Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology B: Biology journal homepage: www.elsevier.com/locate/jphotobiol
Measurement of photodegradation-caused roughness of wood using a new optical method Laszlo Tolvaj ⇑, Zsolt Molnar, Endre Magoss University of West Hungary, Bajcsy Zs. u. 4, HU-9400 Sopron, Hungary
a r t i c l e
i n f o
Article history: Received 6 December 2013 Received in revised form 25 March 2014 Accepted 27 March 2014 Available online 5 April 2014 Keywords: Wood Photodegradation Roughness Infrared spectrum Baseline shift
a b s t r a c t The aim of this study was to clarify the intensity of the surface roughening of wood caused by light radiation using a fast optical method. The samples were irradiated by mercury lamp and the roughness change was monitored traditionally using a perthometer. The infrared (IR) diffuse reflectance spectrum was measured and the baseline shift was found to be a proper parameter to monitor the roughening effect of photodegradation. Linear correlation was found between the traditionally measured roughness and the baseline shift. This newly developed optical method is able to detect the degradation difference between earlywood and latewood. Some of the samples were immersed in distilled water for a day after an all light irradiation period of two days. This new baseline shift method was able to visualise and determine the small change in roughness caused by the leaching effect of water. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Wood is a chemically highly complicated natural product. The basic component is the cellulose biopolymer surrounded by a lignin matrix. The components are naturally arranged into tubular structures and eventually form a cylindrically layered composite. This structure is sensitive to biotic and abiotic degradations. The chemical components of solid wood are sensitive to light irradiation. The main factor that causes the greatest change during exposure to sunlight is the ultraviolet (UV) radiation [1]. Chemical analyses showed that the deterioration is primarily related to the decomposition of lignin [2–7]. The chromophoric groups of lignin are strong UV light absorbers. The energy of the absorbed UV photons is large enough to create free phenoxyl radicals. These free radicals react with oxygen to produce carbonyl chromophoric groups [2–8]. Within the cell structure, the middle lamella between two cell walls is mostly destroyed by light irradiation [9]. This degradation increases the roughness of the wood surface. Temiz et al. [10] and Nzokou et al. [11] examined the roughness change of preservativetreated and finished wood samples during periodic light irradiation and water spray. They reported a considerable increase of the surface roughness of the control (the unfinished and untreated samples) during photodegradation and water spray. Ozgenc et al. [12] also examined the protective effect of vegetable oil treatments and concluded that the roughening of oil-treated samples was ⇑ Corresponding author. Tel.: +36 99 518140; fax: +36 99 518259. E-mail address: [email protected] (L. Tolvaj). http://dx.doi.org/10.1016/j.jphotobiol.2014.03.020 1011-1344/Ó 2014 Elsevier B.V. All rights reserved.
significantly lower than those of untreated controls during photodegradation and water spray cycles. The earlywood is more degradable by light radiation than the latewood [13]. This fact causes roughening that is clearly visible and differentiated on the surface of wooden construction, especially those being left outdoors for a long time such as that shown in Fig. 1. This photo taken in Japan shows the weathered cross section of a fence part that was left outdoors for approximately 500 years. The photo clearly shows the degradation difference between earlywood and latewood. The surface roughness of timber is an important parameter for further processing and it is sensitive to the modification processes [14–16]. Some authors also mentioned roughness change due to the alteration of light scattering on the irradiated surface [17–19]. Light scattering is wavenumber dependent. The baseline shift of the infrared (IR) reflectance spectrum is usually caused by such scattering. This problem can be minimized by baseline correction in spectroscopic practice. The aim of this study was to find a simple optical method to monitor the roughness change of wood caused by photodegradation. The baseline shift increases during photodegradation due to light scattering. When this change is calculated, then the correlation between roughness change and the baseline shift can be determined. 2. Materials and methods Samples of three hardwood and two softwood species were used for this study. The hardwood species were black locust (Robinia pseudoacacia L.), oak (Quercus petraea Liebl.), and poplar (Populus
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
R (%)
24
Wavenumber (cm-1) Fig. 2. The diffuse reflexion spectra of oak wood indicating the baseline shift. Fig. 1. The photodegraded cross section of an old temple fence part. (Myajima island, Japan).
