Volume 70, Issue 5

Specific degradation of the bonds between lignin and carbohydrates is an important step towards separating individual lignocellulosic biopolymers for sustainable production of materials and chemicals. One of the most established covalent lignin-carbohydrate (LC) interactions is the ester bond between the α- or γ-hydroxyl group of a lignin phenylpropane unit and a glucuronic acid side chain of xylan. In this work, a model of the LC benzyl ester bond was synthesized in a one-pot reaction from a β- O -4 lignin unit and d -glucuronic acid, both from commercial sources. The resulting lignin-carbohydrate complex (LCC) model was unstable in aqueous solution. However, at pH 4, the rate of spontaneous hydrolysis was sufficiently low to allow for enzymatic splitting experiments. The enzymatic hydrolysis of the LC benzyl ester bond of the LCC model was demonstrated by means of the glucuronoyl esterase St GE2 from Sporotrichum thermophile , which showed a preference for erythro forms of the LCC model.

Presteaming is a well-established technique in pulp mills, which improves cooking liquor impregnation by removing air from within and between chips. The aim of the study was to investigate how conditions during steaming affect the subsequent kraft cook and properties of the obtained pulp. It was found that higher pressure and temperature during chip presteaming led to increased degradation and dissolution of hemicelluloses. Lower refinability and tensile index was obtained for pulps cooked after presteaming at high pressure and for a long time.

The parenchymal cells in bamboo are an attractive source of raw materials due to their low degree of lignification and relatively loose cell wall structures. In this study, nanocellulose fibrils (NCFs) were isolated via a combined process of ultrasonication and chemical pretreatment of parenchymal cells separated from Moso bamboo ( Phyllostachys pubescens ) by means of a simple screening approach. As indicators of the fibrillation degree served the morphology, optical properties, and dynamic viscosity of the prepared NCF hydrogel as function of ultrasonication time. The mechanical properties of NCF derived films were also determined. The results show that high-quality NCFs can easily be prepared from bamboo parenchymal cells through the above-mentioned process, with an optimal ultrasonication time of 40 min. The utilization of bamboo processing residues via the ultrasonication route is promising and for energy saving production of high-quality NCFs at large scale.

One aim of this work was the chemical modification of surfaces of Scots pine ( Pinus sylvestris L.) sapwood veneer chips by covalently bonded substances for improved hydrophobicity. The durable attachment of organosilyl moieties to the surface was in focus. Several benzotriazolyl-activated p -silylated benzoic acid derivatives were applied to the esterification of OH groups at different temperatures and reaction times. The reactions resulted in weight percent gains from 8% to 43% and corresponding quantities of covalently bonded organomaterials of 0.3–2.1 mmol g -1 wood. The hydrophobicity was significantly increased as indicated by contact angles from 121° to 142°. All modified wood samples were analyzed by attenuated total reflection-infrared, contact angle measurements, and X-ray photoelectron spectroscopy.

Solvent-free acetylation of rubberwood ( Hevea brasiliensis Müll.Arg) with acetic anhydride (Ac 2 O) and by means of N-bromosuccinimide (NBS) as catalyst was carried out in an oil bath at 105°C and 120°C. The effect of catalyst concentration, temperature, and reaction time was studied. The extent of acetylation was measured by determining the weight percent gain (WPG), and the acetylated wood was characterized by FTIR-ATR, CP/MAS 13 C NMR, and XRD spectroscopy. The presence of NBS in concentrations between 1.0% and 3.0% elevated the acetylation rate to a great extent. WPG increased from 8.1% without catalyst to 22.1% for 2% NBS concentration after 60 min reaction at 120°C. Similarly, after 60-min reaction time at 105°C, WPG with 3% NBS concentration was 19.0% compared to 7.6% with un-catalyzed reaction under the same reaction conditions. The effect of microwave heating (MWh) on the NBS-catalyzed acetylation was also investigated. A significant level of modification was achieved within a few minutes of MWh. The hydrophobic properties and dimensional stability of the acetylated wood were elevated. NBS was found to be an effective catalyst for wood acetylation.

The objective of this study was to promote the adhesion of waterborne and solvent-borne coatings [polyurethane (PU) and alkyd] on wood surfaces by silane nanofilm formation by means of sol-gel processes. Tetraethoxysilane and glycidoxypropyltrimethoxysilane served as sol-gel materials. The silane-based materials improved the adhesion strength. The positive effects can be explained by the changes in the wood surface chemistry induced by the sol-gel process. High-resolution X-ray photoelectron spectroscopy (XPS) showed an increase in -C-H and -C-C bonds and a decrease in -C-O bond. Microscopic observation by fluorescence and confocal laser scanning microscopy together with NIS-Elements analysis software showed that the silica component of nanosol covered the whole wood surface homogeneously, whereas alkyd and PU coatings were deposited preferentially in the surface depressions. The combined analysis of energy-dispersive X-ray analysis and XPS demonstrated that the surface was covered with silicon oxides (SiO 2 ) attached to hydrocarbon chains.

