Special Issue "Wood Modification: Characterization, Modelling and Applications"

A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: closed (15 May 2021).

Special Issue Editors

Dr. Anna Sandak
E-Mail Website
Guest Editor
InnoRenew CoE, Izola, Slovenia & Faculty of Mathematics, Natural Sciences and Information Technologies, University of Primorska, Koper, Slovenia
Interests: bio-based materials; wood modification; materials functionalization; biomimicry; multi-sensor characterization; spectroscopy; chemometrics
Prof. Dr. Jakub Sandak
E-Mail Website
Guest Editor
InnoRenew CoE, Izola, Slovenia & Andrej Marušič Institute, University of Primorska, Koper, Slovenia
Interests: wood surface; inorganic materials; lignin; biomass; spectroscopy; numerical modelling; chemometrics; machining

Special Issue Information

Dear Colleagues,

Wood has been recognized (again) as an attractive alternative to several traditional construction solutions, and it is often called the “building material of the 21st century”. However, compared with traditional materials, wood possesses some technical limitations and properties that, because they are less understood, remain difficult to control. The most problematic are low-dimensional stability, thermal steadiness, limited fire resistance, biotic and abiotic degradation resistance, and varying mechanical properties highly affected by the morphological structure of wood. These properties need to be improved to further enlarge wood application fields, as well as reinforce the confidence of architects, engineers, and consumers when using wood. New developments in the field of wood modification resulted in the discovery of highly innovative materials with enhanced properties for natural timber. Several of these reached the highest readiness level and are now mass-produced in high volumes. Further intensive research is in progress to discover new wood modification solutions to assure improvement of wood properties and functionality, allowing elongated service life and reducing the risk of unexpected product failure.

We would like to invite you to disseminate your latest research results by contributing to a Special Issue of the Coatings journal. This Special Issue will report on progress in enhancement of native wood properties through a wide range of chemical, biological, or physical agents. Both surface and bulk modifications are within the scope, with contributions regarding diverse aspects of surface coating especially appreciated.

In particular, the topics of interest include, but are not limited to the following:

  • Assessment and monitoring of service life performance
  • Bioinspired modification methods
  • Effect of materials preparation and modification procedure
  • Environmental impact of treatments
  • Machinability and finishing of modified wood
  • Maintenance action and renovation scheduling
  • Modelling and characterization methods
  • Multifunctional treatments
  • Novel formulations and serviceability
  • Perception and marketing of modified wood
  • Surface and bulk modification processes
  • Understanding of deterioration processes

We are looking forward to receiving your contribution.

With sincere regards,

Prof. Dr. Anna Sandak
Prof. Dr. Jakub Sandak
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (13 papers)

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Editorial

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Editorial
Special Issue “Wood Modification: Characterization, Modelling, and Applications”
Coatings 2021, 11(7), 869; https://doi.org/10.3390/coatings11070869 - 20 Jul 2021
Viewed by 516
Abstract
Wood has been recognized as an attractive alternative to several other traditional construction solutions, and it is often called the “building material of the 21st century” [...] Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)