Baseline shift ¼ Rð3800Þ=Rð1900Þ where R(3800) is the reflection intensity at 3800 cm1 and R(1900) is the same at 1900 cm1. Applying this definition, the correlation between baseline shift and roughness was calculated. 3. Results and discussions The roughness parameters were recorded after five days of UV light irradiation, which was followed by two-day intervals. There was a total of five irradiation periods. The samples were soaked in distilled water for a day after each irradiation period. The necessary parameters were measured right after subjecting the samples to light irradiation. The data presented below are the average of the five samples. The selected roughness parameters increased continuously during UV irradiation for all examined species. Figs. 3 and 4 show the results for black locust and spruce, representing the hardwoods and softwoods, respectively. The increase was linear for poplar, Scots pine and spruce. For black locust the increase was a little higher during the first 6 days compared to the later period. Parallel with conventional roughness measurement, the IR reflexion spectra were also recorded. After calculating the baseline shift parameters (reflexion intensity at 3800 cm1 divided by reflection intensity at 1900 cm1), the correlation between roughness and baseline shift was tested. The results are presented in Fig. 5 for black locust, Scots pine and spruce wood species. The
Roughness (µm)
tremula L.). The softwood species were Scots pine (Pinus sylvestris L.) and spruce (Picea abies Karst.). The dimensions of the samples for roughness measurement were 40 40 20 mm. Five replicates were prepared for all wood species selected. For the IR diffuse reflectance measurement, the sample dimensions were 40 10 2 mm and six replicates were prepared. It was necessary to prepare a different size for each of the two types of measurement because the spectrophotometer required thin samples while the perthometer needed thicker and wider samples to be able to fix these samples in the same position. The traditional roughness measurement was carried out using the perthometer on the radial surface of the sample along 10 parallel lines. The distance between the lines was 0.5 mm and the place of measured lines was always the same after each individual treatment period. The unfiltered P profile was computed from the traced profile (EN ISO 3274). The surface roughness parameters (Pz; Pt; Pa; Pmax) can be applied also for this profile [20]. The roughness parameters were calculated by the Curve Cutter program from the unfiltered P profile. A strong UV light emitter, mercury vapour lamp provided the light irradiation. The total electric power of the applied double mercury lamps was 800 W and the samples were located 64 cm from the lamp. An irradiation chamber set for 70 °C ensured ambient temperature conditions. The total irradiation time was 15 days in all cases. The irradiation was interrupted (two-day intervals were applied) for measuring the changes. After measuring the roughness and the IR spectra, the irradiated samples were soaked in distilled water for a day to imitate the leaching effect of the rain. One series of samples was not leached by water to determine the effect of UV radiation separately. All the IR measurements were performed on the tangential surfaces of the specimens. The sample surface contained only one type of tissue which was either earlywood or latewood. The diffuse reflectance infrared Fourier transform (DRIFT) spectrum of the samples was measured before and after irradiation and also after water leaching. Measurements were carried out with an IR spectrophotometer (JASCO FT/IR 6300), applying a diffuse reflectance unit. The resolution was 4 cm1 and 64 scans were obtained and averaged. The same area of the samples was always measured. The background spectrum was determined against an aluminium plate. Wood had no absorption at 1900 and 3800 cm1. It meant the reflexion should be 100% at these places. But the reflexion was less than 100% because of the light scattering; this is called the baseline shift in IR spectroscopy (Fig. 2). Calculating the absorption spectrum, these reflexion values are lifted up to 100% (lifting up the whole spectrum) to eliminate the scattering effect. This is the baseline correction, which is regularly used in diffuse reflectance IR
spectroscopy. The scattering depends on the roughness of the surface. It means the baseline shift gives information about the surface roughness. We gave the baseline shift as the quotient of two reflexion intensities.
Pz Pa Pt Pmax
Irradiation time (day) Fig. 3. Selected roughness parameters of treated (light and water) black locust wood, measured after light irradiation.
Pz Pa Pt
25
R(3800)/R(1900)
Roughness (µm)
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
Pmax
Irradiation time (day)
Irradiation time (day)
Fig. 6. Roughness difference between earlywood (E) and latewood (L) of black locust (B) and oak (O) caused by photodegradation and water leaching.
R(3800)/R(1900)
Roughness, Pz parameter (µm)
Fig. 4. Selected roughness parameters of treated (light and water) spruce wood, measured after light irradiation.
