Volume 64, Issue 5

TEMPO/hypochlorite oxidation of cellulosics are frequently used to obtain water-soluble polyglucuronates or nano-disperse materials. The reaction under neutral conditions offers a big advantage over hitherto applied alkaline systems as base-induce β-elimination reactions causing severe cellulose degradation are suppressed. Although 4-acetamido-TEMPO seems to offer high initial activities in cellulose oxidation, the TEMPO derivative is irreversibly converted into species with much lower reactivity. The degradation pathways and the chemical structure of the 4-acetamido-TEMPO-derived (by)products have been clarified. Degradation is strongly dependent on the pH value of the reaction mixture. In acidic conditions (pH<5), 4-oxo-TEMPO is formed by an oxidative deamination process, the 4-oxo-derivative still being capable of performing cellulose oxidation. In alkaline media, a similar process proceeds, but is immediately followed by a Favorskij rearrangement to a pyrrolidine-3-carboxylic acid (PROXYL) derivative. In both cases, the released acetamido moiety is slowly converted into methylamine by a decarboxylative rearrangement (Hofmann degradation). The results suggest that the instability and the chemical fate of 4-acetamido-TEMPO needs to be considered when cellulose oxidations and their kinetics are addressed: the recyclability of the 4-acetamido-TEMPO catalyst is rather limited.

The role of chlorine (III) compounds, i.e. chlorous acid (HClO 2 ) and chlorite (ClO 2 - ), in chlorine dioxide bleaching were investigated by treating different pulps with Cl(III). It was discovered that in addition to its fully inorganic reactions, chlorous acid is consumed by organic structures present in the pulp. These structures were assumed to be aldehydes. The aldehydes might exist already in unbleached pulps, but chlorine dioxide bleaching was also found to generate new aldehyde groups. The reactive groups were concluded to originate both from carbohydrates and lignin.

High-yield pulp (HYP) is gaining increasing interest in wood-free papers, because it can improve the bulk, formation, and opacity of papers. However, one of the challenges for the papermakers is the strength of papers when a large amount of HYP is replaced with hardwood kraft pulp. In this work, we explored the potential of using cationic-modified polyvinyl alcohol (C-PVA) in increasing the strength properties of HYP. Also, C-PVA was applied to the paper-sheets made of softwood/hardwood bleached kraft pulps (SBKP/HBKP) and HYP under various conditions, and the corresponding paper properties were evaluated. It was observed that C-PVA increased the strength properties of these paper-sheets, and the results obtained from using C-PVA were only slightly less effective than those obtained from using cationic starch (C-starch). Furthermore, the addition of C-PVA to HYP, and subsequently mixing with the blend of SBKP/HBKP (option no. 1) improved the tensile and burst indices, light scattering coefficient and apparent density of paper-sheets more significantly than did the addition of C-PVA directly to the mixed furnish of SBKP/HBKP/HYP (option no. 2). Additionally, atomic force microscope (AFM) analysis showed that the attraction force, developed between the AFM-tip and the fiber surface, was changed by the C-PVA modification. The tensile and burst indices of paper-sheets were improved by adding 10 mg g -1 C-PVA and substituting 30% of HYP for HBKP, whereas the tear index, apparent density, PPS-roughness, and brightness decreased.

Phytochemical investigation of Eucommia ulmoides bark led to the isolation of a new phenolic glucoside which was named eucophenoside. The structure of eucophenoside was elucidated by extensive spectroscopic data analysis. In addition, seven known flavonoids were reported for the first time to be present in the bark of E. ulmoides : wogonin, oroxylin A, baicalein, 4,2′,4′-trihydroxychalcone, (α R )-α,4,2′,4′-tetrahydroxydihydrochalcone, (α R )-α- O -β- d -glucopyranosyl-4,2′,4′-trihydroxydihydrochalcone, and wogonoside.

