Volume 68, Issue 8

The industrially produced chemical pulps have lower strength properties than those obtained under laboratory conditions, and this difference is referred to as the strength delivery (SD) problem. In this study, the hypothesis was put forward that the SD could, at least in part, be accounted for by the supramolecular structure of the cellulose microfibrils of the fiber wall. To test the hypothesis, two bleached softwood kraft pulps (BSKP) were manufactured from the same starting material with different degrees of cellulose aggregation, but the pulps were otherwise as similar as possible in other controllable respects. The chemical and physical properties, including the pulp strength, were tested. A selective increase of the degree of cellulose microfibril aggregation resulted in a pulp with a decreased tear index (TI) at a specified tensile index, and this decrease was similar in magnitude to what is typically encountered in SD. Accordingly, the current experimental study succeeded in mimicking the SD problem. The lateral fibril aggregate dimensions (LFAD) seem to play a pivotal role and it can be safely concluded in general that the supramolecular structure of cellulose in the fibers may be an important factor contributing to the SD problem.

The pulping properties of cypress species are not known and the present paper aims to filling this gap. Namely, Cupressus lusitanica Mill., C. sempervirens L. and C. arizonica Greene have been submitted to kraft pulping and the pulp properties are compared with those of Pinus pinaster Aiton. and P. sylvestris Watereri as references. Schopper Riegler degree, density, Bekk’s smoothness, tensile index, tear index, burst index, stretch, dry zero-span strength, wet zero-span strength, brightness, opacity and light scattering coefficient have been tested. The pulp yields and delignification degrees of cypress woods were lower than those of the pine references. Fibre length, width and coarseness were statistically different between pines and cypress species and C. sempervirens pulps have corresponding data close to those of pine species. Cypress pulps can be refined much faster than pine pulps. The papers sheets of cypress fibres have, in general, lower mechanical performance than those of pine fibres. Papers from C. arizonica and C. lusitanica are similar and C. sempervirens has intermediate properties being between the other cypress and pine species. However, cypress fibres are relatively short, flexible and collapsible and can be refined with low energy demand, and thus could be incorporated into papers resulting in products with better light scattering and smoothness.

A method based on column chromatography has been developed for determination of ion exchange (IE) constants for pairs of metal ions for different types of wood, pulp, and bark samples. Bark was found to have higher selectivity than wood and pulp for the metal ions studied. Of the 14 different metal ions studied, the toxic transition metal ions Pb, Cu, and Cd were most strongly bound to all the materials used in this work. The validity of the column method was tested by means of different mixtures of metal ions as the loading solution. The IE constants obtained by the column method showed a good agreement with those obtained by the batch method reported earlier by our group. The IE constants were also determined for synthetic cation exchanger (CE) based on weak and strong acid groups. The IE constants of most pairs of metal ions are highest for the weakly acidic CE followed by bark, wood, pulp, and strongly acidic CE.

The modification of wood with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) is an efficient strategy to improve its dimensional stability and durability during its service period. In this study, oak wood ( Quercus mongolica L.) was treated with DMDHEU and the combustion behavior of the treated wood was examined. The bench-scale thermogravimetry and cone calorimetry showed that the treatment with DMDHEU alone enhanced the flammability of wood, but a combined treatment with DMDHEU and traces of magnesium chloride as a catalyst lowered the flammability to the level of untreated wood. In full-scale fire tests for flooring materials, it could be confirmed that both the untreated and treated woods have similar combustion behavior and can be classified as D fl -S1 (capable of resisting a small flame and, for a certain period, a heat flux attack; the total smoke production is limited). Accordingly, further fire-retardant treatments may be required if DMDHEU-treated wood is used in public areas.

In the search of novel potent bioactive compounds, 18 novel camphoric acid-based acylhydrazone compounds 4a – 4r were designed and synthesized by the condensation reaction of N -amino camphorimide ( 3 ) with substituted benzaldehyde based on camphoric acid as the starting material. The target compounds were characterized by means of Fourier transform infrared (FTIR), 1 H nuclear magnetic resonance (NMR), 13 C NMR, electrospray ionization-mass spectrometry (ESI-MS), and elemental analysis. The preliminary bioassay showed that the following camphoric acid-based compounds exhibited excellent antifungal activity with an inhibition ratio of 95% against Physalospora piricola at the concentration of 50 μg ml -1 : o -bromophenyl acylhydrazone ( 4f ), p -bromophenyl acylhydrazone ( 4g ), p -methoxyphenyl acylhydrazone ( 4m ), and p -hydroxyphenyl acylhydrazone ( 4p ).

