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Maderas. Ciencia y tecnología

On-line version ISSN 0718-221X

Maderas, Cienc. tecnol. vol.21 no.3 Concepción July 2019

http://dx.doi.org/10.4067/S0718-221X2019005000310 

ARTICULOS

Evaluation of degradation in chemical compounds of wood in historical buildings using FT-IR and FT-Raman vibrational spectroscopy

Seyed Mahdi Moosavinejad1 

Mehrab Madhoushi2 

Mohammad Vakili3 

Davood Rasouli4 

1PhD Student, Department of Wood Engineering and Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

2Associate Professor, Department of Wood Engineering and Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

3Associate Professor, Department of Chemistry, Ferdowsi University of Mashhad, Mashhad, Iran.

4Assistant Professor, Department of Wood Engineering and Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

Abstract:

Vibrational spectroscopy approaches like FT-IR and FT-Raman, as analytical method, can be used to assess chemical changes in historical wood structures. In this study, wood samples of three historical buildings, in Gorgan, Iran, namely Tekie Estebar, Molla Esmaiel Mosque, and the Esmaieli Buildings were selected. Wood species was determined by their macroscopic characteristics which were hornbeam (Carpinus betulus), oak (Quercus castaneifolia), beech (Fagus orientalis), and elm (Ulmus glabra), as hardwood species, and yew (Taxus baccata) as a softwood species. Also, some samples of oak were collected from northern and southern sides of the Esmaieli Building in order to compare deterioration environmental factors.. The approximate assignment of the experimental bands was completed by comparing. For this purpose, the experimental bands with the calculated band frequencies of cellulose, hemicellulose and lignin. In addition, the reported assignment for softwood and hardwood was used to confirm the vibrational assignments. The results of spectroscopy revealed that biodegradation had occurred in all species. Comparison between the most important vibrational band frequencies related to carbohydrates and lignin in hardwood species suggested that degradation of carbohydrates was greater than lignin, which could be attributed to brown rot and hydrolysis. Reduction of chemical compounds in south oak samples was higher and could be associated with prevailing wind and UV ray in this side. In the only softwood species (yew), because of its highest exposure to frequent raining, deterioration was observed in both carbohydrates and lignin.

Keywords: Guaiacyl lignin; hardwood; softwood; wood carbohydrates; wood durability.

Introduction

Wood has a complicated chemical structure which depends largely on the plant species.. However, the major components of wood are the same in all species, namely; cellulose (a linear polymer containing glucose units), hemicellulose (polysaccharides containing many different sugar monomers), and lignin (a class of complex organic polymers belonging to a group of aromatic alcohols) (Sjostrom 1993).

Vibrational spectroscopy (FT-IR, FT-Raman) has been applied in typical conservational experimental analysis. This approach is often used in studying ancient wood samples to evaluate the level of their degradation (Casadio and Toniolo 2001, Petrou et al. 2009, Pucetaite 2012, Sandak et al. 2010). Because of the small amount of wood needed to obtain the spectrum through these spectroscopy techniques and the low level of biodegradation of samples, they are frequently utilized (Picollo et al. 2011). The chemical characterization of historical wood is importance, as it can not only reveal the degradation processes that have occurred but it can also direct conservation practices. For instance, the identification may guide the suitable conservation methods and a comprehension of the preservation of excavated material may assist in the proper handling of archaeological timbers (Derrick et al. 1999). Various biological applications of these techniques, particularly on wood, have been reported including evaluation of organic substances in plants, characterization of wood type and its chemical compounds such as carbohydrates, sugars, extracts, resins (Akhtari 2010, Faix et al. 1991; Lionetto et al. 2012, Mirshokraie et al. 2014, Rodrigues et al. 1998). In addition, these techniques have been used in analyzing chemical changes in weathered rotten wood, treated wood, and also degraded wood (Derrick et al. 1999, Faix 1992, Pandey and Pitman 2003, Popescu et al. 2006). There are a great number of wooden parts in ancient buildings whose conservation is of great importance regarding cultural, historic, religious and touristic aspects.

