Band 67, Heft 8

Milled wood lignin (MWL) of Eucalyptus globulus has been treated by a selective degradation method for β-O-4 linkages, which lets the lignin carbohydrate complexes (LCC) intact. The method consists of four reaction steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation and (4) mild alkali treatment (γ-TTSA method). Each step was followed by spectroscopies for chemical structural analysis; especially, the HSQC-NMR analysis was in focus. It was demonstrated that β-O-4 linkages were selectively and quantitatively cleaved by the γ-TTSA method while the β-β linkages in the MWL remained intact. The method leads to an enrichment of LCCs.

The extraction conditions have been evaluated concerning the recovery of specific polyphenols from Scots pine ( Pinus sylvestris ) knots by means of an accelerated solvent extractor. The composition of the extracts was determined by gas chromatography, gas chromatography-mass spectrometry, and high-performance size-exclusion chromatography. The main phenolic compounds are the stilbenes pinosylvin and its monomethyl ether and the lignan nortrachelogenin (NTG), and their amounts vary a lot from sample to sample. The sequential extraction with a nonpolar solvent as a first step for removing the lipophilic compounds was the most efficient approach for the recovery of both pinosylvins and NTG. For food applications, hot water and 85% aqueous ethanol were good solvents for the production of the substances in focus. An industrial knotwood sample from a pulp mill was sequentially extracted with cyclohexane and ethanol/water (95:5) in a large-scale Soxhlet equipment. The results show that the industrial production of pinosylvins and NTG from knots is feasible.

The impact of grafted surface of cellulose fibers on the mechanical and physical properties of fiber-cement composites (FCC) has been investigated. The grafting was performed with n -octadecyl isocyanate [i.e., with an aliphatic isocyanate (AI)], with the intention to protect the cellulose fiber from alkali degradation in the cement matrix. The chemical changes, observed by contact angle measurements and X-ray photoelectron spectroscopy, showed a higher hydrophobic character of AI-treated fibers. The strength of FCC was tested during 28 days of curing treatment. The extracted AI-treated fibers contributed to higher specific energy and final specific deflection after accelerated aging cycles in comparison with the reference composites reinforced with untreated fibers. The higher values of limit of proportionality and modulus of elasticity for composites with AI-treated fibers are an evidence of the densification of the fiber-matrix transition zone. The modulus of rupture values were higher for composites with AI-treated and Soxhlet-extracted fibers after 200 soak and dry aging cycles. In comparison with the reference, AI-treated fibers decreased the water absorption and the apparent porosity of the FCC. The modification of fibers could be a new strategy to improve the performance and stability of cement products reinforced with natural fibers.

The alkaline and acid preextraction of giant bamboo ( Bambusa balcooa Roxburgh), grown in South Africa, before kraft and soda-anthraquinone (AQ) pulping was in focus and the effects of NaOH concentration, temperature, and time on hemicelluloses extraction were studied by means of a statistical experimental design. The NaOH concentration exerted the strongest influence, solubilizing up to 20.4% of the available xylan with 2.0 M NaOH at 90°C for 240 min. The optimal extraction condition was achieved with 1 M NaOH at 90°C for 240 min, in the course of which 13.6% of the xylan was removed; the screened pulp yield was 50.4% without viscosity reduction, whereas the burst index of the handsheets was even improved. In the case of dilute acid preextraction before soda-AQ pulping, 11.3% xylan could be removed without affecting the pulp quality. The viscosity of the pulp was even better than that of pulps from nonextracted bamboo. The biorefinery approach, alkaline preextraction in combination with kraft pulping, is superior to the approach, acid prehydrolysis/soda-AQ pulping.

Hydrothermal treatments (HT) of birchwood were conducted at various intensities to extract the hemicelluloses before pulping. The amount of hemicellulose-derived sugars in the hydrolysates, including xylulose, an isomerization product of xylose, reached first a maximum and then decreased with further increasing treatment intensity. The hydrolysates also contained furanic compounds, carboxylic acids, and a large variety of aromatics, the amounts of which were dependent on HT intensity. At high treatment intensities, furfural and acetic acid were the main products quantified. Numerous nonvolatile, low molar mass carboxylic acids were also formed, with 3-deoxypentonic acid being the most abundant. Additionally, almost 40 aromatic monomers and up to 30 dimers were detected. Syringaldehyde was the main monomer and syringaresinol was the main dimer. Some aromatic compounds could not be identified. The complexity of the hydrolysates, particularly after high-intensity HT, requires selective filtration and purification methods before the hydrolysates can be utilized in downstream processes.

