Advances in Surface Modification and Treatment of Wood

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

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 27630

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Special Issue Editor

Institute of Cellulose and Paper Technology, Celltech-paper Ltd., 9400 Sopron, Hungary
Interests: cellulose; biomacromolecular materials and technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Timber is a biosynthetic end-product, so the making of wood is a function of gene expression, the catalytic rates of structural enzymes and environmental factors. Thus, to achieve a full understanding of wood formation, each component of the full set of intrinsic processes essential for cut wood surface (i.e., chemical reactions and physical changes) must be known, investigate in complex form and information on how each one of those components is affected by other processes. Variations within a species are caused by genetic differences and regional differences in growth rate. Differences of the wood surfaces also occur between the manufacturing processes within single trees. Wood surface attributes can be established by examining a number of different physical or chemical properties. Understanding how their unique, anisotropic molecular organization, chemical linkages, branching, and other molecular features govern the micro- and macroscale accessibility is essential for coating and complex modification processes.

It is, therefore, important for scientific as well as practical reasons to qualify and quantify the wood surface treatments and modifications.

This Special Issue welcomes submissions from a wide spectrum of research with a specific focus on the comprehensive surface modification and treatment of wood. The Special Issue not only accepts wood surface modification for bio or green-related applications, but also welcomes new modification systems that have potential applications in the construction or built-in applications. In particular, papers on the structural and fundamental changes occurring in naturally aged wood surfaces, which need mechanical load-bearing functionality, are strongly desired. The interfacial interactions of the wood surface components are key concerns for the reliability of structural changes.

The papers should have a significant novelty in the wood chemical, physical, or mechanical surface modification and treatment mean and/or in the engineering applications to be considered for publication. New modification systems for potential applications will be considered as well if they offer thorough analysis and characterization of the treated surface that justify the suitability of the developed coatings for intended applications. All submissions must contain original unpublished works that are not under consideration elsewhere. Submissions will be peer-reviewed according to standard procedures for Coatings. Information about the journal can be found at https://www.mdpi.com/journal/coatings/about.

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

  • Chemical modification and treatment of wood surfaces
  • Physical modification and treatment of wood surfaces
  • Surface free energy of wood surfaces
  • Interfacial interactions
  • Wood surface modification chemicals
  • Aged wood surfaces
  • Coatings on wood surfaces etc.

Prof. Levente Csoka
Guest Editor

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 submissions that pass pre-check are 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 2600 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 (9 papers)

