Band 66, Heft 1

Maleated high oleic sunflower oil (maleated SOHO, MSOHO) is a promising substitute for alkenyl succinic anhydrides (ASA) that are widely used as sizing agents for paper. The part of the MSOHO molecule that is believed to be responsible for adhesion of the molecule onto cellulose, i.e., the maleated oleic acid moiety, was separately prepared and analytically characterized. Structural analysis was completed by studies of the molecular fragments obtained upon ozonolysis. The interesting question of whether there was a preferential reactivity during the ene- reaction of maleic anhydride with oleates was answered in a way that the newly formed double bond was placed to either side with no apparent selectivity.

Composites of cellulose and conjugated polymers based on oligo- and polythiophene are reported, inspired by the assembly of cellulose and lignin in wood as a composite that survives harsh environmental conditions and meets most complex demands. The regioselectively oligothiophene-substituted cellulose derivatives were synthesized according to a protecting group strategy and used to prepare the polythiophene-cellulose composites through a FeCl 3 -initiated oxidative co-polymerization with thiophene co-monomers. The optical property of the cellulose derivatives with mono-, bi- and terthiophene moieties at the C-6 position was investigated with ultraviolet-visible (UV-Vis) and circular dichroism (CD) spectroscopy. The UV-Vis absorption spectra exhibited a broad band reflecting the intense π-π* transition within the conjugated oligothiophene side chains, which were greater than those of the corresponding reference monomers owing to their intermolecular π-electron interactions, even in solution. This was also supported by the negative CD band, indicative of cellulosic supramolecular stacking structures in solution. The soluble polythiophene-cellulose composites were prepared by the oxidative co-polymerization of the oligothiophene substituted celluloses with excess 3-hexylthiophene in the presence of FeCl 3 as the oxidative initiator. The supplied amount of thiophene co-monomer was crucial for producing large π-conjugated structures and a cross-linked network structure. The soluble composites, with properties, such as electric conductivity, semiconductivity, or photoelectroactivity, were applied for the preparation of thin films which will have to be optimized for the respective application.

Carboxymethyl cellulose (CMC) is produced commercially in a two stage process consisting of a mercerization stage in which the pulp is treated with alkali in a water alcohol solution and a second etherification stage whereby monochloro-acetic acid is added to the pulp slurry. In this study, the influence of the conditions of an extended mercerization stage was evaluated on the etherification stage concerning the degree of substitution (DS) and the filterability of the resulting CMC. The parameters studied were: (1) the ratio of cellulose I and cellulose II in the original pulp, (2) the concentration of alkali, (3) the temperature and (4) the retention time in the mercerization stage. The DS results indicate that the NaOH concentration in the mercerization stage is the most important among the parameters studied. When the NaOH concentration in the mercerization stage was high (27.5%), cellulose II showed a lower reactivity than cellulose I with respect to the DS obtained in the resulting CMC. The results from the filtration ability of CMC water solutions are interpreted that the amount of cellulose II in the original pulp and the temperature has a negative influence, while the NaOH concentration in the mercerization stage has a positive influence on the filtration ability. Retention time between 1 h–48 h in the mercerization stage had no effect on the DS or the filtration value. The filtration ability was assumed to be highly influenced by the presence of poorly reacted cellulose segments. The CMC samples with the lowest filtration ability at a given DS can be assumed to have the highest degree of unevenly substituted segments.

