Anna Kosmalska

Characteristics of compounds in hops using cyclic voltammetry, UV-VIS, FTIR and GC-MS analysis

The article presents the antioxidant properties of the extracts of hop EI and EII, by the electrochemical methods on a platinum electrode and comparative analysis of the composition of the extracts of hops using UV-VIS, FTIR and GC-MS methods. The hops extract EI, was obtained from the waste of the hops cone. The hops extract EII, was obtained from the hops cone itself. Hops contain a wide range of polyphenolic compounds with antioxidant properties divided in various chemical classes. Flavonoids and other polyphenolic compounds contained in hops show antioxidant capacity because of the presence of hydroxyl groups in various configurations and numbers within their molecules. The electrochemical properties and antioxidant capacity of hop samples were determined to select the most effective antioxidant. Based on the cyclic and pulse voltammograms, it was observed that hop extract EI contains polyphenols that are oxidised at a less positive potential than extract EII, i.e., it shows better antioxidant capacity. From the analysis of the UV-VIS and FTIR spectra and the GC-MS analysis, it was observed that extract EI contains less phenyl compounds than EII. In addition to flavonoids, EII contains hop acids and chlorophyll. The solutions of hop extracts show very good antioxidant capacities; therefore, they can effectively inhibit or slow negative oxidation reactions and scavenge free radicals and reactive oxygen species (ROS).

Properties of POSS/HNBR Elastomer Nanocomposites

A series of composite materials containing polyhedral oligomeric silsesquioxanes (POSS) and hydrogenated butadiene-acrylonitrile rubber (HNBR) were prepared. The goal of the work was to evaluate the effect of the type and reactivity of functional groups in the POSS cage on properties of the resulting elastomeric nanocomposites. The paper presents some of the preliminary results obtained from the studies. The results indicate that incorporation of POSS into silica-filled HNBR elastomer network increases interfacial interactions of the systems and the POSS molecules can be successfully used as coagents of crosslinking towards the elastomer matrix and efficient additives improving the mechanical properties of elastomeric nanocomposites. Furthermore, evaluation of changes in mechanical properties, induced in a result of POSS/HNBR composites ageing, show that the inclusion of POSS in the HNBR network is directly influencing the stabilizing effect and improves the ageing resistance of elastomer composites.

POSS as promoters of self-healing process in silicone composites

AbstractThis article focuses on the methods used to create self-healing silicone composites. It has been shown how incorporation of polyhedral oligomeric silsesquioxanes (POSS) molecules with acid and basic groups into silicone rubber affects the barrier properties, mechanical properties in room temperature or the influences on relaxation rates of the methylvinylsilicone rubber vulcanizates. Moreover, the presence of silsesquioxanes, their content and the way of composites preparation affect the amount of ionic bonds, as indicated by measurements of equilibrium swelling in toluene. The self-healing effect of preparing samples is best visualized by SEM images of samples after destruction and conditioning. Composites presented in this work based on the methylvinylsilicone rubber with fumed silica as the fillers were manufactured and studied. To obtain self-healing effect, various silsesquioxanes were used, such as amic acid-isobutyl POSS (AAIb-POSS), aminopropylisobutyl-POSS (APIb-POSS) and aminoethylaminopropylisobutyl-POSS (AEAPIb-POSS). Every tested sample demonstrated the ability to the self-treatment. The most significant effect was observed for system containing amic acid-isobutyl POSS/aminopropylisobutyl-POSS.

Silsesquioxanes as Modifying Agents of Methylvinylsilicone Rubber

The idea and methods of methylvinylsilicone rubber modification are present. Polyhedral oligomeric silsesquioxanes (POSS) functionalized by vinyl-, carboxyl or amino-organic groups were used with the goal of modifying the rubber matrix. Additionally, oxazoline derivative and itaconic acid were used as the coupling agents. Generally, the process of modification contributed to increasing of rubber-filler interactions, however the useful properties of composites depended on a kind of active groups and way of modifications. It has been shown how grafting of POSS molecules to silicone backbone affects the cross-link density, rheometrical and mechanical properties, hysteresis and relaxation rates of the methylvinylsilicone rubber vulcanizates. Moreover, both the presence of silsesquioxanes and the way of composites preparing affect the improvement of filler dispersion degree in the rubber matrix, as indicated by SEM images. The most significant effect was observed for vinylisobutyl-POSS grafting to the silicone backbone which resulted in the considerably improved mechanical properties of the resulting network.