Volume 66, Issue 8

The structure of lignin in the compound middle lamella (CML) of softwood tracheids differs from that in the secondary wall (SW) in regard to the content of condensed structures (5-5′-biphenyl, dibenzodioxocin and 4-O-5′-diphenyl ether). In an early stage of cell wall formation, random coarse networks composed of thin cellulose microfibrils (CMFs), hemicelluloses, and pectin are formed in the CML, then globular p -hydroxyphenyl/guaiacyl lignin (HG-lignin) is deposited quickly into the network. The globular lignin is assumed to be a micellar aggregate of oligolignols folded at the β-O-4 bond with their phenolic ends on the outer part of the aggregate. When 3D clusters of the globules are deposited on the preformed network of polysaccharides, further growth of the oligolignols by endwise addition of new monolignols is spatially limited, so frequent condensation occurs between growing aromatic ends of adjacent HG-oligolignols within the globule and between the wide contact boundaries of the 3D clustered globules to produce a highly condensed supramolecule in CML. In SW, the folded G-oligolignols are deposited slowly in the narrow tubular space surrounding thick CMFs coated with hemicelluloses. Condensation occurs mostly between adjacent growing ends of the oligolignols within the tubular aggregates. Spatial regulation of condensation of folded polylignols is one of the factors producing a different supramolecular structure for CML lignin than for SW lignin.

Pulp mill effluents contain potentially valuable compounds and will gain even greater importance than today in future biorefinery scenarios as possible resources. Analysis of effluents of process streams is not straightforward because of the vast variety of substances embedded in the complex inorganic matrix of high concentration. In the present comparative investigation, different combinations of gas chromatography (GC) and derivatisation techniques were tested and critically evaluated aiming at a comprehensive description of all major compound classes (low-molecular weight and long-chain carboxylic acids, lignin fragments, carbohydrates and aldehydes). As derivatisation techniques, trimethylsilylation, (trimethylsilyl)methylation and methylation were applied. In addition, the effluents were analysed by pyrolysis-GC/mass spectrometry (MS), either directly or with simultaneous methylation. The study provides comprehensive information on the composition of effluents, the suitability of the various combinations of derivatisation and GC/MS techniques. The discrimination effects of the different approaches are compared. The comprehensive analytical approach led to a coherent balance in terms of the contribution of the major portion of organic compounds to the total organic carbon (TOC) content in pulp mill effluents.

The effects of thermal compression on the organic-soluble material of a uniform wood substrate, hybrid poplar (clone OP-367), has been studied. Poplar veneers were preconditioned to 0% or 8% moisture content and subsequently hot pressed at 150°C, 200°C, and 250°C. The dichloromethane (DCM) extracts were characterized by various hyphenated analyses [gas chromatography-mass spectrometry (GC-MS), analytical pyrolysis (Py-GC-MS), electrospray ionization-mass spectrometry (ESI-MS), and gel permeation chromatography (GPC)]. The yields and composition of extractable compounds were markedly influenced by treatment at 250°C compared to those obtained at lower temperatures. Most importantly, the organic extracts contained a significant portion of lignin-derived compounds after treatment at 250°C.

Few Scandinavian pulp mills produce dissolving pulps; however, the demand on textile fibers is increasing. This study investigates the chemical interaction of dissolving pulp with ionic liquids (ILs), where softwood and hardwood industrial dissolving pulps were pretreated with ILs 1-butyl-3-methy-limidazolium acetate ([C 4 mim + ]CH 3 COO - ) and 1-butyl-3-methyl-imdazolium chloride ([C 4 mim + ]Cl - ). Time and temperature dependence of the dissolution process as well as the impact of the pretreatment on the molecular weight properties, thermal stability, morphology, and crystallinity of the cellulose were evaluated by means of size exclusion chromatography (SEC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR). It was shown that the dissolution of cellulosic material in ILs is a temperature-dependent process; however, the viscosity of ILs affected the efficiency of dissolution at a given temperature. Molecular weight properties were affected negatively by increased dissolution temperature, while the type of antisolvent for the regeneration had no major impact on the degree of polymerization of cellulose. Water was more efficient than ethanol for the regeneration of cellulose when performed at an elevated temperature. The pretreatment decreased the crystallinity of cellulosic material. This might lead to the increased accessibility and reactivity of cellulose.

