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Wood Coatings: Formulation, Testing and Performance

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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Surface Characterization, Deposition and Modification".

Deadline for manuscript submissions: 30 September 2024 | Viewed by 11123

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Special Issue Editors

Prof. Dr. Maria Cristina Timar

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Guest Editor

Department of Wood Processing and Design of Wood Products, Faculty of Furniture Design and Wood Engineering, Transilvania University of Brașov, 500036 Brașov, Romania
Interests: wood chemistry; wood modification; wood preservation; wood finishing; wood gluing; materials ageing; microscopy; colour changes; FTIR investigation; scientific conservation of wooden cultural heritage; furniture restoration

Prof. Dr. Lidia Gurau

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Guest Editor

Faculty of Furniture Design and Wood Engineering, Transilvania University of Brasov, 500068 Brasov, Romania
Interests: wood structure and properties; mechanical wood processing and surface quality; surface metrology
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Dr. Emanuela Beldean

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Guest Editor

Department of Wood Processing and Design of Wood Products, Faculty of Furniture Design and Wood Engineering, Transilvania University of Brașov, 500036 Brașov, Romania
Interests: wood finishing; wood preservation and field tests; wood anatomy; wood properties; microscopic investigation; conservation of wooden cultural heritage; furniture restoration; formaldehyde emission tests; forestry

Special Issue Information

Dear Colleagues,

A great variety of products made of wood or wood-based materials, ranging from furniture to floors, windows, doors, and various other elements designed for both inside and outside environments are part of our everyday lives contributing to its quality through both functionality and aesthetics. Wood finishing is a complex surface coating technology with a key role in conferring the desired consumer- or market-tailored aspects and properties of the finished products, such as increasing their value and quality or extending their service life.

The coating of wood and wooden substrates should primarily ensure a long-lasting desired aesthetic appearance (for example: transparent or opaque finish, specific colour, envisaged gloss, maybe special effects) and surface roughness while also providing some protection to the substrate against different types of physical, mechanical, chemical, or even biological nature degradation factors. These factors and their intensity are different depending on the environment (indoors or outdoors finishes) and on the type of application, and they may affect the integrity and appearance of the coating films over time, also reducing their protective effects. To prevent degradation, coating materials with bio-protection or fire-protection effects are special formulations for specific uses.

Accordingly, there are different standards and methods as well as many properties employed to define and check the quality of finished surfaces, as a complex concept including aesthetic aspects, surface metrology (surface roughness), resistance to different degradation factors and adhesion to the substrate. The long-term performance of finished wood surfaces depends on the substrate properties (type of material, previous processing before coating, surface roughness, wetting properties), the formulation of the coating materials, the technological parameters of the wood finishing process, and on the action of ongoing aggressive factors. Natural ageing tests (e.g., natural weathering for outdoors finishes) and accelerated artificial ageing are important tools to assess the performance of coatings and to assist service-life prediction. UV- and temperature-induced ageing are also important to consider for indoor finishes, as the complex chemical processes that are involved may not only affect the colour of the coated surfaces (which is a non-desirable aspect on its own), but also the properties of the coating film in terms of resistance to specific degradation factors and adherence to the substrate.

We are pleased to invite you to submit a manuscript to this Special Issue of the Coatings. This Special Issue will report on progress in the field of the finishing of wood and wood-based materials, with a special focus on the quality and performance of both indoor and outdoor wood finishes over time. Papers dealing with all of the factors involved in the quality and performance of finished wood surfaces, from processing the substrate and its surface properties to coating formulation, finishing technology, and the testing methods involved, are welcome.

This Special Issue aims to collect at least 10 articles so that the Special Issue may be printed in book form. Considering the scientific importance and practical relevance of the topics proposed, we consider this to be a reachable target, and we express our gratitude for your contributions in advance.

In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following topics:

Coatings formulation;
Additives for specific/increased properties (e.g., photo-stability, bio-protection, fire-protection, anti-microbial, etc.);
Wood substrate processing and surface properties;
Pre-treatments and surface functionalization;
Technological aspects of wood finishing;
Factors affecting the quality/performance of finished wood surfaces;
Testing the quality /long-term performance of finished wood surfaces by standard and in-house-developed methods;
Ageing of coating materials and finished wood surfaces;
Natural ageing versus artificial accelerated ageing tests;
Ecological aspects of wood finishing.

