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Safer alternative reagents for colour differentiation of heartwood and sapwood
1994 - IRG/WP 94-20028
Benzidine and dimethyl yellow reagents have been used for distinguishing heartwood from sapwood in the Pinaceae and Araucariacae families, and in Eucalypt species. Both have been classified as carcinogenic by European and United States authoritites, yet the need for effective heartwood/sapwood differentiation remains, not only in the laboratory but also out in the timber processing chain. Safer alternative reagents have been proposed over the past twenty years, but some of these have since been linked with health problems, and most of the rest lack the specificity and general usefulness of those traditionally used. Recent research has investigated various azo, diazo, and other nitrated reagents. Safe but useful alternative methods of sapwood/heartwood differentiation are being established, and recommendations are made for several timber species.
A Zosars, M J Kennedy


Towards a colour assay of wood degradation
1982 - IRG/WP 2180
A colour assay for the enzyme catalase is described. Since the activity of this enzyme has previously been shown to be correlated with degree of wood degradation as determined by other methods, this assay may provide a rapid quantitative indicator of superficial and internal wood decay.
M A Line


Correlation between changes in colour and chemical composition during photo-degradation of wood surfaces
2005 - IRG/WP 05-40301
Changes in colour of wood (yellowing) during photo degradation or weathering reflect chemical changes in wood. Therefore, the relationship between changes in chemical composition and CIELAB colour parameters is very important to characterize photodegradation of lignocellulosic surfaces. In this study, the changes in chemical composition and yellowing due to photo-degradation was studied by exposing wood surfaces of Pinus roxburghii (chir pine) to a xenon source. Changes in chemical composition were monitored by measuring IR and fluorescence spectra and were correlated with colour changes. A linear correlation between degradation of lignin and total colour change (E) was observed.
K K Pandey


Some practical implications from recent research on the fixation of CCA preservatives
1975 - IRG/WP 358
The mechanism of fixation of CCA preservatives is briefly described. If the temperature is increased during the primary fixation period, the formation of intermediate fixation compounds is less extensive. The length of the primary fixation period is of practical interest. It is determined by preservative composition and concentration, temperature and wood species. Diagrams are given for Pinus sylvestris. Light exposure and drying during the primary fixation period cause variability in colour intensity of CCA treated wood. Disproportionation of preservative elements with penetration depth is explained by the fixation mechanism. Conversion of intermediate fixation compounds into stable ones occurs even below the fibre saturation point, as long as the moisture ratio is sufficiently high to allow ion transport. Conversion reactions are very slow. A correlation was found between the final pH of treated timber and leachability in fresh water of copper and arsenic. The final pH depends on preservative composition and concentration, wood species and to some degree of drying and storage conditions. An electrolyte such as sodium sulfate does not affect the leachability. In saline waters leachability is increased by complex formation of Cu(II) and Cr(III) with chloride and hydroxide and the salt effect on activity coefficients. The leaching of arsenic is delayed.
S-E Dahlgren


Preference of swarming termites for various colored lights
1984 - IRG/WP 1238
The ability of the alates of the drywood termite Bifiditermes beesoni (Gardner) to discriminate ten different colored lights was studied. When an alternative choice of any of two colors was offered, the light-blue was preferred to all other tested colors by 97.7% of the alates. A lower degree of attractivity was found for some other colors and certain other colors were indistinguishable. Furthermore, the effects of light intensity and preconditioning to certain colors have been studied and finally the response of swarming alates from natural colonies is compared to that of the individuals from laboratory colonies.
M Afzal


Heat treatment of less-valuable Nigerian-grown Ceiba pentandra wood for improved properties
2006 - IRG/WP 06-40332
The hardwood Ceiba pentandra locally known as “ araba “ in Nigeria is rarely used for structural and construction works due to its high dimensional instability, low strength and durability values. Samples (10 x 10 x 150mm) were removed from four green boards (25 x 200 x 3000mm) of this species originating from a natural forest stand in Nigeria and subjected to 2-hour heat treatment at 160°C and 220°C. Heat treatment reduced swelling, hygroscopicity and swelling intensity of Ceiba pentandra wood with the reductions being generally higher in the 220°C treatment than the 160°C treatment. The reductions constitute improvements in these properties. These improvement in properties have the potential to increase the market value of this species through wider acceptability for various purposes hitherto considered impossible. This however is subject to further investigations on the effects on durability and strength properties which are other key features in the choice of wood for various purposes.
L Awoyemi