Irradiation time (day) R(3800)/R(1900) Fig. 5. Correlation between roughness and baseline shift of black locust, Scots pine and spruce samples.
baseline shift data are the average of earlywood and latewood data. The linear trend lines are close to parallel. The high values of the coefficient of determination (R2) show good correlation between roughness and baseline shift in all cases. The R2 was above 0.9 for all investigated wood species. This close correlation suggests that it is possible to monitor the roughness alteration effect of photodegradation by measuring the IR reflection data. The background information on this correlation is as follows: The baseline shift of the IR spectrum is created by the light scattering on the wood surface. This scattering increases with intensifying roughness. It must be noted that the baseline shift is a sensitive method to monitor the roughness change but it is not able to substitute the conventional roughness measurement. The big difference between the two methods is that the measured area in the case of IR measurement is smaller than 10 mm2. Using the perthometer, the measured area is much larger. Fig. 1 showed that the earlywood was more degraded than latewood by photodegradation. We tested whether our new optical method is able to show this degradation difference between earlywood and latewood at the early stage. The results are shown in Figs. 6 and 7. The IR spectrum was measured right after the light irradiation. The roughness (baseline shift) increased continuously for all tissues of all wood species. Similarly, after five days treatment the roughness of earlywood was higher than the roughness of latewood for all species. For poplar this difference (not presented here) was hardly visible. Preparing the poplar samples was rather difficult because it was hard to differentiate between earlywood and latewood with the naked eye, too. The oak samples showed the greatest difference and they have the greatest initial roughness as well. The Scots pine produced moderate roughness
Fig. 7. Roughness difference between earlywood (E) and latewood (L) of Scots pine (P) and spruce (S) caused by photodegradation and water leaching.
while the black locust and spruce produced similar but small difference in roughness between earlywood and latewood. The chosen hardwoods represent three different types of wood. Poplar is a low-density diffuse-porous tree species. Hence, it was not surprising that there was no discernable difference between the roughness of earlywood and latewood for poplar wood. Oak and black locust are ring-porous trees but the vessels of the black locust are heavily clogged by tyloses. The optically measured initial roughness of black locust is lower than the initial roughness of oak because of the tyloses clogging. The same explanation can be stated to interpret the small difference between the roughness of earlywood and latewood for black locust and the high difference found for oak. These results further illustrate the sensitivity of the baseline shift method to smaller differences in the roughness of wood surfaces. The effect of water leaching also can be monitored by our newly developed optical method. Fig. 8 represents the effect of UV treatment and water leaching, with one treatment following the other, for black locust earlywood. The first dot represents the initial roughness (baseline shift) of a sample. The second dot corresponds to one day UV treatment. The third dot was produced by one day water leaching. The following UV treatments were two days long and the water leaching was only for one day. All UV treatments caused an increase in the roughness of the wood, but the water leaching reduced this roughness. The changes were identical for UV treatments and for water leaching, but these changes were in opposite direction and these differences were smaller with increasing treatment time. The baseline shift is able to show the effect of leaching if we compare the roughness change of UV treated and water leached sample to that sample which gave only UV irradiation without
26
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
R(3800)/R(1900)
change, we were able to detect the photodegradation difference between earlywood and latewood in the early stage of the treatment as well. This sensitive optical method also showed that water leaching slightly reduces the roughness of the UV light irradiated wooden surface. Acknowledgements This study was supported by the Environment conscious energy efficient building TAMOP-4.2.2.A–11/1/KONV-2012-0068 Project sponsored by the EU and European Social Foundation. References
Fig. 8. Baseline shift of black locust earlywood. Starts with the initial data (0D) followed by 1 day UV treatment (1D) and water leaching (1D + W), and it is repeated. (These are the data of one sample).
