Key Engineering Materials Vol. 800

Abstract: This study deals with the restoration of columns of the VEF Culture Palace. A complete restoration of the building was performed in 2016–2017 [1]. The methodology of physico-chemical investigation of the stone materials of two facade columns includes visual observation, granulometric analyses, classic wet chemical analyses, XRD and determination of soluble salts’ content. The data obtained indicate, that for rendering of columns dolomitic and calcitic lime mortars were used. An efflorescence of sulphates on the bricks’ surface is observed.

Abstract: Despite intensive research in wood protection, no simple wood treatment method is available for satisfactory wood protection that could ensure appropriate strength and bio-resistance of wood products during their service life. The present study is a part of a project that is aimed to improve wood service properties by combining wood thermal treatment and impregnation with copper containing preservatives. The objective of the present study was to investigate the effect of conventional modifications (thermal modification at relatively mild temperature range (150 - 180°C) and impregnation) and double-treatments (impregnation after thermal treatment and vice versa) on the bending properties of birch (Betula spp.) and pine (Pinus sylvestris L.) wood. Bending strength considerably decreased after thermal modification of wood, however MOE values generally did not significantly change. Moreover, impregnation had no effect on the bending properties for both unmodified and thermally modified wood specimens. For double-treatment in which impregnation was carried out before thermal modification no changes in bending strength were observed comparing to thermally modified wood. However, MOE values of these specimens were 10 % for birch and 19 % for pine smaller comparing to just thermally modified wood. The results of double-treatment tests imply that, regarding wood bending properties, wood impregnation after thermal modification is more appropriate.

Abstract: In this study, Silver birch (Betula pendula) wood veneers and solid wood blocks were treated with commercial phenol-formaldehyde (PF) resin water solutions. Birch veneers and solid wood blocks of different size were impregnated with PF resin solutions in water with concentrations of 10, 20 and 30 wt%. The weight percent gain (WPG) and bulking after drying and curing of resin treated wood specimens were determined to evaluate the impact of specimen sizes and density. The leaching procedure according to EN 84 was performed to evaluate the PF resin fixation stability. The anti-swelling efficiency (ASE) of untreated and treated specimens during seven soaking-drying cycles was examined. Higher WPG values were obtained for specimens with lower density, but no correlation was found between the specimen size and WPG. The WPG of veneers and solid wood was 8.7 - 17.7% and 8.5 - 24.4%, respectively. The ASE of wood blocks treated with PF resins after the 1^st cycle was in the range of 37 - 51% depending on the resin loading in the wood. However, the ASE values decreased after every next soaking-drying cycle, reaching 33 - 48% after the 7^th cycle. After leaching, the WPG of specimens decreased by 2.3 - 3.0%.

Abstract: In the study, birch outer bark`s suberinic acids (SA), appropriate for binding the plywood, obtained in a water medium and precipitated in two acidification stages under various medium pH levels, were characterized, which could become a sustainable, environmentally friendly alternative to toxic, formaldehyde-containing plywood binders. In the process of obtaining SA, it was found that all SA of the first acidification stage filtrated successfully. With increasing the pH level of precipitation from 2 to 6, the yield of SA decreased from 35.6 to 18.8 wt% from oven dry (o.d.) extracted birch outer bark or 69.5-36.6 wt% from total o.d. raw material SA. Meanwhile, only one sample of SA from the second acidification stage with the initial pH level 6 filtrated successfully, reaching the yield of 4.4 wt% from total o.d. raw material SA. The SA obtained in the first acidification stage at the pH level 2 contained a lower amount of epoxy groups – 1.7 wt% from o.d. SA, but at the same time, the highest acid value – 84.4 mg KOH/g. In turn, increasing the pH level to 6, the amount of epoxy groups increased gradually up to 19.9 wt% from o.d. SA, and the acid value of SA decreased to 67.4 mg KOH/g. The acid value of SA from the second acidification stage was 133.0 mg KOH/g, but epoxy groups in the composition were not observed.