The Effect of Flavonoids on Colour and Spectral Changes of the Wood Surface Caused by Heat Treatment or Ultra-violet Irradiation
2006 - IRG/WP 06-40341
Both heat treatment and UV irradiation can cause discolouration and change in the spectral properties of wood surface. Some of the characteristic flavonols have significant role on colour and spectral changes, despite of their relative small quantities in wood. Colour changes and spectral properties of natural and extracted black locust (Robinia pseudoacacia L.) and poplar (Populus nigra L.) were investigated by CIELAB colour measurement system, FTIR and UV/Vis spectrophotometry. Spectral properties of representative flavonols, impregnated on inert silica gel thin layer, were studied in addition to the two types of wood samples. Chemical structure of flavonols was established to have both influence on the colour and spectral changes of woods and close connection with their thermal and photo stability. A slow but continuous decrease of lightness was observed in the case of quercetin and its homologous compounds. Chemical reaction of robinetin was detected by thermal analysis and differential scanning calorimetry under 200 °C and both oxidative and inert conditions. The colour changes of quercetin homolog compounds, kaempferol and fisetin, which contain one and two hydroxyl group on their “B” ring, are similar to quercetin; while myricetin with three hydroxyl groups on its “B” ring shows “robinetin-type” changes. The colour changes of the hardwoods are depended on the time and temperature of heating, as well as on the time of light irradiation. The character of spectral changes of black locust can be classified on the type of robinetin, in contrast with the “quercetin-type” of poplar.
R Csonka-Rákosa, L Molnár-Hamvas, E Börcsök, J Molnár, K Németh


Photo-degradation of modified and non-modified wood, coated with water borne acrylic coatings during artificial light exposure
2007 - IRG/WP 07-30416
A series of experiments were carried out to investigate photo-degradation of thermally modified (at 210oC and – 0.9 bars for two hours) and non-modified spruce wood (Picea abies L (Karst)), coated with transparent and semitransparent (with 3% pigment content) acrylic coatings during artificial UV light irradiation for 200 hours. Photo-degradation was evaluated in terms of colour changes throughout the irradiation period at an interval of 50 hours, along with IR and EPR spectroscopic study. One set of modified and non-modified woods was painted with coatings, while the other set was covered with free films made of coatings, just to simulate coated wood. The average thickness of paint-coats and dried free films at 25oC and 50% RH was 144.8?m and 143.4?m for transparent and semitransparent coating, respectively. The colour changes for both modified and non-modified wood samples without paint-coat and free film cover were comparable to that of wood samples with paint-coat and free film cover for transparent coat type, which indicated its ineffectiveness to prevent photo-degradation of wood underneath. However, the colour changes for both modified and non-modified wood samples with paint-coat and free film cover were much more lower than that of samples without paint-coat and free film cover for semitransparent coat type, which might be due to hindrance of transmission of light energy through pigment to reach the underlying wood surface. On the other hand, whole substrate-coating systems showed better photo-stability, when thermally modified wood was used as substrate. It might be due to increase in lignin stability by condensation during thermal modification process of wood substrate. However, the colour changes of coat-painted and free-film covered samples for both modified and non modified woods might be due to due colour changes of wood specimen underneath, because free films of both the coat types showed negligible colour change during UV irradiation.
M Deka, M Tomažic, M Petric


Effectos de la intemperización artificial sobre la madera de mezquite (Prosopis laevigata)
2008 - IRG/WP 08-40430
The effects of artificial weathering on Prosopis laevigata wood were studied on eight replicates (150 x 72 x 15mm (l x t x r)) free of knots, cracks and resin. The samples were exposed tangentially to UV light and to water spray during three cycles (1 cycle corresponded 1 week of artificial weathering). The conditioning time between each cycle was thirty days. The effects were measured according to visual appearance, crack formation, and colour changes; the results were then compared to two other well known timber species, namely teak (Tectona grandis) and beech (Fagus sylvatica). The specimens displayed changes in colour after three cycles of exposure. P. laevigata changed from brown to white. Delta C (Delta colour) increased from 5.6 to 9.6. There was less crack formation than in F. sylvatica but more than in T. grandis. Lightness was reduced from 61 to 37 after the first cycle; the lightness value of 35 was maintained at the end of the second and third cycles. The P. laevigata specimens showed several changes in colour after artificial weathering. The Delta C was higher due to the photodegradation of lignin and phenolic compounds caused the UV light and the leaching caused by water.
A Carrillo-Parra, F Hapla, C Mai