R(3800)/R(1900)
UV UV+W
Irradiation time (day) Fig. 9. Baseline shift of spruce earlywood caused by UV irradiation and UV irradiation combined with water leaching (UV + W).
water leaching. Fig. 9 presents this information for spruce earlywood. The roughness increase of the sample which received only UV treatment was considerably greater than the same parameter for the UV treated and water leached sample. This figure indicates the roughness reducing effect of leaching similar to that presented in Fig. 8. 4. Conclusions Samples were irradiated using strong UV emitter mercury lamp. Some of the samples were immersed in distilled water for a day after each 2-day UV treatment period. To monitor the roughness change caused by the treatments, measurements were done using the perthometer and IR reflectance spectrum. The treatments caused baseline shift for the IR reflectance spectrum. A close correlation was found between traditionally measured roughness and the baseline shift. Using the baseline shift as an indicator of roughness
[1] L. Tolvaj, K. Mitsui, Light source dependence of the photodegradation of wood, J. Wood Sci. 51 (2005) 468–473. [2] L. Tolvaj, O. Faix, Artificial ageing of wood monitored by DRIFT spectroscopy and CIE Lab color measurements. I. Effect of UV light, Holzforschung 49 (1995) 397–404. [3] K.K. Pandey, Study of the effect of photo-irradiation on the surface chemistry of wood, Polym. Degrad. Stabil. 90 (2005) 9–20. [4] C.M. Popescu, M.C. Popescu, C. Vasile, Structural analysis of photodegraded lime wood by means of FT-IR and 2D IR correlation spectroscopy, Int. J. Biol. Macromol. 48 (2011) 667–675. [5] L. Tolvaj, L. Persze, L. Albert, Thermal degradation of wood during photodegradation, J. Photochem. Photobiol. B 105 (2011) 90–93. [6] C.A. Teaca, D. Rosu, R. Bodirilau, L. Rosu, Structural changes in wood under artificial UV light irradiation determined by FTIR spectroscopy and color measurements – a brief review, Bioresources 8 (2013) 1478–1507. [7] G. Agresti, G. Bonifazi, L. Calienno, G. Capobianco, A. Lo Monaco, C. Pelosi, R. Picchio, S. Serranti, Surface investigation of photo-degraded wood by colour monitoring, infrared spectroscopy, J. Spectrosc. 1 (2013). Paper 380536. [8] C.M. Popescu, B.C. Simionescu, Structural study of photodegraded acryliccoated lime wood using Fourier transform infrared and two-dimensional infrared correlation spectroscopy, Appl. Spectrosc. 67 (2013) 606–613. [9] H. Turkulin, SEM methods in surface research on wood, COST E18 Final Seminar 26–27/04/2004 Paris, pp. 1–9. [10] A. Temiz, U.C. Yildiz, I. Aydin, M. Eikenes, G. Alfredsen, G. Çolakoglu, Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test, Appl. Surf. Sci. 250 (2005) 35–42. [11] P. Nzokou, D.P. Kamdem, A. Temiz, Effect of accelerated weathering on discoloration and roughness of finished ash wood surfaces in comparison with red oak and hard maple, Prog. Org. Coat. 71 (2011) 350–354. [12] O. Ozgenc, O.T. Okan, U.C. Yildiz, I. Deniz, Wood surface protection against weathering with vegetable seed oil, Bioresources 8 (2013) 6242–6262. [13] L. Tolvaj, Monitoring of photodegradation for wood by infrared spectroscopy, COST Action IE0601 Conference, Hamburg, 07.10.2009. [14] M. Kilic, S. Hiziroglu, C. Güllü, Z. Sezgin, Influence of steaming on surface roughness of beech and sapele flooring material, J. Mater. Process. Technol. 199 (2008) 448–451. [15] E. Tanritanir, S. Hiziroglu, N. As, Effect of steaming time on surface roughness of beech veneer, Build. Environ. 41 (2006) 1494–1497. [16] D.S. Korkut, S. Hiziroglu, A. Aytin, Effect of heat treatment on surface characteristics of wild cherry wood, Bioresources 8 (2013) 1582–1590. [17] L. Tolvaj, K. Mitsui, Surface preparation and direction dependence of DRIFT spectra of wood, Appl. Spectrosc. 58 (2004) 1137–1140. [18] L. Tolvaj, K. Mitsui, Validity limits of Kubelka–Munk theory for DRIFT spectra of photodegraded solid wood, Wood Sci. Technol. 45 (2011) 135–146. [19] L. Tolvaj, Zs. Molnar, R. Nenemth, Photodegradation of wood at elevated temperature: infrared spectroscopic study, J. Photochem. Photobiol. B 121 (2013) 32–36. [20] E. Csanády, E. Magoss, Mechanics of Wood Machining, Springer, 2013, pp. 168– 171.
