Volume 7 Issue 3

Particle boards were produced from different types of wood particles, i.e. spruce, recovered particles, willow, poplar, and locust. Effects of raw material, as well as varying resin content on mechanical and fracture mechanical properties were investigated. For the analysis of mechanical properties, specific fracture energy, stress intensity factors, and the industrial European standard methods internal bond strength according to EN 319 and bending strength according to EN 310 were used. The total fracture energy was measured, and the stress intensity factor was calculated by means of data achieved through finite element simulations. Results of the fracture energy analysis were compared to internal bond strength (IB) and bending strength. While IB and the modulus of elasticity (MOE) showed a high variability, data scattering for fracture energy tests and modulus of rupture (MOR) were smaller, which are due to significant differences between the resin contents of the various board types.

The performance of zinc borate (ZB)-treated oriented structural straw board (OSSB) against mold fungi, decay fungi, and termites was examined in standard laboratory evaluations. OSSB was fabricated with split wheat straw strands and diphenylmethane diisocyante (pMDI) resin. The ZB was added during panel manufacture to achieve preservative levels (wt.%) of 1.0%, 1.5%, 2.0%, and 3.0%. It was observed that after a four-week exposure to mold fungi all samples had some mold coverage, but the coverage on the ZB-treated samples was significantly lighter compared to the untreated OSSB. Decay test showed that the weight losses of ZB-treated OSSB blocks at 1.0% and 1.5% levels were significantly reduced compared to the untreated OSSB and solid wood controls, indicating superior performance of ZB-treated OSSB against decay fungi. The termite mortality indicated that none of the termites were alive at the conclusion of the test for ZB-treated OSSB. The results from these specific laboratory studies demonstrated that ZB retentions of 1.5% and greater provide performance against decay fungi and termites for OSSB panels. In addition, untreated OSSB has high susceptibility to mold due to the chemical features of wheat straw and incomplete removal of kernels.

Wood strands either prepared in the laboratory or from a manufacturing plant were assessed for their ultimate tensile strength, tensile MOE, bending strength, and bending stiffness, and then near infrared spectroscopy was utilized for prediction. The ability to predict ultimate tensile strength and stiffness was generally weaker than bending strength and stiffness, perhaps due to the homogeneous distribution of stresses that occur within the strand during 3-point bending. Prediction of ultimate tensile strength and elasticity of plant based strands were generally weak due to imperfections in the strands that originate during biomass breakdown; however, for laboratory strands, prediction of tensile strength and stiffness was moderate/better. The modulus of elasticity for strands under bending exhibited the strongest correlation (R² = 0.76). Principal component loadings were assessed, and it was found that the cellulose crystalline- and semi-crystalline-associated wavelengths were most important in predicting the stiffness for both tensile and bending forces; however, the influence of lignin-associated wavelengths increased in importance when predicting bending strength, and it was hypothesized that this was attributable to the plastic response of lignin above the proportional limit in the stress-to-strain curve. This study demonstrates the potential of near infrared spectroscopy to monitor the biomass quality prior to composite manufacture.

Cellulose was treated in ethylene glycol with p-toluene sulfonic acid monohydrate as a catalyst at different temperatures. At the highest treatment temperature (150 °C) liquefaction of wood pulp cellulose was achieved and was dependant on cellulose polymerization degree (DP). Furthermore, the rate of amorphous cellulose weight loss was found to increase with cellulose degree of polymerization, while the rate of crystalline cellulose weight loss was reciprocal to the size of the crystallites. The cellulose degradation was studied by monitoring of the molecular mass decrease by size-exclusion chromatography. It was revealed that microcrystalline cellulose degrades via a ‘quantum mode’ mechanism, while the degradation of Whatman filter paper no 1. and cotton linters proceeded randomly and were partly dependent on the starting polymerization degree, crystallinity, and treatment temperature. The kinetics of cellulose degradation in heterogeneous media was described by means of a one-stage model, characterised by the consumption of glycosidic bonds in amorphous and crystalline cellulose regions until the levelling-off degree of polymerization is reached.

Compression wood is commonly found in Masson pine. To evaluate the mechanical properties of the cell wall of Masson pine compression and opposite wood, nanoindentation was used. The results showed that the average values of hardness and cell wall modulus of elasticity of opposite wood were slightly higher than those of compression wood. With increasing age of the annual ring, the modulus of elasticity showed a negative correlation with microfibril angle, but a weak correlation was observed for hardness. In opposite and compression wood from the same annual ring, the differences in average values of modulus of elasticity and hardness were small. These slight differences were explained by the change of microfibril angle (MFA), the press-in mode of nanoindentation, and the special structure of compression wood. The mechanical properties were almost the same for early, transition, and late wood in a mature annual ring of opposite wood. It can therefore be inferred that the average modulus of elasticity (MOE) and hardness of the cell walls in a mature annual ring were not being affected by cell wall thickness.