To improve the conversion of enzymatic hydrolysis of biomass in an energy-efficient manner, two short-time ultrasonication strategies were applied on six types of biomass with different structures and components. The strategies include pre-sonication before the hydrolysis and intermittent sonication during the ongoing hydrolysis. The microstructures of each type of biomass were characterized by scanning electron microscopy to investigate the potential correlation between biomass structure and ultrasonicaton. The concentration of resultant reducing sugar was measured to evaluate the efficiency of the hydrolysis. The results indicate that hydrolysis efficiency greatly depends on the initial structures of biomass and that short-time ultrasonication can yield up to 27.5% improvement in hydrolysis efficiency with only 120 s of sonication.

Lignin, esterified with palmitic and lauric acid chloride, has been studied for the application as coating on fiber-based packaging material. The aim was to improve the barrier properties against water vapor and oxygen of paperboard. The esterification was followed by Fourier transform infrared spectroscopy, 31 P nuclear magnetic resonance spectroscopy, and gel permeation chromatography measurements. The lignin esters were applied on paperboard and formed a continuous film. The moisture barrier property of the coated paperboards was characterized by the water vapor transmission rate (WVTR). A significant decrease in WVTR was observed, for example, 40 g m -2 (for 24 h) for a paperboard coated with 10.4 g m -2 hardwood kraft lignin palmitate. The contact angle of water on the lignin ester coatings was high and stable. For all paperboard samples coated with lignin esters, a significant decrease in oxygen transmission rate was observed. Accordingly, lignin palmitate and laurate have a high potential as a barrier materials in packaging applications.

In this study, the extractive contents and the storage-induced emissions from chips of Salix alba , Betula pendula , Populus tremula , and Alnus glutinosa are compared with emissions from Pinus sylvestris chips. Soxhlet extraction was performed, and carbon monoxide (CO) and O 2 concentration in the gas phase as well as gas chromatography-mass spectrometry analysis of volatile organic compounds were analyzed. Pinus sylvestris showed the highest extractive content in the petrol ether fraction and emitted CO in the highest concentration. Salix alba , B. pendula , P. tremula , and A. glutinosa have lower extractive contents in the petrol ether fraction and the CO concentrations decreased in the headspace accordingly. The emission of aldehydes was lower in the case of woods with lower petrol ether contents ( P. sylvestris , S. alba , and B. pendula ), but the situation was not as clear for P. tremula and A. glutinosa . The origin of CO and aldehyde emissions is discussed in view of the possible oxidative degradation processes of lipids and terpenes.

The cohesive laws (CLs) have been investigated by means of direct and inverse methods concerning wood bonded joints under pure mode I. The experimental results were obtained by tests with double cantilever beam. The direct method is based on the differentiation of the relation between strain energy release rate and crack opening displacement at the crack tip. An equivalent crack method was used to evaluate the strain energy release rate in the course of the test without monitoring the crack length, which is difficult to observe exactly. The crack opening displacement was determined by postprocessing local displacements measured by digital image correlation. The inverse method requires a previous assumption of the CL shape, and as such, a trilinear law with bilinear softening relationship was selected. The cohesive parameters were identified by an optimization procedure involving a developed genetic algorithm. The idea is to minimize an objective function that quantifies the difference between the experimental and the numerical load-displacement curves resulting from the application of a given law. A validation procedure was performed based on a numerical analysis with finite elements. Both methods in focus provided good agreement with the experimental data. It was observed that CLs adopted by the inverse method are consistent with the ones obtained with the direct method.

Furans (furfural and hydroxymethylfurfural) are the results of dehydration of monosaccharides, which can be obtained by acid hydrolysis of wood or other lignocellulosic materials. In this work, Pinus pinaster wood was subjected to aqueous autohydrolysis processing to obtain dissolved hemicellulose-derived polymeric or oligomeric saccharides made up of mannosyl, glucosyl, galactosyl, xylosyl, and arabinosyl structural units. The aqueous liquors were then heated in the presence of sulfuric acid and methyl isobutyl ketone to obtain furans. The effects of selected operational variables, such as the ratio of organic to aqueous phase, temperature, and reaction time, were assessed by empirical modeling in terms of the conversion into furans and levulinic acid. The maximum furfural conversion (71.4%) was predicted to occur operating at 165°C and a ratio of organic to aqueous phase of 2 for 68.5 min. In additional experiments, dimethyl sulfoxide and/or 1-butanol were added to the aqueous phase and the change in furan conversion rates was observed.

