Heat treatment is a method of wood modification with increasing market acceptance in Europe. The major patented European commercial heat treatment processes have trade names ThermoWood, Platowood, ...Retiwood, Le Bois Perdure, and Oil-Heat-Treated Wood (OHT). To what extent modification of wood affects the resistance of wood to weathering is also an important aspect for wood applications, especially where appearance is important. Unfortunately, heat-treated wood has poor resistance to weathering, and surface treatment with coatings is required for both protection and aesthetic reasons. As a substrate for coating, heat-treated wood has altered characteristics such as lower hygroscopicity and liquid water uptake and changed acidity, wettability, surface free energy, and anatomical microstructure. Various wood species, heat treatment method, treatment intensity, and treatment conditions exhibited a different extent of changes in wood properties. These altered properties could affect coating performance on heat-treated wood. The reported changes in acidity and in surface energy due to heat treatments are inconsistent with one another depending on wood species and temperature of the treatments. This paper gives an overview of the research results with regards to properties of heat-treated wood that can affect coating performance and weathering of uncoated and coated heat-treated wood.
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•TiO2 efficiently improves the surface durability of coated thermally modified wood.•The addition of ZnO leads to poor adhesion strength, cracking and peeling of coating.•The addition ...of TiO2 helps to maintain sufficiently good adhesive of coating on TMT.•Discoloration of TMT out of doors cannot be eliminated, but can be reduced by addition of TiO2.
In this research the samples of thermally modified (TMT) beech wood samples, finished with waterborne polyacrylate clear coatings modified with nano-sized ZnO and TiO2-rutil were naturally and artificially exposed to weathering conditions. To extend the lifetime of wood and maintain its natural look, the research and development of clear coatings with minimal use of harmful chemicals has become very important. Therefore nano-sized inorganic UV absorbers are increasingly used to enhance the durability of the coating and wood substrate, still retaining the transparency of the coating. During exposure the visual inspection was performed, further the changes of colour, gloss and adhesion were recorded. Interaction of the film with the thermally modified substrate surface were studied. Results showed that the addition of TiO2-rutil and ZnO nanoparticles to the waterborne polyacrylate coating improved the colour stability of thermally modified beech-wood. However, nano-sized ZnO increased the cracking and peeling, and caused the loss in adhesion strength of the film on thermally modified beech wood.
•Nano ZnO reduced flow time of waterborne polyacrylate coating and increased pH.•Nano ZnO decreased elongation of waterborne polyacrylate coating.•Nano TiO2 and ZnO caused chemical changes in coating ...after accelerated exposure.•Nano TiO2 and ZnO increased colour stability of waterborne polyacrylate coating.
The rapid development of nanotechnology allowed implementation of metal oxide nanoparticles in coatings and protection of coatings without significant influence on transparency. To avoid negative impact on coating properties it is important that nanoparticles are uniformly dispersed and that the emulsion of nanoparticles is compatible with the components in coating. In this article the effect of TiO2 and ZnO nanoparticles on properties of polyacrylate waterborne coating and on stability of coating films exposed to outdoor conditions are studied. The results of this research show that ZnO nanoparticles reduce flow time of waterborne polyacrylate coating and increase pH. Furthermore, TiO2 and ZnO nanoparticles increase colour stability of waterborne polyacrylate coating. Moreover TiO2 nanoparticles have a great impact on increase of Tg, and ZnO nanoparticles on decrease of elongation and thereby on increase of brittleness of waterborne polyacrylate coating.
In this research, the influence of titanium dioxide (TiO2) nanoparticles and their modifications on the weathering resistance of untreated and heat-treated wood was studied. The wood samples were ...coated with polyacrylate waterborne emulsion coatings that contain nano-TiO2 in the amount of 0.75 wt.%. Two types of modifiers were used to modify the nano-TiO2 surface: 2,2′-azobis(2-methylpropionamide) dihydrochloride (AIBA) and 3-aminopropyltrimethoxy silane (AMPTS). Coated and uncoated wood samples were exposed to accelerated weathering by application of sunlight, water and moisture for 360 h. During the research, the dry film thickness, color, gloss and hardness of the surface of the samples were measured. The obtained results showed that the effect of the addition and surface modification of nano-TiO2 on the color and gloss stability was different on untreated and heat-treated ash wood, and that accelerated weathering causes an increase in surface hardness and a decrease in thickness of the dry coating.
Oriented strand board (OSB) is a commonly used structural wood-based panel for walls and roof siding, but recently the industry has become interested in OSB as a substrate for indoor and outdoor ...furniture. Particleboard is mainly used in furniture productions and has become popular as a construction material due to its numerous usage possibilities and inexpensive cost. Moisture is one of the most important factors affecting wood-based panel performance and the post-treatment conditions affected their affinity to water. When OSB and particleboard are used as substrates for coatings, their surface characteristics play an important role in determining the quality of the final product. Furthermore, roughness can significantly affect the interfacial phenomena such as adsorption, wetting, and adhesion which may have an impact on the coating performance. In this research particleboard and OSB panels were sanded, re-pressed and IR heated and the influence of surface treatments on hardness, roughness, wetting, water, and water vapour absorption was studied. Results showed that sanding improved the wetting of particleboard and OSB with water. Moreover, studied surface treatments increased water absorption and water penetration depth of OSB panels, and re-pressing had a positive effect on reducing the water vapour absorption of particleboard and OSB panels.