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Research

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16 pages, 9605 KiB  
Article
Plasma Treatment of Thermally Modified and Unmodified Norway Spruce Wood by Diffuse Coplanar Surface Barrier Discharge
Coatings 2021, 11(1), 40; https://doi.org/10.3390/coatings11010040 - 01 Jan 2021
Cited by 6 | Viewed by 2044
Abstract
This work deals with the treatment of wood surfaces by diffuse coplanar surface barrier discharge (DCSBD) generated at atmospheric pressure. The effect of the distance of the sample from the electrode surface and the composition of the working gas in the chamber was [...] Read more.
This work deals with the treatment of wood surfaces by diffuse coplanar surface barrier discharge (DCSBD) generated at atmospheric pressure. The effect of the distance of the sample from the electrode surface and the composition of the working gas in the chamber was studied. Norway spruce (Picea abies) wood, both unmodified and thermally modified, was chosen as the investigated material. The change in the surface free energy (SFE) of the wood surface was investigated by contact angles measurements. Chemical and structural changes were studied using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Activation at a 0.15 mm gap from the electrode led in all cases to an increase in the SFE. The largest change in SFE components was recorded for wood thermally modified to 200 °C. At a 1 mm gap from the electrode increase of SFE occurred only when oxygen (O2) and argon (Ar) were used as working gas. Treatment in air and nitrogen (N2) resulted in an anomalous reduction of SFE. With the growing temperature of thermal modification, this hydrophobization effect became less pronounced. The results point out the importance of precise position control during the DCSBD mediated plasma treatment. A slight reduction of SFE on thermally modified spruce was achieved also by short term ultra-violet (UV) light exposure, generated by DCSBD. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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15 pages, 9763 KiB  
Article
Peroxide Post-Treatment of Wood Impregnated with Micronized Basic Copper Carbonate
Coatings 2020, 10(12), 1213; https://doi.org/10.3390/coatings10121213 - 12 Dec 2020
Cited by 1 | Viewed by 2421
Abstract
Wood is vulnerable to significant color changes when used in exterior applications. Some copper-based wood preservatives use colorants to minimize this color change. This paper examines the ability of a peroxide post-treatment to turn wood impregnated with micronized basic copper carbonate (CuCO3 [...] Read more.
Wood is vulnerable to significant color changes when used in exterior applications. Some copper-based wood preservatives use colorants to minimize this color change. This paper examines the ability of a peroxide post-treatment to turn wood impregnated with micronized basic copper carbonate (CuCO3·Cu(OH)2) (MBCC) a stable brown color. MBCC-treated wood, with and without peroxide post-treatment, along with associated controls were evaluated for color change, erosion and black-stain fungal resistance after exposure to artificial photo-degradation. The impact of the peroxide treatment on copper leaching was assessed in a laboratory experiment, and the impact on copper reactivity was assessed by electron parametric resonance (EPR) spectroscopy. Peroxide post-treatment of wood pressure impregnated with MBCC was shown to reduce color change by more than 50% compared to controls. Erosion due to photo-degradation and colonization by black-stain fungi were lower in samples treated with MBCC than in untreated controls and were relatively unaffected by peroxide post-treatment. The peroxide post-treatment was associated with increased amounts of mobile copper. This led to increased susceptibility to leaching and to a more than 60% increase in the amount of copper than had reacted with the wood. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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13 pages, 4971 KiB  
Article
Caffeine and TiO2 Nanoparticles Treatment of Spruce and Beech Wood for Increasing Transparent Coating Resistance against UV-Radiation and Mould Attacks
Coatings 2020, 10(12), 1141; https://doi.org/10.3390/coatings10121141 - 24 Nov 2020
Cited by 19 | Viewed by 2976
Abstract
The effect of the initial modification of beech and spruce wood using a solution of caffeine and of a commercial product FN-NANO® FN-1 containing a water dispersion of TiO2 nanoparticles for increasing the service life of a transparent oil and acrylate [...] Read more.
The effect of the initial modification of beech and spruce wood using a solution of caffeine and of a commercial product FN-NANO® FN-1 containing a water dispersion of TiO2 nanoparticles for increasing the service life of a transparent oil and acrylate coatings during 6 weeks of artificial accelerated weathering was tested. Changes in colour, gloss, and the contact angle of water were monitored. Degradation of the coating film was also evaluated visually and microscopically. The resistance of the coatings to mould growth was also subsequently tested. Based on the results, it is possible to recommend the initial treatment of spruce and beech wood with a 2% caffeine solution or 15% solution of FN-NANO® dispersion to increase the overall life of a transparent acrylic coating in exterior applications. No positive effect of the applied treatments was observed with the oil coating. In addition, lower concentrations of FN-NANO® did not have a sufficient effect, and the synergistic effect of using FN-NANO® in a mixture with a 1% caffeine solution was also not confirmed. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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15 pages, 1144 KiB  
Article
The Impact of Fungicides, Plasma, UV-Additives and Weathering on the Adhesion Strength of Acrylic and Alkyd Coatings to the Norway Spruce Wood
Coatings 2020, 10(11), 1111; https://doi.org/10.3390/coatings10111111 - 19 Nov 2020
Cited by 17 | Viewed by 2037
Abstract
The adhesion strength between the transparent acrylic or alkyd coatings and the Norway spruce (Picea abies Karst L.) wood was determined by EN ISO 4624 and analyzed concerning four variables: (a) fungicidal pre-treatment of wood with boric acid or benzalkonium chloride, (b) [...] Read more.
The adhesion strength between the transparent acrylic or alkyd coatings and the Norway spruce (Picea abies Karst L.) wood was determined by EN ISO 4624 and analyzed concerning four variables: (a) fungicidal pre-treatment of wood with boric acid or benzalkonium chloride, (b) cold plasma modification of wood surfaces, (c) presence of hindered amine light stabilizer (HALS) or hydroxyphenyl-benzotriazoles (BTZ) in the role of UV-additives in coatings, and (d) weathering of coated wood—lasting 1 week in Xenotest by a modified EN 927-6, or 14, 28 and 42 weeks outdoors at 45° by EN 927-3. In the un-weathered state, the adhesion strength was positively affected by the initial plasma modification of wood surfaces, more evident with the application of acrylic water-borne coatings. On the contrary, the adhesion strength was not influenced by the fungicidal pre-treatment of wood and by the UV-additive’s presence in coatings. The adhesion was negatively affected by weathering—exponentially outdoor—irrespective of the fungicidal pre-treatment of wood, the plasma modification of wood surfaces, the coating type, and the presence of UV-additive in coatings. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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15 pages, 13301 KiB  
Article
Shelling of Growth Rings at Softwood Surfaces Exposed to Natural Weathering