Wood flour/polylactic acid (WF/PLA) composites were produced with a WF content of 50% based on three types of waterborne polyacrylate (PA) emulsions including a PA homopolymer emulsion and two types of silane-PA copolymer emulsions as coupling agents. Two silanes were in focus, namely, γ-methacryloxypropyl- trimethoxysilane (silane-1) and vinyltrimethoxysilane (silane-2). The emulsions and the modified WFs were characterized, and the effects were investigated in terms of emulsion type and their loading levels on the mechanical properties of WF/PLA composites. (1) Both types of silanes could be successfully copolymerized with PA to form stable emulsions. (2) With increasing PA loading, the mechanical properties (except for flexural modulus) of the composites increased at first before reaching the maximum values at 4% PA loading and then the properties worsened. However, these values were larger than those of pure composites, especially in cases when PA-silane emulsions were applied. (3) PA modified with silane-1 showed the best coupling effect among all the three PA emulsions. The results can be interpreted that PA emulsions are effective coupling agents for the preparation of high-performance WPCs.

Open-hole compression tests on Sitka spruce ( Picea sitchensis Carr.) were conducted, and the effect of the hole notch on the compressive strength has been investigated. A circular hole was cut at the centre of the longitudinal (R)-radial (R) plane. A compression load was applied to the specimen along the L or R direction, and the nominal stress at the onset of nonlinearity and the nominal compressive strength were obtained. In the test, the diameter of the hole was varied, and the effect of the diameter was analysed based on point stress criterion (PSC). It was revealed that the notch sensitivity of Sitka spruce was not so significant, and this tendency was more pronounced for the compressive strength in the R direction than in the L direction. Despite the notch insensitivity, however, the open-hole compressive strength could be predicted appropriately by the PSC.

The cylindrical orthotropy, inherent time-dependency response, and variation between and within samples make the stiffness characterisation of wood more challenging than most other structural materials. The purpose of the present study is to compare static loading with resonant ultrasound spectroscopy (RUS) and to investigate how to combine the advantages of each of these two methods to improve the estimation of the full set of elastic parameters of a unique sample. The behavior of wood as an orthotropic mechanical material was quantified by elastic engineering parameters, i.e. Poisson’s ratios and Young’s and shear moduli. Recent and waterlogged archaeological oak impregnated with polyethylene glycol (PEG) from the Vasa warship built in 1628 was in focus. The experimental results were compared, and the difference between RUS and static loading was studied. This study contributes additional information on the influence of PEG and degradation on the elastic engineering parameters of wood. Finally, the shear moduli and Poisson’s ratios were experimentally determined for Vasa archaeological oak for the first time.

Wood-based panels made of waste and recycled raw material are lacking of dimensional stability. The aim of this study is to evaluate the potential beneficial effect of heat treatment (HT) on the properties of particleboards produced from waste of Pinus sp. used for packaging. The wood particles were heat treated at 180°C, 200°C and 220°C after grinding, and panels were produced with incorporation of 25%, 50%, 75% and 100% HT particles. The materials served as reference were particles without HT. Mass loss at 180°C and 200°C was small but increased significantly to 10.6% at 220°C. The HT caused a partial degradation of hemicelluloses, thereby the relative lignin content increased from 29.7% to 37.8% for the HT 220 ° C samples. Thermogravimetry revealed higher thermal stability of the HT particles. The equilibrium moisture content decreased with HT, e.g. panels with HT 220°C showed 30% lower compared to the reference. Swelling of the panels was lowered by 30% (panel with 75% HT material) compared to the reference. The results with HT pine were successful in terms of dimensional stability and lower hygroscopicity; however, the panels lost some strength properties.

Cork and phloem from Pseudotsuga menziesii outer bark were separated, fractionated and the 40- to 60-mesh fractions chemically analyzed. Cork and phloem showed a different grinding behavior with the highest yields for cork and phloem, respectively, for the 40- to 60-mesh fraction (31.4%) and the <0.180-mm fraction (49.2%). Cork chemical composition was (% o.d. mass): ash 0.9%; extractives 29.2% (mostly polar, 23.5%); lignin 16.8%, and suberin 36.2%. Polysaccharides (16.9%) contained glucose (55.4% of total neutral carbohydrates), xylose (13.3%), mannose, arabinose, and galactose as minor components. Lipophilic and suberin extracts from cork and phloem were analyzed by GC-MS, directly and after alkaline hydrolysis. In cork, catechin was the major compound identified in the lipophilic extract, accompanied by ferulic acid and acylglycerols. In phloem, β-sitosterol was the major compound. The content of fatty alcohols and fatty acids increased after hydrolysis confirming their esterification in both extracts. Suberin from P. menziesii cork is rich in saturated ω-hydroxyacids (ω-hydroxyacids 36.2%, α,ω-diacids 18.6%, alkanoic acids 6.2%, and alkanols 8.7%), being different from suberin of Quercus suber where α,ω-diacids are dominant.

The change of microfibril angle (MFA) in wood cell wall was assessed after drying at 60°C and 70°C to a target moisture content (MC) of 8% or 15%. Despite literature contradictions about the effect of drying on MFA, this study showed that drying increased significantly the MFA, possibly as a result of lateral deformation of cellulose microfibrils during water desorption from wood cell walls. Moreover, MFA increased when target MC decreased.