Wood is increasingly used in the bathrooms for furniture due to its beauty, warm and organic look, but also for floors, walls, and even for wooden sinks and bathtubs. Wood in the bathroom is exposed ...to changes in temperature and humidity as well as spillage and splashing of water and should therefore be properly finished with an effective coating to protect it from extreme changes in moisture content. In this research ash and larch wood were finished with penetrating and film-forming coatings and subsequently were exposed to liquid water and water vapor. During exposure to liquid water and water vapor, the mass of the samples and the moisture content in the samples were measured. Results showed that penetrating coatings provided some protection against liquid water absorption but very little protection against water vapor, especially on ash wood. Moreover, the moisture excluding effectiveness reduced rapidly during exposure to high humidity and depending on the wood species and coating systems.
•Wood species did not affect liquid water uptake of wood finished with an alkyd film-forming system.•Penetrating coatings should be used in the bathroom only on durable wood species.•Penetrating coatings provided some protection against liquid water absorption, but they provide very little protection against water vapor.•Moisture excluding effectiveness reduced rapidly during exposure to high humidity and depending on the wood species and coating systems.
In this research, the influence of face milling, sanding and UV irradiation of the hornbeam and ash wood sample on the wetting and adhesion strength of solvent-based and water-borne coating was ...studied. The adhesion of coatings to substrates is one of the most important parameters for finishing quality and service life of wood coatings, while wetting properties are usually used to assess the quality of surfacing process and could also provide important information on the adhesion ability of coatings. Surface roughness, contact angle of coatings and water as well as adhesion strength of coatings were tested on differently prepared (face milled, sanded and UV irradiated) samples of unmodified and thermally modified ash and hornbeam wood. Surface roughness was measured with stylus-type profilometer over the traverse of 12.5 mm and with a cut-off value of 2.5. Contact angle was measured using the sessile drop method 2 s, 10 s and 30 s after the application of the liquid drop on the sample surface, and adhesion strength was measured according to ASTM D4541. Results showed that sanding of hornbeam and ash wood resulted in the least rough surface compared to the face milled and UV irradiated surface. Contact angles of the water-borne coating were on average three times higher than the contact angles of the solvent-based coating. Sanding the surface of hornbeam and ash samples increased the adhesive strength in relation to the face milled surface, while UV irradiation of the sanded surface decreased the adhesive strength of most samples coated with solvent-based coating.
U radu je istraživan utjecaj čeonog blanjanja, brušenja i UV zračenja grabovine i jasenovine na kvašenje i adhezivnu čvrstoću premaza na bazi organskih otapala i vodenog premaza. Adhezija premaza jedan je od najvažnijih parametara za kvalitetu površinske obrade i trajnost premaza za drvo, dok svojstva kvašenja obično služe za ocjenu kvalitete nanošenja i adhezije premaza. Na različito pripremljenim uzorcima (obrađenim čeonim blanjanjem, brušenjem ili UV zračenjem) nemodificirane i toplinski modificirane grabovine i jasenovine ispitivana je hrapavost, kontaktni kut premaza i vode te adhezivna čvrstoća premaza. Hrapavost površine mjerena je profilometrom na duljini vrednovanja 12,5 mm, uz referentnu duljinu od 2,5 mm. Kontaktni kut mjeren je metodom s kapljicom, i to 2 s, 10 s i 30 s nakon nanošenja kapljice na površinu uzorka, a adhezivna čvrstoća određivana je prema normi ASTM D4541. Rezultati su pokazali da je brušenje grabovine i jasenovine rezultiralo najmanje hrapavom površinom u usporedbi s čeono blanjanom i UV zračenom površinom. Kontaktni kutovi vodenog premaza bili su u prosjeku tri puta veći od kontaktnih kutova premaza na bazi organskih otapala. Brušenjem površine uzoraka grabovine i jasenovine adhezivna je čvrstoća postala veća od čvrstoće čeono blanjanih površina, dok je UV zračenjem na brušenim površinama većine uzoraka smanjena adhezivna čvrstoća premaza na bazi organskih otapala.
