Photodegradation Of Wood Research Articles

INFLUENCE OF WOOD SPECIES ON QUALITY OF EXTERIOR TRANSPARENT ACRYLIC COATING DURING OUTDOOR EXPOSURE

Coating systems are a popular way to protect wood against the effects of weathering when used outdoors. This study evaluates the impact of the basic wood species on the overall durability and color fastness of the selected water-based acrylic exterior paint. Spruce (Picea abies L.) and oak (Quercus roburL.) wood samples were subjected to external weathering according to EN 927-3 (2000) for 6 and 12 months. The evaluation by instrumental methods related to co changes in color, gloss, surface wettability contact angle, at which paint damage was also visually evaluated. The results showed that the durability of the tested coating was higher for spruce. Still, on the other hand, thanks to its lighter shade, a significant color change caused by the base wood's photodegradation was detected, showing that oak wood has a negative effect on the overall life of the tested coating.

Wood discoloration patterns depending on the light source

The wood photodegradation, including discolouration caused by exposure to UV and solar radiation, has been intensively studied, while the effect of artificial lighting on wood has been little investigated. In the present study, the effect of three types of artificial light sources (LED, incandescent, and fluorescent lamps) on the colour changes of wood was evaluated. LEDs with high (6500 K) and low (3000 K) correlated colour temperature were employed in the experiments. Wood colour was assessed by spectrophotometric measurements of reflectance spectra, which were converted into colour parameters of the CIELAB colour system. The total discolouration as well as the changes in colour lightness, chroma (saturation), and hue were evaluated for two hardwood species (birch, oak) and two softwood species (spruce, pine - sapwood and heartwood) depending on the irradiation dose. Visually perceivable changes in colour of all woods were observed already at relatively low irradiation doses, indicating a high sensitivity of the wood to radiation emitted by artificial light sources. Comparing the softwoods and hardwoods included in the study, the latter proved to be more resistant to discolouration caused by the tested light sources. Overall, greater colour changes in long-term exposure were caused by incandescent and fluorescent lamps, although more rapid discolouration developed in the early stage irradiation with LEDs. A substantial difference between the effect of the tested LEDs was only observed in the initial phase, when the cool LED (6500 K) caused more discolouration. The changes in the colour parameters were complex and varying in directions, including a reversal with the accumulation of the irradiation dose, indicating that the exposure to artificial light sources resulted in continuous alteration in the shade of the wood colour.

Application of image processing programs in color analysis of wood photodegradation

In general, polymer photodegradation is an important aspect of polymer science that is of great interest to chemistry, materials science, biology, and physics students who engage in this field of research. Wood consists of three main polymers, which makes it a good candidate for such photodegradation studies. Aside from structural changes based on chemical analysis, color change assessment can also be employed to check any extent of degradation on wood without the need for sophisticated analytical equipment. This study presents the application of two image processing programs in color analysis of wood photodegradation: ImageJ and Colormath library, which are Java-based and Python-based software, respectively. Images of unexposed and UV-exposed wood samples were taken using a smartphone as an affordable digital camera. RGB channel values from these images were analyzed and quantified by ImageJ software. These values were converted to the corresponding CIEL*a*b* parameters using the Colormath library to calculate the color change, ΔE. For the 3-hour exposed sample, ?E is equal to 4.29. This value indicates appreciable color change, according to the criteria from literature. Regardless of the exposure time, the wood samples become darker as indicated by the negative value in the change in lightness L*

Effect of photodegradation on fungal colonization on wood during initial stage of brown-rot decay

Abstract Photodegradation and decay may happen simultaneously on wood under many exposure conditions. The aim of this study was to explore the effect of photodegradation on fungal colonization during initial stage of brown-rot decay of wood. For this purpose, southern pine (Pinus spp.) wood was exposed to accelerated UV weathering for different durations, and then decayed by a brown-rot fungus (Gloeophyllum trabeum). The changes in wood microstructure, chemical composition, surface color, crystallinity, fungal colonization pathways, and photodegradation products after weathering and decay were evaluated and characterized. The results showed that both weathering and decay led to obvious color change on wood surface. The photodegradation of wood resulted in the formation of cracking in cell wall, thus creating new voids. The photodegradation products, which mainly consisted of phenols, diterpenoid acids, and other lignin derived compounds, appeared in the cell lumen. During the initial stage of brown-rot decay, fungal hyphae invaded into wood through inherent voids such as ray cells, axial tracheids, and pits, and completed the initial colonization after 20 days. After photodegradation, hyphae could also invade wood from the new voids, and the acidic photodegradation products promoted the non-enzymatic degradation process of brown-rot. However, lignin derived compounds seemed to inhibit the further activity of decay fungi.

