[1.88]
(A)		3.2
[0.53]
(B)		1.8
[0.31]
(C)		4.3
[0.40]
(B)		1.5
[0.40]
(C)		1.7
[0.29]
(C)
1 (Figures in square brackets represent the standard deviation values for each treatment). 2 (Letters in parenthesis represent the Duncan groupings, α < 0.05).
Table 2. The mechanical property of compression strength parallel to grain values (N·mm−2) in different beech, poplar, and spruce treatments; exposure to Trametes versicolor was carried out for a duration of four months in glass jars (Painted = coated specimens with acrylic paint that contained no additive; Graphene-Painted = coated specimens with acrylic paint that were enriched with graphene).
Table 2. The mechanical property of compression strength parallel to grain values (N·mm−2) in different beech, poplar, and spruce treatments; exposure to Trametes versicolor was carried out for a duration of four months in glass jars (Painted = coated specimens with acrylic paint that contained no additive; Graphene-Painted = coated specimens with acrylic paint that were enriched with graphene).
TreatmentsCompression Strength Parallel to Grain (N·mm−2)
UnheatedHeat-Treated at 185 °C
Wood SpeciesUnpaintedPaintedGraphene-PaintedUnpaintedPaintedGraphene-Painted
BeechUnexposed52.1
[8.11] 1
(BC) 2		53.1
[6.10]
(BC)		53.6
[4.19]
(BC)		62.1
[3.55]
(A)		59.0
[5.77]
(AB)		64.1
[4.62]
(A)
Exposed13.0
[2.69]
(G)		23.1
[2.35]
(F)		42.3
[2.89]
(D)		34.1
[3.51]
(E)		48.5
[4.83]
(CD)		57.9
[5.31]
(AB)
PoplarUnexposed39.4
[6.00]
(AB)		40.7
[3.19]
(AB)		38.7
[6.49]
(AB)		44.0
[5.24]
(A)		41.9
[3.07]
(A)		44.9
[3.98]
(A)
Exposed17.7
[3.47]
(D)		30.7
[5.09]
(C)		29.1
[2.79]
(C)		41.1
[5.15]
(AB)		41.2
[6.48]
(AB)		39.7
[3.93]
(BC)
SpruceUnexposed34.8
[3.58]
(CD)		35.8
[2.10]
(BCD)		39.3
[3.82]
(B)		37.9
[1.95]
(BC)		39.3
[2.55]
(B)		45.6
[2.90]
(A)
Exposed20.1
[1.86]
(F)		30.5
[3.59]
(E)		34.0
[2.16]
(CDE)		32.8
[1.89]
(DE)		37.0
[2.72]
(BCD)		36.4
[2.00]
(BCD)
1 (Figures in square brackets represent the standard deviation values for each treatment). 2 (Letters in parenthesis represent the Duncan groupings, α < 0.05).
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Taghiyari, H.R.; Nadali, E.; Pizzi, A.; Majidi, R.; Taheri, M.; Sowlat, M.H.; Schmidt, O.; Papadopoulos, A.N. Graphene-Enriched Acrylic Paint to Preserve Wood Substrates from Trametes versicolor. Forests 2026, 17, 871. https://doi.org/10.3390/f17080871

AMA Style

Taghiyari HR, Nadali E, Pizzi A, Majidi R, Taheri M, Sowlat MH, Schmidt O, Papadopoulos AN. Graphene-Enriched Acrylic Paint to Preserve Wood Substrates from Trametes versicolor. Forests. 2026; 17(8):871. https://doi.org/10.3390/f17080871

Chicago/Turabian Style

Taghiyari, Hamid R., Elham Nadali, Antonio Pizzi, Roya Majidi, Mohammad Taheri, Mohammad Hassan Sowlat, Olaf Schmidt, and Antonios N. Papadopoulos. 2026. "Graphene-Enriched Acrylic Paint to Preserve Wood Substrates from Trametes versicolor" Forests 17, no. 8: 871. https://doi.org/10.3390/f17080871

APA Style

Taghiyari, H. R., Nadali, E., Pizzi, A., Majidi, R., Taheri, M., Sowlat, M. H., Schmidt, O., & Papadopoulos, A. N. (2026). Graphene-Enriched Acrylic Paint to Preserve Wood Substrates from Trametes versicolor. Forests, 17(8), 871. https://doi.org/10.3390/f17080871

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