Lignin depolymerization is a necessary process step in utilizing the carbohydrates in biomass and in potentially converting the lignin into a chemical feedstock. Lignin contains several aryl-alkyl ether linkages and the β-O-4 linkage is dominant among lignins. Base-mediated cleavage of the β-O-4 bond in a lignin model compound, guaiacylglycerol-β-guaiacyl ether, is reported. Ionic liquids have shown promise in a variety of biomass processes and this study explores the potential to use an ionic liquid solvent (1-butyl-2,3-dimethylimidazolium chloride) and non-aqueous bases in cleaving the β-O-4 bond. N-bases of varying basicity and structure were used at temperatures up to 150°C. The cleavage reaction was not found to be catalytic. Among all the tested N-bases, 1,5,7-triazabicyclo[4.4.0]dec-5-ene was the most active, leading to more than 40% β-O-4 ether bond cleavage, and the higher activity is probably associated with the exposed nature of the N-atoms.

The migration and deposition of hot melting wax in wax-treated wood is not described in detail in the literature, although such products are available on the market. In the present study, this topic was investigated based on pine sapwood ( Pinus sylvestris L.) and beech ( Fagus sylvatica L.). The behavior of three different waxes was studied by means of 2D X-ray measurements and scanning electron microscopy observations. The three waxes did not show distinct differences in their deposition patterns. An intensive wax deposition could be observed within the vessels, tracheids, and fibers. In P. sylvestris the ray tracheids were penetrated with hot melting waxes, therefore there is a lateral wood penetration from the outer to the inner wood. In general, no wax penetration was visible within the parenchyma tissue and epithelium cells. Cracks were detected within the wax deposits as well as secondary microcapillaries, which were visible between the deposits and the cell walls.

The quantification of wax and remaining voids filled with air in wax-treated wood has not been described in detail in the literature, although such products are commercially available. In this paper, Scots pine ( Pinus sylvestris L.) and beech ( Fagus sylvatica L.) samples were impregnated with a hot melting amide wax and characterized. The apparent densities were measured with helium pycnometry and mercury intrusion porosimetry. The pore size distribution was determined by means of mercury intrusion porosimetry and samples were visualized with 3D X-ray tomography. The remaining void spaces were calculated based on the data of all three methods. The apparent densities range from 1.18 to 1.19 g cm -3 for treated pine and from 1.21 to 1.23 g cm -3 for treated beech. As a result of the wax impregnation, the pore volume decreases from 65–68% to 12–13% for pine and from 53–58% to 7–9% for beech. The pore size distribution shifts to smaller pores. The amount of the micropores measured by mercury intrusion porosimetry is overestimated. On the one hand, blocked large pores are compressed by the movement of wax deposits under high pressure during the mercury intrusion porosimetry (“movement-effect”). On the other hand, large pores remain inaccessible or are only accessible via smaller openings (“bottle-neck-effect”). Non-invasive 3D X-ray imaging detects such macropores but the size of the detected pores is limited by the given resolution of the method. Therefore, mercury intrusion porosimetry and X-ray tomography are complementary techniques.

The objective of the present work is to evaluate the effects of the surface properties of unrefined eucalyptus pulp fibres concerning their performance in cement-based composites. The influence of the fibre surface on the microstructure of fibre-cement composites was evaluated after accelerated ageing cycles, which simulate natural weathering. The surface of unbleached pulp is a thin layer that is rich in cellulose, lignin, hemicelluloses, and extractives. Such a layer acts as a physical and chemical barrier to the penetration of low molecular components of cement. The unbleached fibres are less hydrophilic than the bleached ones. Bleaching removes the amorphous lignin and extractives from the surface and renders it more permeable to liquids. Atomic force microscopy (AFM) helps in understanding the fibre-cement interface. Bleaching improved the fibre-cement interfacial bonding, whereas fibres in the unbleached pulp were less susceptible to the re-precipitation of cement hydration products into the fibre cavities (lumens). Therefore, unbleached fibres can improve the long-term performance of the fibre-cement composite owing to their delayed mineralization.