One undesirable reaction during ECF bleaching is the formation of resistant quinones during the oxidation of lignin phenolic rings by ClO 2. Occurrence of this side reaction was confirmed by the implementation of a new in situ method for quinone detection. It is based on the selective reaction of free-phenol groups in pulp with ClO 2 at low temperature (0°C) and on the reduction of quinones into free phenols by sodium dithionite. Although not absolutely quantitative, it gives valuable information on the quinone content without any need of lignin extraction. It is proposed to apply a hydrogen peroxide treatment after each ClO 2 (D) stage to solve this problem. Another undesirable reaction is the consumption of ClO 2 by the muconic acid type structures which are the primary oxidation products of lignin during a D stage. Experiments with Z,Z -2, 5-dimethyl muconic acid, a model for lignin oxidized units, indicated that this reaction is most probable. Although phenolic moieties in lignin are more reactive than the muconic acid structures, the use of high ClO 2 charges respective to lignin may favour its consumption by the muconic acid structures. One solution to this problem is to apply lower charges of ClO 2 in each D treatment. The relevance of these findings was demonstrated by the high efficiency of (DEP)(DEP) sequences, where DEP stands for a ClO 2 stage at low charge of chlorine dioxide immediately followed by an alkaline hydrogen peroxide treatment.

The dynamic vapour sorption behaviour of two Malaysian hardwoods, acacia ( Acacia mangium Wild) and sesendok ( Endospermum malaccense Bent ex Müll. Arg.) was studied over a narrow temperature range (20–40°C). The rate of sorption or desorption of water into or out of the wood cell wall was considered to be limited by the viscoelastic behaviour of the material and the sorption kinetics was accordingly analysed in terms of a canonical series of Kelvin-Voigt elements. A two series and three series model have been applied to the kinetic data and the results are compared. Characteristic times and moisture contents were obtained from the models. The Arrhenius equation was used in conjunction with the reciprocals of the characteristic times to calculate the activation energy and activation entropy of sorption, and the Gibbs free energy of activation for the sorption process was also determined. This is the first time that entropy of activation and Gibbs free energy of activation for sorption processes with wood have been reported. Interpretation of these data invokes a model describing the polymeric relaxation processes occurring within the cell wall during adsorption or desorption. A possible link between sorption kinetics, polymeric relaxation processes, and sorption hysteresis is discussed.

Pinus radiata wood specimens were heat-treated at 160–210°C in linseed oil and the effects of treatment on chemical composition, color, dimensional stability, and fungal resistance were examined. The degradation of hemicelluloses was the most remarkable feature, which is the principal reason for alterations in wood properties. Removal or migration of extractives, oil uptake and the accumulation of oil on the wood surface were observed. The color of heat-treated wood became more uniform and darker, and its dimensional stability (i.e., anti-swelling efficiency) and fungal resistance were improved by up to 60% and 36%, respectively. The viscosity of the oil after treatment was elevated with the treatment temperature and was higher in comparison to heated oil without wood present.

A novel two-step combined treatment of poplar wood was developed to improve its dimensional stability. Maleic anhydride (MAN) was first employed to swell and bond to the wood cell wall, and then mixed monomers of glycidyl methacrylate/methyl methacrylate (GMA/MMA) were grafted to the cell wall through the chemical reaction with MAN within the wood cell lumen. The results of scanning electron microscopy and energy dispersive X-ray apparatus (SEM-EDX) and Fourier transform infrared spectroscopy (FTIR) analyses indicate that MAN penetrated and chemically bonded to the cell wall causing 9% volume swelling, and the copolymer from GMA/MMA monomers was grafted onto the wood cell wall, resulting in the improved interfacial compatibility between the polymer and wood matrix. The dimensional stability of poplar wood modified by the combined two-step treatment was remarkably improved compared with that of untreated poplar wood. The combination treatment of wood employed in this study proved to be more effective for improving the dimensional stability than treatment with PEG-1000 aqueous solution with 30% concentration.

Wood of Cryptomeria japonica (Japanese cedar) was liquefied in phenol with H 2 SO 4 or HCl as catalysts and used as raw materials to prepare phenol-formaldehyde (PF) resins. The curing behavior and adhesion properties of resins prepared were investigated. Wood liquefied with H 2 SO 4 as a catalyst had better liquefaction effect than that with HCl; however, the reaction of resin synthesis was hard to control due to its quickly increasing viscosity. Differential scanning calorimetry analysis shows that PF resins prepared from HCl-catalyzed liquefied wood had higher reactivity than those of H 2 SO 4 -catalyzed wood. These PF resins were employed for manufacturing three-layer plywood. The wet bonding strength of plywood prepared with resins from HCl-catalyzed liquefied wood exceeded 0.7 MPa and fulfilled the requirement of the CNS 1349 standard.