Coatings 2020, 10(9), 862; https://doi.org/10.3390/coatings10090862 - 05 Sep 2020
Cited by 1 | Viewed by 2256
Abstract
Shelling is the delamination of growth rings and the projection of woody tissue from wood surfaces. Shelling disrupts coatings and makes refinishing difficult, and a better understanding of the phenomenon is needed to help alleviate its unwanted effects. We tested whether confocal profilometry [...] Read more.
Shelling is the delamination of growth rings and the projection of woody tissue from wood surfaces. Shelling disrupts coatings and makes refinishing difficult, and a better understanding of the phenomenon is needed to help alleviate its unwanted effects. We tested whether confocal profilometry could quantify shelling in flat-faced and profiled-faced western larch deckboards exposed to natural weathering and examined the effects of growth-ring orientation and angle on shelling. Confocal profilometry was able to quantify shelling in both deckboard types. Shelling developed at the surface of flat-faced deckboards oriented pith-side-up, whereas it was absent from boards oriented bark-side-up. We found an inverse correlation between the height of shelled growth rings and the angle of growth rings to the surface of flat-faced boards. Shelling occurred in profiled-faced boards oriented pith-side-up due to the delamination of growth ring tips and projection of latewood from wood surfaces. A superficially similar although less pronounced phenomenon was seen in profiled-faced boards oriented bark-side-up. The shelling of profiled-faced boards oriented pith-side-up created lanceolate-shaped slivers of latewood that projected from the peaks of profiles. Some of these latewood tips were sharp and, for this reason, we suggest that profiled-faced western larch deckboards should always be oriented bark-side-up rather than pith-side-up. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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13 pages, 642 KiB  
Article
Wettability of Wood Surface Layer Examined From Chemical Change Perspective
Coatings 2020, 10(3), 257; https://doi.org/10.3390/coatings10030257 - 10 Mar 2020
Cited by 9 | Viewed by 2513
Abstract
The effect of artificial ageing on spruce (Picea abies), beech (Fagus sylvatica L.), birch (Betula pendula), and sessile oak (Quercus petraea) wood surfaces were investigated using qualitative (total phenolic and total soluble carbohydrate content) chemical examination [...] Read more.
The effect of artificial ageing on spruce (Picea abies), beech (Fagus sylvatica L.), birch (Betula pendula), and sessile oak (Quercus petraea) wood surfaces were investigated using qualitative (total phenolic and total soluble carbohydrate content) chemical examination methods. During ageing (∑240h), the influence of surface chemistry modifications was monitored by contact angle measurements of polar, dispersive (distilled water), and dispersive (diiodomethane) liquids. The results clearly show the relation between the ratio of main chemical components of the wood surface layer and surface wettability during artificial radiation. The identified surface chemistry modifications cause more significant change in the contact angle of polar and dispersive liquid, relative to the change of dispersive liquid contact angle. Chemical changes of the wood surface layer are due to the degradation of the main wood components (cellulose, hemicelluloses, and lignin) which can be properly monitored by total phenolic (TPC) and total soluble carbohydrate content (TSCC) measurements. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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15 pages, 11394 KiB  
Article
Comparison of Exterior Coatings Applied to Oak Wood as a Function of Natural and Artificial Weathering Exposure
Coatings 2019, 9(12), 864; https://doi.org/10.3390/coatings9120864 - 16 Dec 2019
Cited by 10 | Viewed by 2800
Abstract
Artificial weathering can significantly reduce the testing time needed for proving coating durability, nevertheless its reliability is still not thoroughly proven. In this study, eight different transparent and pigmented coating systems, namely oil, acrylate, alkyd and urethane alkyd were evaluated through natural and [...] Read more.
Artificial weathering can significantly reduce the testing time needed for proving coating durability, nevertheless its reliability is still not thoroughly proven. In this study, eight different transparent and pigmented coating systems, namely oil, acrylate, alkyd and urethane alkyd were evaluated through natural and artificial weathering tests on oak samples by measuring colour, gloss and surface wettability and by macroscopic and microscopic evaluation. The oil coatings performed well in wood colour stability evaluations, while the best gloss and wettability change results were noted for acrylate coatings. Pigmented coatings were characterized by significantly lower colour changes than transparent ones. The gloss and wettability changes were more sensitive to coating disruption than to total colour changes of coated wood associated with chemical changes in wood. The findings in this work showed that values of gloss changes and surface wettability for all types of coatings exposed to artificial and natural weathering resulted in significant differences from each other. The data obtained by artificial weathering method provide basic results of coatings durability and, ideally, natural weathering should be performed at the same time to support the results from laboratory tests by exposing wood under real conditions. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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10 pages, 1975 KiB  
Article
Paint Pull-Off Strength and Permeability in Nanosilver-Impregnated and Heat-Treated Beech Wood
Coatings 2019, 9(11), 723; https://doi.org/10.3390/coatings9110723 - 01 Nov 2019
Cited by 15 | Viewed by 2424
Abstract
The effects of impregnation with nanosilver suspension as well as heat treatment on pull-off adhesion strength and specific air permeability in beech specimens were studied here. The size range of silver nanoparticles was 30–80 nm. The cross-section of specimens was cold-sprayed with unpigmented [...] Read more.
The effects of impregnation with nanosilver suspension as well as heat treatment on pull-off adhesion strength and specific air permeability in beech specimens were studied here. The size range of silver nanoparticles was 30–80 nm. The cross-section of specimens was cold-sprayed with unpigmented sealer-clear, polyester, and lacquer paints. Heat treatment, as the most commonly used wood modification, was applied at three different temperatures of 145, 165, and 185 °C. Results showed that the highest and lowest pull-off strengths were found in the un-impregnated and unheated specimens painted with polyester (8.98 MPa) and the unpainted unheated nanosilver-impregnated specimens (3.10 MPa), respectively. Impregnation with nanosilver resulted in the rupture of perforation plates and pit openings, and eventually, permeability increased significantly. As for the pull-off adhesion strength, the increased permeability resulted in the adhesive being penetrated in to the pores in the wood substrate, and eventually, a significant decrease in the pull-off strengths occurred. No significant correlation was found between pull-off strength versus specific air permeability, although both properties depend on the porous structure. This was due to the fact that permeability depends on the continuous pore system, while pull-off strength is dependent on the surface pore system of the substrate. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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Review

