Volume 58, Issue 4

Knots (i.e., branch bases inside tree stems) in spruce trees contained remarkably higher concentrations of lignans and oligolignans than the adjacent stemwood. The amount of lignans in some knots exceeded 10% (w w −1 ) and some knots contained hundreds of times more lignans than the heartwood in the same tree. However, there were large variations between different species and even between different knots in the same tree. 7-Hydroxymatairesinol was the predominant lignan in knots of Picea abies, P. glauca , P. koraiensis , P. mariana , and P. omorika , while liovil and secoisolariciresinol dominated in P. sitchensis and P. pungens . The lignans occur in free form in knots and are easily extracted with polar solvents. In addition to the true lignans, especially the knots contained large amounts of lignan-related oligomeric aromatic substances, here called oligolignans, consisting of three or four phenylpropane units. 7-Hydroxymatairesinol, but also other lignans, could be extracted in large scale from spruce knots at pulp and paper mills. Other potentially important lignans could be produced from 7-hydroxymatairesinol by semisynthesis. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the basis for applications in medicine and nutrition or as natural antioxidants and antimicrobial agents in a variety of technical products.

Oligolignans present in substantial amounts in Norway spruce and Scots pine knots were characterised. The hydrophilic knotwood substances were extracted and different chromatographic methods were applied to obtain fractions for analysis by GC, GC-MS, HR-EI-MS, LC-ESI-MS, NMR, and FTIR. β- O -4-Linked guaiacylglyceryl ethers of hydroxymatairesinol (Ia, Ib, Ic), secoisolariciresinol (II), lariciresinol (III), isolariciresinol (IV), lignan A (V), liovil (VI), conidendrin (VII), and pinoresinol (VIII) were identified in the spruce knotwood extract and β- O -4-linked guaiacylglyceryl ethers of nortrachelogenin (IX) and secoisolariciresinol (II) in the pine knotwood extract. The structures of allo-hydroxymatairesinol-4′-guaiacylglyceryl ether (Ia), hydroxymatairesinol-4-guaiacylglyceryl ether (Ib), hydroxymatairesinol-4′-guaiacylglyceryl ether (Ic), secoisolariciresisinol-4-guaiacylglyceryl ether (II), and lariciresinol-4′-guaiacylglyceryl ether (III) were determined via GC-MS, HR-MS, and 1 H and 13 C NMR analyses. The structures of (Ia), (Ic), (IV), (V), (VI), (VII), and (IX) have not been reported earlier. Spruce stemwood, both heartwood and sapwood, also contained oligolignans in small amounts. In addition, some dilignans with four phenylpropanoid units were tentatively identified in the hydrophilic knotwood substances.

In order to investigate the delignification mechanism during high-boiling solvent (HBS) pulping, softwood HBS lignin samples from todo fir ( Abies sachalinensis ) were analyzed by 1 H– 13 C correlation NMR spectroscopy (HMQC). Nine lignin model compounds that may represent the substructures in HBS lignin were prepared. The 1 H and 13 C NMR spectral data were compared with HBS lignin samples. The HMQC spectra of HBS lignin samples showed the disappearance of β - O -4 structures. Introduction of a pulping solvent into lignin was plainly observed with new signals in aliphatic regions. Only the erythro β -1 structure was detected in softwood milled wood lignin from todo fir by HMQC spectra. The β -1 structure was very reactive and probably produced the stilbene structure. The β - β and β -5 structures remained in HBS lignin. The 4- O -5 structure was successfully detected by HMQC spectra, and it was found to be stable under the conditions used.

The chemistry of ozone bleaching of chemical pulps was explored by ozonating residual lignins isolated from conventional kraft and SuperBatch pulps in methanol/water medium to detect possible differences in the reactivity of the two types of lignin. SuperBatch lignin was ozonated also in water to study the effect of ozonation medium on the lignin reactivity. The residual lignins were found to display similar reactivities in methanol/water, implying that ozonation should result in equal delignification rates for both conventional kraft and SuperBatch pulps unless the rates of reagent diffusion in the pulps are different. The lignins were partly oxidized to volatile and nonvolatile low-molecular weight oxidation products by the so-called “peeling mechanism”, according to which oxidation products go into solution and insoluble reaction products resemble the starting lignins. The reaction products obtained upon ozonation of SuperBatch lignin in neutral water resembled those formed in methanol/water, but their yield was much lower. This is probably due to the better solubility of lignin in methanol/water than in water and/or higher degradability of lignin by ozone than by radicals formed as ozone decomposition products.