Mechanical and chemical properties of blue stained wood
2009 - IRG/WP 09-10686
Discoloration of wood is frequently caused by blue-staining fungi. In the previous researches there was general opinion that blue-stain fungi do not influence mechanical properties. On the other hand, there were some opposite results reported as well. In order to elucidate this issue, specimens made of Pinus sylvestris sapwood were exposed to two the most frequent and important blue stain fungi Aureobasidium pullulans and Sclerophoma pithyophila for various periods between two and eight weeks. Before and after exposure, FTIR, weight, colour and modulus of elasticity measurements were performed. The data obtained showed, that blue stain fungi besides considerable discoloration, does not cause any significant damage to wood. Surprisingly the non-destructive MoE analysis showed, that modulus of elasticity even slightly increase after the experimental exposure.
M Humar, V Vek, B Bučar


Colour change monitoring of photodegradation in Scots pine (Pinus sylvestris) – a short term focus
2009 - IRG/WP 09-40442
Colour change monitoring of photodegradation is a quick and easy method for monitoring rates of photodegradation in timber. A study was undertaken to compare this technique to other monitoring methods, including microtensile strength changes and weight loss. Colour changes due to accelerated sunlight exposure were monitored using a Datacolor check spectrophotometer and compared with a set of controls. Measurements on both samples and controls were performed hourly for the 1st 24 hours and there after daily until 168 hours’ exposure with extra measurements at 200, 350 and 500 hours. A subset of samples, were extracted prior to exposure to check the effects of any colour change due to the presence of extractives. Data was analysed using the reflectance spectra (400-700nm) as well as the CIE-L*a*b* system and ΔE. The majority of colour changes were found to occur within the 1st 24 hours. This was unaffected by the removal of extractives from the wood and was independent of temperature. When compared to the other monitoring methods, colour monitoring has been shown to be the most sensitive method out of the methods compared for monitoring photodegradation in Scots pine.
V Sharratt, C A S Hill, D P R Kint


Comparison of colour change in wood clear-coating systems including inorganic and organic UV absorbers for exterior use
2010 - IRG/WP 10-40499
The aim of this work is to compare the performance of inorganic and organic UV absorbers used in a wood coating application against weathering. Our study has investigated the colour changes of selected UV absorbers; hombitec 402 RM from the Sachtleben Company as an inorganic UV absorber, tinuvin 477 DW from the Ciba Company as an organic UV absorber. The study was carried out on two wood species; Fagus sylvatica L., Pinus sylvestris L. The results obtained after 28 days (672h) of accelerated weathering showed that the colour stability was the same for hombitec 402 RM and tinuvin 477 DW and both systems showed a significant improvement of colour stabilization compared to the control samples. In addition, the wood surface from cracks was protected with the clear-coat containing both of UV absorber.
Ö Özgenç, B Forsthuber, A Teischinger, C Hansmann


Performance of selected types of coated and uncoated modified wood in artificial and natural weathering
2010 - IRG/WP 10-40510
The objective of the present work was to investigate the influence of commercial wood modification methods on weathering behaviour and coating performance. It was aimed to compare modification methods and to set up maps of weathering behaviour for these methods with and without a semi-transparent wood stain. Artificial and natural weathering trials were carried out with a selection of different types of modified wood. Unmodified pine sapwood was used as reference. Acetylated radiata pine wood revealed outstanding performance in colour stability and as coating substrate in all weathering trials. The performance of thermally modified pine sapwood was comparable to the unmodified reference. Its colour change was characterised by bleaching of the original dark colour. Uncoated furfurylated pine sapwood samples showed strong colour change with extensive bleaching, whereas coated furfurylated wood showed good colour stability. Coated Cr-free impregnated pine sapwood showed sensitivity to mechanical defects of the semi-transparent coating film, leading to strong discolouration. These results indicate the possible influence of preservative impregnation on coating performance of semi-transparent stains.
G Grüll, L Podgorski, M Truskaller, I Spitaler, V Georges, S Bollmus, A Steitz


