Volume 70, Issue 12

Vulcanisation is a process of transforming a plastic rubber compound into a highly elastic product by forming a three-dimensional cross-linked network structure in the rubber matrix. Many systems have been developed to vulcanise rubber compounds, among which sulphur and peroxide curing systems remain the most desirable. The application of sulphur systems leads to the forming of sulphidic cross-links between elastomer chains, while carbon–carbon bonds are formed in peroxide-curing. Both vulcanisation systems provide certain benefits to the cross-linked rubber articles, but also some disadvantages. The present work seeks to provide an overview on both vulcanisation systems; their composition, possibilities of their application, reaction mechanisms, structure of the cross-links formed and the main feature of the final cross-linked materials – vulcanisates.

The study sought to isolate asporopollenin-like biopolymer from Aspergillus niger ( A. niger ) spore. The spore exine (Sp-exine) from A. niger was isolated using four different methods. The highest isolation efficiency (9.32 %) was found for the method based on H 2 SO 4 treatment. Optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the isolated Sp-exine had a spherical shape with a spun morphology and was highly uniform in size. The elemental compositions of the bodies of the Sp-exine materials, as well as their surfaces, were observed by means of CHN combustion analysis and SEM with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. The result demonstrates C, H and O to be the main structural elements in all the Sp-exine samples. Fourier-transform infrared (FTIR) spectroscopy coupled with solid state 13 C nuclear magnetic resonance (solid state 13 C NMR) spectroscopy and UV-Vis spectroscopy were used to compare the changes in the functional groups of the Sp-exine samples isolated using the different methods. A thermogravimetric analysis (TGA) study demonstrated all the Sp-exine samples showed high thermal stability. Among all tested methods, the treatment with H 2 SO 4 and alcoholic potassium hydroxide exhibited the best results in removing cellular and other contents with minimal drastic effect on the structure and morphology and is proposed as the best method for isolating Sp-exine since it required minimal isolation time and showed good isolation efficiency.

This study describes the analysis of total hops essential oils from 18 cultivated varieties of hops, five of which were bred in Lithuania, and 7 wild hop forms using gas chromatography-mass spectrometry. The study sought to organise the samples of hops into clusters, according to 72 semi-volatile compounds, by applying a well-known method, k -means clustering analysis and to identify the origin of the Lithuanian hop varieties. The bouquet of the hops essential oil was composed of various esters, terpenes, hydrocarbons and ketones. Monoterpenes (mainly β -myrcene), sesquiterpenes (dominated by β -caryophyllene and α -humulene) and oxygenated sesquiterpenes (mainly caryophyllene oxide and humulene epoxide II) were the main compound groups detected in the samples tested. The above compounds, together with α -muurolene, were the only compounds found in all the samples. Qualitative and quantitative differences were observed in the composition of the essential oils of the hop varieties analysed. For successful and statistically significant clustering of the data obtained, expertise and skills in employing chemometric analysis methods are necessary. The result is also highly dependent on the set of samples (representativeness) used for segmentation into groups, the technique for pre-processing the data, the method selected for partitioning the samples according to the similarity measures chosen, etc. To achieve a large and representative data set for clustering analysis from a small number of measurements, numerical simulation was applied using the Monte Carlo method with normal and uniform distributions and several relative standard deviation values. The grouping was performed using the k -means clustering method, employing several optimal number of clusters evaluation techniques (Davies-Bouldin index, distortion function, etc.) and different data pre-processing approaches. The hop samples analysed were separated into 3 and 5 clusters according to the data filtering scenario used. However, the targeted Lithuanian hop varieties were clustered identically in both cases and fell into the same group together with other cultivated hop varieties from Ukraine and Poland.

A method for the determination of vapor–liquid phase diagram structure of five-component systems based on the analysis of types and Poincare indexes of singular points of the geometric scan and full structure of the concentration simplex is proposed. Validity of the proposed method was demonstrated by vapor–liquid equilibrium modeling in five-component mixtures: ethanol + water + toluene + butanol + chlorbenzene and acetone + chloroform + ethanol + cyclohexane + water.