The lignification process from sapwood (sW) to heartwood (hW) in ray parenchyma cells (P ray ) of Pinus densiflora has been analyzed by means of ultraviolet (UV) microscopy, acetyl bromide (CH 3 COBr) lignin determination, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The cell wall layers were localized by polarized optical microscopy (POM). POM revealed that P ray have almost no secondary wall in sW and have only the outer layer of secondary wall (S 1 ) in the transition zone (TZ) and hW. UV microscopic observations indicated that the secondary wall of P ray , which is in contact with ray tracheids (Tr ray ), begins to lignify in sW, while the secondary wall of P ray , which is not in contact with Tr ray , is partially lignified in the TZ. The secondary wall of both types of P ray is completely lignified in hW. The CH 3 COBr lignin content in sW is slightly lower than that in hW. In the TOF-SIMS measurements, the relative intensities of the secondary ions of guaiacyl-lignin (G-lignin) in the rays in sW are significantly lower than those in hW.

The lignification of ray parenchyma cells in the sapwood (sW) and heartwood (hW) of Pinus densiflora was investigated by thioacidolysis and the subsequent Raney nickel desulfuration. The samples rich and less rich in ray parenchyma cells were prepared by laser microdissection (LMD). The whole sections burned randomly by the laser served as the controls. Guaiacyl (G) monomers were detected in all the samples, and p -hydroxyphenyl (H) monomers were detectable only in trace amounts, while syringyl (S) units were absent, as expected in softwood. In sW samples rich in ray parenchyma cells, the yields of G monomers are significantly lower than in the other samples. The various types of G-G and one G-H dimers were detected, and the β-1′, β-5′, and 5-5′ dimers were dominant. The relative distributions of lignin interunit linkages were very similar in all the samples regardless of the abundance of the ray parenchyma cells in the sW or hW tissues.

The topochemical distribution of lignin in vascular bundles separated from different radial positions of Mexican coconut wood stems ( Cocos nucifera ) has been studied with focus on the relationship between the degree of lignification and tensile strength properties. The cellular lignin distribution was analyzed by UV-microspectrophotometry (UMSP) scanning at 280 nm of sections of vascular bundles (VBs) of 1 μm thickness. The fibers of the VBs with high tensile strength reveal a relatively low UV-absorbance at 280 nm (A 280 nm 0.39), whereas the VBs with low tensile strength display the highest A 280 nm (0.59). The S 2 of fiber walls are characterized by the typical lamellar structure with increasing lignin contents from the cell lumen towards the compound middle lamellae (CML). The A 280 nm data of CMLs are higher (0.67 to 0.87) than those of the S 2 wall layers. Overall, the A 280 nm values of S 2 of fibers walls within single VBs of coconut are in the range of 0.36 to 0.59.

Rattan is a unique unidirectional vascular bundles-reinforced biocomposite with many nodes along its canes. Mechanical compression tests have been performed from rattan samples taken from different parts of the cross section. Compression strength increased with increasing amounts of vascular bundles (VBs) in the tissues was investigated. Samples including the outer ring with many VBs have the highest apparent Young’s modulus of 1.08 GPa and the highest compression strength of 17.6 MPa. However, samples consisting of parenchyma cells had an apparent Young’s modulus of 25 MPa, and the compression strength of 1.81 MPa. The compression properties of core samples improved with increasing amounts of VB. The apparent Young’s modulus and compression strength of a single VB were 730 MPa and 6.87 MPa, respectively, and were calculated according to the rule of mixture of composites.

The water sorption and mechanical properties of wood-plastic composites (WPCs) made of extracted and delignified wood flour (WF) has been investigated. WF was prepared by extraction with the solvent systems toluene/ethanol (TE), acetone/water (AW), and hot water (HW), and its delignification was conducted by means of sodium chlorite/acetic acid (AA) solution. A 2 4 full-factorial experimental design was employed to determine the effects of treatments and treatment combinations. WPCs were prepared with high-density polyethylene (HDPE) and treated WF was prepared by means of extrusion followed by injection molding, and the water absorption characteristics and mechanical properties of the products were evaluated. WPCs produced with extracted WF had lower water absorption rates and better mechanical properties than those made of untreated WF. WPCs containing delignified WF had higher water absorption rates and improved mechanical performance compared with those made of untreated WF.

Hardwoods in principle show a similar orthotropic behavior as softwoods; however, the ratios of the mechanical parameters between the three anatomical directions and their magnitudes are different and depend strongly on the individual microstructure of the species. The aim of the current study was to characterize the 3-D elastic behavior of common ash ( Fraxinus excelsior L.) by tensile, compression, and shear tests in the three anatomical directions and stepwise in between, by means of a universal testing machine in combination with a digital image correlation technique. Young’s moduli, shear moduli, and Poisson’s ratios have been determined for the different load directions. From studies on the radial-tangential plane of other wood species, it is known that the elastic moduli in the principal directions and the off-axis elastic moduli vary in a nonlinear correlation, depending on density gradients between earlywood and latewood. This angular dependency has been experimentally and theoretically proven for ash. Furthermore, the dependency of mechanical parameters on the fiber-load angle has been experimentally determined. The measurements for principal and off-axis load directions provide a sound basis for modeling of hardwood structures.