A comparative study and evaluation of methodologies used for determining wood preservative penetration
2011 - IRG/WP 11-20475
A series of methods for determining penetration of wood preservatives into the wood structure have been developed for either quality control (QC) or research and development purposes. QC methods range from monitoring the solution uptake, applying colour indicators or sampling specific wood samples followed by wood acid digestion/atomic absorption spectroscopy (AAS) or solvent extraction/chromatography analysis. Several standard methods for penetration analysis were developed by various standardization groups (e.g. AWPA, CEN). They are mostly used in correlation with a specific wood preservative system. Additional analytical tools are necessary for detailed penetration studies, especially during product development of a new wood preservative. Sufficient penetration of the active components into the wood structure plays an essential role in determining the service life of treated wood. Depending on the desired end use (use class) of the treated wood component, different penetration requirements apply. Therefore studying and optimizing the penetration characteristics of new wood preservatives must be an integral part during their development. Furthermore monitoring that the penetration requirements are fulfilled in the wood treatment process is an important aspect to ensure the quality of treated wood products. The aim of this study was to review several methods currently employed to determine the penetration of the wood preservative actives e.g. colour indicators, solution uptake of treated wood, direct gradient studies by wood acid digestion/atomic absorption spectroscopy or solvent extraction/chromatography analysis, and microbiological studies using different types of fungi. Factors which can impact on the outcome from these methods are being discussed based on some “model” wood preservative systems.
R Craciun, R Moeller, J Wittenzellner, T Jakob, J Habicht


Effects of microclimate, wood temperature and surface colour on fungal disfigurement on wooden claddings
2012 - IRG/WP 12-20490
Wooden claddings are common in façades in Norway, and Norway spruce (Picea abies) is the most frequently used species. The cladding is a major part of the facade, and it has visual requirements that may define the aesthetic service life. The visual changes that occur during weathering can be colour changes, abrasion or wear, blistering, flaking, and even cracks in the wood or coating, but more often growth of mould and blue stain fungi are the main challenge. A field test with synchronous monitoring of relative humidity, air temperature, material temperature and wood moisture content in Norway spruce claddings has been established in southern Norway as part of the ClimateLife project. Visual evaluation of blue stain and mould growth according to EN 927-3 was performed, and evaluation data after 10 months exposure is presented. The objectives were to study the effect of 1) environment, 2) cardinal direction and 3) colour of the cladding on growth of blue stain and mould fungi, and further study the variation in relative humidity, air temperature in front of a surface and the material temperature due to change in 1) environment, 2) cardinal direction and 3) colour of the cladding. After 10 months exposure, the red coating system had lowest mould ratings and the uncoated claddings had the highest. Claddings facing south tend to have higher mould ratings than those facing north. No difference was found between shaded and open environment. The relative humidity was higher in front of the claddings exposed in a shaded environment compared to an open environment, and in an open environment the relative humidity was lower against south than north. The temperature in front of the red coloured claddings was highest. Except for the red-coated claddings, the air temperature was higher than the material temperature.
L Ross Gobakken, G I Vestøl


Initial investigations into the spalting potential of Peruvian hardwoods
2014 - IRG/WP 14-10813
This study was performed to determine if several moderately-utilized Peruvian hardwoods had potential for spalting applications. We applied a modified decay jar methodology with six native Peruvian woods and three moulds, with a period of incubation of six weeks. Results showed that Nigrospora sphaerica and Marupa (Simarouba amara) resulted on the highest significant internal pigmentation (black), followed by Congona (Brosimum alicastrum) and Zapote (Matisia cordata) tested with Cladosporium herbarum. No spalting occurred on woods with darker sapwood – spalting occurred only on white woods.
S M Vega Gutiérrez, S C Robinson


Study of UV resistance and natural weathering of coatings on chemically modified wood
2013 - IRG/WP 13-40629
In this study, UV resistance and weathering performance of rubberwood (Hevea brasiliensis) and radiata pine (Pinus radiata) modified with benzoyl chloride and acetic anhydride was studied. Performance of polyurethane based wood coatings on modified wood was also evaluated. Unmodified and chemically modified specimens were exposed to accelerated and natural weathering. Modified and unmodified wood specimens were coated with commercially available polyurethane based transparent and opaque finishes and exposed to natural weathering for a period of 2 years. Physical and chemical deteriorations on uncoated / coated wood panels due to weathering were periodically monitored. Analysis of colour changes and chemical deteriorations of weathered specimens showed rapid discolouration and lignin degradation on unmodified wood surface exposed to weathering. Modified wood showed resistance to weathering and was partially effective in inducing UV resistance as compared to unmodified wood. Results clearly indicate that performance of coating can be significantly improved by chemically modifying wood substrate with benzoyl chloride. Benzoylation of wood polymers improved coatings adhesion and enhanced life of paints by 3-4 times. The performance of opaque coating was better than transparent coating, presumably due to photodegradation of wood substrate in transparent coating.
K K Pandey, K Srinivas