Eucalyptus pulp is increasingly used for the manufacture of printing papers. However, its major drawback, the vessel picking, is still waiting for a solution. The detailed features and the characteristic behaviour of vessel elements (VEs) in pulp and paper processes are poorly understood. This study focusses on the chemistry, surface chemistry and morphology of eucalyptus VEs. These properties were followed through the changes introduced by different stages of elemental chlorine-free (ECF) bleaching, by studying separated VEs. Microprobe X-ray photoelectron spectroscopy (μ-XPS) and field emission-scanning electron microscopy (FE-SEM) were applied to elucidate the surface chemical composition and morphological ultrastructure, respectively. The bulk chemical composition was investigated among others by Py-GC/MS. Lignin was detected in vessels still after completed bleaching sequence, whereas the fibres were lignin-free. The vessel lignin was mainly composed by syringyl-type units. Surface coverage by lignin and amount of surface anionic groups were practically unaffected by bleaching. The vessel cell wall structure was observed to be layered in a complex way with no particular orientation of cellulose fibrils, and the different layers seemed to be exfoliated during different bleaching stages.

A Holocenic coniferous bogwood salvaged from the 70 to 100 m-deep seabed after the 2007 Niigataken Chuetsu-oki Earthquake was analyzed anatomically and chemically. The main anatomical features of the wood were the presence of (i) large window-like pits in cross field and (ii) smooth-walled cells of ray tracheid. Feature (i) allowed identification of the wood as genus Pinus . Feature (ii) is characteristic of section Quinquefoliae , but possible decay by the long burial (3400–3210 cal BP) left the identification inconclusive. Chemical analysis showed that the major volatile components of the bogwood were cadinane-type sesquiterpenes. In contrast, those of modern pine samples were longifolene and monoterpenes from Pinus densiflora and Pinus thunbergii , nerolidol from Pinus parviflora and P . parviflora var. pentaphylla , and monoterpenes from Pinus koraiensis . Thus, none of the modern pines contained cadinane-type sesquiterpenes as major components. As organic components of wood are known to undergo diagenetic transformation under geological conditions, recent samples were subjected to heat treatment at 180°C for 24 h to simulate the long burial time. As a result, nerolidol, the main component of P . parviflora and P . parviflora var. pentaphylla was converted to cadinane-type sesquiterpenes. Therefore, it is highly likely that the bogwood sample was P . parviflora or P . parviflora var. pentaphylla , section Quinquefoliae subsection Strobus , agreeing with the anatomical feature of section Quinquefoliae .

The time-dependent mechanical behaviour (TDMB) of wood is important when using the material for structural purposes. Recently, a new method for predicting the TDMB by numerical modelling was established based on the assumption that TDMB is caused by the sliding of the microfibrils past each other. In this study, the TDMB is examined via creep experiments on small specimens of Norway spruce latewood. The results of these are compared with results from numerical modelling. The experiments include results at two levels of moisture content and three levels of temperature, enabling an investigation of these two climatic factors on TDMB of wood. It was found that the mechanical response of wood tissue is the sum of responses from both tracheids and middle lamella, with only the previous being reversible. The effect of moisture and temperature differed in that the latter affected the elastic and time-dependent responses equally. Moisture, on the other hand, reduced both the elastic properties and the activation energy barrier for sliding of the microfibrils, but furthermore changed the microfibril angle of the sample as a result of swelling. Hereby, moisture had a larger effect on the time-dependent response than the elastic. All of these effects were predicted by numerical modelling.

A solvent-free process has been developed concerning the chemical modification of rubberwood and the isolates from it (holocellulose and Klason lignin) by means of acetic anhydride (Ac 2 O) and butyric anhydride (But 2 O), with iodine as the catalyst. The effect of temperature and reaction time was in focus, and the conversion products were characterized by Fourier transform infrared (FTIR) spectroscopy. The acetylation of holocellulose and lignin with Ac 2 O was performed at 120°C, whereas the modification of wood with Ac 2 O and But 2 O was carried out in the temperature range of 90–120°C for different reaction times between 15 and 240 min. The extent of the chemical modification was measured by the weight percent gain, and the modified wood was characterized by FTIR-attenuated total reflectance (ATR) method. The presence of small amounts of iodine (0.02 or 0.035 M) elevated the conversion rate of modification. The dimensional stability of the modified woods was essentially improved.

To understand better the structure-property relationships of wood in situ , nondestructive synchrotron-based tomographic microscopy (SbTM) with subcellular resolution is useful. In this context, an in situ testing device was developed to determine the cellular response of wood to mechanical loading. Different rotationally symmetric specimens were tested to synchronize the failure areas to the given scanning areas. Norway spruce samples were uniaxially compressed in the longitudinal direction and scanned in situ at several increasing relative forces ending up in the plastic deformation regime. A sufficiently high quality in situ tomography was demonstrated. The reconstructed data allowed the observation of the load-dependent development of failure regions: cracks and buckling on the microstructure were clearly visible. Future investigations with SbTM on different wood species, loading directions, and different moisture contents are promising in terms of the micromechanical behavior of wood.