This study elucidates the relationship between the dissolution of pulp components and the development of fiber bonding properties in alkaline peroxide bleaching of aspen mechanical pulp. In general, bleaching reactions cause the removal of pulp substances from the fibers, which in turn improves pulp strength properties. Nonetheless, alkaline hydrolysis is particularly important to the development of strength because this reaction mechanism plays a key role in imparting additional carboxylic acid groups onto the fibers. The strong correlation between fiber carboxylic acid group concentration and the amount of anionic dissolved substances makes it possible for us to predict the strength properties of bleached pulps by estimating the anionicity of bleaching filtrates using analytical methods such as cationic demand. The paper also provides insights into the importance of the alkalinity in peroxide bleaching to the dissolution of pulp materials and the strength development.

The use of calibrated near infrared (NIR) spectroscopy for predicting tracheid length of Pinus taeda L. (loblolly pine) wood samples is described. Ten-mm sections of 14 P. taeda radial strips were selected and NIR spectra obtained from the radial longitudinal face of each section. The fibers in these sections were characterized in terms of arithmetic and length-weighted mean tracheid length using a fiber quality analyzer, and calibrations with NIR spectra were developed for both measures of tracheid length. Relationships were good, with coefficients of determination ( R 2 ) of 0.88 for arithmetic tracheid length and 0.96 for length-weighted tracheid length. The accuracy of NIR predicted length-weighted tracheid length was sufficient for ranking purposes.

A heat transfer model for estimating pinene emissions from hot-pressing strand for the manufacture of flake-board has been constructed from first principles and validated. The model predicts α-pinene emissions of 0.4 kg/1000 kg from a 0.95-cm board, which is within the 0.3–0.6 kg/1000 kg range reported for commercial operations. Most of the emissions originate from the hot 1-mm layer of wood adjoining the platen surface. As a result, residual pinene in the board is depleted at the surface for both commercial and laboratory-prepared boards. Emissions are drastically reduced when the mat is surfaced with a layer of aspen, which prevents the hot platen from directly contacting softwood.

Creep-rupture studies of large specimens of commercial oriented strandboard (OSB) were conducted using a fourpoint flexural test in combination with an acoustic emission (AE) monitoring system. Four equilibrium moisture content (EMC) conditioning and testing regimens were used: ambient room conditions, constantly moderate EMC (12/12), dynamic rising EMC (12/24), and constant high EMC (24/24). Compared with deflection, the cumulative event AE parameter was found to be more sensitive and representative to detect cumulative damage to final failure. Under 80% ultimate stress, the 24/24 specimens had the highest creep rate (1.43 mm h −1 ) as compared with 0.27 and 0.04 mm h −1 for 12/24 and 12/12 specimens, respectively. However, for the 12/24 specimens, a step-like deflection occurred, accelerating the rupture process and attaining the greatest creep factor of 2.28—a recommended safety factor for prolonged exposure to humid service conditions. The total recovered deflection under ambient conditions was 85% recoverable elastic, 5% recoverable viscoelastic, and 10% permanent irreversible creep. Correspondingly, the total recovered stiffness was 70% recoverable elastic, 10% recoverable viscoelastic, and 20% permanent irreversible creep. The observed creep-rupture limit of the OSB was 24 days to failure.

Wood adhesives derived from softwood bark pyrolysis oils (PO) and isocyanates (pMDI) have been developed for particleboards with a non-conventional blending system. The PO produced by the vacuum pyrolysis Pyrocycling™ process was used to replace between 30 and 40% by weight of the pMDI in a 4% adhesive-containing particleboard. Results showed that mechanical properties (IB, MOE and MOR) and thickness swelling of homogeneous boards exceeded the minimum requirements set by ANSI A208.1-1993 and ASTM 1037-96a standards. The study showed that pyrolysis oils can be mixed at ratios as high as 40% with pMDI and give acceptable interior grade particleboard properties. It was also shown that PO reduces panel to metal adhesion by 86%, in comparison to the control.

Knowledge of pH and buffering capacity of raw fiber materials is important for understanding the effects of raw material on the curing rate of urea formaldehyde (UF) resin, used for panel manufacturing, especially with some less-desirable wood materials such as bark, top, and commercial thinnings. The effects of pH and buffering capacity as well as catalyst content on the gel time of UF resin were investigated. The results obtained from this study indicate that bark has a lower pH value as well as higher acid and alkaline buffering capacities than wood of the same species due to their extractives. The pH values of the raw fiber materials studied decrease with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution. At lower levels of added catalyst, the effect of raw material pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main acid catalyst source of the mixture at lower levels of added catalyst, while at higher levels, catalyst is the main source. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than does UF resin alone.

This paper describes an improved stochastic model designed to simulate systems, such as green timbers, that cannot be analyzed as a unit but as a collection of a large number of similar components. The stochastic model provides a piecewise green moisture content frequency distribution curve by using nondestructive measurements such as of timber weight. A new, relatively simple two-parameter function was designed to describe the log-normal moisture concentration distribution above the fiber saturation point, and the parameters of this function were determined by fitting the experimental timber weights with the results of the stochastic model. The simulated green moisture content distributions showed good agreement with the experimental data for Pacific coast hemlock (hemfir) timbers, thus providing a piece of information that is indispensable for applying stochastic simulation to industrial drying of timbers.