Identification of the key factors influencing development of the blue stain fungi
2016 - IRG/WP 16-10872
Service life of wood is more and more frequently affected by aesthetic requirements than functional ones. In order to elucidate various aspects of service life, model house with façade elements made of 22 materials was built on the field test site at Department of Wood Science and Technology in Ljubljana. Colour and fungal disfigurement is among other parameters monitored on this house. In parallel specimens made of the same materials as façade were analysed in laboratory as well. Samples were exposed to blue staining organisms in various standard and non-standard tests. Part of the samples was artificially weathered after blue staining and afterwards exposed to blue staining organisms again. The results of the colour measurements and blue staining test clearly indicate that this type of the laboratory exposure fits the best with the results of the outdoor tests.
D Kržišnik, B Lesar, N Thaler, M Humar


Aesthetic changes of coated thermally modified wood after artificial weathering
2017 - IRG/WP 17-40819
The thermal modification process affects the chemical configuration of the wood matrix improving some physical properties and durability. In addition, the distinctive dark tones of thermally modified timber increase the economic value of several light-coloured species. However, heat-treatment alters the substrates and it could influence in the application of coating products, necessaries to maintain the surface features in certain end-use sectors. Ash wood (Fraxinus excelsior L.) samples industrially treated at 212 ºC were coated with decorative and industrial coatings. Afterwards, the samples were subjected to accelerated weathering test and estimated the aesthetical response compared to untreated wood. The surface topography was monitored with a 3D scanner and a profilometer, showing slight visual changes although finding dissimilar roughness where irregularities in modified -samples increased with waterborne product but not with UV-curable; remarkable the changes in roughness below 5% in modified samples. The colour changes were calculated by hyperspectral information of the visible range, generating the profile map of L*, a*, b* parameters. The results point out an acceptable photostability of coated thermally modified wood. Heat-treated wood could be an appropriate substrate with similar conditions as unmodified wood; nevertheless the interaction with water-base products could vary depending on the treatment temperature and the layer thickness.
R Herrera, J Sandak, E Robles, J Labidi


Colour changes in unpainted wooden façades – Fifty Shades of Grey
2018 - IRG/WP 18-10903
In Norway the use of weathered unpainted, wooden façades has increased in popularity the last 20 years, both in single family houses as well as in multi-story and non-residential buildings. The benefit of using unpainted wood as façade material can be several: low maintenance costs, low environmental impact and low carbon footprint as well as contemporary and trendy aesthetic appearance. The variation in colour and pattern seen in an unpainted weathered wooden façade tells the story of the chosen design and construction and the loads of the environmental factors the building is exposed to. Usually unpainted façades do not get an even and homogeneously grey façade, but the weathering rather gives a variety of grey and brown tones in the wood. For building owners, architects, building contractors and others, the gradual colour change and patchiness of the wood can be rather surprising and sometimes unwanted. In some building projects, the character of the colour development did not reflect the consumer expectations, and entire façades were exchanged or given a surface treatment after some years even though an unpainted wooden façade can fulfil its function for more than 60 years if correctly executed. It is therefore important to disseminate the information on how an unpainted wooden façade changes its colour over time and how construction details and design options influence this process. The ‘visual guide’, Colour changes of unpainted wooden façades - examples and experiences, has been published as a report in Norwegian as collaboration between the Norwegian Institute of Bioeconomy Research (NIBIO) and The Oslo School of Architecture and Design (AHO) in the course of the Wood Be Better project. The guide is based on building projects from different climatic regions in Norway and the target group of this publication are architects, house owners, building engineers and contractors and others who are interested in exploring the possibility of using unpainted wood in façades. Our main goal is to show through examples of building projects that colour changes on unpainted wooden façades are not random but follow predictable patterns and logic. We want to illustrate some of the requirements and mechanisms of weathering of wood to give a structured overview over features and constructive details in a façade that is followed by colour changes and describe how these details influences the colour of the wooden façades in existing buildings.
K Zimmer, L R Gobakken, O Flindall, M Nygaard