Nanosheet structures of copper oxide@graphene oxide (CuO@GO) composite were developed as a host material to embed sulphur nanoparticles for use as cathodes in lithium–sulphur (Li-S) batteries. The homogeneous immobilisation of sulphur in the conductive matrix of CuO@GO within a strong chemical bond between carbon and polysulphide intermediates through the Lewis acid function of CuO provides a high specific discharge capacity of the CuO@GO/S electrode in comparison with the GO/S nanocomposite. The CuO@GO/S cathode delivers a discharge capacity of 1048.95 mA h g -1 , 841.74 mA h g -1 , 736.49 mA h g -1 , 695.17 mA h g -1 , 643.86 mA h g -1 , and 457.08 mA h g -1 at different current rates of 0.1 C, 0.4 C, 0.7 C, 0.8 C, 1 C, and 2 C, respectively. The application of CuO@GO/S maintains the average coulombic efficiency of 96 % after 300 cycles at 1 C rate with a capacity retention of approximately 55.8 %. The rapid ion transportation within the efficient physicochemical confinement of polysulphides confirmed the role of the CuO@GO/S nanocomposite as a promising cathode material for the next generation of high-energy density Li-S batteries.

The spinel-type ferrites NiFe 2 O 4 and Zn 0.5 Ni 0.5 Fe 2 O 4 modified by lanthanide ions Eu 3+ and Tb 3+ were prepared by a sol-gel process with propylene oxide as a gelating agent. The phase homogeneity of the samples was tested by XRD and Mössbauer spectroscopy. Transmission electronic microscopy used for characterisation of the morphology of the samples revealed nanosized powdered samples with a narrow distribution of particle sizes. It was noted that the presence of Ln 3+ ions influenced the magnetic properties of nanosized NiFe 2 O 4 and Ni 0.5 Zn 0.5 Fe 2 O 4 ferrites. The dependence of the magnetic properties of the samples on the rare-earth doping may be explained by the different grain sizes. The saturation magnetisation tends to decrease with increasing rare-earth doping and decreasing crystallite size. A similar trend was observed for the coercive field, with the exception of the Tb 3+ -doped Zn 0.5 Ni 0.5 Fe 2 O 4 where it remained the same as in the pure ferrite.

Electroless deposition of a Co–Ni–P alloy on the surface of graphite felt filaments was performed in a low-temperature pyrophosphate solution under flow-through conditions. The loading, composition, morphology, and structure of electroless the Co–Ni–P alloy deposit on the filaments of the modified graphite felt were investigated by gravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction, respectively. Electrochemical characterization of a graphite felt electrode modified with electroless Co–Ni–P alloy was performed by cyclic voltammetry, chrono-techniques, and the electrochemical impedance spectroscopy test in an aqueous solution of polysulfide composed of the mixture of 1 M Na 2 S, 1 M NaOH and 1 M S. It was found that the electroless Co–Ni–P alloy deposit on graphite felt has good cycling stability and high electrocatalytic activity toward reversible electrochemical redox reactions of polysulfide species. In comparison with the bare graphite felt electrode, the electrode modified with the electroless Co–Ni–P alloy showed five to seven times lower values of anodic and cathodic overpotentials in the aqueous solution of polysulfide. It is very likely that the good electrochemical performance of the modified graphite felt electrode is related to the high surface area of the electroless Co–Ni–P alloy deposit.

In this work, a series of fluorosilicone vinyl acetate/acrylic/epoxy (FVAE) polymers for protection of stone relics were prepared with different content of hexafluorobutyl methacrylate (HFBMA) by the seed emulsion polymerization process. Properties and structure of FVAE materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and transmission electron microscopy (TEM). Viscosity, particle size, surface tension, gel content, adhesion and surface hardness of polymer materials were also determined. Surface morphology of the stone sample was observed by scanning electron microscopy (SEM). Compared with a commercial copolymer, ethyl methacrylate/methyl acrylate (EM/MA, Paraloid B72), protection ability of the prepared FVAE polymer was investigated using artificial ageing tests such as the freeze-thaw aging test, acid aging test and the soluble salts aging test. It was found that the FVAE polymers prepared can effectively prevent corrosion caused by H + , formation of an interface crack and further weathering, which indicates their possible application in stone protection.