Wood physical and mechanical properties in seven tropical hardwood species viz., Acacia auriculiformis A. Cunn. ex Benth., Artocarpus hirsutus Lamk., Artocarpus heterophyllus Lamk., Swietenia macrophylla King, Xylia dolabriformis Benth., Hevea braziliensis (H.B.K.) M. A.), and Tectona grandis L.f. have been studied by means of destructive and non-destructive techniques (NDT). Mechanical strength properties and specific gravity were evaluated by conventional methods. NDT was carried out by a Pilodyn and Treesonic Microsecond Timer (TMT) to measure a steel pin penetration depth into wood and dynamic MOE, respectively. In focus was the question, whether NDT data are suitable predictors for physical and mechanical properties of the indicated hardwood species. Dynamic MOE obtained by TMT correlated strongly positive with all the strength properties studied, except shearing stress. TMT data also correlated very well to static bending MOE and MOR. A linear relationship was found between Pilodyn steel pin penetration depth and oven dry specific gravity in all the species. Both Pilodyn and TMT proved to be useful predictors of timber properties, and these instruments have a high potential for timber grading.

The results of a 2D simulation model have been validated by experimental data to check the possibility of infrared (IR) heating of rotating green logs in the course of veneer production. The assumption that the experimental situation can be described by simplified analytical solutions has been confirmed. In the knowledge of the thermal and physical characteristics of green wood, two methods are now available to calculate rapidly the temperature within the wood log and the maximum surface temperature reached by a green log rotating under an IR heating source: (1) by numerical simulation and (2) by analytical equations, which are simpler than the computationally intensive finite element method. Experimental results, validated by both methods, show that an IR heating system as part of an industrial peeling machine would not warm-up green wood to the required peeling temperature at current peeling speeds.

Most adhesive studies employing wood veneer as the substrate assume that it is a relatively uniform material if wood species and veneer thickness are constant. In the present study, veneers from rotary cut birch ( Betula pendula Roth) were produced from logs harvested in spring, autumn and winter, and soaked at 20°C and 70°C prior to peeling. Firstly, veneers produced from logs felled in autumn were dried at 103°C for 24 h and subsequently half of these veneers were heat-treated at 180°C for 3 h. In addition, veneers produced from logs felled in all three seasons were dried at 160°C for 3.5 min to simulate industrial drying. The wettability of veneers was evaluated goniometrically, and bonding strength was evaluated with an automated bonding evaluation system (ABES). The results show that soaking birch logs at 70°C rather than at 20°C before peeling, or harvesting trees in the spring rather than in the autumn or winter, gives rise to veneers with enhanced wettability and higher bond strengths with a phenol-formaldehyde adhesive. Changes in the preparation and history of a veneer surface may have a profound effect on the development of adhesive bonds.

Various lignin determination methods have been applied to hemicellulose-rich wood extracts obtained after pressurized hot-water extraction (PHWE) and membrane ultrafiltration (UF). In focus were the chlorine number (Cl no.) method, the acetyl bromide method, and the four modifications of the Klason lignin determination, such as the KCL, TAPPI, LAP, and Goldschmid methods. The furfural (F) and hydroxymethylfurfural (HMF) concentrations in the acid hydrolysates were also determined. The mass balances of the fraction were calculated with respect to the contents of dry solids and lignin, including the acid-soluble lignin. The reliability of the methods was evaluated based on the lignin mass balances and the gross chemical composition of the extracts. Although the results were dependent on the method applied, the lignin mass balance calculations yielded similar results in general.

Wood basic density (BD) is related to other wood characteristics and its determination is important in forest inventory, though BD must be differentiated from the apparent density (AD), which relates to the moisture content (MC) of wood. The aim of this study is to demonstrate a reliable conversion from BD to AD for any MC of Eucalyptus grandis wood based on two exponential and linear models that relate volumetric shrinkage to MC. To this end, wood specimens were submitted to drying and the volumetric shrinkage was determined as a function of MC. The two models proved to be efficient in the conversion of BD to AD and vice versa.

To quantify the postpeak residual capacity and to gain insights into the load transfer mechanism of a shear wall, nail connection tests were performed on salvaged connections after a monotonic shear wall test loaded up to peak load. Experimental results reveal that there is a loss of strength in most of the fasteners studied, indicating that almost all the fasteners contribute toward racking resistance of the wall. The maximum loss of strength was observed for the fastener in the uplift corner and for the fastener along the middle stud. Another area where fasteners exhibited a significant loss of strength was in plate connection located at the bottom plate. The performance of a shear wall can be enhanced by strengthening the two areas – uplift corner and bottom plate.