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology B: Biology journal homepage: www.elsevier.com/locate/jphotobiol
Measurement of photodegradation-caused roughness of wood using a new optical method Laszlo Tolvaj ⇑, Zsolt Molnar, Endre Magoss University of West Hungary, Bajcsy Zs. u. 4, HU-9400 Sopron, Hungary
a r t i c l e
i n f o
Article history: Received 6 December 2013 Received in revised form 25 March 2014 Accepted 27 March 2014 Available online 5 April 2014 Keywords: Wood Photodegradation Roughness Infrared spectrum Baseline shift
a b s t r a c t The aim of this study was to clarify the intensity of the surface roughening of wood caused by light radiation using a fast optical method. The samples were irradiated by mercury lamp and the roughness change was monitored traditionally using a perthometer. The infrared (IR) diffuse reflectance spectrum was measured and the baseline shift was found to be a proper parameter to monitor the roughening effect of photodegradation. Linear correlation was found between the traditionally measured roughness and the baseline shift. This newly developed optical method is able to detect the degradation difference between earlywood and latewood. Some of the samples were immersed in distilled water for a day after an all light irradiation period of two days. This new baseline shift method was able to visualise and determine the small change in roughness caused by the leaching effect of water. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Wood is a chemically highly complicated natural product. The basic component is the cellulose biopolymer surrounded by a lignin matrix. The components are naturally arranged into tubular structures and eventually form a cylindrically layered composite. This structure is sensitive to biotic and abiotic degradations. The chemical components of solid wood are sensitive to light irradiation. The main factor that causes the greatest change during exposure to sunlight is the ultraviolet (UV) radiation [1]. Chemical analyses showed that the deterioration is primarily related to the decomposition of lignin [2–7]. The chromophoric groups of lignin are strong UV light absorbers. The energy of the absorbed UV photons is large enough to create free phenoxyl radicals. These free radicals react with oxygen to produce carbonyl chromophoric groups [2–8]. Within the cell structure, the middle lamella between two cell walls is mostly destroyed by light irradiation [9]. This degradation increases the roughness of the wood surface. Temiz et al. [10] and Nzokou et al. [11] examined the roughness change of preservativetreated and finished wood samples during periodic light irradiation and water spray. They reported a considerable increase of the surface roughness of the control (the unfinished and untreated samples) during photodegradation and water spray. Ozgenc et al. [12] also examined the protective effect of vegetable oil treatments and concluded that the roughening of oil-treated samples was ⇑ Corresponding author. Tel.: +36 99 518140; fax: +36 99 518259. E-mail address: [email protected] (L. Tolvaj). http://dx.doi.org/10.1016/j.jphotobiol.2014.03.020 1011-1344/Ó 2014 Elsevier B.V. All rights reserved.
significantly lower than those of untreated controls during photodegradation and water spray cycles. The earlywood is more degradable by light radiation than the latewood [13]. This fact causes roughening that is clearly visible and differentiated on the surface of wooden construction, especially those being left outdoors for a long time such as that shown in Fig. 1. This photo taken in Japan shows the weathered cross section of a fence part that was left outdoors for approximately 500 years. The photo clearly shows the degradation difference between earlywood and latewood. The surface roughness of timber is an important parameter for further processing and it is sensitive to the modification processes [14–16]. Some authors also mentioned roughness change due to the alteration of light scattering on the irradiated surface [17–19]. Light scattering is wavenumber dependent. The baseline shift of the infrared (IR) reflectance spectrum is usually caused by such scattering. This problem can be minimized by baseline correction in spectroscopic practice. The aim of this study was to find a simple optical method to monitor the roughness change of wood caused by photodegradation. The baseline shift increases during photodegradation due to light scattering. When this change is calculated, then the correlation between roughness change and the baseline shift can be determined. 2. Materials and methods Samples of three hardwood and two softwood species were used for this study. The hardwood species were black locust (Robinia pseudoacacia L.), oak (Quercus petraea Liebl.), and poplar (Populus
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
R (%)
24
Wavenumber (cm-1) Fig. 2. The diffuse reflexion spectra of oak wood indicating the baseline shift. Fig. 1. The photodegraded cross section of an old temple fence part. (Myajima island, Japan).