Xylo-oligosaccharides (XOS) are reported to have beneficial health properties, and they are considered to be functional food ingredients. Corn fiber separated from distillers dried grains with solubles (DDGS) could be a valuable feedstock for XOS production. The objective of this study was to determine the efficacy for autohydrolysis to produce XOS using fiber separated from DDGS and to determine the optimum temperature for XOS production. Corn fiber was treated with deionized water in a Parr-reactor, at temperatures ranging from 140 to 220 °C to produce XOS. The maximum total yield of XOS in the solution was 18.6 wt% of the corn fiber at 180 °C.

This study outlines research concerning wheat straw fines, including their impact on pulp bleachability, their modification by chemical means, and their use as a dry strength enhancer in a paper application. Results show that primary fines constituting about 23% of the whole wheat straw pulp had a large negative impact on pulp bleachability. The differences in response to bleaching were due to the different properties of the fines, i.e. higher kappa number, higher metal ion content, lower brightness, and lower viscosity compared to that of fibers. It was also shown that the fines fraction is more difficult to oxidize and does not reach as high fiber charge levels as that of the other fractions. However, at a dosage of ≥ 3 mmol hypochlorite/g it was possible to prepare nanofibers from wheat straw fines that showed a good strength-enhancing effect in a paper product. The fact that removal of fines from wheat straw pulps by fractionation improves bleachability and also drainage properties at the same time, while simultaneously the fines can be modified and used as a strength enhancer, is very interesting when evaluating the potential of this type of annual plant as a source for production of different paper products.

Cellulose nanofibril/phenol formaldehyde (CNF/PF) composite films with high work of fracture were prepared by filtering a mixture of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized wood nanofibers and water-soluble phenol formaldehyde with resin contents ranging from 5 to 20 wt%, followed by hot pressing. The composites were characterized by tensile testing, dynamic mechanical analysis, scanning electron microscopy, atomic force microscopy, thermo-gravimetric analysis, and moisture/water absorption. Neat CNF films had tensile stress and Young’s modulus of 232 MPa and 4.79 GPa, respectively. PF resin was found to be well dispersed in the composites, although the resin increased the roughness of the film surfaces. Hygroscopic capacities of the composites were dramatically reduced, as compared to neat films, in both high humidity environments and when soaked in water. The composites exhibited slightly reduced tensile strength with modestly increased storage modulus compared to neat CNF films. Remarkably, the work of fracture ranged from 20 to 27 MJ/m³, making these films among the toughest reported for cellulose nanocomposites.

This is the second part of a large research initiative aimed at characterizing Changbai larch (Larix olgensis Henry) for veneer and high-valued product potential. The objective of this work was to investigate the effect of the tree growth characteristics, particularly diameter at breast height (DBH) and radial growth from pith (or peeler core) to bark on clear wood and veneer properties. A population of 36 trees was chosen and classified into three DBH classes, namely 20, 25, and 30 cm, and crosscut into six segments each along the vertical stem. With the entire veneer ribbon peeled from the pith to bark for each segment, the effect of sapwood and heartwood on wood properties was revealed. The tree DBH and height were moderately and positively correlated. The tree DBH significantly affected properties of both clear wood and veneer in a similar pattern. For the larch veneer population, veneer mean ultrasonic propagation time (UPT) and density decreased but veneer mean dynamic modulus of elasticity (MOE) increased from the heartwood to sapwood or from the pith to bark. Among the three DBH classes, the 25 cm DBH yielded the highest mean veneer density and MOE, followed by the 20 cm DBH and 30 cm DBH. This was found to be caused by the radial evolution of veneer properties from the pith to bark in combination with the variation of veneer yield and stem position.

In Chile the amounts of wood sawdust, shavings, and chips available is around 2.72 million, 340 thousand, and 4.25 million m³/year, respectively, and about 30% of this material is employed in the manufacture of particleboards. Two types of particleboards were made from wood residues as moisture-resistant particleboards, and the main goal was to meet the requirements for P3 moisture resistance according to the European Standard EN 312. Five mats of each type were pressed without stops in a 30 cm diameter electrically heated hot press at 180°C for 3.5 min. Target board density was 680 kg/m³ (T1) and 720 kg/m³ (T2), mat moisture was 10%, resin dosage applied was 6%, and board thickness was 15 mm for both boards (0.5 x 0.5 m). Samples were designated as T1 and T2, on which both physical and mechanical tests were conducted. Density, moisture content, thickness swelling, and water absorption were measured. Mechanical tests included internal bond before and after cyclic test, as well as fire retardancy. The analysis of the high resolution images allowed us to ensure that there was no gap between the veneer and the particleboard; therefore it can be concluded that there was no adherence loss. Results for all tests showed that both boards met all the P3 standards for moisture resistant non-structural board for use in humid conditions.