Research

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Article
Bioinspired Living Coating System in Service: Evaluation of the Wood Protected with Biofinish during One-Year Natural Weathering
Coatings 2021, 11(6), 701; https://doi.org/10.3390/coatings11060701 - 11 Jun 2021
Cited by 1 | Viewed by 796
Abstract
The service life performance of timber products exposed to natural weathering is a critical factor limiting the broad use of wood as an external building element. The goal of this study was to investigate the in-service characterization of an innovative biofinish coating system. [...] Read more.
The service life performance of timber products exposed to natural weathering is a critical factor limiting the broad use of wood as an external building element. The goal of this study was to investigate the in-service characterization of an innovative biofinish coating system. It is a novel surface finishing solution based on the bioinspired concept of living fungal cells designed for effective wood protection. The performance of Scots pine (Pinus sylvestris L.) wood coated with biofinish was compared with uncoated references. Samples were exposed to natural weathering for 12 months under the climatic conditions of northern Italy. The visual appearance, colour, gloss, wettability, and 3D surface topography of the wood surface were examined. Results revealed that the total colour changes (∆E) of biofinish-coated wood were negligible. Untreated Scots pine wood revealed the changes in colour after just three months of exposure. The gloss changes of both surface types were small. The contact angle measured on biofinish-coated wood was higher compared to that of uncoated Scots pine. Surface roughness increased in uncoated wood due to the erosion effect caused by the weathering progress. Conversely, the surface roughness of biofinish-coated samples decreased along the exposure time. This phenomenon was explained by two self-healing mechanisms: migration of non-polymerized oil to the cracked surface, where it polymerizes and creates a closed layer, and local regrowth to cover damaged spots by living fungal cells present in the coating. The obtained results revealed the superior aesthetic performance of the biofinish surface treatment against natural weathering. By considering the fully bio-based nature of the investigated coating, it was concluded that this solution can be an attractive alternative for state-of-the-art wood protection technologies. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Hybrid Approach for Wood Modification: Characterization and Evaluation of Weathering Resistance of Coatings on Acetylated Wood
Coatings 2021, 11(6), 658; https://doi.org/10.3390/coatings11060658 - 30 May 2021
Cited by 1 | Viewed by 772
Abstract
Wood, as a biological material, is sensitive to environmental conditions and microorganisms; therefore, wood products require protective measures to extend their service life in outdoor applications. Several modification processes are available for the improvement of wood properties, including commercially available solutions. Among the [...] Read more.
Wood, as a biological material, is sensitive to environmental conditions and microorganisms; therefore, wood products require protective measures to extend their service life in outdoor applications. Several modification processes are available for the improvement of wood properties, including commercially available solutions. Among the chemical treatments, acetylation by acetic anhydride is one of the most effective methods to induce chemical changes in the constitutive polymers at the cellular wall level. Acetylation reduces wood shrinkage-swelling, increases its durability against biotic agents, improves UV resistance and reduces surface erosion. However, even if the expected service life for external cladding of acetylated wood is estimated to be 60 years, the aesthetics change rapidly during the first years of exposure. Hybrid, or fusion, modification includes processes where the positive effect of a single treatment can be multiplied by merging with additional follow-up modifications. This report presents results of the performance tests of wood samples that, besides the modification by means of acetylation, were additionally protected with seven commercially available coatings. Natural weathering was conducted in Northern Italy for 15 months. Samples were characterized with numerous instruments by measuring samples collected from the stand every three months. Superior performance was observed on samples that merged both treatments. It is due to the combined effect of the wood acetylation and surface coating. Limited shrinkage/swelling of the bulk substrate due to chemical treatment substantially reduced stresses of the coating film. Hybrid process, compared to sole acetylation of wood, assured superior visual performance of the wood surface by preserving its original appearance. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Communication
Glossiness Evaluation of Coated Wood Surfaces as Function of Varnish Type and Exposure to Different Conditions
Coatings 2021, 11(5), 558; https://doi.org/10.3390/coatings11050558 - 09 May 2021
Cited by 4 | Viewed by 590
Abstract
The objective of this study was to evaluate the glossiness of black alder wood (Alnus glutinosa L.) samples coated with two varnish types as a function of exposure to dry heat and artificial aging. The chemical resistance of the coated samples to [...] Read more.
The objective of this study was to evaluate the glossiness of black alder wood (Alnus glutinosa L.) samples coated with two varnish types as a function of exposure to dry heat and artificial aging. The chemical resistance of the coated samples to cold liquids was also evaluated. Based on the findings in this work, it appears that the varnish types and their structural differences influenced the overall glossiness of the coated samples. The UV varnish exhibited higher gloss values than those coated with the water-borne product within the range of silky gloss and silky matte grades. The heat exposure influenced the surface glossiness of the UV-coated samples more than the samples coated with water-borne varnish. The overall gloss values of the samples decreased with the exposure time to artificial aging, resulting in no layer cracks. The cold household liquids left less visible traces on the surfaces and alcohol was found to be the strongest agent. This study could have practical applications in the furniture industry to produce value-added furniture units according to their specific conditions of indoor use. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Environmental Impact of Wood Modification
