Crack growth in glass matrix composite reinforced by long SiC fibres

Theoretical and experimental work are made for bridged cracks in chevron-notched three point bend specimens made of glass matrix composite reinforced by long SiC fibres. The fracture toughness (K_IC) values are determined using the chevron-notch technique and compared with the theoretical predictions based on micromechanical analysis exploiting weight functions. The weight functions for orthotropic material are obtained numerically by means of detailed FEM analysis using the ANSYS package and they are further used together with appropriate bridging models for the theoretical prediction of the R-curve behaviours typical of the investigated composites.     

Effect of an Antioxidant Based on Red Beetroot Extract on the Abiotic Stability of Polylactide and Polycaprolactone

This study investigated the effect of natural antioxidants inherent to beetroot (Beta vulgaris var. Vulgaris) on the ageing of environmentally friendly plastics. Certain properties were examined in this context, comprising thermal, mechanical, and morphological properties. A visual evaluation of relevant changes in the given polymers (polylactide and polycaprolactone) was conducted during an ageing test in a UV chamber (45 °C, 70% humidity) for 720 h. The films were prepared by a casting process, in which samples with the extract of beetroot were additionally incorporated in a common filler (bentonite), this serving as a carrier for the extract. The results showed the effect of the incorporated antioxidant, which was added to stabilize the biodegradable films. Its efficiency during the ageing test in the polymers tended to exceed or be comparable to that of the reference sample.     

Polymere Carbodiimide als Vorstufen für keramische Werkstoffe: Reaktionsmechanismen und Tautomeriebeziehungen

Polymeric Carbodiimides as Precursors for Ceramic Materials: Reaction Mechanisms and Tautomerism The reaction mechanisms for the synthesis of polymeric silicon and titanium carbodiimides via the element chlorides and bis(trimethylsilyl)‐carbodiimid, used as precursors for ceramic materials, have been investigated using quantumchemical methods. The influence of organic bases as catalysts on the transition state and the thermodynamics of the reaction are discussed. The ratio of the tautomers carbodiimid ‐ cyanamid depending on the heteroatom, the solvent and the temperature, has been determined using ab‐initio methods (density functional theory). The results of the theoretical calculations are confirmed by IR and UV spectroscopic data.     

Thermochemistry of gaseous ethylsilanes and their radical cations

The dissociation behavior of energy-selected tetraethylsilane, triethylsilane, and diethylsilane photocations is studied using the threshold photoelectron-photoion coincidence (TPEPICO) technique. In the 8–12. 5 eV photon energy range, 0 K dissociation onsets have been measured from the TPEPICO data. The dissociation channels observed include loss of ethane, hydrogen molecule, ethyl radical and hydrogen atom, depending upon the molecular ion under investigation. The thermochemistry of the molecular ions and dissociation fragments is obtained by an analysis that takes into account the kinetics and internal energy distributions of the ions. The various dissociation onsets permit the reevaluation of both neutral and ionic silane thermochemistry. We observed 298-K ethyl group values of 60±10 and 94±10 kJ mol^?1 for neutral and ionic silanes, respectively. These values are considerably smaller than the previously reported values of 86 and 130 kJ mol^?1, respectively. Finally, a Δ _f H ^° (298 K) of ?141.5 ± 21 kJ/mol for neutral diethyl silane is derived from the dissociative ionization onset of diethylsilane.     

Design and Synthesis of C-1 Methoxycarbonyl Derivative of Narciclasine and Its Biological Activity

A 15-step chemoenzymatic total synthesis of C-1 methoxycarbonyl narciclasine (10) was accomplished. The synthesis began with the toluene dioxygenase-mediated dihydroxylation of ortho-dibromobenzene to provide the corresponding cis-dihydrodiol (12) as a single enantiomer. Further key steps included a nitroso Diels–Alder reaction and an intramolecular Heck cyclization. The C-1 homolog 10 was tested and evaluated for antiproliferative activity against natural narciclasine (1) as the positive control. Experimental and spectral data are reported for all novel compounds.     

Analysis of the Leaves and Cones of Lithuanian Hops (Humulus lupulus L.) Varieties by Chromatographic and Spectrophotometric Methods

This work involves a comprehensive chemical composition analysis of leaf and cone samples of Lithuanian hop varieties. This study aimed to determine the chemometric properties of the leaves and cones of five Lithuanian hop varieties. Determined properties were the following: (a) xanthohumol content, (b) phenolic compounds, (c) flavonoids, (d) radical scavenging activity, and (e) the qualitative composition of volatile compounds. The total content of phenolic compounds in aqueous 75% methanolic extracts varied between 31.4–78.2 mg of rutin equivalents (RE)/g, and the concentration of flavonoids was between 11.0–23.3 mg RE/g. Radical scavenging activity varied between 34.4–87.2 mg RE/g. A QUENCHER analysis procedure showed 91.7–168.5 mg RE/g of the total phenolic compound content, 12.7–21.4 mg RE/g of flavonoids, and 48.4–121.0 mg RE/g of radical scavenging activity. ‘Fredos taurieji’ and ‘Fredos derlingieji’ varieties have shown maximum values of phenolic compounds and radical scavenging activity both in leaf and cone suspensions. These varieties accumulated a higher amount of xanthohumol in leaves. The concentration of xanthohumol in the samples varied between 0.0014–0.2136% of dry mass, with the highest concentration in the cones of ‘Kauno gražieji’. We identified 19 volatile compounds in leaves, and in cones, we identified 32. In both of them, α-humulene and β caryophyllene dominated. ‘Raudoniai’ leaves were exceptional in their aroma due to dominating compound nagina ketone (Kovats index 1306). The QUENCHER procedure has shown a great potential for the unextractable residue of hop raw material. Further investigation and valorization of different hop biomass components, not only cones, are essential.     

Electron Energy Loss Spectra of Carbodiimides

Compounds with carbodiimide bonds are of special interest to organic syntheses, materials science and biochemistry. The chemical reactivity of carbodiimides and their utilization ensue from their electronic structure, which can be studied via electron spectroscopic methods. Electron energy loss spectra of dicyclohexylcarbodiimide, polysilyl‐ and polytitanylcarbodiimides have been recorded. The energy loss near edge structures (ELNES) of the C–K, N–K, Si–L_2,3 and Ti–L_2,3‐ionization edges and their onsets as well as the features of the low‐loss region have been interpreted by ab‐initio quantumchemical calculations using density functional theory (DFT).