Abstract: Replacing fossil resources with biomass for the production of chemicals is another step closer to a sustainable bio-economy. To make the production of biomass based chemicals economically feasible, several valuable products need to be obtained from a single feedstock in a bio-refinery. In our work the pyrolysis products obtained from wood are explored with a focus on the separation of particular groups of added value chemicals. Anion exchange resins can be used to separate carbohydrates from phenolics, by adsorbing the latter onto the resin, but further desorption is needed to obtain concentrated fractions of phenol derivatives.

Abstract: Hydrochar has already been applied directly or indirectly in various applications. It has electrochemical and catalytical properties, and can be used for sorption, ion exchange and complexing. It can also be applied as the CO₂ adsorbent, electrode material for supercapacitors and fuel cells, and as a fossil fuel. The studied hydrochar samples produced under different reaction times were chemically activated by NaOH. The obtained hydrochar samples pre-and post-activation were studied and compared depending on HTC reaction time.

Abstract: Various electrooptic and magnetooptic effects enable the electric and magnetic field control of the holographic information recording. They can become significant if the frequency of light irradiation is close enough to the absorption line of a material. In this paper, these effects are theoretically considered, and the influence of applied external electric (up to 17 kV/cm) as well as magnetic field (0.15T) is experimentally studied on the transmission holographic grating recording in azobenzene-based molecular films at 632.8 and 532 nm. Recording beam polarizations were s-s, p-p, L-L and L-R . Self-diffraction efficiency (SDE) exposure time dependences were measured with and without the applied fields, and maximum SDE values as well as recording energies corresponding to 0.017% SDE were determined. No effect of electric field was found within the measurement accuracy (1-5%). Some trend to recording efficiency increase by magnetic field was observed. This result is in the agreement with the theoretical analysis. Unfortunately, these results are within experimental errors (usually 15-24%).

Abstract: A series of glassy 6-(tert-butyl)-4H-pyran-4-ylidene malononitrile (DCM) derivatives with covalently attached amorphous state promoting bulky 1,1,1-triphenylmethyl (trityl) moieties through several chemical design approaches have been synthesized and investigated for suitability in organic solid state laser applications. Results showed that the bonding type of such functional groups had a considerable influence on glass structure forming dye thermal properties and a slight influence on their optical properties. Thermal stability up to 346 °C was achieved with glass transitions in the range from 39 to 138 °C. Incorporation of bulky triphenyl substituents via ester groups showed remarkable amplified spontaneous emission (ASE) threshold energy value reduction by 1.7 times in comparison to other bonding approaches with excitation threshold energy density up to 91 µJ/cm². Synthesized dyes show potential as the light-amplification medium component in organic solid state lasers.

Abstract: A modular approach was used in the synthesis of the 3-(diphenylamino)carbazolyl- functionalized 2-(4-(dimethylamino)benzylidene)-1H-indene-1,3(2H)-dione (DMABI) derivatives. For this purpose, carboxyl functional group was introduced into the framework of DMABI molecule. Additionally, a regioselective method for substitution of carbonyl group of DMABI with dicyanomethylene group was investigated and verified using the heteronuclear multiple bond correlation NMR spectra. Steglich esterification method was used to connect the 3‑(diphenylamino)carbazolyl moiety via an unconjugated spacer. The UV-Vis absorption spectra and molecular energy level data were obtained for the evaluation of the synthesized compounds as donor materials in bulk-heterojunction solar cells.

Abstract: The present study describes ice characterization technique by utilizing light microscopy. Two different optical setups were used and compared. For ice structure characterization, ice was formed by adding water to an ice base layer: pouring hot water (+20 °C), pouring cold water (+3 °C) and spraying of hot water (+20 °C) water. Ice substrate specimens were made (20 x 30 x 20 mm prepared in a polypropylene mould) at -20 °C for 48 h. The heat flow direction governed the orientation of the air bubbles, and set the inner structure of ice. Pouring hot water onto ice slowly solidified the top layer and created channel-like pores perpendicular to the top surface, but cold water quickly solidified the top layer and created chaotically oriented air bubbles.