Coatings 2021, 11(3), 366; https://doi.org/10.3390/coatings11030366 - 23 Mar 2021
Cited by 2 | Viewed by 835
Abstract
The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a [...] Read more.
The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a number of environmental product declarations (EPDs). Using these data, it is possible to determine what the extra impact associated with the modification is. The process of modification results in a life extension of the product, which has implications regarding the storage of sequestered atmospheric carbon in the harvested wood products (HWP) materials’ pool and also extended maintenance cycles (e.g., longer periods between applying coatings). Furthermore, the life extension benefits imparted by wood modification need to be compared with the use of other technologies, such as conventional wood preservatives. This paper analysed the published data from a number of sources (peer-reviewed literature, published EPDs, databases) to compare the impacts associated with different modification technologies. The effect of life extension was examined by modelling the carbon flow dynamics of the HWP pool and determining the effect of different life extension scenarios. Finally, the paper examined the impact of different coating periods, and the extensions thereof, imparted by the use of different modified wood substrates. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Thermal Transmittance, Dimensional Stability, and Mechanical Properties of a Three-Layer Laminated Wood Made from Fir and Meranti and Its Potential Application for Wood-Frame Windows
Coatings 2021, 11(3), 304; https://doi.org/10.3390/coatings11030304 - 07 Mar 2021
Cited by 3 | Viewed by 581
Abstract
The aim of this paper was to investigate the physical (thermal transmittance and dimensional stability) and mechanical properties of two types of three layer laminated wood made from fir and meranti; fir in surface layers and meranti in core (FMF) and vice versa [...] Read more.
The aim of this paper was to investigate the physical (thermal transmittance and dimensional stability) and mechanical properties of two types of three layer laminated wood made from fir and meranti; fir in surface layers and meranti in core (FMF) and vice versa (MFM) and to examine its potential application for wood-frame windows. An additional objective was to compare the properties of the laminated wood with those of solid wood, namely meranti and fir. Both types of laminated wood had by far substantial lower bending properties than solid wood. MFM laminated wood performed better than the FMF as far as the physical and mechanical properties are concerned. Water absorption and thickness swelling of MFM laminated wood were substantially lower than those of the FMF type, and all the differences were statistically significant. Longitudinal width swelling, and bending properties of MFM laminated wood were higher than those of FMF but these differences were not statistically significant. The thermal transmittance (rate of the heat transferred) of the FMF window is 13.3% better (less) compared to the MFM window. The main reason for this is believed to be the lower overall density of the FMF window, which also makes it more competitive as a result of the reduced manufacturing cost since fir is less expensive compared tomeranti. It was concluded that wood-frame windows can be successfully made from these types of laminated wood, employing therefore easily renewable materials, with low environmental impact, recyclable and manageable in the medium term. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Characterization of Arctic Driftwood as Naturally Modified Material. Part 1: Machinability
Coatings 2021, 11(3), 278; https://doi.org/10.3390/coatings11030278 - 26 Feb 2021
Cited by 1 | Viewed by 645
Abstract
Arctic driftwood has reached the coast of Iceland for centuries. This material was used by the inhabitants of the island as a building material for houses, boats, churches and pasture fences. Nowadays, the driftwood is used in the furniture industry, for the finishing [...] Read more.
Arctic driftwood has reached the coast of Iceland for centuries. This material was used by the inhabitants of the island as a building material for houses, boats, churches and pasture fences. Nowadays, the driftwood is used in the furniture industry, for the finishing of internal and external walls of buildings and also by artists. The properties of driftwood differ to that of original resource due the long-term effects of exposure to Arctic Sea water and ice. This process can be considered as a natural modification, even if its effect on various wood properties and the potential use of driftwood are not yet fully understand. This research is focused on the comparison of cutting forces measured for Siberian larch (Larix sibirica L.) from Siberia provenance and driftwood found on the coast of Iceland. The cutting forces were determined directly from the cutting power signal that was recorded during the frame sawing process. A new procedure for compensation of the late/early wood ratio variation within annual rings is proposed to homogenize mechanical properties of wood. It allows a direct comparison of machinability for both types of larch wood investigated (driftwood and natural). Noticeable differences of normalized cutting force values were noticed for both wood types, which were statistically significant for two set values of feed per tooth. These results provide a new understanding of the effect of the drifting process in the Arctic Sea (natural modification) on mechanical and physical properties of wood. Such a natural modification may influence transformation processes of driftwood as well as performance of the coating systems applied on its surface. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Physical, Optical, and Visual Performance of Coated Cross-Laminated Timber during Natural and Artificial Weathering
Coatings 2021, 11(2), 252; https://doi.org/10.3390/coatings11020252 - 20 Feb 2021
Cited by 3 | Viewed by 656
Abstract
Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based [...] Read more.
Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based on visual appearance, color change (CIE*L*a*b), gloss changes, and water intrusion. From the five exterior wood coatings evaluated, only two showed adequate performance after twelve months field exposure. Based on visual ratings following the ASTM procedures, coating failure occurs more quickly in Mississippi than in Wisconsin, due to its greater decay zone. Both location and coating type impacted the aging of the samples. Artificial weathering results were consistent with natural weathering indicating the two adequate coatings were the most resistant to failure, color, and gloss change. For future studies, new coatings designed for the protection of end-grain in CLT panels should be a target of research and development. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