Wavelength-dependent photodegradation of wood and its effects on fluorescence

Abstract Apart from some strongly fluorescent wood species, the general fluorescence of wood has long been ignored. Recent studies suggest that each species has a distinct fluorescence, originating from both basic components and characteristic extractives. However, wood colour and fluorescence rapidly change upon exposure to sunlight. In this study, 288 samples of Acer pseudoplatanus, Quercus robur, Picea abies and Juglans nigra were irradiated with different bands of ultraviolet (UV) and visible (VIS) light. Photosensitivity was examined in regards of colour, infrared absorbance (FTIR), and fluorescence imaging. UV light caused strong yellowing in all examined species, mostly correlating with lignin degradation, carbonyl formation and the appearance of a broad banded fluorescence emission. VIS light above 420 nm, however, caused different, partly contradicting effects in colour and fluorescence, and did not affect lignin. J. nigra proved to be most sensitive towards VIS-induced yellowing and bleaching. The main new finding of this study is that the native long wave fluorescence of wood was strongly decreased by VIS-irradiation above 510 nm wavelength in all samples. This effect was not species-specific, probably originating from a cross-species wood component. The results have potential impacts on non-destructive image-based evaluation methods and wood identification.

Influences of merbau heartwood extracts and their metal complexes on wood photodegradation

Merbau (Intsia spp.) heartwood is a highly valued commercial wood but has problems with extractive bleeding when used as a construction material outdoors. The metal complexation method is one solution to resolve this problem. However, properties of merbau heartwood extracts would be modified and the anti-weathering ability changed. This study investigates the wood photo-protection ability of the merbau heartwood extract and its metal complexes. The results reveal that merbau heartwood extract has good free radical scavenging ability and UV absorptivity, which could inhibit wood photodegradation. After metal complexation, the extract-metal complexes also have wood photo-protection ability that inhibits wood photodegradation. Furthermore, since catecholic phenols were chelated by iron(II)/copper(II), the oxidative derivatives were consequently inhibited. Accordingly, these findings show that both merbau heartwood extract and its metal complexes have the ability to remove photo-induced hazards and enhance wood photostability for short periods of UV irradiation. Additionally, these results can be a reference for the environmentally benign utilization of merbau heartwood.

Sustainable wood coatings made of epoxidized vegetable oils for ultraviolet protection

Environmental policies are becoming more restrictive in preserving ecosystems, encouraging the use of renewable resources such as wood. Wood products need to be protected, notably in outdoor situations, because wood is aging under the effect of climate conditions such as light, water and biodegradation. Surface color modifications occur, accompanied by a decline in physico-mechanical properties. Classical wood coatings are progressively prohibited due to their environmental toxicity, thus calling for safer coatings. Here we review wood photodegradation and protective coatings made of vegetable oils and epoxy resins. Epoxy resins allow high crosslinking and solve the common incompatibility of wood surface and coatings.

Investigation of Photo-Induced Discoloration on Wood Treated with the Polyphenols from Acacia Confusa Heartwood

Previous studies have clearly demonstrated that the polyphenols of the ethyl acetate (EtOAc) fraction in the heartwood extract from Acacia confusa (AcHWE) had good photostabilities to prevent photodegradation of wood. The wood photostabilizing actions of condensed tannins and flavonoids from the EtOAc fraction in AcHWE have been individually established, but the effects of these polyphenols on photo-induced discoloration are unknown and merit investigation. The results of this study showed that the six sub-fractions (EA1–EA6), which were fractionated from the EtOAc fraction in AcHWE and contained various condensed tannins and flavonoids, caused different photo-induced discoloration of treated wood. Treating the wood with abundant condensed tannins with little or no flavones and flavonols gave a dramatic dark reddish discoloration after irradiation. Treating the wood with abundant flavones and flavonols with/without condensed tannins produced a moderate dark reddish discoloration with faded yellow tone after irradiation. However, if there are abundant flavanones in the treated wood, their flavanones could transform to chalcones, which increased the yellow tone of treated wood surfaces after initial irradiation. These results illustrated explicit discoloration tendencies for polyphenols in the photodegradation processes for wood and can be the references for further applications.

