Utilization of hierarchically aligned natural cellulosic structures has become a leading natural template scaffold for a diverse range of functional applications. This natural scaffold derived from ...wood by partial or full removal of lignin without altering or disturbing the hierarchically aligned cellulosic structure is known as delignified wood (DW). Over the past five years, various types of functional materials for diverse applications have been fabricated using DW. This review aims to highlight the significance of DW in functional material development by discussing the delignification impacts on the wood cell wall properties and review the different strategies used in functional materials fabrication. The first part of this review discusses the fundamental aspects of wood cell wall structure in relation to wood chemistry and lignin biosynthesis. The second part focuses on the different delignification methods used in partial and full lignin removal from wood cell walls and the fundamental properties (i.e., physical, mechanical, and chemical) of DW. The third part of this review discusses the strategies and the detailed current literature regarding the development of diverse functional materials based on DW. A greater understanding of DW provides the potential for further development of DW‐based functional materials for a diverse range of future applications.
Delignified wood is a natural material with a cellulosic template scaffold. It can be applied for many attractive functional materials, like transparent wood, membranes, thermal insulators, and many more. This review brings detailed insights into the structure of wood, delignification, and preparation of high‐tech natural delignified wood‐based functional materials.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The treatment of wood surfaces with gas discharges is one of the methods to achieve better surface adhesion properties. Good penetration, spreading and wettability of the applied liquid adhesives and ...coatings is a crucial factor for their adequate mechanical properties. Plasmas are the result of electrical discharge and can be created in different ways. The plasma treatment (PT) is frequently executed prior to material bonding or coating via the so-called dielectric barrier discharges (DBD) at atmospheric pressure. This literature review summarizes the essential aspects of DBD PTs aiming at a better wettability and surface adhesion. After introduction of the principle of DBD, the individual effects of internal and external parameters of the process will be discussed, which influence the final properties of treated materials.
Silicon (Si) is the second most abundant element in the earth's crust and it is no surprise that various contents of this element may be found in plants, and also in different lignocellulosic ...materials. This may have some undesired effects when products from wood or other lignocellulosic
materials are produced and utilised, typically with regards to adhesion of adhesives or surface coatings. However, there are plenty of positive effects of silicon-containing compounds in wood- and lignocellulose- based products, so very often silicon-containing compounds are added into the
products on purpose. Sometimes, they might decrease adhesion properties of adhesives and coatings, but their advantages are a major priority and care has to be taken to make sure the drawbacks do not become predominant. Moreover, sometimes the silicon-containing compounds in lignocellulosic
products are a necessity. A typical example is silicon-containing compounds to function as coupling agents in wood-polymer composites. The number of publications on Si in lignocellulosics, including wood, is enormous. Even if we narrow our search on this topic only to reports related to adhesion,
the number of papers is still astonishing. Therefore, this review does not discuss all recent publications about this topic and it must be rather regarded as a critical review, exhibiting the most important issues that must be taken into account when considering the influence of Si in lignocellulosic
materials with regards to adhesion. On the basis of selected papers, it is hoped that the reader will gain a satisfactory insight into the topic. In the first part, after Introduction, there is a brief overview of the most important compounds of Si that are relevant for the field of wood science
and technology. In the next section, the influence of the presence of silicon in adhesives or in coatings or substrates on adhesion is discussed. In order to understand these effects, it is essential to know about the interactions/reactions of Si-compounds with cellulose, lignin and
wood, which is the topic of the subsequent section.Reactions with the components of lignocellulosics are essential for proper functioning of coupling agents in wood-polymer composites, so these agents are presented in this review as well. Finally, an insight into the vast field of lignocellulosic
composites is given, with a focus on a variety of different compounds of silicon and their function in the composites.
Silica or silica-precursor systems are attractive for the protection of wood against biotic and abiotic damages and for improvement of the fire resistance. Alkali metal silicate solutions, also known ...as water glasses, colloidal silica (nanosilica dispersions) and other inorganic–organic hybrids resulting from the sol-gel chemistry of alkoxysilane compounds, are products available for this purpose. These chemicals are increasingly considered to formulate wood modification products or to develop surface coatings. This review article is focused on in-depth treatments of wood through dipping, soaking or vacuum-pressure impregnation methods. The techniques used to convert monomers and low molecular weight silicate species in water glasses into less soluble and leaching-resistant silica particles, such as heat treatment, acid treatment and reactions with multivalent metal cation salts, are discussed. The similarities and differences between the various raw-impregnation materials and the properties of the final products are highlighted. Water glasses after appropriate curing, colloidal silica and tetraalkoxysilane-based formulations all lead to deposition of silica particles (SiO
2
) at the surface of the cell walls, in lumens and pores. Low molecular weight organosilanes and other organo-modified formulations that are able to penetrate the wood cell walls and react with wood components are good dimensional stabilizers. The treated wood exhibits, in general, increased mechanical properties (strength, hardness) and improved resistance to biodegradation and fire retardancy. The efficiency of the treatments can significantly be enhanced to a level fulfilling the requirements for industrial applications by the addition of biocides, ultraviolet absorbers or antioxidants, fireproofing compounds (boron or phosphorus-based compounds, multivalent metal salts) and hydrophobic alkylalkoxysilanes. Silica acts as a barrier/support to many of these additives preventing them from leaching.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The present research deals with a simple dipping method to insert octadecyltrichlorosilane (OTS) into cell walls of spruce wood and to deposit OTS layers on its inner and outer surfaces. Distribution ...and chemical interactions of OTS with wood polymers has been investigated by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The OTS/n-hexane solution penetrated into wood via capillary forces through ray tracheids and bordered pits and was deposited as OTS organic-inorganic layers on wood cell walls. The hypothesis is supported by the results, according to which the OTS molecules are hydrolysed by the wood moisture and by free OH groups of the cell wall components. The hydrolysed OTS molecules react with the OH groups and elevate the hydrophobicity of wood.
