Anthony J. Michell

Studies of the degradation and protection of wood surfaces

SummaryLarge weight losses occurred in thin veneers of radiata pine (P. radiata) during natural weathering due mainly to loss of lignin and hemicelluloses. This was demonstrated by direct chemical analysis and by spectrocopic techniques. Treatment of veneers with dilute aqueous solutions of the recognized surface stabilizing compound chromium trioxide was found to dramatically restrict weight loss during weathering, but similar applications of ferric compound were less effective (Evans, Schmalzl 1989). In order to rationalize these protective effects FTIR internal reflectance spectroscopy was used to study chemical changes taking place at the wood surface upon treatment and during weathering. The spectra obtained provide direct evidence for the modification and stabilization of the lignin aromatic system with aqueous chromium trioxide and to a lesser extent with ferric salts. It is postulated that photostable lignin complexes are formed. The implications of these findings for the development of improved surface stabilizing compounds for wood are discussed briefly.

Second-derivative F.t.-i.r. spectra of native celluloses

Abstract F.t.-i.r. spectra of algal, bacterial, cotton, ramie, and wood celluloses, obtained in the second-derivative mode, have improved resolution. The spectra support the hypothesis that the crystalline structures of these celluloses can be divided into algal-bacterial and cotton-ramie-wood types. Bands that differ in the spectra of the two types are different from those sensitive to the change cellulose I→II.

Nondestructive sampling of Eucalyptus globulus and E. nitens for wood properties III: predicted pulp yield using near infrared reflectance analysis

Abstract  Within-tree variation in kraft pulp yield, predicted using near infrared reflectance analysis, was studied in thirty trees of E. globulus and fifty trees of E. nitens to develop a non-destructive sampling strategy. Trees, aged 5 to 9 years, were sampled across a range of sites in southern Australia. Simulated core samples were removed at six fixed heights easily accessible from the ground (0.5, 0.7, ... 1.5 m) and at seven percentage heights (0, 20, 30, ... 70%). Whole-tree values, calculated from percentage height data, were correlated with the core data to determine the optimal sampling height. Core samples were found to be good predictors of whole-tree pulp yield for E. globulus, with simulated cores taken from the recommended sampling height (1.1 m) explaining more than 50% of variation in whole-tree pulp yield. Results for E. nitens were variable with large site differences apparent. On high quality sites, core samples from the recommended sampling height (0.9 m) were good predictors of whole-tree pulp yield, explaining around 60% of the variation. On poor quality sites, cores were poor predictors of whole-tree pulp yield. Radial orientation of cores was not important and predicted pulp yield was not related to tree size, basic density or fibre length. To estimate stand mean pulp yield to an accuracy of ±1% would require sampling 6 trees of E. globulus and 4 trees for E. nitens using either multiple discs or core samples. A single sampling height (1.1 m) is recommended for sampling for basic density, fibre length, fibre coarseness and predicted pulp yield in E. globulus. For E. nitens the recommended sampling height for basic density and fibre length is 0.7 m and 0.9 m is recommended for predicted pulp yield on good quality sites.

Second derivative F.t.-i.r. spectra of celluloses I and II and related mono- and oligo-saccharides

Abstract Second derivatives F.t.-i.r. bands in the OH and CH stretching regions of the spectra of celluloses I and II and of related mono- and oligo-saccharides are much sharper than those in normal absorption spectra and the improved resolution enables more precise measurements of their frequencies. A multiplicity of bands was found in the OH stretching region, which indicated coupling. A much simpler pattern of bands was observed in the OD stretching region of the lightly deuterated compounds, indicating decoupling of the vibrations. There was a close correspondence between the peaks in the second derivative mode in the OH stretching regions of the spectra of cellotetraose and cellulose II, in agreement with postulates of a strong resemblance between their structures.

Second-derivative FTIR spectra of native celluloses from Valonia and tunicin

Abstract The greater resolution afforded by the second-derivative mode has enabled differences previously observed in bands near 3240, 750, and 710 cm −1 in the FTIR spectra of Valonia and tunicin celluloses to be confirmed, and revealed new differences near 2900 and 650 cm −1 . These bands are assigned largely to vibrations of groups involved in the system of hydrogen bonds. The remaining bands in the spectra correspond well, which indicates strong similarities in the structures at the conformational level. Differences between the spectra obtained for films and potassium bromide discs are attributed largely to the different orientations of the samples.