We look forward to receiving your contributions!

Prof. Dr. Maria Cristina Timar
Prof. Dr. Lidia Gurau
Dr. Emanuela Beldean
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 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.

Keywords

wooden substrates (wood, wood composites)
surface processing
surface properties
surface roughness
coating materials and additives
color changes
quality of finished surfaces
interior finishes
exterior finishes
ageing and degradation.

Published Papers (7 papers)

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Research

22 pages, 5224 KiB

Open AccessArticle

A Study of Visual Perception Based on Colour and Texture of Reconstituted Decorative Veneer

by Ting Huang, Chengmin Zhou, Xiaomeng Wang and Jake Kaner

Coatings 2024, 14(1), 57; https://doi.org/10.3390/coatings14010057 - 29 Dec 2023

Viewed by 902

Abstract

Color and texture, as vital physical attributes of recombinant decorative thin wood, represent the initial visual information perceived by the human eye. These elements play a crucial role in shaping the human viewing experience. This paper centers on the user’s visual perception of recombinant decorative thin wood and is divided into two main sections: the extraction and analysis of color and texture features, and experimental research evaluating combinations of color and texture. The experiments yielded conclusions indicating that the design of color and texture significantly influences objective eye movement data. Specific findings include: (1) The gaze duration, gaze counts, and hotspot maps of the subjects consistently demonstrate high agreement across the three eye movement indicators. Notably, a significant difference is observed between gaze indicators and color blending modes. (2) Asymmetric oblique blending and high-brightness circumferential blending tend to attract subjects’ eye attention more effectively. These color groups are characterized by transparent layers, increased brightness, and a pronounced visual impact. Such features enhance the design effect of the texture, highlighting its layers. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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22 pages, 9513 KiB

Open AccessArticle

Comparative Surface Quality of Maple (Acer pseudoplatanus) Cut through by CNC Routing and by CO₂ Laser at Different Angles as Related to the Wood Grain

by Lidia Gurău, Camelia Coșereanu, Maria Cristina Timar, Antonela Lungu and Cristina Daria Condoroţeanu

Coatings 2022, 12(12), 1982; https://doi.org/10.3390/coatings12121982 - 17 Dec 2022

Cited by 4 | Viewed by 1269

Abstract

The evaluation of surface quality is an important criterion to understand the effect of the cutting angle in relation to the grain and of the processing tool on wood. This paper examines, in a comparison, the surface quality of maple cut through by CNC and CO₂ laser, for different angles with regard to the wood grain: 0°, 15°, 30°, 45°, 60°, 75°, and 90° and at different feed speeds of the CNC router: 2; 2.5; 3; 3.5 and 4 m/min. The direction of processing as related to the grain was a more significant factor in comparison with the feed speed when CNC was used, with best options for 0°, 90° and 75° and worst for 15°, where fuzzy grain was predominant, followed in order by 30°, 45°, and 60°, where pull-out material prevailed. The laser smoothed the core roughness, Rk, with no significant differences as related to the wood grain direction and enhanced an anatomical waviness earlywood-latewood, with the earlywood processed deeper. As the cutting advanced from along to across the grain, the laser uncovered more wood anatomical details and with less destruction. No significant differences in Rk between CNC cutting and laser processing were found for angles: 0°, 60°, and 75°, but surfaces processed at 15°, 30°, and 45° were significantly rougher in the case of CNC cutting. Comparative FTIR investigation of surfaces cut by laser and CNC (at 0° and 90°) clearly revealed temperature-induced chemical changes, such as hemicelluloses degradation, possibly demethylation and advanced condensation in the structure of lignin, in the case of laser processing. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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13 pages, 2560 KiB

Open AccessArticle

Surface Wettability and Coating Performance of Plasma-Treated Wood-Based Composite Panels

by Hadi Gholamiyan, Javad Ashouri, Peyman Ahmadi and Reza Hosseinpourpia

Coatings 2022, 12(12), 1894; https://doi.org/10.3390/coatings12121894 - 05 Dec 2022