Baseline shift ¼ Rð3800Þ=Rð1900Þ where R(3800) is the reflection intensity at 3800 cm1 and R(1900) is the same at 1900 cm1. Applying this definition, the correlation between baseline shift and roughness was calculated. 3. Results and discussions The roughness parameters were recorded after five days of UV light irradiation, which was followed by two-day intervals. There was a total of five irradiation periods. The samples were soaked in distilled water for a day after each irradiation period. The necessary parameters were measured right after subjecting the samples to light irradiation. The data presented below are the average of the five samples. The selected roughness parameters increased continuously during UV irradiation for all examined species. Figs. 3 and 4 show the results for black locust and spruce, representing the hardwoods and softwoods, respectively. The increase was linear for poplar, Scots pine and spruce. For black locust the increase was a little higher during the first 6 days compared to the later period. Parallel with conventional roughness measurement, the IR reflexion spectra were also recorded. After calculating the baseline shift parameters (reflexion intensity at 3800 cm1 divided by reflection intensity at 1900 cm1), the correlation between roughness and baseline shift was tested. The results are presented in Fig. 5 for black locust, Scots pine and spruce wood species. The
Roughness (µm)
tremula L.). The softwood species were Scots pine (Pinus sylvestris L.) and spruce (Picea abies Karst.). The dimensions of the samples for roughness measurement were 40 40 20 mm. Five replicates were prepared for all wood species selected. For the IR diffuse reflectance measurement, the sample dimensions were 40 10 2 mm and six replicates were prepared. It was necessary to prepare a different size for each of the two types of measurement because the spectrophotometer required thin samples while the perthometer needed thicker and wider samples to be able to fix these samples in the same position. The traditional roughness measurement was carried out using the perthometer on the radial surface of the sample along 10 parallel lines. The distance between the lines was 0.5 mm and the place of measured lines was always the same after each individual treatment period. The unfiltered P profile was computed from the traced profile (EN ISO 3274). The surface roughness parameters (Pz; Pt; Pa; Pmax) can be applied also for this profile [20]. The roughness parameters were calculated by the Curve Cutter program from the unfiltered P profile. A strong UV light emitter, mercury vapour lamp provided the light irradiation. The total electric power of the applied double mercury lamps was 800 W and the samples were located 64 cm from the lamp. An irradiation chamber set for 70 °C ensured ambient temperature conditions. The total irradiation time was 15 days in all cases. The irradiation was interrupted (two-day intervals were applied) for measuring the changes. After measuring the roughness and the IR spectra, the irradiated samples were soaked in distilled water for a day to imitate the leaching effect of the rain. One series of samples was not leached by water to determine the effect of UV radiation separately. All the IR measurements were performed on the tangential surfaces of the specimens. The sample surface contained only one type of tissue which was either earlywood or latewood. The diffuse reflectance infrared Fourier transform (DRIFT) spectrum of the samples was measured before and after irradiation and also after water leaching. Measurements were carried out with an IR spectrophotometer (JASCO FT/IR 6300), applying a diffuse reflectance unit. The resolution was 4 cm1 and 64 scans were obtained and averaged. The same area of the samples was always measured. The background spectrum was determined against an aluminium plate. Wood had no absorption at 1900 and 3800 cm1. It meant the reflexion should be 100% at these places. But the reflexion was less than 100% because of the light scattering; this is called the baseline shift in IR spectroscopy (Fig. 2). Calculating the absorption spectrum, these reflexion values are lifted up to 100% (lifting up the whole spectrum) to eliminate the scattering effect. This is the baseline correction, which is regularly used in diffuse reflectance IR
spectroscopy. The scattering depends on the roughness of the surface. It means the baseline shift gives information about the surface roughness. We gave the baseline shift as the quotient of two reflexion intensities.
Pz Pa Pt Pmax
Irradiation time (day) Fig. 3. Selected roughness parameters of treated (light and water) black locust wood, measured after light irradiation.
Pz Pa Pt
25
R(3800)/R(1900)
Roughness (µm)
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
Pmax
Irradiation time (day)
Irradiation time (day)
Fig. 6. Roughness difference between earlywood (E) and latewood (L) of black locust (B) and oak (O) caused by photodegradation and water leaching.
R(3800)/R(1900)
Roughness, Pz parameter (µm)
Fig. 4. Selected roughness parameters of treated (light and water) spruce wood, measured after light irradiation.