The purpose of this work is to compare the weathering properties of different types of wood-plastic composites (WPCs) based on high-density polyethylene (HDPE), recycled high-density polyethylene (rHDPE-I and rHDPE-II), low-density polyethylene (LDPE), polypropylene (PP), recycled polypropylene (rPP), polystyrene (PS), and recycled polystyrene (rPS). The modulus of rupture (MOR) and modulus of elasticity (MOE) of all WPCs decreased with increasing exposure time of weathering. Of these, the rHDPE-II-based composite exhibited the highest MOR and MOE retention ratios after 2000 h of accelerated ultraviolet (UV) weathering, while the PS-based WPC had the lowest values. In addition, the carbonyl index difference (CID) of various WPCs increased significantly as a function of exposure time. Among them, the PS-based WPCs exhibited the most severe degradation due to photo-oxidation on the surface, while the degradation of PE-based WPCs was the mildest. These results are consistent with the change in the surface cracking and flexural properties of the composites. The PS-based WPCs also exhibited higher moisture diffusion coefficients. The mechanical behavior of WPCs after weathering is influenced by a combination of factors, such as surface oxidation, morphology changes, and moisture absorption.

Molecular interactions between cellulose and hemicelluloses, such as xyloglucan and xylan, play an important role in the formation of ordered layers in the cell wall of higher plants. This study attempts to characterize an ordered state of a matrix consisting of cellulose and hemicellulose induced by stretching never-dried binary blended films. In non-stretched films, the xylan component easily adapted into the semicrystalline state, while the xyloglucan component remained amorphous. Once both blended films were stretched, each component tended to be close enough to the adherent macromolecule, and the interaction resulted in typical morphological orders at the nano- and microscale levels. These studies could be useful in constructing new bio-derived materials, as well as understanding the molecular interactions between the polymers.

Cellulose aggregate fibrils (CAFs) with dimensions of 100,000×3000×300 nm from unbleached kraft pulp (KP), oxygen delignified KP (KP ox.del ), and fully bleached kraft pulp (BKP) were liberated by a series of high shear and fractionation operations. The CAFs served as microfibril model material to evaluate their dimensional and hygroexpansive behaviors when submitted to variable relative humidities (RHs). The atomic force microscopy images of CAFs from different sources of kraft fibers were obtained during a RH cycle from 50% RH to 78% RH and then to 21% RH while being kept at 23°C. The resulting images were analyzed to determine dimensional changes in length, its concurrent cross-sectional area, width, and height. The mean value of changes in length and width was in the range of 2.3–3.2% and 1.9–3.3%, respectively. The changes in area and height were in the range of 14.5–18.2% and 12.4–17.3%, respectively. The length of CAFs showed a negative correlation with RH, whereas cross-sectional area, width, and height changes correlated positively with RHs. In the out-of-plane direction, such as area and height, the hygroexpansivity was one order of magnitude larger than the in-plane hygroexpansivity, i.e., in terms of length and width.

Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.) wood samples treated with quaternary (quat)- and amino-silicone (QS and AS) solutions of different chain lengths were tested against brown-rot and white-rot fungi as well as with regard to blue stain colonisation. The treatment with short-chained silicones bearing quat and amino functional group reduced the mass loss (ML) by decay fungi at 15% treatment concentration. The release of metabolic heat by decayed samples determined in a microcalorimeter corresponded with the ML of the samples, i.e., samples with high ML produced more heat indicating higher fungal activity. Short-chain ASs reduced the blue staining more strongly than long-chain ones. However, the opposite was true in the case of QS. It was assumed that the combined effect of hydrophobation, cell wall bulking and change of the wood surface energy are responsible for a successful performance of silicone compounds as wood preservatives.

Copper precipitation is one of the important Cu fixation mechanisms of Cu-amine-treated wood. In the present work, possible pathways of Cu precipitation have been investigated via in vitro and in situ studies focusing on effects of pH and temperature and Cu species formed in Cu-monoethanolamine (Cu-Mea)-treated wood. Higher-concentration Cu-Mea solutions required a lower pH and higher amounts of acid for the precipitation because of the higher amount of free Mea in the preservative-wood system. For this reason, Cu fixation during wet conditioning of wood treated to high Cu retention (2.0% treating solution) resulted in only a slight pH decrease and low Cu fixation. When lower-concentration solutions (0.67% and 0.2%) were applied, the pH decreased enough for Cu precipitation, and the much higher Cu fixation rate was driven by both chemisorption and precipitation. Evaluation of leaching after wet conditioning and drying showed that additional Cu precipitation could occur during drying. Wet conditioning of Cu-Mea-treated wood at 50°C showed outwardly faster and higher Cu fixation, but resulted in higher Cu leaching. According to X-ray diffraction analysis, the in vitro precipitated Cu was a mixture of azurite and malachite, and possibly, Cu 2 O formed as a result of Cu-Mea decomposition.

No abstract available.

No abstract available.

No abstract available.