The bark of deciduous trees grown in Latvia: grey alder, black alder, ash tree and goat willow were sequentially extracted using solvents of increasing polarity. The data about total content of both lipophilic and hydrophilic compounds were obtained using sequentially extraction with hexane and ethanol. The highest yields of hydrophilic extractives were found for grey alder and ash tree barks (25.7% and 25.8%, respectively). Hydrophilic extract from the both alder species contained high amount (up to 12% on bark dry mass) of condensed tannins (CT) or oligomeric proanthocyanidins, whereas CT content of extract from ach tree was negligible. The main component of ethanol-water extract from alder bark was identified using 13 C NMR and MALDI-TOF MS spectroscopy as a mixture of A-and B-type oligomeric procyanidins with the epicatechin units polymerization degree of 2-7. Ecologically friendly wood adhesives were obtained on the condensed tannin basis.
Toxic formaldehyde emissions, and the necessity to reduce the consumption of petrochemicals, stimulates the development of environmentally friendly adhesives. The aim of this research was to study, for the first time, the possibility of using condensed tannins (CTs)-rich extracts from grey alder (Alnus incana) and black alder (Alnus glutinosa) bark in the production of particleboards and plywood adhesives. The chemical structure, composition, and molecular weight of the CTs were identified by a 13C-NMR and TOF-MS analysis. Three innovative adhesive systems were studied: CTs-phenol-formaldehyde (CTs-PF) resin; a CTs-polyethyleneimine (PEI) adhesive system; and CTs–PEI combined with an ultra-low emitting formaldehyde resin (ULEFR)—CTs–PEI–ULEFR. The results showed that CTs-PF resin has properties close to commercial PF resin, and the formaldehyde emission was twice lower. CTs–PEI bonded particleboards corresponded to the requirements of the EN 312:2010 standard for particleboards in dry conditions (Type P2). CTs–PEI–ULEFR, with a 40–60% substitution of ULEFR by CTs–PEI, had adhesive properties very close to ULEFR; the plywood shear strength fit the requirements of the EN 314-2:1993 standard for application in internal and external system conditions. The introduction of extracted alder bark residues microparticles into the composition of the adhesive system showed their positive potential for application as a filler.
Abstract. Wood is renewable stock that is used for shield, heating and defence since the times men emerged. Wood product dimensional alterations are a serious drawback in the wood practical applications. These alterations are caused by atmospheric moisture absorbance into wood and water interaction with hemicelluloses and cellulose amorphous part hydroxyl groups to entail wood swelling or shrinking in the case of wood drying that leads to wood products cracking and properties loss. It is assumed that the accessible to water hydroxyl group's hydrogen atom substitution with more voluminous and less polar organic radical arouse wood permanent swelling or hydroxyl group shielding. Modified wood has less water absorption and diminished water equilibrium content (EMC) that is considered as the main reason of biological resistance improvement. Wood furfurylation with furfuryl alcohol (FA) catalysed with maleic anhydride (MA) is one of the wood modification approaches. Wood dimensional stability and biological resistance to decay increase by modification with furfuryl alcohol FA is assumed as a result of FA polymers grafting to cell wall polymers. Sufficient amount of FA must be infused into wood cell walls, but FA diffusion into the wood cell wall might be hampered by formation of more voluminous π-complex between MA and FA that favour useless polymerisation in wood voids and increased FA and MA consumption. The objective of the given research was to attain maximal modification of the wood cell wall by saturation with FA and subsequent its polymerization by catalysis with formic acid vapour. Assessment of furfurylated and reference wood specimens durability in hot water -freezing -drying treatment was tested by the cyclic hydrothermal treatment (CHT) test. Wood furfurylation decreased water absorption by 80 % and swelling by 40 % during CHT in comparison with untreated wood.
The hidden nature of a glued-in rod joint presents considerable challenges with regards to quality control, and there has been minimal research on the subject to fully understand the influence of defects on the joint performance. In this study, voids in adhesive line or glue-free zones were simulated in various depths of the embedded rod, and the results were compared to a reference sample population without defects. Withdrawal capacity of glued-in steel threaded rods were lower compared to reference group samples without gluing defects, when glue simulated voids or glue-free zones were positioned in the middle part and upper (closer to sample crosscut surface) part of the glued-in rods. And no difference was observed of simulated glue-free zones in the lower (the deepest) part, closer to the end of the glued-in rod, compared to reference group samples without gluing defects.
Different types of wood are used to manufacture of various wood products. In direct production processes, additional resources such as energy, adhesives, labor, etc. are also used. In line with sustainable environmental policies, all resources must be used more rationally, while simultaneously increasing the efficiency of the direct production processes. This research examined whether it is possible to reduce energy and labor resources in the technological process of hot pressing of birch plywood (nominal thickness 9 mm), by varying the holding time under pressure, pressure, and adhesive consumption. The Box-Behnken experimental design for a multifactor experiment was used to investigate the influence of technological parameters of plywood pressing. The highest strength in static bending both parallel and perpendicular to the plywood grain was achieved by pressing plywood with the following gluing parameters: highest pressing pressure, 3.2 MPa; minimal holding time under pressure, 9 minutes; and average phenol-formaldehyde adhesive consumption 150 grams per square meter.
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