Thermal modification leads to the degradation of the compounds in wood, thereby changing the chemical composition of wood, which can affect the further wood finishing. In order to determine the ...effect of thermal modification on wood finishing, it is important to know the properties of its surface. In this research, the influence of thermal modification on pH, surface free energy, contact angle of coating and chemical composition of beech wood was studied. The results of this study show that acidity and water contact angle on beech wood was higher and polar component of surface free energy was lower after thermal modification. Furthermore, contact angle of waterborne coating on beech wood was increased by increasing the modification temperature and the content of extractives soluble in hot water and in organic solvent was increased after thermal modification of beech wood. Key words: thermal modification, contact angle, surface free energy, wood chemical composition Toplinska modifikacija uzrokuje razgradnju spojeva u drvu, cime se mijenja kemijski sastav drva sto moze utjecati na njegovu povrsinsku obradu. Kako bi se utvrdio ucinak toplinske modifikacije na povrsinsku obradu drva, vazno je znati svojstva njegove povrsine. U ovom je radu istrazivan utjecaj toplinske modifikacije na pH drva, njegovu slobodnu povrsinsku energiju, kvasenje premaza i na kemijski sastav bukovine. Rezultati istrazivanja pokazuju da je toplinska modifikacija povecala kiselost drva i kut kvasenja vode na bukovini i smanjila polarne komponente slobodne povrsinske energije. Nadalje, kut kvasenja vodenog premaza na bukovini povecao se s povecanjem temperature modifikacije, a sadrzaj ekstraktiva topljivih u vrucoj vodi i organskom otapalu povecao se nakon toplinske modifikacije bukovine. Kljucne rijeci: toplinska modifikacija, kut kvasenja, slobodna povrsinska energija, kemijski sastav drva
Knowing the properties of wood-based building materials is essential for their proper use. Moisture transfer properties of building materials are crucial to proper building design and the prevention ...of moisture-related problems. In selecting materials for the building, it is important to know their water vapour transmission properties. In this research the water vapour transmission properties of uncoated and coated particleboard, oriented strand board (OSB) and birch plywood were studied using wet cup method and a moisture gradient in the samples was additionally measured. The water vapour transmission rate of free films of three commercial transparent coatings was also studied. Results showed that particleboard had the highest water vapour permeability and that the coatings reduced the water vapour permeability of all tested wood-based panels. Moreover, sanding increased the water vapour permeability of uncoated particleboard and OSB. The moisture gradient in all tested wood-based panels was linear. The highest water vapour transmission rate was recorded for acrylic water-borne coating, followed by polyurethane water-borne coating and the lowest for polyurethane solvent-based coating.
The present study investigates the relationship between the roughness of beech wood and oak wood surfaces treated with oil and polyurethane coating and the slip resistance in dry, water-wet and oily ...conditions. Pendulum tests were conducted for slip resistance assessment, and roughness measurements were performed by stylus instrument using Ra, Rt, Rp, Rz and Rsm parameters for surface roughness evaluation. Slip potential in dry conditions was low for all finished wood floors studied. Contamination of the surface with water and oil reduced the slip resistance of finished oak and beech flooring. The strong negative correlation was found between slip resistance on dry finished flooring and roughness parameters Ra, Rz, Rt and Rp, and positive correlation between slip resistance on water-wet finished flooring and roughness parameters Ra, Rz, Rt and Rp. Moreover, the correlations between roughness parameters Ra, Rt, Rp and Rz and slip resistance were very similar, and the roughness parameters correlated more strongly with the slip resistance on dry and water-wet surfaces than with the slip resistance on oil-wet surface. Comparison of the slip potential classifications of finished wood floors based on pendulum data and based on Rz surface roughness parameters showed that in some cases the Rz parameter appeared to overestimate the slip potential of the floors in wet conditions. The results confirm previous research that roughness measurements should only be used as a guide and should not be used as the only indicator of the slip potential of wood flooring materials.
U radu je istraživan odnos između hrapavosti bukovine i hrastovine površinski obrađenih uljem i poliuretanskim lakom i klizavosti suhe površine te površine na koju su se prolili voda i ulje. Klizavost površine određena je klatnom, a hrapavost joj je izmjerena kontaktnim uređajem uz pomoć parametara Ra, Rt, Rp, Rz i Rsm za procjenu hrapavosti. Vjerojatnost poskliznuća u suhim uvjetima za sve je ispitivane drvene podove bila niska. Vlaženje površine vodom i uljem smanjilo je otpornost na klizanje površinski obrađenih podova od hrastovine i bukovine. Utvrđena je velika negativna korelacija između otpornosti na klizanje na suhoj površini drvenih podova i parametara hrapavosti Ra, Rz, Rt i Rp te pozitivna korelacija između otpornosti na klizanje na podovima zalivenim vodom i parametara hrapavosti Ra, Rz, Rt i Rp. Nadalje, korelacije između parametara hrapavosti Ra, Rt, Rp i Rz i otpornosti na klizanje bile su vrlo slične. Parametri hrapavosti jače su korelirali s otpornošću na klizanje na suhim površinama i površinama zalivenim vodom nego s otpornošću na klizanje na površinama zalivenim uljem. Usporedba razredbi vjerojatnosti poskliznuća na površinski obrađenim drvenim podovima dobivena klatnom i na temelju parametra hrapavosti površine Rz pokazala je da je u nekim slučajevima parametar Rz dao precijenjenu vjerojatnost poskliznuća na podovima u mokrim uvjetima. Rezultati potvrđuju prethodna istraživanja prema kojima mjerenja hrapavosti trebaju služiti samo kao vodilja i ne smiju se primjenjivati kao jedini pokazatelj klizavosti drvenih podnih materijala.
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