The co-precipitation behaviour of a simulated Al 2 (SO 4 ) 3 –TiOSO 4 –Na 2 SiO 3 solution that imitated the lixivium of Ti-bearing blast furnace slag (Ti-slag) leached by sulphuric acid was investigated in this study. Various chemical analyses were employed to study the selective precipitation of multiple target components. Based on the high-added-value applications of Ti-slag, a new method was developed to prepare aluminium titanate composites from titanium-containing silicates. The findings demonstrate that the onsets of Ti and Al precipitation occur at pH values of 3.5 and 5.0, respectively, followed by Si precipitation. The particle sizes of the co-precipitates were greatly influenced by the precipitants, pH and the initial Al/Ti mole ratio. The results also show that the precipitation ratio of Ti, Al and Si generally increases with the pH and temperature, regardless of the Al/Ti mole ratio. The Si-O-Al, Ti-O-Al, and Ti-O-Si bonds that were formed were dependent on the pH and the initial Al/Ti mole ratio. There was a synthesis path for β -Al 2 TiO 5 (AT) from the solid-state reaction between rutile and α -Al 2 O 3 at 1362.5°C. The AT composites were successfully prepared by sintering the co-precipitates at 1450°C, which exhibited good thermal stability as estimated by the XRD measurements of the sample annealed at 1200°C for 4 hours.

To improve the magnetic fluids’ stability and demonstrate the relationships between the bilayer-coated structure and the stability, a simple method was proposed for preparingoleic acid bilayer-coated Fe 3 O 4 magnetic fluids. The hydrophilic Fe 3 O 4 nanoparticles coated with the bilayer-oleic acid were synthesised by a one-pot process through the chemical co-precipitation under alkaline conditions. Next, the hydrophilic Fe 3 O 4 particles were transformed to hydrophobic particles via carboxyl-protonated modification. Carboxyl-protonated modification was found to be a reversible process, i.e. the lipophilicity of the coated Fe3O4 nanoparticles could be controlled by protonating/deprotonating the terminal carboxyl group. In addition, the space steric effect could be significantly enhanced by maximising the oleic acid adsorption and increasing the thickness of the coated layer, resulting in the oleic acid bilayer-coated Fe3O4 nanoparticles exhibiting better performance in the stability of the hexanemagnetic fluids than oleic acid monolayer-coated Fe 3 O 4 nanoparticles.

In combination with non-corrosive and low-toxic boric acid, AlCl3 ·6H2O was found to be effective for the synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose. In this work, a 5-HMF yield of ≈ 60 % was obtained at 170°C for 40 min in a H 2 O/THF biphasic solvent mixture. An addition of NaCl not only improved the partition coefficients but also inhibited by-product formation. THF was identified as an ideal extraction solvent in biphasic systems containing C4 solvents. However, low concentration of ZnCl 2 , CoCl 2 ·6H 2 O, MnCl 2 ·4H 2 O, NiCl 2 ·6H 2 O, FeCl 3 ·6H 2 O were not suitable for the catalyst system, while ZrOCl 2 ·8H 2 O, InCl 3 ·4H 2 O showed high activity for the reaction. Boric acid increased the amount of Lewis acid sites in the reactive phase and enhanced the isomerization of glucose to fructose. A mechanism of the AlCl 3 ·6H 2 O and boric acid catalyzed glucose dehydration reaction was proposed to proceed through the isomerization of glucose to fructose followed by the transformation of fructose to 5-HMF.

Xanthenedione derivatives were synthesised in one-pot reactions between arylaldehyde derivatives and 1, 3-cyclohexanedione promoted by niobium pentachloride. This new method is simple, cost-effective, high-yielding with a good variety of substrates generality, and can be conducted within reasonable reaction times.