An Anomalous Effect in the Drift Spectra of Woods and Papers

Abstract Diffuse Reflectance Fourier Transform Infrared (DRIFT) Spectroscopy is a very useful and convenient means of obtaining the infrared spectra of woods and papers. However, distortions can occur in the intensities of bands in the region 950–1200 cm−1 when the spectra are obtained by reflection directly from wood and paper surfaces due to interference from specularly reflected radiation. Such distortions are reduced in spectra obtained from very thin sheets of paper of from fibres diluted in potassium bromide.

Extending near infrared reflectance(NIR) pulp yield calibrations to new sites and species

Abstract Recently, we demonstrated that the accuracy of pulp yield predictions for wood samples from a site (Gog) new to their calibration (Tasmania‐wide Eucalyptus nitens) was greatly improved by adding five Gog samples to the calibration set. In this study we investigated the addition of Gog samples to the Tasmania‐wide E. nitens set, with the aim of further improving predictive accuracy. It was demonstrated that the addition of a single Gog sample to the Tasmania‐wide calibration set was sufficient to greatly reduce predictive errors and that the inclusion of at least 3 Gog samples in the Tasmania‐wide set was sufficient to give relatively stable predictive errors. The addition of different sets of 5 Gog samples to the Tasmania‐wide calibration, however, caused predictive errors to vary between sets. The standard deviation of pulp yield for the prediction set (20 Gog samples) was important, with sets having the largest standard deviations giving the best predictive statistics. Finally, the Tasmania‐wide E. nitens calibration was enhanced using samples from a different species (Eucalyptus globulus) and applied successfully to other E. globulus samples.

Assessment of the pulpwood quality of standing trees using near infrared spectroscopy

In Australia, considerable effort has been directed at improving the pulp yield of plantation grown trees through tree breeding programs. However, an improvement in pulp yield relies on the assessment of large numbers of trees. Traditional methods of assessment are expensive, time consuming and destructive, inhibiting their use. Cores can be extracted non-destructively from standing trees using TRECOR, a handheld motor driven drill. The cores are milled, their near-infrared spectra obtained and pulp yield estimated using an appropriate calibration model. The height at which the core is taken is very important. It must represent the whole tree and sampling must be easy and practical. The longitudinal and radial (within-tree) variation of pulp yield for 15 Eucalyptus nitens trees was examined using near-infrared (NIR) spectroscopy. The trees were taken from three families (five trees per family) selected for giving high, medium and low pulp yields respectively. Three trees (one from each family) were examined in detail. Maps of within-tree variation of pulp yield were developed. Pulp yield was found to be highly variable within individual trees and between trees of the same family. The yield of samples from 10% of tree height (approximately 2.2 m) gave the best correlation with whole-tree yield. Samples from 5% of tree height (approximately 1.1 m) gave a slightly lower correlation but provided a more convenient sampling height. Ten Eucalyptus globulus and ten E. nitens trees growing on five sites in Australia were used to examine the longitudinal variation of pulp yield. Trees from sites in Tasmania, Western Australia and Victoria were sampled. The optimal sampling height for E. globulus was 1.1 m. No single sampling height could be recommended for E. nitens due to large site effects.

Diffuse reflectance infrared Fourier transform (drift) spectroscopic study of bleaching and yellowing of eucalypt cold soda pulp

Abstract E. regnans cold soda pulp has been bleached to a high brightness (about 87) in a single-stage treatment with alkaline hydrogen peroxide, and also in 2- and 3-stage sequences which used sodium borohydride in the second stage. The sequences did not provide further appreciable increases in the brightness level, but the borohydride-treated pulp showed greater brightness stability when irradiated with UV light, even when the pulp had been subjected to a third stage hydrogen peroxide bleach. Chemical changes in the pulps resulting from the bleaching treatments and from their exposure to UV light have been followed by studying the DRIFT spectra (1400–1800 cm−1) of the wire side of handsheets. Variations in band intensity have been related to changes in pulp brightness and to oxidation of the pulps. Some features of the observed variations are not readily explicable.