Irradiation time (day) R(3800)/R(1900) Fig. 5. Correlation between roughness and baseline shift of black locust, Scots pine and spruce samples.
baseline shift data are the average of earlywood and latewood data. The linear trend lines are close to parallel. The high values of the coefficient of determination (R2) show good correlation between roughness and baseline shift in all cases. The R2 was above 0.9 for all investigated wood species. This close correlation suggests that it is possible to monitor the roughness alteration effect of photodegradation by measuring the IR reflection data. The background information on this correlation is as follows: The baseline shift of the IR spectrum is created by the light scattering on the wood surface. This scattering increases with intensifying roughness. It must be noted that the baseline shift is a sensitive method to monitor the roughness change but it is not able to substitute the conventional roughness measurement. The big difference between the two methods is that the measured area in the case of IR measurement is smaller than 10 mm2. Using the perthometer, the measured area is much larger. Fig. 1 showed that the earlywood was more degraded than latewood by photodegradation. We tested whether our new optical method is able to show this degradation difference between earlywood and latewood at the early stage. The results are shown in Figs. 6 and 7. The IR spectrum was measured right after the light irradiation. The roughness (baseline shift) increased continuously for all tissues of all wood species. Similarly, after five days treatment the roughness of earlywood was higher than the roughness of latewood for all species. For poplar this difference (not presented here) was hardly visible. Preparing the poplar samples was rather difficult because it was hard to differentiate between earlywood and latewood with the naked eye, too. The oak samples showed the greatest difference and they have the greatest initial roughness as well. The Scots pine produced moderate roughness
Fig. 7. Roughness difference between earlywood (E) and latewood (L) of Scots pine (P) and spruce (S) caused by photodegradation and water leaching.
while the black locust and spruce produced similar but small difference in roughness between earlywood and latewood. The chosen hardwoods represent three different types of wood. Poplar is a low-density diffuse-porous tree species. Hence, it was not surprising that there was no discernable difference between the roughness of earlywood and latewood for poplar wood. Oak and black locust are ring-porous trees but the vessels of the black locust are heavily clogged by tyloses. The optically measured initial roughness of black locust is lower than the initial roughness of oak because of the tyloses clogging. The same explanation can be stated to interpret the small difference between the roughness of earlywood and latewood for black locust and the high difference found for oak. These results further illustrate the sensitivity of the baseline shift method to smaller differences in the roughness of wood surfaces. The effect of water leaching also can be monitored by our newly developed optical method. Fig. 8 represents the effect of UV treatment and water leaching, with one treatment following the other, for black locust earlywood. The first dot represents the initial roughness (baseline shift) of a sample. The second dot corresponds to one day UV treatment. The third dot was produced by one day water leaching. The following UV treatments were two days long and the water leaching was only for one day. All UV treatments caused an increase in the roughness of the wood, but the water leaching reduced this roughness. The changes were identical for UV treatments and for water leaching, but these changes were in opposite direction and these differences were smaller with increasing treatment time. The baseline shift is able to show the effect of leaching if we compare the roughness change of UV treated and water leached sample to that sample which gave only UV irradiation without
26
L. Tolvaj et al. / Journal of Photochemistry and Photobiology B: Biology 134 (2014) 23–26
R(3800)/R(1900)
change, we were able to detect the photodegradation difference between earlywood and latewood in the early stage of the treatment as well. This sensitive optical method also showed that water leaching slightly reduces the roughness of the UV light irradiated wooden surface. Acknowledgements This study was supported by the Environment conscious energy efficient building TAMOP-4.2.2.A–11/1/KONV-2012-0068 Project sponsored by the EU and European Social Foundation. References
Fig. 8. Baseline shift of black locust earlywood. Starts with the initial data (0D) followed by 1 day UV treatment (1D) and water leaching (1D + W), and it is repeated. (These are the data of one sample).