The properties of materials are presented, which are resulting from a combined inorganic-organic modification of wood with phenyltrimethoxysilane or phenyltriethoxysilane in a simple one-step impregnation treatment. The permanent swelling of the wood showed that the precursors entered the cell walls. The inclusion of phenyl groups, manifest by nuclear magnetic resonance spectroscopy, made the resulting wood composites highly hydrophobic, as evidenced by their low wettability and antishrink efficiencies of up to 44%. Impedance spectroscopy indicated that wood methylol groups took part in the condensation reactions with hydrated siloxanes, contributing to the high hydrophobicity and making the added phase resistant to leaching. The composites exhibited high weight percentage gains of up to 52% and ash contents up to 19%. The thermal properties of precursor solutions and products were assessed by differential scanning calorimetry and thermogravimetric analysis and compared with the more common silica precursor, tetraethyl orthosilicate.

The flexural Young’s modulus of western hemlock, medium-density fiberboard, and 5-plywood (made of lauan) has been determined by conducting three- and four-point bending tests with various span lengths and by flexural vibration test. The Young’s modulus was significantly influenced by the deflection measurement method. In particular, the Young’s modulus was not reliable based on the difference between the deflections at two specific points in the specimen, although this test is standardized according to ISO 3349-1975 and JIS Z2101-2009.

Glued laminated timber (glulam) is known in timber constructions since more than 100 years. Glulam members can delaminate due to aging and excessive changes of temperature and humidity. This results in significantly reduced load bearing capability of the affected structural members. This contribution focuses on the ultrasonic point-contact inspection of gluing plane delamination as a nondestructive method. Ultrasonic measurements on a section of a 90-year-old roofing glulam member are presented. The results are compared with manual detection and evaluation of delamination with a feeler gauge, with X-ray computed tomography analyses, and with numerical simulations. Appropriate data evaluation of the mechanized ultrasonic results allows the determination of material separation that are deeper than 20 mm in the signature of the surface wave and large-scale delamination (>80% of the complete bonding width) in the back-wall echo. Numerical simulations based on the finite-difference time-domain method shed light into the details of the wave propagation and support the experimental findings.

A sugar solution containing 31 g l -1 xylose was prepared from the culm of Sasa kurilensis by hydrolysis with 2% sulfuric acid with a liquor-to-solid ratio of 6 (g g -1 ) at 121°C for 1 h. During acid hydrolysis, also some byproducts were generated, such as acetic acid, furfural, 5-hydroxymethylfurfral, and low molecular weight phenolics, which inhibit bioconversion of xylose to xylitol. Except for acetic acid, these inhibitors were successfully removed from the hydrolysate by contacting with a steam-activated charcoal (15 g l -1 dose) for 24 h. Bioconversion of the detoxified hydrolysate to xylitol by the yeast, Candida magnoliae , was investigated under various microaerobic conditions. The oxygen transfer rate (OTR) varied from 8.4 to 27.6 mmol-O 2 l -1 h -1 . The maximum xylitol yield (0.62 g-xylitol g-xylose -1 ) was attained at the OTR of 1.2 mmol-O 2 l -1 h -1 . An additional increase in the OTR brought about cell growth, which consumed xylose. A proper control of the oxygen supply is necessary to produce efficiently xylitol from the culm hydrolysate.

Capillary zone electrophoresis (CZE) in an alkaline glycine buffer is suggested for the quantification of lignin content in black liquors (BL). The method was first tested by an external calibration with LignoBoost lignins. Then, the lignin content in BL was determined by means of a multivariate calibration with the application of a standard normal variate filter and partial least squares approach based on five principal components. The results are in agreement with those obtained by sulfuric acid lignin precipitation combined with ultraviolet measurement of the lignin in solution. The advantage of the CZE method is its independence from the knowledge of the exact absorptivity coefficient, which is needed for direct spectrophotometric lignin determination. Moreover, interfering substances and degradation products could be recognized and excluded from lignin determination; thus, the selectivity was increased significantly.