A Method for Accelerated Natural Weathering of Wood Subsurface and Its Multilevel Characterization
Coatings 2021, 11(2), 126; https://doi.org/10.3390/coatings11020126 - 23 Jan 2021
Cited by 4 | Viewed by 882
Abstract
The function of altering weathering factors and degradation mechanisms are essential for understanding the weathering process of materials. The goal of this work was to develop a method for the acceleration of natural weathering and to investigate the molecular, microstructure and macrostructure degradation [...] Read more.
The function of altering weathering factors and degradation mechanisms are essential for understanding the weathering process of materials. The goal of this work was to develop a method for the acceleration of natural weathering and to investigate the molecular, microstructure and macrostructure degradation of wood caused by the process. Tests were performed in the whole month of July, which, according to previous research, is considered as the most severe for weathering of wood micro-sections. Sample appearance was evaluated by colour measurement. Scanning electron microscopy was used for evaluation of the structural integrity and changes in the microstructure of wood morphological components. Changes on the molecular level were assessed by means of FT-IR spectroscopy. Observation of the effects of weathering allowed a better understanding of the degradation process. Typical structural damage, such as cracks on bordered pits and cross-field pits, and, as a consequence, their erosion, revealed the sequence of the degradation process. It was confirmed that earlywood was more susceptible to damage than latewood. Even if the weathering test was conducted for a relatively short time (28 days) the ultra-thin wood samples changed noticeably. The progress of alteration was similar as usually noticed for wood surfaces, but occurred at shorter exposure times. The estimated acceleration factor was ×3, compare to the natural weathering kinetics of wood. The research methodology presented can be used for the determination of the weather dose-response models essential to estimate the future service life performance of timber elements. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
The Potential Use of Seaweed (Posidonia oceanica) as an Alternative Lignocellulosic Raw Material for Wood Composites Manufacture
Coatings 2021, 11(1), 69; https://doi.org/10.3390/coatings11010069 - 08 Jan 2021
Cited by 7 | Viewed by 696
Abstract
A big challenge in the composites industry is the availability of cheap raw lignocellulosic materials, potential candidates to replace slow growing trees, in order to minimize the production cost. Therefore, a variety of plants were studied and tested worldwide in composites manufacturing. The [...] Read more.
A big challenge in the composites industry is the availability of cheap raw lignocellulosic materials, potential candidates to replace slow growing trees, in order to minimize the production cost. Therefore, a variety of plants were studied and tested worldwide in composites manufacturing. The objective of this study was to investigate the technical feasibility of manufacturing particleboards from seaweed leaves (Possidonia oceanica—PO). The use of such a material may benefit both socioeconomic and environmental development since these leaves settle on seashores and decay. The results showed that an incorporation of up to 10% PO leaves did not significantly affect the mechanical properties of the board. Internal bond strength was more severely affected than the other mechanical properties. The incorporation of PO leaves up to 25% did not significantly improve the dimensional stability of the boards. Markedly, boards made from 50% wood particles and 50% PO leaves showed the best thickness swelling values. It is suggested that higher resin dosage and an alternative resin system, such as isocyanates, may improve the panel properties. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Insight of Weathering Processes Based on Monitoring Surface Characteristic of Tropical Wood Species
Coatings 2020, 10(9), 877; https://doi.org/10.3390/coatings10090877 - 11 Sep 2020
Cited by 5 | Viewed by 922
Abstract
The main aim of the presented research was to compare the influence of selected ageing factors, such as UV radiation and complex artificial weathering methods, on the colour, wettability and roughness changes in garapa, tatajuba, courbaril and massaranduba from South America—tropical wood species [...] Read more.
The main aim of the presented research was to compare the influence of selected ageing factors, such as UV radiation and complex artificial weathering methods, on the colour, wettability and roughness changes in garapa, tatajuba, courbaril and massaranduba from South America—tropical wood species that are popular for external usage in European countries. Both processes caused wood surfaces to become darker and turn to shades of brown. The highest total colour changes were shown in courbaril wood (wood with the highest extractives content). The wood surface roughness demonstrated variation, depending on the wood section and measurement direction, and increased after ageing treatments. Changes in surface contact angle were significant after the inclusion of water and drying in the weathering process (wettability decreased). Anatomical analyses of the tested tropical woods revealed structural changes after used artificial weathering treatments (distortion between cell elements, degradation of the middle lamella, micro-cracks in cell walls, thinning and degradation of parenchyma cells, cracks along pits within vessels). As a result of desorption tension, the changes caused by UV irradiation were much smaller than those caused by full artificial weathering. Fourier-transform infrared spectroscopy (FTIR) analysis indicated the occurrence of lignin and hemicelluloses oxidative changes after the weathering process which resulted in the formation of carbonyl and carboxyl compounds. The depolymerisation of cellulose was also identified. The results show that the observed changes may affect the long-term durability of finishes applied over wood subjected to weathering factors for a short period before finishing. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Review