The development of adhesives that have good initial adhesion (tack) that provides improved mat integrity during shape-forming of wood composites has been the subject of recent research. Hybrid adhesives were made based on thermosetting phenol-formaldehyde (PF), to which three tacky adhesives were added: high tack fish glue (FG), dextrin glue (DX) and a commercial acrylic, pressure-sensitive adhesive (PSA). Tacky adhesives were blended with PF at weight levels of 25%, 50% and 75%. The time-dependent tack development of the resulting hybrid adhesives was evaluated by means of a texture analyzer. The bond strength of adhesives was measured after curing by shear block test. PF/DX blends exhibited the highest tack during longer open times, while blends of PF and FG had low tack during shorter times. PF/PSA blends lost their bond strength completely after being heated at the curing temperature of PF. PF/FG blends did not show a significant decrease in bond strength compared to pure PF. The addition of DX had no effect on shear strength at ratios <75%.

Thermal treatment of solid timber and oriented strandboards (OSB) improves durability against fungal decay and dimensional stability (swelling and shrinking). It is not clear whether thermal treatment of medium-density fibreboards (MDF) has the same effects. In this work, four variants of phenol-formaldehyde (PF)-bonded MDF with varying contents of resin and hydrophobing agent were thermally post-treated according to the Mühlböck procedure at three different maxi-mum temperatures. The short-term properties internal bond, modulus of rupture, modulus of elasticity, thickness swelling and equilibrium moisture content and the long-term property creep behaviour of treated variants and of one untreated variant have been tested. The results are presented and discussed in comparison with the respective European standards. Altogether, the thermal treatment had a positive effect on most of the tested mechanical short-term properties. The moisture-related properties, i.e., thickness swelling and equilibrium moisture content, were also positively influenced. The creep behaviour of heat-treated MDF could also be improved by thermal modification.

The objective of this study was to investigate the carbonization induced by microwave treatment (MWT) of spruce ( Picea sp.) wood, which was treated in a domestic microwave oven at 2.45 GHz. Structural changes were observed by elemental analysis, thermal analysis, and by IR and Raman spectroscopy. The degradation of the samples was completed within 3 min. The carbonization was comparable to that caused by heat treatment at ca. 420°C. In the MWT samples, a graphitic layer was not detected, which behaves as a sensitizer for MW irradiation and sometime elevates the temperature drastically. This study shows that MWT leads to a carbonaceous material, and that the carbonization levels off with the loss of heat-inducing functional groups, such as O-H, CO-OH, C=O, upon MW irradiation. MWT is better suited as a kind of controlled and short pretreatment method before carbonization. Its suitability for porous absorbents should be investigated.

Violation of CITES regulations in tropical timber trade necessitates the development of accurate species identification systems. The application of available methods, mostly based on visual illustrations and descriptions of wood anatomical characteristics, proved to be difficult or even impossible, particularly on lower taxonomic levels. Further, because most of the chain-of-custody documents are externally applied marks which can easily be manipulated, control methods should be based on wood features which are inherent in the wood itself. In a case study on five closely-related genera of the Meliaceae (mahogany) family, including Swietenia sp. (listed on CITES appendix II), Khaya , Entandrophragma , and Carapa sp. (legal trade timbers), this study demonstrates the process of developing DNA markers for identification purposes. A detailed sequence analysis of several non-coding cpDNA regions resulted in an assay of seven genus-specific SNP (single nucleotide polymorphism) markers. Tools have been designed that could be applied with low-cost equipment on the basis of PCR-RFLPs without the need for sequencing or capillary electrophoresis techniques. In addition, the application of the method to wood material with degraded DNA of low overall quantity is highlighted.