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31 pages, 4756 KiB  
Review
Wood Surface Modification—Classic and Modern Approaches in Wood Chemical Treatment by Esterification Reactions
Coatings 2020, 10(7), 629; https://doi.org/10.3390/coatings10070629 - 30 Jun 2020
Cited by 26 | Viewed by 7209
Abstract
Wood surface modification is a comprehensive concept which, in time, turned out to be as successful as challenging when it comes to improve the resistance of wood during its life cycle in both indoor and outdoor applications. The initial approaches have aimed at [...] Read more.
Wood surface modification is a comprehensive concept which, in time, turned out to be as successful as challenging when it comes to improve the resistance of wood during its life cycle in both indoor and outdoor applications. The initial approaches have aimed at simple methods with immediate results. Nowadays, the paradigm has slightly changed due to the scientific and technical advances, and some methods has become intermediate stages in more complex processes, after being used, for long time, as stand-alone procedures. The esterification was employed as a convenient method for wood surface modification due to the high amount of free hydroxyl groups available at the surface of wood and other lignocellulosic materials. Therefore, different esterification approaches were tested: activated condensation with carboxylic acids (monocarboxylic, as well as dicarboxylic acids, fatty acids, etc.) in the presence of condensation activating agents (such as trifluoroacetic anhydride); reaction with β-halogen-substituted carboxylic acids; esterification using carboxylic acids derivatives (acyl chlorides, anhydrides) or even multifunctional carboxylic acids (i.e., tricine). Thus, wood with improved dimensional stability and weathering resilience, higher fire resistance, enhanced hydrophobic character, and mechanical durability was obtained. This paper offers an overview of some of the most recent advances reported in the field, presented in a systematic manner, using the type of reaction as classification criterion. The main improvements will be outlined in a critical assessment in order to provide an useful tool for a wise choice in future applications. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Treatment of Wood)
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