A theoretical model to calculate the dielectric constant of masson pine ( Pinus massoniana ) in the longitudinal direction was developed by considering the effect of wood moisture content, density, ratio of earlywood to latewood, and the volume fraction of ray cells. The calculated results were used to explore the relationship between dielectric constant and moisture content, density, and other factors. The results indicated that the dielectric constant of masson pine increased with the moisture content. From 0% to 30% moisture content, the longitudinal dielectric constant increased more than 5 times from 2.3 to 13.3. In the range of density from 0.450 to 0.650 (g cm −3 at 15% moisture content, the longitudinal dielectric constant increased from 7.7 to 10.0. However, the longitudinal dielectric constant decreased as the volume fraction of ray cells increased.

In order to reduce the internal stress of wood during drying, an attempt was made to dry wood with superheated steam above 100°C. Sugi ( Cryptomeria japonica D. Don) wood specimens were dried with radial restraint using superheated steam at up to 180°C, and the resulting restrained shrinkage stress was examined. A load cell capable of measuring shrinkage stress inside an autoclave was developed and the shrinkage stress was measured at temperatures from 80 to 180°C and a relative humidity of 0% to 80%. It was found that the shrinkage stress decreased dramatically with drying above 140°C and above 60% relative humidity. It was also found that the shrinkage stress above 140°C occurred even at 100% RH and was ascribed to the structural change in cell-wall components.

The study explores the effect of dry-bulb ( T db ) and wet-bulb ( T wb ) temperature oscillation in a conventional kiln on the drying characteristics of 105-mm-square Pacific coast hemlock. Five kiln-charges were dried using four oscillating drying schedules and a control. The base drying temperatures for the control were T wb =53°C, T db =60°C for the first drying phase and increased to T wb =65°C, T db =80°C in the second phase. These temperatures were oscillated at two amplitude and frequency combinations, namely, 3°C for 4 h (low) and 6°C for 8 h (high). The results indicated that the total impact of oscillating schedules on the drying rate was more pronounced at the early stages of the drying process. Oscillating T db at higher amplitudes increased drying rate by 12%, whereas the low amplitude counterpart reduced kiln residence time by 10–14%. The final moisture content variability decreased in both T wb oscillated schedules. Core and shell moisture content variation also slightly decreased in the low amplitude T wb oscillated schedules. High amplitude oscillated T db also showed 5% less casehardening than the control, whilst its low amplitude counterpart increased. The low amplitude T wb oscillated schedule had the least surface checks and splits.

We investigated how biopulping modifies chemical and physical properties of wood and how these changes affect the properties of the resulting fiber. Mechanical and chemical testing revealed wood cell changes during 2 weeks of colonization by Ceriporiopsis subvermispora . Typical mechanical properties, such as modulus of elasticity and maximum load, tracked reductions in energy needed for mechanical refining to pulp. The data indicate the fiber saturation point of spruce increased from 29% to 42% during biopulping. At the same time, titratable acid groups increased up to 62%. Chemical analysis showed that oxalic acid esters were produced in the wood during biopulping in sufficient amounts to account for the increase in acid groups. The benefits of biopulping—energy savings and increased handsheet strength—as well as other physical property changes are consistent with the mechanism we propose: biopulping increases the acid group content of wood.

Phenolic compounds were studied as natural preservatives against wood decaying fungi. Vanillin and tannin decreased the growth of the test organisms Coniophora puteana and Coriolus versicolor and decreased the weight losses caused by these organisms in wood blocks. Both compounds were, however, leached in standard washing tests, and higher weight losses were observed in leached samples. Enzymatic polymerization with laccase was used as a means of binding the phenolic preservatives into the wood. Using an optimized laccase dosage, wood impregnation with enzymatically polymerized vanillin reduced the weight loss by C. puteana from 25% to 5%.

The termiticidal efficacy of sodium octaborate tetrahydrate, boric acid, borester-7, and tri-methyl borate as wood preservatives was evaluated after each was impregnated into seasoned sapwood of Pinus radiata D. Don and Eucalyptus regnans F. Muell in laboratory bioassay against Coptotermes acinaciformis (Froggatt). There was clear difference between the different borate retentions in treated and untreated blocks, mass loss, and mortality rate of the termite used in the bioassay units. After 8 weeks of laboratory bioassay, the results suggested that borate was toxic to termites even at 0.24% m/m BAE and caused significant termite mortality, but termites were not deterred from attacking the borate-treated timber at a higher retention of >2.0% m/m BAE. These laboratory results indicated that the minimum borate treatment required to protect timber against termite attack and damage was >1.0% m/m BAE.