Cited by 3 | Viewed by 1143

Abstract

The effect of dielectric barrier discharge (DBD) plasma treatment was studied on the surface characteristics and coating performance of transparent epoxy resin on the surface of particleboard (PB) and medium-density fiberboard (MDF). The plasma treatment was performed at three plasma energies (10, 15, and 20 kW) and three distances from the nozzle (10, 20, and 30 mm). Analyzing the samples by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated the changes of their chemical structure by means of the plasma treatment. The contact angle study showed a significant increase in surface wettability after plasma treatment with a pronounced effect observed by treatment parameters. The surface roughness was also significantly increased by the plasma treatment. The strength of the coating adhesion to the surface of the PB and MDF composite panels was also significantly improved by the plasma treatment, while no obvious trend was observed by treatment parameters. The highest adhesion strength of 2.03 MPa and 3.63 MPa were obtained by the PB and MDF samples, respectively, treated at a 10 mm nozzle distance and 15 kW plasma energy. The scratch resistance of the epoxy coatings showed a similar trend as the adhesion strength illustrating an inferior isolated surface of the coating after the plasma treatment. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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17 pages, 8998 KiB

Open AccessArticle

Colour and Surface Chemistry Changes of Wood Surfaces Coated with Two Types of Waxes after Seven Years Exposure to Natural Light in Indoor Conditions

by Xinyou Liu, Maria Cristina Timar, Anca Maria Varodi, Ruxandra Nedelcu and Mihai-Junior Torcătoru

Coatings 2022, 12(11), 1689; https://doi.org/10.3390/coatings12111689 - 06 Nov 2022

Cited by 9 | Viewed by 1946

Abstract

The ageing of materials is an irreversible, in-time occurring complex phenomenon, which affects both wood surfaces and the coating materials. This paper focuses on the light-induced natural ageing of wood-coated surfaces in indoor conditions. Two wood species: European maple (Acer pseudoplatanus) and European walnut (Juglans regia) and two types of waxes: bees wax and Chinese wax were employed in the experiments presented in this paper. Uncoated and coated wood samples were exposed to the natural sunlight filtered by window glass in a simulated indoors natural ageing test for a total period of 7 years. Colour measurements in the CIE-Lab system and FTIR-ATR investigation were employed to evaluate the ageing phenomena. The uncoated wooden samples underwent progressive colour changes perceived as darkening for European maple and lightening for European walnut, corresponding to total colour differences values (ΔE) after 7 years of exposure of 12.54 and 11.66, respectively. Coating of wood samples with the two types of waxes differently influenced the total colour changes for the two wood species: reduced colour changes corresponding to ΔE values of 4.79–6.44 were determined for European maple, whilst increased colour changes corresponding to ΔE values of 13.80–20.83 were determined for European walnut. FTIR analysis highlighted different surface chemistry changes for the uncoated and wax-coated wood samples. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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19 pages, 4134 KiB

Open AccessArticle

Modification of Shellac with Clove (Eugenia caryophyllata) and Thyme (Satureja hortensis) Essential Oils: Compatibility Issues and Effect on the UV Light Resistance of Wood Coated Surfaces

by Maria Cristina Timar and Emanuela Carmen Beldean

Coatings 2022, 12(10), 1591; https://doi.org/10.3390/coatings12101591 - 20 Oct 2022

