Proceedings e report - Firenze University Press

NIR ARCHAEOMETRY AS A POWERFUL TOOL FOR INVESTIGATING THE
ARCHAEOLOGICAL WOOD - SPECTROSCOPIC OBSERVATION OF THE
DEGRADATION PROCESS IN THERMALLY TREATED WOOD USING A
DEUTERIUM EXCHANGE METHOD
Tetsuya Inagaki*, Satoru Tsuchikawa
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601 Japan
Abstract
The NIR diffuse-reflectance spectroscopy was applied to monitor the diffusion process of deuterium-labeled
molecules in hinoki wood, where the sample was thermally treated for increasing periods of time. The saturation
accessibility varied characteristically with thermal treatment time reflecting the OH groups in different states of
order in the wood substance. The variations of saturation accessibility with hydrothermal treatment time were
applied to reveal the hydrothermal change of crystalline and amorphous regions in cellulose.
1. Introduction
Near-infrared (NIR) spectroscopy has shown its significant potential in analyzing changes due to
ageing in mechanical, physical and chemical properties of wood based materials [1]. Tsuchikawa et al
applied NIR spectroscopy for monitoring the diffusion process of deuterium-labeled molecules in
archeological wood [2]. It was revealed that, for polymers with labile hydrogen atoms in OH
functionalities, H/D isotope exchange (deuteration) in combination with FT-NIR spectroscopy is a
powerful technique to determine the accessibility. In this study, degradation mechanism of wood due
to the variation of accessibility was analyzed in conjunction with NIR spectroscopy and deuterium
exchange, where the sample was thermally treated in steam atmosphere. The accessibility of the
artificially degraded hinoki cypresses as an analogue of archaeological object was systematically
measured.
2. Experimental
2.1. Sample preparation and hydrothermal treatment
We prepared hinoki cypress (Chamaecyparis obtusa) which had almost the same oven-dried density.
The number of sample is 16. The sample dimensions were 20×20×2 mm in tangential, longitudinal
and radial directions, respectively. Gradual hydrothermal treatment was performed at 140 o C under
steam atmosphere condition to make artificially degraded wood as an analogue of archaeological
objects. The hydrothermal treatment times (tht) were set up to 150 hours (0, 2, 5, 10, 20 50, 100, 150
hours). Two wood samples were prepared at same thermal treatment time to check the reproducibility.
2.2. Deuterium exchange and NIR measurements
After the treatment, wood samples were immersed in 5 ml of the deuteration agent at 40 o C and NIR
diffuse-reflectance spectra of oven-dried wood were recorded before and after 24 h immersion. NIR
diffuse-reflectance spectra were obtained from tangential face of each sample using a FT-NIR
spectrophotometer (Bruker MATRIX-F) with a fiber optic probe with a diameter of 7 mm and a
measurement area of 49 mm 2 . This measurement area contains three or four year tree rings, where
averaged spectral information of early-wood and late-wood were acquired. In order to improve the
signal-to-noise ratio, 128 scans were coadded at a spectral resolution of 8 cm -1 over the wavenumber
range 10000-4000 cm -1 . A good reproducibility was observed for the spectroscopic data for the
investigated samples.
* E-mail: inagaki.tetsuya@e.mbox.nagoya-u.ac.jp
Joseph Gril (edited by), Wood Science for Conservation of Cultural Heritage –Braga 2008: Proceedings of the International
Conference held by COST Action IE0601 (Braga - Portugal, 5-7 November 2008, ISBN 978-88-6453-157-1 (print)
ISBN 978-88-6453-165-6 (online) © 2010 Firenze University Press