In thermoforming of profiled wood-strand composites, an adhesive system is needed to provide a weak initial bond to maintain mat integrity and architecture during the forming process and eventually a durable bond when the final cross-sectional shape is achieved. A hybrid adhesive composed of phenol formaldehyde (PF) and poly(vinyl acetate) (PVAc) is proposed in this study. The cure kinetics of this hybrid adhesive and bond development in a multi-step hot-pressing is discussed. Cure kinetics studied by differential scanning calorimetry indicated that adding PVAc slowed down the curing reaction of PF resin; however, the full cure of PF was not inhibited. The n th-order Borchardt Daniels ( n th-BD) model provided good prediction for the curing of adhesives with a PF/PVAc ratio lower than 1:1. To simulate roll forming of wood-strand mats, a hot-pressing schedule at low temperature combined with multi-stage closing and opening was developed. The n th-BD model was able to predict the actual bond development for composites made with neat PF resin. The results indicated that cure kinetics of a PF/PVAc hybrid adhesive would not significantly differ from neat PF resin for blend ratios of 1:1 or lower, thus potentially providing a resin system for roll forming or matched-die forming of wood-strand composites.

Stresses perpendicular to the grain arising from moisture changes might cause cracks and thereby severely affect the load bearing capacity and serviceability of timber structures. The present paper reviews parameters and mathematical models commonly applied for numerical simulation of moisture-induced stresses in glulam members. The basis of the calculations is a hygro-mechanical model coupled with a moisture transport model. Several models and ranges of parameters reported in the literature are compared and the significance of the parameter selection is evaluated. It was found that geometrical properties as well as material parameters have a significantly stronger effect on the outcome of the simulations than the selection of a certain numerical formulation of mechanosorption.

A new three-dimensional (3D) computer simulation model is proposed to study structure development in wood composites, particularly strand or short fiber wood composites. The model takes into account the stochastic positioning and orientation of the strands within the mat. It also predicts the response of individual strands within the structure to the compressive and shear forces produced during mat consolidation. The model provides a complete description of mat structure in three dimensions, including spatial distribution of porosity, inter-strand contact, and density. Predictions for porosity obtained with the 3D model compare very well with those from an earlier two-dimensional analytical model. Mat structure is dictated by mat density in a two-step process: rapid removal of macrovoids before the mat density reaches the original wood density and asymptotic elimination of microvoids at higher mat densification. Other factors of importance include original wood density and strand dimensions, particularly strand thickness and width. Although known for its influence on mechanical properties, strand orientation seems to have little effect on mat porosity and strand contact.

Deformation behaviors of cell cross-sections from wood blocks were observed during water adsorption by confocal laser-scanning microscopy. In the tangential (T) direction, cells swelled linearly with increasing moisture content, whereas in the radial (R) direction, cell deformation varied from cell to cell, and some cells showed even shrinkage. This confirms that the well-known swelling/shrinking anisotropy for intact wood blocks is T>R.

A theoretical model was developed to better understand the process of microwave explosion treatment of wood cells. The cell expansion and critical conditions concerning pressure and temperature of ray parenchyma cells in Eucalyptus urophylla were simulated during microwave pretreatment. The results indicate that longitudinal and circumferential stresses were generated in the cell walls owing to the internal steam pressure during extensive microwave treatment. The circumferential stress is twice as high as the longitudinal stress. The pressure difference reaches its maximum value of 0.84 MPa when the extension ratio is 1.20 for the longitudinal direction and 1.62 for the circumferential direction. The maximum pressure difference at the theoretical yielding point is the critical pressure difference that can eventually rupture the ray cell. The critical pressure difference decreases with increasing cell radius and decreasing shear modulus in the cell wall. This simulated result provides useful information to modify wood at the level of ray parenchyma cells.

Water transport in wood is vital for the survival of trees. With synchrotron radiation X-ray tomographic microscopy (SRXTM), it has become possible to characterize and quantify the three-dimensional (3D) network formed by vessels that are responsible for longitudinal transport. In the present study, the spatial size dependence of vessels and the organization inside single growth rings in terms of vessel-induced porosity was studied by SRXTM. Network characteristics, such as connectivity, were deduced by digital image analysis from the processed tomographic data and related to known complex network topologies.