This study aims to investigate changes and degradation in chemical compounds of the woods in historical buildings of the old parts of the city Gorgan, located in the northern part of Iran, compared with the fresh woods using FT-IR, FT- Raman spectroscopy as an analytical approach and we used the Raman portable device in historical building for the first time. The advantages of raman spectroscopy over FT-IR are many organic and inorganic materials are suitable for Raman analysis, no sample preparation needed, not interfered by water, non-destructive, the region from 4000 cm-1 to 50 cm-1 can be covered by a single recording and Raman spectra can be collected from a very small volume (< 1 μm in diameter).The use of vibrational spectroscopy for historical buildings in this study is the first case in Iran and can be localized and considered as a start point for future studies, including historical buildings, monuments and museums.

Materials and methods

Materials

Wood samples were collected from three historical building in the old part of the city Gorgan, namely Tekie Estebar, Molla Esmaiel Mosque, and the Esmaieli Building (Figure 1). Table 1 presents locations of the collected samples. In addition, some samples of oak were collected from the northern and southern sides of the Esmaieli Building in order to compare degradation environmental factors in those sides. To determine the wood species, cross, tangential, and radial sections were collected from the healthy parts of historical samples and then compared with the fresh samples of the same species.

Figure 1: Photos of historical wood: (a) Elm, (b) Hornbeam, (c) Beech, (d) Yew, (e) Northern side oak, (f) Southern side oak. 

Table 1: Characteristics of the collected samples from historical building and their locations. 

Methods

FT-IR spectroscopy

Spectroscopy of the samples was performed using FT-IR instrument (Model Bomem MB-154, Germany). For this purpose, wood flour collected by cordless drill equipped with a drill bit (3 mm diameter to depth of 2-3 mm into the sample) was used. Afterwards, the wood flour was dried in the oven at 103 °C for 24 hours to reach the lowest moisture and immediately KBr pellets composed of the wood flour were made. Finally, the spectrum of the samples was obtained at a spectral range of 4000-500 cm-1 and resolution of 4 cm-1 and 11 scans were made and then edited using Win-Bomem Easy software.

FT-Raman spectroscopy

FR-Raman spectra were obtained using a portable Rigaku Firstguard Spectrometer instrument with Nd/YAG laser excitation at 1064 nm. 180° scattering was used in the sample illumination geometry. Spectra were recorded over the wavenumber range of 200-2000 cm-1 at 4 cm-1 spectral resolution with 256 scans accumulated, and the applied laser powers were between 0 mW and 180 mW. The OMNIC software (Thermo Scientific Company) was utilized to edit the spectra and determine the peak positions.

Finally, the spectral differences associated with the deterioration in the historical samples were compared with equivalent fresh samples. We normalized the spectrums based on the peak about 1460 cm-1 that relates asymmetric bending of CH3 in methoxyl groups.

Results and discussion

All compounds of the wood structure exhibit bands in the FT-Raman spectrum. It has been demonstrated in relevant applications of Raman spectroscopy to historical materials that as cellulose, hemicellulose and lignin deteriorate, their characteristic peaks in the spectra typically reduce in intensity or completely disappear (Smith and Clark 2004), and this was observed in the historical wood specimens from Gorgan. Also some related bands to these compounds were changed which are presented in Table 2 and Table 3.

Analysis of FT-IR spectroscopy

Most of major factors in wood are present between 800 and 1800 cm-1 are individually considered as a fingerprint. Comparison of the obtained infrared spectra revealed some significant differences between the historical and fresh samples (Zhou et al. 2012).