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Review
Review of Functional Treatments for Modified Wood
Coatings 2021, 11(3), 327; https://doi.org/10.3390/coatings11030327 - 12 Mar 2021
Cited by 5 | Viewed by 972
Abstract
Wood modification is now widely recognized as offering enhanced properties of wood and overcoming issues such as dimensional instability and biodegradability which affect natural wood. Typical wood modification systems use chemical modification, impregnation modification or thermal modification, and these vary in the properties [...] Read more.
Wood modification is now widely recognized as offering enhanced properties of wood and overcoming issues such as dimensional instability and biodegradability which affect natural wood. Typical wood modification systems use chemical modification, impregnation modification or thermal modification, and these vary in the properties achieved. As control and understanding of the wood modification systems has progressed, further opportunities have arisen to add extra functionalities to the modified wood. These include UV stabilisation, fire retardancy, or enhanced suitability for paints and coatings. Thus, wood may become a multi-functional material through a series of modifications, treatments or reactions, to create a high-performance material with previously impossible properties. In this paper we review systems that combine the well-established wood modification procedures with secondary techniques or modifications to deliver emerging technologies with multi-functionality. The new applications targeted using this additional functionality are diverse and range from increased electrical conductivity, creation of sensors or responsive materials, improvement of wellbeing in the built environment, and enhanced fire and flame protection. We identified two parallel and connected themes: (1) the functionalisation of modified timber and (2) the modification of timber to provide (multi)-functionality. A wide range of nanotechnology concepts have been harnessed by this new generation of wood modifications and wood treatments. As this field is rapidly expanding, we also include within the review trends from current research in order to gauge the state of the art, and likely direction of travel of the industry. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Review
Fungal Degradation of Wood: Emerging Data, New Insights and Changing Perceptions
Coatings 2020, 10(12), 1210; https://doi.org/10.3390/coatings10121210 - 11 Dec 2020
Cited by 10 | Viewed by 863
Abstract
Wood durability researchers have long described fungal decay of timber using the starkly simple terms of white, brown and soft rot, along with the less destructive mold and stain fungi. These terms have taken on an almost iconic meaning but are only based [...] Read more.
Wood durability researchers have long described fungal decay of timber using the starkly simple terms of white, brown and soft rot, along with the less destructive mold and stain fungi. These terms have taken on an almost iconic meaning but are only based upon the outward appearance of the damaged timber. Long-term deterioration studies, as well as the emerging genetic tools, are showing the fallacy of simplifying the decay process into such broad groups. This paper briefly reviews the fundamentals of fungal decay, staining and mold processes, then uses these fundamentals as the basis for a discussion of fungal attack of wood in light of current knowledge about these processes. Biotechnological applications of decay fungi are reviewed, and an overview is presented on how fungi surmount the protective barriers that coatings provide on surfaces. Advances in biochemical analyses have, in some cases, radically altered our perceptions of how wood is degraded, and even the relationships between fungal species, while other new findings have reinforced traditional perspectives. Suggestions for future research needs in the coatings field relative to enhanced fungal and environmental protection are presented. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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