Photodegradation of wood flour/polypropylene composites incorporated with carbon materials with different morphologies

ABSTRACTIn this study, wood flour/polypropylene (WF/PP) composites were prepared by incorporating 2 wt% carbon materials with different morphologies, including carbon black (CB), graphite (G), and multi-walled carbon nanotubes (CNTs). WF/PP composite without any additives was included as a reference. All composites were placed in the accelerated UV weathering tester for a total of 960 h. The physical and mechanical properties of composites were compared. The changes in surface morphology and surface chemistry were characterized by SEM AFM, and ATR-FTIR. The results showed that: (1) the addition of CNTs improved both flexural and impact properties of composites; (2) composites containing CNTs exhibited better color stability and less severe surface cracking during weathering; and (3) ATR-FTIR results revealed that all the additives alleviated surface photo-oxidation of composites due to their UV-screening effect. Overall, due to the improved interfacial bonding between WF and PP, CNTs were more effective in protecting wood–plastic composites from photodegradation.

Wood photostabilization roles of the condensed tannins and flavonoids from the EtOAc fraction in the heartwood extract of Acacia confusa

Lignin, one of the three major components in wood, can absorb UV light and react with 1O2, leading to wood photodegradation. Previous studies demonstrated the ethyl acetate (EtOAc) fraction of the heartwood extract in Acacia confusa (AcHW) has good photostabilities to prevent photodegradation of the wood. However, these effective constituents have different structural characteristics and may affect their photostabilities and protection efficacies on wood which need to be clarified. This study analyzed the polyphenolic contents, chemical constituents and photostabilities of the six subfractions (EA1–EA6) which successively fractioned from the EtOAc fraction in AcHW by the colorimetric methods, UV/Vis spectrophotometry and high-performance liquid chromatography and evaluated the wood photoprotection abilities of these treatments. The results showed the more flavones and flavonols contained in the subfractions, the better the UVA absorptivity was. Besides, the catecholic-condensed tannins and flavonoids in these subfractions also provide good 1O2 quenching abilities and phenoxyl radical scavenging abilities. Advanced results also established in these subfractions, melanoxetin, transilitin, 7,3′,4′-trihydroxy-3-methoxyflavone, 7,8,3′-trihydroxy-3,4′-dimethoxyflavone (flavonols), 7,8,3′,4′-tetrahydroxyflavone, 7,3′,4′-trihydroxyflavone, 7,3′,4′-trihydroxy-5-methoxyflavone (flavones) and okanin (chalcone) can absorb the energy of UVA light; the condensed tannins, 3,4-dihydroxybenzoic acid (phenolic acid), melacacidin-based oligomers, melacacidin, 4-O-methylmelacacidin, 4′-O-methylmelacacidin (melacacidin-based flavanols), 3,7,8,3′,4′-pentahydroxyflavanone (flavanonol), 7,8,3′,4′-tetrahydroxyflavanone (flavanone), the flavones, flavonols and chalcone can suppress the phenoxyl radicals; the condensed tannins, melacacidin-based oligomers and the flavonoids can quench 1O2. Hence, the photostability of extract-free wood slices treated with these effective constituents was consequently enhanced. In summary, these results clearly demonstrated the multiple wood photoprotection actions of these effective constituents and their potential as natural wood photostabilizers.

Temperature dependence of wood photodegradation. Part 2: Evaluation by Arrhenius law

The temperature dependence of photodegradation for wood was evaluated applying the Arrhenius law. Hardwood (beech, Fagus sylvatica L. and poplar, Populus x euramericana cv. Pannonia) and softwood (Scots pine, Pinus sylvestris L. and spruce Picea abies Karst.) species were involved in the test. Samples were irradiated by a strong UV emitter mercury lamp at 30 °C, 80 °C, 120 °C and 160 °C. The chemical changes were detected by diffuse reflectance infrared spectroscopy. The absorption changes were determined by difference spectrum method. After IR data processing, the dominant seven IR bands were selected for generating the Arrhenius plots for all examined species.The results show that the Arrhenius law is useful in interpreting the kinetics of some photochemical reactions during the photodegradation of wood. The photodegradation of guaiacyl lignin absorbing at 1270 cm−1 was found a single rate-limited, thermally activated process for all examined species. These results indicated that the temperature dependence of this degradation was exponential. The absorption increase of quinones at 1596 cm−1 and the absorption decrease of ether bond in cellulose and hemicellulose at 1175 cm−1 also showed exponential temperature dependence for conifers.In most of the cases, at least two different (and sometimes antagonistic) types of chemical changes generated absorption change at the same wavenumber region. In these situations, the Arrhenius equation was unable to indicate whether the temperature dependence is exponential or not.