Oak

The obtained spectra from the historical samples of the north and south sides and fresh samples are demonstrated in Figure 2. In these two historical samples, the bands located in the regions 1000-1180 cm-1 which are assigned to stretching and asymmetric vibrations of C-O, C-C and C-O-C and 1375 cm-1 attributed to symmetric and asymmetric bending of CH3 groups (Table 2) are related to cellulose and hemicellulose. The region of 1245 cm-1 assigned to carbohydrates and lignin also decreased. So the region of 1730 cm-1 assigned to stretching of C=O in xylan related to hemicellulose showed a significant decrease. In higher frequencies the regions of 2800-3400 cm-1 assigned to C-H and OH showed a significant decrease in cellulose and hemicellulose. The region of 1505 cm-1 assigned to Stretching vibrations of aromatic structure C=C in lignin was increase due to loss of extractives and carbohydrates. As can be seen in Figure 2, decrease of chemical compounds in south oak sample was higher and as a result, which could be associated with prevailing wind and UV ray on this side.

Figure 2: FT-IR spectra for historical and fresh sample of oak. 

Table 2: FT-IR band assignments for fresh hardwood and softwood species. 

Hardwod (cm-1) Softwood (cm-1) Functional group Assignment Reference
897 895 In-plane symmetric vibration of C-H Cellulose (Pucetaite 2012, Lionetto et al. 2012)
1033 1029 Stretching vibrations of C-O Cellulose- hemicelluloses (Faix 1992, Pucetaite 2012)
1049 1056 Stretching vibrations of C-O and C-C Cellulose- hemicelluloses (Pandey et al. 1999, Pucetaite 2012)
1118 1110 Asymmetric stretching of C-O-C Cellulose- hemicelluloses (Pucetaite 2012)
1160 1159 Asymmetric stretching of C-O and C-C Cellulose- hemicelluloses (Pucetaite 2012, Moosavinejad et al. 2016)
1243 1234 Stretching vibrations of C-O in Xylene and syringyl ring Lignin- hemicelluloses (Pandey et al. 2003, Moosavinejad et al. 2016)
- 1273 Stretching vibrations of C-O in guaiacyl ring and wagging in OH and CH Lignin, cellulose, hemicellulose (Faix 1992, Pucetaite 2012)
1330 - Vibrations of C-H and stretching in C-O related to syringyl ring Cellulose- Lignin (Lionetto et al. 2012)
1375 1375 Symmetric and asymmetric bending of CH3 groups Cellulose- Lignin (Faix 1992, Pucetaite 2012)
1425 1428 Vibrations of aromatic structure Lignin (Pandey et al. 1999)
1464 1460 Asymmetric bending of CH3 in methoxyl groups Lignin (Lionetto et al. 2012, Moosavinejad et al. 2016)
1508 1512 Stretching vibrations in aromatic structure C=C Lignin (Faix 1992, Gelbrich et al. 2009, Lewis et al. 1994)
1595 1608 Stretching vibrations in aromatic structure C=C Lignin (Pucetaite 2012, Moosavinejad et al. 2016, Emmanuel et al. 2015)
1654 1655 Stretching vibrations of conjugated C=O Lignin (Mirshokraie et al. 2014, Pucetaite 2012)
1739 1736 Stretching vibrations of unconjugated C=O and related to carbonyl groups Hemicellulose (Pucetaite 2012, Bodirlau et al. 2009)
2843 2841 Symmetric stretching vibrations of C-H related to methyl and methylene Lignin, cellulose, hemicellulose (Pandey et al. 1999, Carrillo et al. 2004, Schwanninger et al. 2004)
2933 2934 Asymmetric stretching vibrations of C-H related to methyl and methylene Lignin, cellulose, hemicellulose (Faix 1992, Pandey et al. 1999, Bodirlau et al. 2009, Carrillo et al. 2004, Schwanninger et al. 2004)
3423 3421 Stretching vibrations of O-H Cellulose- hemicellulose (Hergert 1971, Rodrigues et al. 1998, Michell et al. 2002)