Traditional wood preservatives based on biocides are effective against wood-deteriorating organisms because of their toxicity. By contrast, modified woods are non-toxic by definition. To investigate the efficiency of various wood modifications, quantitative real-time polymerase chain reaction (qPCR) was used to profile the DNA amounts of the white-rot fungus Trametes versicolor (L.) [Lloyd strain CTB 863 A] during an 8-week-long growth period in treated Pinus sylvestris (L.) sapwood. The studied wood was modified by acetylation, furfurylation, and thermal treatment. The traditional wood preservatives bis-( N -cyclohexyldiazeniumdioxy)-copper (Cu-HDO) and chromated copper arsenate (CCA) were used as references, whereas untreated P. sylvestris (L.) sapwood served as a control. The maximum levels of fungal DNA in native wood occurred at the end of the experiment. For all wood treatments, the maximum fungal DNA level was recorded after an incubation period of 2 weeks, followed by a decline until the end of the trial. For the preservative-treated woods, Cu-HDO showed the lowest level of fungal DNA throughout the experiment, indicating that exploratory hyphal growth is limited owing to the phytotoxicity of the treatment. The other treatments did not inhibit the exploratory hyphal growth phase. We conclude that qPCR studies of hyphal growth patterns within wood should provide a powerful tool for evaluating and further optimizing new wood protection systems.

To investigate the chemical adsorption capacity of copper-monoethanolamine (Cu-Mea) components on wood, the Na + cation exchange capacity (CEC) of red pine ( Pinus resinosa Ait.) was determined and compared with the adsorption capacity of free Mea, Cu 2+ and Cu-Mea complexes. Red pine showed higher CEC as pH increased. Free Mea adsorption as a function of pH followed the Na adsorption curve except at pH over 9, when it exceeded the CEC. Below pH 5, where Cu-Mea complexes do not form, divalent Cu 2+ was adsorbed as if it were monovalent. Cu-Mea adsorbed up to the CEC at pH 9.0–9.5 apparently as [CuMea] + , whereas the complex in solution is predominantly of the form [Cu(Mea) 2 ] + . FTIR analysis showed that the same sites of wood are related to Mea, Na, and Cu adsorption.

To measure the chemical adsorption capacity of wood for copper (Cu) and amine in Cu-amine solution, Cu was formulated with different ratios of mono- (Mea), di- (Dea), tri- (Tea) ethanolamine, ethylenediamine (En) and ammonia (Am), and the Cu adsorption was compared with the cation exchange capacity (CEC) of red pine ( Pinus resinosa Ait.). The chemisorption capacity of the wood for Cu was highly pH dependant and varied with ligand types investigated in this study. Although wood chemisorption capacity increases with pH, high amine ratio Cu-ethanolamine complexes showed very limited adsorption at high pH owing to competition with free ethanolamine in combination with the formation of uncharged ion complexes. During Cu-Mea treatment, negligible Cu 2+ was converted to Cu + and no significant delignification was detected even at very high Mea ratios. Cu appeared to be adsorbed as if it were singly charged, even though most of the complexes present are 2+ charged. The three ethanolamine ligands generally showed similar adsorption tendencies, although their pH dependencies differed. Cu in En was much less adsorbed at intermediate pH compared with the CEC, but had higher adsorption at high pH. Cu in Am also showed higher adsorption at high pH compared with Mea and the [Cu(NH 3 )(H 2 O) 5 ] 2+ form of Cu might be fixed in wood.

The soil block test is the most widely employed laboratory method for determination of biocide efficacy in North America. However, surprisingly little is known about the effect of different soil properties and soil amendments on fungal decay. Four soils with different textures and chemical properties were obtained and characterized. These soils, with and without pH amendments, were submitted to one soil block decay study using untreated southern pine wood and two brown-rot fungi. A second study examined the effect of adding water-soluble calcium chloride to soils, or directly to wood, on brown-rot decay. Based on the results of the first study with a limited number of soils, changes in the specified properties of the soil are suggested. Generally, fungal decay was reduced by raising the soil pH for acidic soils by hydrated lime as specified in the standards, or by adding water-soluble acidic calcium chloride to basic soils.

A ground-contact field test which would yield faster deterioration data when testing new wood preservative systems would be useful. This paper reports on an accelerated field test concept where wood samples are treated with a proposed preservative and a reference system with known efficacy, with the treated samples installed next to ground-contact wood feeder stakes that are already infected with wood decay fungi. This method was employed to compare decay efficacies of wood treated with four copper systems commonly available in the US. Two preliminary short-term studies show that this test method can provide differentiation between preservatives systems after only a short exposure period.

No abstract available