Cited by 1 | Viewed by 1834

Abstract

Shellac (SL) is a natural resin employed for wood finishing, while clove (Eugenia caryophyllata) and thyme (Satureja hortensis) essential oils (C-EO, T-EO) are organic natural products of vegetal origin with antifungal, antimicrobial and antioxidant properties. The present paper aims at exploring the potential of modifying alcoholic shellac solutions with essential oils (C-EO, T-EO), focussing on the recurrent effects of this modification on the traditional wood finishing technique, the colour and the UV light resistance of the wood coated surfaces. The compatibility of C-EO and T-EO with ethyl alcohol and the alcoholic reference SL solution was evaluated, and modified SL solutions with a content of 5% and 10% C-EO and T-EO were prepared. Wood samples of European maple (Acer pseudoplatanus) and European walnut (Juglans regia) were finished with reference and modified SL solutions. An accelerated UV ageing test was run, and the samples were evaluated after 24, 48 and 72 h of exposure. Colour measurements in the CIELab system and FTIR–ATR investigation were employed for monitoring colour and surface chemistry changes. Coating with SL resulted in visible colour changes for both wood species (ΔE values of 31.06 for maple and 13.00 for walnut) and increased UV resistance, reducing colour changes after 72 h UV exposure (by 83% for maple and by 59% for walnut) as compared to the uncoated controls. Modification of SL solutions with C-EO and T-EO only slightly influenced the colour of finished surfaces (ΔE = 1.88–5.41 for maple, ΔE = 1.36–3.41 for walnut) and their UV resistance. The colour changes (ΔE) of coated surfaces after 72 h exposure varied in the range 1.63–4.53 for maple and 2.39–3.58 for walnut, being generally slightly higher (by 1.7–2.9 units for maple and 0–1 unit for walnut) for the modified SL solutions. FTIR investigation highlighted only minor chemical changes of the shellac coating films after 72 h of UV exposure. A photo-induced oxidative process of eugenol seemed possible in the case of SL modified with C-EO. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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16 pages, 6292 KiB

Open AccessArticle

Adding Value to Maple (Acer pseudoplatanus) Wood Furniture Surfaces by Different Methods of Transposing Motifs from Textile Heritage

by Antonela Lungu, Maria Cristina Timar, Emanuela Carmen Beldean, Sergiu Valeriu Georgescu and Camelia Coşereanu

Coatings 2022, 12(10), 1393; https://doi.org/10.3390/coatings12101393 - 24 Sep 2022

Cited by 3 | Viewed by 1552

Abstract

The present paper is part of an ongoing research project carried out to find methods to transpose traditional motifs from Romanian textile heritage to furniture ornamentation, as an additional method of preserving the motifs besides conventional conservation. Modern technology, such as Computer Numerical Control (CNC) routing or laser engraving can revive furniture ornamentation, eliminating manual labor and long execution time. Three methods were applied to transpose a bicolored motif from a traditional Romanian blouse from Transylvania onto the surface of maple wood furniture. The first method utilized was nitrogen laser engraving, in which ten power settings between 10 W and 150 W were applied and color measurements were carried out on the resulting engraved surfaces. Following the International Commission on Illumination (CIELab) system analysis, two laser power settings were selected to engrave the ornament on a maple wood surface for an accurate reproduction. The second method employed a staining solution applied on flat wood surface, followed by routing the model on a CNC machine and further coating with lacquer. The third method consisted of CNC routing the model on the wood surface, then coloring the engraved ornament followed by surface sanding to remove color from the flat wood surface and, finally, lacquering. The ornaments transposed onto maple wood surfaces were aesthetically assessed, the technologies were analyzed, and the details of the processed ornaments were highlighted by Stereo Microscope investigation. The conclusions showed that each method adds value to the wood surface by original ornamentation and can be applied as furniture decoration. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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14 pages, 1994 KiB

Open AccessArticle

Sustainable Manufacturing Process in the Context of Wood Processing by Sanding

by Alena Očkajová, Martin Kučerka, Richard Kminiak and Adrián Banski

Coatings 2021, 11(12), 1463; https://doi.org/10.3390/coatings11121463 - 28 Nov 2021

Cited by 2 | Viewed by 1668

Abstract

The aim of this paper is the issue of a sustainable manufacturing process in the context of woodworking by sanding, as one of the most important technological operations before its final treatment, focusing on a selected pillar of sustainable manufacturing process, waste management. The first step of the experiment was to optimize the pressures of the sanding means on the surface. The optimal pressure of 1.04 N·cm⁻² was chosen. The second level was to obtain the wear curves of the abrasive means with grain size 80 (evaluated by wood removal) and the optimal pressure in dependence on the sanding direction (along and perpendicular to the wood fibres and in the direction of 60° to the wood fibres) and different types of woods (beech, oak, alder, pine). The set parameters were suitable for beech and were not suitable for alder and pine. By extending the operating life of the sanding belts via appropriate choice of input factor settings it can be influenced metrics of pillar waste management-savings of material and waste minimization. Full article

(This article belongs to the Special Issue Wood Coatings: Formulation, Testing and Performance)

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