Visual appearance of unpainted wooden claddings during the first year of outdoor exposure: Evaluation of surface mould growth, lightness (L*) and wasp attack
2018 - IRG/WP 18-40841
This study addresses changes in visual appearance of unpainted wood materials exposed outdoors. Specimens of Norway spruce (Picea abies) Scots pine (Pinus sylvestris), aspen (Populus tremula), acetylated Radiata pine (Pinus radiata) and DMDHEU-modified Scots pine sapwood were exposed facing south in Ås, Norway for 60 weeks. During this period, surface mould growth development and wasp attack were assessed visually. Development in lightness (L*) and the uniformity of the weather grey colour were assessed by image analysis. The mould rating of the tested wood materials developed in varying speed, but all specimens had reached the maximum rating after 42 weeks. Our results indicate that most specimens continued to darken after the specimens had reached maximum mould rating, and that evaluation of L* can provide additional information about the surface mould growth. Furthermore, our results indicate that most materials developed a less uniform appearance than what was initially, except from DMDHEU which obtained a more uniform appearance as a consequence of the weathering. This study also shows that wasp attack can give a lighter appearance of the wood by chewing off the top weathered layer. Different wood substrates were attacked in varying degree. Aspen was the substrate most severely attacked by wasps while the acetylated wood was not attacked at all during the 60 weeks of exposure.
S Karlsen Lie, L Ross Gobakken, G I Vestøl, O Høibø


Charring of Norway spruce wood surface – an alternative surface modification technique?
2019 - IRG/WP 19-40870
Charring is an old wood surface treatment technique, mainly performed on wooden façade elements with the aesthetical aims, but also with the purpose of protection. This flame treatment method can be grouped into heat treatment processes. Below the top charred layer of damaged wood there is a layer which is during flame treatment exposed to high temperatures in anoxic or semi-anoxic conditions. The conditions of forming this layer are similar to those wood is exposed during a conventional thermal modification process to. As such, it might have similar properties than surfaces of conventionally thermally modified wood. Therefore, the aim of our preliminary study was to compare some selected surface characteristics of charred, thermally modified and unmodified Norway spruce wood in order to indicate possible similarities between thermally modified and charred wood surfaces. The charred surfaces that were in the focus of our investigation became substantially darker than surfaces of thermally modified spruce wood, presumably due to substantially higher treatment temperatures. The charred wood became hydrophobic, in wettability similar to that of thermally modified wood. ATR FT-IR measurements indicated that both during charring and thermal modification similar chemical reactions might occurred. The pull-off adhesion strength test of a polyurethane coating that was applied to the substrates exhibited low tensile strength of thermally modified wood and of the charred but undamaged second layer below the surface of flame treated wood. There are only limited scientific data available on properties of charred wood surfaces and so, it is believed that this topic deserves more attention in future, so from scientific as well as from applicative points of view, respectively.
M Petric, M Pavlic, J Zigon


Effect of nano-particle characteristics and concentration on UV protection of timber: A field exposure test
2022 - IRG/WP 22-40941
Wood has a well-known susceptibility to ultra-violet light degradation, leading to premature replacement. A variety of products have been developed to protect against this damage, but most provide less than 12 months of protection and must be regularly reapplied. Developing improved coatings would help reduce wood losses and reduce maintenance costs. Nano-particles have a variety of attractive properties that may make them suitable UV protectants. The effects of nano-particles on surface appearance, colour, and wettability of radiata pine (Pinus radiata) sapwood samples were investigated over 20 weeks of outdoor exposure. Nanometer to micron-sized water dispersions of ZnO, α and γ Fe2O3, rutile and anatase TiO2, Fe3O4, Fe(OH)3, spherical and porous SiO2, and α and γ Al2O3 were used to evaluate the effects of concentration and crystal shape on UV performance. Surface colour changes were characterized by measuring CIE L*a*b* parameters, while surface wettability changes were assessed using water droplet contact angle. Wood appearance changed markedly over the 20-week exposure and mould fungi appeared on the surface. Nano-particles protected wood from photo-discoloration to differing degrees with rutile TiO2 and alpha Fe2O3 providing the most effective protection especially at higher concentrations. Larger micron-sized alpha Fe2O3 provided more sustained UV protection. Mould growth reduced the yellowness on wood surfaces and thus influenced overall colour change. Nano-particles did not reduce wettability of wood after UV exposure. While none of the systems completely prevented UV damage, some showed promise and further trials are underway using combinations of nano-particles.
T Yi, J J Morrell