Elm, hornbeam, beech

Comparison of the historical samples of elm, hornbeam and beech with the fresh samples (Figure 3) revealed that absorption in the region of 1160, 1118, 1050 and 895 cm-1 (assigned to cellulose and hemicellulose) decreased; while a significant decrease in the bands 1240 and 1740 cm-1 was observed which could be attributed to existence of hemicellulose, according to Table 2, the band at 1740 cm-1 is assigned to stretching vibrations of unconjugated C=O and related to carbonyl groups and the band at 1240 cm-1 is assigned to stretching vibrations of C-O in xylan and syringyl ring. On the other hand, almost in all species the absorption in the bands assigned to lignin was determined in the region 1508, 1600 and 1650 cm-1. According to the results, it was clear that degradation of cellulose and hemicellulose was higher than lignin which could be a result of brown rot and hydrolysis in wood.

Comparing the infrared spectra in the historical and fresh samples of hardwood revealed that the samples collected from historical samples of oak from north and south sides (Figure 2) experienced the highest decrease in cellulose and hemicellulose. At the same time, beech species had the lowest decrease of chemical compound compared to the other species. Such decrease could be attributed to the location, exposure condition and natural durability of the species.

Figure 3: FT-IR spectra of historical fresh sample of elm, hornbeam and beech. 

Yew

The obtained spectrum from yew species (Figure 3) in the region 1159, 1110, 1051 and 1029 cm-1 were assigned to cellulose and hemicellulose showed increase in absorption. Moreover, in the region 1650 and 1606 cm-1 increase in absorption was observed, according to Table 2 these bands are assigned to stretching vibrations of aromatic C=C and stretching vibrations of conjugated C=O, respectively. In contrast, in the region 1270 cm-1 assigned to stretching vibrations of C-O in xylan and syringyl ring and 1234 cm-1 attributed to stretching vibrations of C-O in guaiacyl ring and wagging in OH and CH and also in the region 1508 cm-1 related to the aromatic structure of lignin the absorption decreased. The Yew is naturally durable, but high degradation of chemical compounds of it is mostly related to rain damage in historical buildings.

Analysis of FT-Raman spectroscopy

Oak

Raman spectra showed that in both historical samples the region 992 cm-1 were related to CH2 groups in cellulose and the bands located in the regions 1152, 1098, 1051 and 1378 cm-1 related to cellulose and hemicellulose a considerable decrease occurred but the bands in the region 1602 cm-1 related to stretching vibrations of C=C in lignin experienced a significant increase. Like FT-IR spectroscopy, the results of FT-Raman demonstrated higher degradation in south oak (Figure 4).

Figure 4: FT-Raman for historical and fresh sample of oak. 

Elm, hornbeam and beech

The spectrum obtained for the species elm, hornbeam and beech (Figure 5) revealed that the intensity in the region 1600-1660 cm-1 related to stretching vibrations of C=C and C=O in lignin significantly increased. A weak band of the region 1275 cm-1 related to stretching vibrations of C-O and wagging of OH and CH in lignin guaiacyl and carbohydrates showed a slight increase in intensity. On the other hand, the bands located in the region 1050-1150 cm-1 which is mainly attributed to stretching vibrations of C-O and C-C, glycosidic symmetric vibrations of C-O-C and asymmetric stretch of C-O and C-C and are related to cellulose and hemicellulose, The region 896 cm-1 was assigned to in-plane symmetric vibration of C-H in cellulose showed increased intensity. In addition, in these three species, in lower frequencies and the regions 378, 431, 451, 527 cm-1 assigned to symmetric bending CC, bending CCO and CCC , Bending CCO and CCC ring deformation. Skeletal bending and COC bending, glycosidic links/CCC ring deformation, respectively (Table 3). Which is mostly related to cellulose the intensity decrease. FT-Raman spectroscopy demonstrated decreased degradation in all species and oak had the highest decrease. Moreover, beech had the lowest degradation by the climatic factors. These data are in agreement with IR spectra of the samples.

Figure 5: FT-Raman of historical fresh sample of elm, hornbeam and beech. 

Table 3: FT-Raman band assignments for fresh softwood and hardwood species. 