Better access to wood carbohydrates as a result of reduced, or altered, lignin is a goal of biopulping, as well as biofuel research. In the present article, woods from three transgenic trees and one wild-type quaking aspen ( Populus tremuloides Michx.) were analyzed in terms of mass loss of cellulose and lignin after incubation with lignocellulolytic fungi. The transgenic trees had reduced lignin content through transfer of an antisense -4CL gene, elevated syringyl/guaiacyl (S/G) ratio through insertion of a sense CAld5H gene and low lignin content and elevated S/G ratio through simultaneous insertion of -4CL and CAld5H genes, respectively. The lignocellulolytic fungi employed were a lignin-selective white rot fungus Ceriporiopsis subvermispora , a simultaneous white rot fungus Trametes versicolor and a brown rot fungus Postia placenta . Reduced lignin degradation was observed in woods with increased S/G ratios indicating that this analytical feature influences decay resistance, regardless of the fungal decay mechanism.

The objective of this work was to check the fiber network activation parameter developed earlier by the authors for eucalypt pulp fibers to predict technical properties of paper. The fiber size analyses were performed with an optical fiber analyzer that applies 2D image analysis techniques on single fibers. The effects of fiber length, fiber width, fiber wall thickness, and fiber curl distributions on the quality potential of eucalypt fibers were evaluated. Fiber curl and fiber wall thickness based parameters were found to have a high potential for evaluation of eucalypt fiber quality. The variations in technical properties of paper were explained with differences in fiber wall thickness and fiber curl distributions. When the model was tested against industrial long fiber pulps, a further modification for fiber length was needed. The Page tensile strength model and the shear-lag theory were applied for comparison of the results obtained by the network activation model. With the approach presented in this article, the strength characteristics of hardwood and softwood pulps can be easily evaluated based on fiber geometry and water retention value.

Chitosan, a polymer of D-glucosamine, is known for its antimicrobial activity. However, the physicochemical properties of chitosan depend upon three principal factors, i.e., source of raw material, molecular weight and degree of deacetylation. Here, synthesis and characterization of chitosan oligomers is reported, which were prepared by the nitrous acid deaminative depolymerization of chitosan obtained from Sigma Aldrich and China (industrial grade). Subsequently, their antifungal activities were evaluated against selected basid-iomycetes. The nutrient medium bioassay results show that chitosans and chitosan oligomers affected mycelial growth to different magnitudes. Nevertheless, two of the low-MW chitosan oligomers completely inhibited the growth of all the tested fungi as compared to high-MW chitosan oligomers. Accordingly, antifungal activity increases by decreasing degree of polymerization of chitosan oligomers, which is divergent to literature data. The wood decay trial confirmed the antifungal activity of chitosan oligomers against basid-iomycetes. Chitosan is leachable by water.

Anatomical and histometrical investigations were carried out on bark tissues (non-collapsed and collapsed phloem, and periderm) of beech ( Fagus sylvatica L.) trees growing at a forest site near Ljubljana, Slovenia (400 m a.s.l.). Secondary changes in bark, especially sclereid formation and lignification, were followed at cellular and sub-cellular levels by light microscopy (LM), UV microspectrophotometry (UMSP), and transmission electron microscopy (TEM). The average width of the whole bark was 5960 μm; non-collapsed phloem on average occupied 4%, collapsed phloem 89%, and periderm 7% of the bark. Secondary changes in mature phloem were characterized by a collapse of sieve tubes, inflation of axial parenchyma, and development of sclereids. The percentage of sclereid areas and the stage of their development elevated with increasing distance from the cambium. The most pronounced increment in the sclereid proportion was observed in the second- and third-fifth of the bark. Sclereid cell walls were thick and poly-lamellated and had similar spectral characteristics but distinctly higher UV absorbance values than xylem fibers. By means of a combination of LM, TEM and UMSP techniques, the structure and secondary changes in the bark could be precisely identified.

No abstract available

The effect of wood density and extractive compounds on heartwood durability against subterranean termites was studied. Twelve species of Malaysian hardwoods were tested against Coptotermes curvignathus and C. gestroi using a standard laboratory method. The results indicated that amount of extractive content is related to Malaysian hardwood termite durability.