R(3800)/R(1900)
UV UV+W
Irradiation time (day) Fig. 9. Baseline shift of spruce earlywood caused by UV irradiation and UV irradiation combined with water leaching (UV + W).
water leaching. Fig. 9 presents this information for spruce earlywood. The roughness increase of the sample which received only UV treatment was considerably greater than the same parameter for the UV treated and water leached sample. This figure indicates the roughness reducing effect of leaching similar to that presented in Fig. 8. 4. Conclusions Samples were irradiated using strong UV emitter mercury lamp. Some of the samples were immersed in distilled water for a day after each 2-day UV treatment period. To monitor the roughness change caused by the treatments, measurements were done using the perthometer and IR reflectance spectrum. The treatments caused baseline shift for the IR reflectance spectrum. A close correlation was found between traditionally measured roughness and the baseline shift. Using the baseline shift as an indicator of roughness
[1] L. Tolvaj, K. Mitsui, Light source dependence of the photodegradation of wood, J. Wood Sci. 51 (2005) 468–473. [2] L. Tolvaj, O. Faix, Artificial ageing of wood monitored by DRIFT spectroscopy and CIE Lab color measurements. I. Effect of UV light, Holzforschung 49 (1995) 397–404. [3] K.K. Pandey, Study of the effect of photo-irradiation on the surface chemistry of wood, Polym. Degrad. Stabil. 90 (2005) 9–20. [4] C.M. Popescu, M.C. Popescu, C. Vasile, Structural analysis of photodegraded lime wood by means of FT-IR and 2D IR correlation spectroscopy, Int. J. Biol. Macromol. 48 (2011) 667–675. [5] L. Tolvaj, L. Persze, L. Albert, Thermal degradation of wood during photodegradation, J. Photochem. Photobiol. B 105 (2011) 90–93. [6] C.A. Teaca, D. Rosu, R. Bodirilau, L. Rosu, Structural changes in wood under artificial UV light irradiation determined by FTIR spectroscopy and color measurements – a brief review, Bioresources 8 (2013) 1478–1507. [7] G. Agresti, G. Bonifazi, L. Calienno, G. Capobianco, A. Lo Monaco, C. Pelosi, R. Picchio, S. Serranti, Surface investigation of photo-degraded wood by colour monitoring, infrared spectroscopy, J. Spectrosc. 1 (2013). Paper 380536. [8] C.M. Popescu, B.C. Simionescu, Structural study of photodegraded acryliccoated lime wood using Fourier transform infrared and two-dimensional infrared correlation spectroscopy, Appl. Spectrosc. 67 (2013) 606–613. [9] H. Turkulin, SEM methods in surface research on wood, COST E18 Final Seminar 26–27/04/2004 Paris, pp. 1–9. [10] A. Temiz, U.C. Yildiz, I. Aydin, M. Eikenes, G. Alfredsen, G. Çolakoglu, Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test, Appl. Surf. Sci. 250 (2005) 35–42. [11] P. Nzokou, D.P. Kamdem, A. Temiz, Effect of accelerated weathering on discoloration and roughness of finished ash wood surfaces in comparison with red oak and hard maple, Prog. Org. Coat. 71 (2011) 350–354. [12] O. Ozgenc, O.T. Okan, U.C. Yildiz, I. Deniz, Wood surface protection against weathering with vegetable seed oil, Bioresources 8 (2013) 6242–6262. [13] L. Tolvaj, Monitoring of photodegradation for wood by infrared spectroscopy, COST Action IE0601 Conference, Hamburg, 07.10.2009. [14] M. Kilic, S. Hiziroglu, C. Güllü, Z. Sezgin, Influence of steaming on surface roughness of beech and sapele flooring material, J. Mater. Process. Technol. 199 (2008) 448–451. [15] E. Tanritanir, S. Hiziroglu, N. As, Effect of steaming time on surface roughness of beech veneer, Build. Environ. 41 (2006) 1494–1497. [16] D.S. Korkut, S. Hiziroglu, A. Aytin, Effect of heat treatment on surface characteristics of wild cherry wood, Bioresources 8 (2013) 1582–1590. [17] L. Tolvaj, K. Mitsui, Surface preparation and direction dependence of DRIFT spectra of wood, Appl. Spectrosc. 58 (2004) 1137–1140. [18] L. Tolvaj, K. Mitsui, Validity limits of Kubelka–Munk theory for DRIFT spectra of photodegraded solid wood, Wood Sci. Technol. 45 (2011) 135–146. [19] L. Tolvaj, Zs. Molnar, R. Nenemth, Photodegradation of wood at elevated temperature: infrared spectroscopic study, J. Photochem. Photobiol. B 121 (2013) 32–36. [20] E. Csanády, E. Magoss, Mechanics of Wood Machining, Springer, 2013, pp. 168– 171.