Hardwood )cm-1( Softwood )cm-1( Functional group Assignment Reference
378 378 Symmetric bending CC. Ring deformation Cellulose (Petrou et al. 2009)
431 433 Bending CCO, CCC. Ring deformation Cellulose (Petrou et al. 2009)
451 451 Bending CCO, CCC, ring deformation. Skeletal bending Cellulose (Petrou et al. 2009)
527 521 COC bending, glycosilic links/CCC ring deform. Cellulose (Schenzel and Fischer 2001, Wiley and Atalla 1987)
800 - David star mode of phenyl ring Lignin (Wilson 1934)
904 896 In-plane symmetric vibration of C-H Cellulose (Ona et al. 1999, Petrou et al. 2009, Shen et al. 1998)
967 992 CH2 in Cellulose Cellulose (Schenzel and Fischer 2001, Wiley and Atalla 1987, Yamauchi et al. 2005)
1050 1051 Stretching vibrations of C-O and C-C Cellulose, hemicellulose (Yamauchi et al. 2005)
1102 1098 Glycosidic symmetric vibrations of C-O-C Cellulose, hemicellulose (Petrou et al. 2009)
1127 1122 Glycosidic symmetric vibrations of C-O-C Cellulose, hemicellulose (Petrou et al. 2009)
1152 1152 Asymmetric stretch of C-O and C-C Cellulose, hemicellulose (Petrou et al. 2009)
1282 1275 Stretching vibrations of C-O in guaiacyl ring and wagging of OH and CH Lignin, Cellulose, hemicellulose (Shen et al. 1998, Yang et al. 1999)
1330 1335 Absorption related to syringyl ring and stretch of C-O Lignin (Zhou et al. 2012)
1378 1378 Stretch of C-H and wagging of OH and CH Cellulose, hemicellulose (Petrou et al. 2009, Socrates 2004)
1461 1464 Asymmetric bending of CH3 in methoxyl groups Lignin (Ona et al. 1999, Yang et al. 1999)
1608 1602 Stretching vibrations of aromatic C=C structure Lignin (Ji et al. 2013, Kihara et al. 2002, Petrou et al. 2009, Shen et al. 1998, Yang et al. 1999)
1658 1662 Stretching vibrations of conjugated C=O Lignin (Kihara et al. 2002, Ona et al. 1999, Petrou et al. 2009, Shen et al. 1998, Yang et al. 1999)

Yew

In the spectrum of historical and fresh samples of yew (Figure 5) the bands located at 1608 cm-1and 1281 cm-1 mostly related to guaiacyl lignin had decreased intensity. Also the region around 1330 cm-1 related to stretching of C-O in lignin and carbohydrates showed slightly decreased intensity. The region around 1127cm-1 related to glycosidic symmetric vibrations of C-O-C in to cellulose and hemicellulose had the highest increase with an almost hidden peak. The region around 800 cm-1 related to guaiacyl lignin also slightly declined.

Conclusions

The results obtained from FT-IR and FT-Raman could not be applied accurately in quantitative studies; but they could be a powerful tool to evaluate structural changes in chemical compounds of historical wood. This spectroscopy study showed the destruction of wood species in three historical structures in Gorgan, Iran. Comparing changes and degradation in intensity of bands related to lignin and carbohydrates in hardwood species revealed higher degradation of carbohydrates compared to lignin. In contrast, the only softwood species (yew) showed significant degradation both in lignin and carbohydrates which was attributed to its exposure to frequent rain and exposure condition. It was confirmed that degradation characteristics of the historical samples could be attributed to fungal and bacterial factors, and the decreased peaks also could be the result of leaching of organic substances and hydrolysis of wood by water. Finally, this study demonstrated noticeable potential of employing vibration spectroscopy techniques in historical wood samples.

Acknowledgements

The author gratefully acknowledges the financial support from the research deputy of Gorgan University of Agricultural Sciences and Natural Resources.

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Received: September 24, 2017; Accepted: January 22, 2019

Corresponding author: madhoushi@gau.ac.ir

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