Temperature dependence of wood photodegradation monitored by infrared spectroscopy

Abstract The temperature dependence of the photodegradation of hardwoods (beech, Fagus sylvatica L. and poplar, Populus x euramericana cv. Pannonia) and softwoods (Scots pine, Pinus sylvestris L. and spruce, Picea abies Karst.) was investigated. Samples were irradiated by a strong UV emitter mercury lamp at 30 °C, 80 °C, 120 °C and 160 °C. A series of samples was treated in the same chamber set to 30 °C, 80 °C, 120 °C and 160 °C but without light irradiation (pure thermal treatment). The chemical changes were detected by infrared spectroscopy. The same light irradiation generated much greater absorption change at 160 °C than at 30 °C. The simultaneous thermal and UV treatment generated much greater absorption increase in the whole investigated infrared region than the sum of absorption increases generated by the individual thermal treatment and UV radiation, separately. Softwoods were more sensitive to the light irradiation at elevated temperatures than hardwoods. Results revealed that four bands around 1770, 1750, 1720 and 1690 cm−1 emerged in the unconjugated carbonyl region as a result of the UV irradiation at elevated temperatures. The intensity change of these bands is highly dependent on the wood species. Absorption increase was found at 1066 and 1035 cm−1.

Characterization and photodegradation mechanism of three Algerian wood species

Aging is the irreversible change of mechanical, physical, and chemical properties of materials; the main objective of this work was to study the photochemical degradation and structural changes of three major Algerian wood species. For this, we evaluated the photodegradation mechanism for Maritime Pine (Pinus pinaster), zeen oak (Quercus canariensis), and afares oak (Quercus afares) by accelerated aging in a Xenon test chamber. Degradation of the samples was established by an initial color change (after 30 h exposure), followed by roughening and cracking (120 h exposure) as translated by scanning electron microscopy and Fourier transform infrared spectroscopy. The discoloration of irradiated wood samples was primarily related to the decomposition of lignin which is the key structure in wood photodegradation. As expected, a decrease in mechanical properties was observed; for all samples, the modulus of elasticity decreased after aging, indicating that the wood specimens loss some of their stiffness.

Protective behaviour monitoring on wood photo-degradation by spectroscopic techniques coupled with chemometrics

This paper reports the investigation on the effect of protective materials on poplar (Populus sp.) wood modifications as consequence of artificial photo-degradation in controlled environment. The novelty of this work is to try to understand what happens to wood surface under the protective layer. Shellac, beeswax and Linfoil® were tested to compare traditional and novel products generally used for wood. The samples, uncovered and covered by these protective layers, were artificially aged. Colour and chemical modifications due to ageing were investigated at different time intervals by reflectance spectrophotometry, Fourier transform infrared spectroscopy and hyperspectral imaging. The obtained data were elaborated by statistical and chemometric tools in order to verify their significance and to assess the relationship between groups of measurements.The results highlighted that shellac, beeswax and Linfoil® materials have a very low protective effect on wood photo-degradation for long times of exposure, by little reducing the changes of wood components.

Spectral sensitivity in the photodegradation of fir wood (Abies alba Mill.) surfaces: correspondence of physical and chemical changes in natural weathering

The main purpose of this study was to demonstrate and compare the effect of specific wavebands of light on colour changes, chemical breakdown and mechanical properties of fir wood surfaces during different stages of natural exposure. Spectral sensitivity was determined by exposing samples to sunlight behind different glass cut-off filters, under which a pack of three 80-μm-thick wood strips represented the composite surface layer of fir wood. It was found that colour changes, mechanical degradation and chemical changes develop in different chronological orders and at different rates and form different depth profiles. It was demonstrated that all of the methods of exposure and analysis employed in this study on wood photodegradation have their limitations and give different indications as to the development of the degrading processes. Discoloration can register the photodegradation readily, intensively and at a greater depth below the surface compared to the microtensile testing method or FTIR-ATR technique. Only combined observations and comparisons of results of different methods can give a comprehensive image of the photodegradation process.

A new approach for the modelling of chestnut wood photo-degradation monitored by different spectroscopic techniques.

The aim of this work is to study the colour and chemical modifications of the surfaces in chestnut wood samples as a consequence of irradiating in a controlled environment. The changes were investigated by a new analytical approach by combining traditional techniques such as reflectance spectrophotometry in the visible range and Fourier transform infrared spectroscopy with new hyperspectral imaging, in order to obtain forecast models to describe the phenomenon. The statistical elaboration of the experimental data allowed to validate the measurements and to obtain models enabling to relate the investigated parameters; the elaboration of the hyperspectral images by chemometric methods allowed for studying the changes in the reflectance spectra. A result of great importance is the possibility to correlate the oxidation of wood chemical components with the colour change in a totally non-invasive modality. This result is particularly relevant in the field of cultural heritage and in general in the control processes of wooden materials.

