The thermal stability and flame retardancy of polyurethanes is reviewed. The importance of studying thermal degradation, understanding the processes occurring during thermal stress as well as the parameters affecting the thermal stability of PUs are essential in order to effectively design polyurethanes having tailor-made properties suitable for the mechanical vibration by ss rao pdf environment where they are to be used.
A detailed description of TGA, TGA-MS and TGA-FTIR methods for studying the decomposition mechanism and kinetics is also a part of this review. NCO:OH ratio, catalyst nature and crosslink density that affect the nature of PU degradation is given. PUs with an s-triazine ring or increased aromatic ring concentration, azomethane linkages as well as use of hyperbranched polyols as crosslinking agents is given. A part of the review is also concentrated on the improvement of thermal stability via hybrid formation such as the incorporation of appropriate amounts of fillers, e. PU backbone or side chain. PUs and the use of functionalized fullerenes in PUs are also described as these are the newest tools to obtain good thermal stability and flame retardancy.
Part of the review also concentrates on the process that occurs during burning of PUs, flame retardant mechanisms and different additives or reactive type flame retardants used in the PU industry. The use and working function of expandable graphite and melamine as additive type flame retardants are shown. Check if you have access through your login credentials or your institution. Present address: Department of Organic Chemistry, Polymer Chemistry Research Group, Ghent University, Krijgslaan 281 S4 bis, B-9000 Ghent, Belgium. The important role of phenolics in human health has been demonstrated, thus increasing the interest in such products and their demand by consumers. F of 20 was found to be the best solvent for the extraction of phenolic compounds. DPPH analysis confirmed the high antioxidant activity of the ultrasound extracts and HPLC analysis demonstrated that besides in terms of quantity ultrasound irradiation alter the extract composition, supporting the suitability of UAE for the preparation of antioxidant-rich plant extracts.
Veggi, Department of Food Engineering, University of Campinas, Campinas, SP, 13083-862, Brazil. Santos, Anne-Sylvie Fabiano-Tixier, Carine Le Bourvellec, M. The worldwide use of plants for the production of natural extracts has been of crucial importance for human healthcare over the centuries. HIV, antimicrobial, anti-malarial, and hypoglycemic activities. The chemical analysis of jatoba shows that it is rich in biologically active compounds, such as diterpenes, sesquiterpenes, flavonoids, and oligosaccharides.
The high content of phenolic compounds in jatoba bark extracts is due to the presence of condensed tannins, oligomers and polymers formed by the condensation of two or more units of flavonoids, also known as polyflavonoides, that are present in most higher plants. Tannins are known to possess general antimicrobial and antioxidant activities and can also act as an astringent and aid in healing. In traditional medicine, tannins are used in the treatment of various diseases, such as diarrhea, hypertension, rheumatism, stomach problems, urinary system diseases and general inflammations. A previous phytochemical study resulted in the isolation of a number of flavonoids with varied structures. Some of these chemicals, such as copalic acid, delta-cadinene, caryophyllene and alpha-humulene, have reportedly been employed as anodynes, antiseptics, astringents, expectorants, laxatives, purgatives, sedatives, stimulants, and tonics in folk medicine. Many countries are starting to apply strict environmental regulations in almost every aspect of human life due to the growing environmental concerns of society.