There is a growing need to recover raw materials from waste due to increasing environmental concerns and the widely adopted transition to circular economy. For waste tyres, it is necessary to continuously develop methods and processes that can devulcanize rubber vulcanizates into rubber products with qualities and properties that can closely match those of the virgin rubber. Currently, the most common, due to its efficiency and perceived eco-friendliness in recovering raw rubber from waste rubbers, such as tyres, is devulcanization in supercritical carbon dioxide (scCO2) using commercial and typical devulcanizing agents. The scCO2 has been generally accepted as an attractive alternative to the traditional liquid-based devulcanization media because of the resultant devulcanized rubber has relatively better quality than other processes. For instance, when scCO2 is employed to recover rubber from waste tyres (e.g. truck tyres) and the recovered rubber is blended with virgin natural rubber (NR) in various compositions, the curing and mechanical properties of the blends closely match those of virgin NR. The atmospheric toxicity and cost of the commonly used devulcanization materials like chemical agents, oils and solvents have enabled a shift towards utilization of greener (mainly organic) and readily available devulcanization chemical components. This literature review paper discusses the approaches, which have less negative impact on the environment, in chemical devulcanization of rubber vulcanizates. A special focus has been on thermo-chemical devulcanization of waste tyres in scCO2 using common organic devulcanizing agents.
Flavonoids are a class of biologically active compounds with various proven nutraceutical benefits. In flavonoid C-glycosides, the aglycones are attached to sugar residues via cleavage-resistant C-C bonds which alter typical flavonoid pharmacokinetic properties. In these compounds, the combination of biological activities from the flavonoid moieties and sugar residues create unique and more diverse biological functions than those of O-glycosylated and unsubstituted flavonoids. Through a series of reverse phase chromatography techniques and various spectroscopic methods, the phytochemical investigation of Drimia altissima (L.F.) Ker Gawl., a specie from the Asparagaceae family, led to the isolation and chemical characterisation of a novel C-glucosylflavonoid, altissimin, with a unique apioglucoside arrangement to the apigenin aglycone. Altissimin was found to possess strong in vitro anti-proliferative activity against HeLa cervical cancer cells.
Three new pentacyclic triterpenes, henninglupal (3), 19-ethylene henningsyl (4), and 19ethylene henningsal (6), along with the previously reported crystal heninngsal (2) and alphaamyrin acetate (5) were isolated from a methanolic extract of the bark of Strychnos henningsii Gilg. The new pentacyclic triterpenes were elucidated through comprehensive spectroscopic analysis, including 1D, 2D NMR, and High-resolution LCMS. The in vitro MTT cytotoxicity of compound 2 -6 was evaluated on Caco-2 cell lines, where all the isolated compounds exhibited low cytotoxic effects up to concentrations of 125 µM.
This paper evaluates the ability of a,v-alkanedithiols to cross-link high vinyl 3,4-polyisoprene rubber (represented by Isogrip) through the thiol-ene addition reaction and provides microstructural insights into where cross-linking takes place. The thiol-ene reactions are the hydrothiolation of a C5C bond, which can be initiated in a number of ways. It has been postulated that organic peroxides are very effective in initiating such cross-links and that a,v-alkanedithiolene cross-linking of high vinyl 3,4-polyisoprene primarily takes place on the a-carbon of the unsaturated sites of the rubber chains.
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