Effects of mechanical stretching, desorption and isotope exchange on deuterated eucalypt wood studied by near infrared spectroscopy.

Abstract

Deuterium exchange combined with near infrared (NIR) spectroscopy was used to study the roles of accessible and inaccessible cellulose in the load transfer of eucalyptus wood. Monitoring the drying process helped to assign NIR bands of deuterated wood samples. Polarized NIR spectra of protonated and deuterated samples confirmed that inaccessible hydroxyl groups in eucalyptus wood were preferably oriented in the longitudinal direction. The spectral changes on NIR spectra caused by mechanical strain could be highlighted by averaging loading and unloading cycles to compensate for effects of desorption and isotope re-exchange due to environmental fluctuations. After deuteration, the bands affected by mechanical strain at around 6420, 6240 and 4670\u202fcm-1, which had been assigned to hydroxyl groups in cellulose, remained at these positions, suggesting the inaccessible cellulose fraction was the main load-bearing component in wood. A small band at around 4700\u202fcm-1 responding to mechanical strain, becoming visible in the deuterated spectra, indicated that accessible hydroxyls also contributed to the load transfer. Furthermore, the measurements confirmed previous reports of moisture adsorption of wood under tensile stress.