The selection of the wood surface pre-treatment process prior to finishing for an optimal wood-coating relationship can be challenging, but has a great significance for the properties of the coated ...products. The present study compares the surface properties of beech (Fagus sylvatica L.) wood after mechanical (MT), physical (PT) and chemical (CT) treatment and shows the relationships of the pre-treated wood with original (O) and diluted (D, 10% water addition) waterborne opaque coatings. Wood was found to have the most oxidized surfaces (O/C ratio of 0.7) and a pronounced polar character (water contact angle 24°) after PT with atmospheric plasma discharge, followed by surfaces exposed to MT (O/C ratio 0.6, 52°) and surfaces exposed to CT (O/C ratio 0.4, 94°), representing surface treatment with an organic solvent. Changes in the cell structure of the wood and reduced surface roughness (Sa decreased by −2.0%) were observed only after CT. The best wettability with coatings was observed on wood exposed to PT and CT, reaching the values of advancing contact angles of 94° and 89° for O coating and 71° and 75° with D coating, respectively. This shows that it is not the surface condition of the wood that has the greatest influence on the wettability with the coatings used, but the properties of the coatings play a major role. After applying the coatings to the pre-treated wood surfaces, the thicker (between 60 μm and 41 μm) coating films were found on the wood coated with O coating than on the wood coated with D coating (between 47 μm and 37 μm). Despite some differences in the determined coating penetration depths, no general statement could be made about the influence of the type of surface pre-treatment. The highest adhesion strengths of the O coating and the D coating were found on the wood surfaces after CT (6.4 MPa and 5.4 MPa), MT (4.6 MPa and 4.5 MPa) and the smallest on the surfaces after PT (2.2 MPa and 2.5 MPa). The reasons for the contradictions between the wettability with coatings and the adhesion strength could be due to the formulation of the coatings studied, which seems to adhere better to wood substrates pre-treated with an organic solvent.
Display omitted
•The most hydrophilic wood surfaces achieved after mechanical and physical treatment.•Coatings comparatively good wet wood surfaces treated with plasma and organic solvent.•Properties of coatings play a major role in the wetting of wood surfaces.•Highest adhesion strengths of coatings on wood surfaces treated with organic solvent.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Nano ZnO reduced flow time of waterborne polyacrylate coating and increased pH.•Nano ZnO decreased elongation of waterborne polyacrylate coating.•Nano TiO2 and ZnO caused chemical changes in coating ...after accelerated exposure.•Nano TiO2 and ZnO increased colour stability of waterborne polyacrylate coating.
The rapid development of nanotechnology allowed implementation of metal oxide nanoparticles in coatings and protection of coatings without significant influence on transparency. To avoid negative impact on coating properties it is important that nanoparticles are uniformly dispersed and that the emulsion of nanoparticles is compatible with the components in coating. In this article the effect of TiO2 and ZnO nanoparticles on properties of polyacrylate waterborne coating and on stability of coating films exposed to outdoor conditions are studied. The results of this research show that ZnO nanoparticles reduce flow time of waterborne polyacrylate coating and increase pH. Furthermore, TiO2 and ZnO nanoparticles increase colour stability of waterborne polyacrylate coating. Moreover TiO2 nanoparticles have a great impact on increase of Tg, and ZnO nanoparticles on decrease of elongation and thereby on increase of brittleness of waterborne polyacrylate coating.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
These proceedings cover recent measurements of rare charmless decays B+→K‾⁎(892)0K⁎(892)+,B0→η′K⁎(892)0 and B0→π0π0 with a data sample of 772×106BB‾ pairs collected at the ϒ(4S) resonance with the ...Belle detector at the KEKB asymmetric-energy e+e− collider. In the decay channel B+→K‾⁎(892)0K⁎(892)+ an excess of 2.73σ is observed, which corresponds to B=(0.77−0.30+0.35±0.12)×10−6 and a longitudinal polarization fL=1.06±0.30±0.14. A signal strength of 5.0σ is measured in the decay channel B0→η′K⁎(892)0 with the corresponding B=(2.6±0.7±0.2)×10−6 and a CP asymmetry of ACP=−0.22±0.29±0.07. Finally we report an updated measurement of B0→π0π0 decays, with a measured branching fraction of B=(0.90±0.12±0.10)×10−6.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to ...connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (
Fagus sylvatica
L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates’ surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-urea-formaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The development of a simple surface barrier discharge plasma device is presented to enable more widespread access to and utilization of plasma technology. The application of the plasma device was ...demonstrated for pretreatment of wood prior to application of protective coatings for outdoor usage. The coatings' overall performance was increased, showing a reduction or absence of cracking due to weathering on plasma-pretreated specimens. Moreover, after ten months of outdoor weathering, the plasma-pretreated specimens showed fewer infections with biotic factors and improved adhesion performance in cross-cut tests, while the surface gloss performed independently from plasma pretreatment. In contrast to that, plasma-pretreated specimens were slightly more prone to discoloration due to outdoor weathering, whereas the plasma pretreatment did not impact the initial color after coating application.
Graphic abstract
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