Epoxy and succinic anhydride functionalized soybean oil for wood protection against UV light action

Wood is a versatile composite material consisting of natural macromolecules, including carbohydrates (cellulose, hemicelluloses) and lignin. As a natural biological material, wood undergoes photooxidation phenomena under environmental factors action. Colour modification of wood surface is a primary consequence of the photooxidation phenomena. One way to prevent wood photodegradation consists in coating it with protective layers by chemical modification of the surface. The aim of this study is related to the photostability evaluation of chemically modified softwood by successive treatment stages with succinic anhydride and epoxidized soybean oil, respectively, during exposure to UV radiation with wavelength above 280 nm. Wood and wood coated materials photooxidation was monitored in terms of colour and structural modification as functions of irradiation time and dose. Chromatic coordinates values exhibited a slow increase with irradiation time and dose compared to the values of unmodified wood. Lignin exhibited stronger photodegradation tendencies, leading mainly to an increase of redness feature of wood samples surface. The coating layer consisting of epoxidized soybean oil protected the modified wood surface against photooxidation reactions by a screening effect.

Exploitation of Acacia confusa heartwood extract as natural photostabilizers

Heartwood extracts of Acacia confusa (HEAc) were proven to have the capability of ameliorating wood photostability. However, the efficacy of photostability compared with that of commercial photostabilizers was unknown. The aim of this study was to examine whether HEAc can be used as commercial photostabilizers. Comparison was made among commercially available photostabilizers, UV absorber (Eversorb 80, EV80) and hindered amine light stabilizer (Eversorb 93, EV93). Photostability of wood slices soaked in 1, 5 and 10 % HEAc or 1 % commercial photostabilizers (EV80 or EV93) solutions was evaluated. The discoloration of 5 and 10 % HEAc-treated specimens was significantly reduced after UV irradiation. Furthermore, lignin degradation and carbonyl formation were concurrently inhibited by 5 and 10 % HEAc treatments after UV irradiation. Interestingly, 1 % HEAc treatment showed similar effectiveness compared with EV80 treatment, while 5 and 10 % HEAc treatments showed better effectiveness than EV80 treatment. HEAc can absorb UV light and quench radicals; hence, wood photodegradation was consequently prevented. These results revealed that HEAc has great potential to be developed as a natural photostabilizer.

Effects of Antioxidants on Photodegradation of Wood Flour/Polypropylene Composites during Artificial Weathering

The influence of antioxidants and of their compound systems were evaluated relative to the photodegradation of wood flour/polypropylene (WF/PP) composites using ultraviolet accelerated weathering. Six groups of samples were exposed in an accelerated weathering tester for a total duration of 960 h. The surface color, gloss, and flexural properties of the samples during weathering were tested. In addition, the weathered surfaces were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The results revealed the following: (1) after weathering, all samples showed significant color fading and gloss change; (2) composites containing antioxidants showed less loss of flexural strength, fewer surface cracks, and better thermal stability after weathering than the control composite; (3) the crystallinity of polypropylene increased in weathered samples due to recrystallization of lower molecular weight polypropylene; and (4) antioxidant 168 (AO-168) was beneficial to color stability at the early stage of weathering, while composites containing 0.2% antioxidant 1010 (AO-1010) and 1.0% AO-168 (AO-1) maintained the highest retention ratios of flexural properties during weathering.

Effects of vitamin E combined with antioxidants on wood flour/polypropylene composites during accelerated weathering

Abstract The aim of this research was to investigate the influence of different antioxidant systems containing vitamin E (VE) and antioxidant 168 (AO) on the photodegradation of wood flour/polypropylene (WF/PP) composites, as well as to provide insight into the processes taking place in these systems during weathering. Five groups of composites were treated in a QUV accelerated weathering tester for a total of 960 h. The surface color and the flexural properties of the weathered samples were tested. Additionally, the weathered surface was characterized by SEM, ATR-FTIR, and XPS. The results were: (1) composites with VE and AO showed less loss of flexural strength and modulus, as well as less color fading and fewer cracks on weathered surfaces than surfaces without antioxidants; (2) AO reacted with hydroperoxide and quinones and showed a synergistic effect with VE to further improve the anti-weathering ability of the composites; (3) 0.2% VE and 1.0% AO was the optimal formulation, yielding the best anti-weathering properties among all.