دانلود کتاب Databook of Antioxidants

In general terms, the antioxidants are expected to protect status quo by prevention of oxidation. Oxidation is a chain reaction involving free radicals and hydroperoxide intermediates. Antioxidants act by reacting and decomposing free radicals and hydroperoxide intermediate species. In polymeric materials the oxidative changes may lead to a number of undesirable effects, including discoloration, changes in melt viscosity, and deterioration of mechanical properties, impacting useful life of a polymer or a final article. Plastics are susceptible to oxidative degradation during high-temperature melt processing operations and their end-use, as well as during long-term storage. Also, the oxidation processes are accelerated by exposure to UV radiation of sunlight.Antioxidants are likely to form the most crucial protective barrier for cells of living organisms against the effects of free radicals. If these processes are not adequately controlled, they lead to outcomes dangerous to wellbeing because the cancerous cells multiply with accelerating rates. Radical formation on ultraviolet light exposure leads to changes in human skin such as the formation of dark spots, lesions, and frequently skin cancer if radical processes are not stopped by preventive measures, such as UV radiation filtration and use of antioxidants.In similar reactions to oxidation, food and pharmaceutical products deteriorate faster, which can be prevented by small additions of antioxidants. Food products lose their nutritive value and may drastically change color and flavor. Pharmaceutical products become inactive and potentially toxic. In summary, the antioxidants form the most important group of compounds aiming at retardation of deterioration of organic materials and keeping living cells in their original conditions, which is the most common means to a healthy life.Antioxidants are typically divided into primary and secondary antioxidants. Primary antioxidants, such as hindered phenols, function mainly by scavenging the peroxy radical intermediates formed in the oxidation processes. They are effective over a wide temperature range, improving both the processing and long-term thermal stability of materials. Secondary antioxidants, such as phosphites and thioethers, function by decomposition of hydroperoxides. Phosphites are most effective at the high temperatures of melt processing operations, while thioethers operate best in the solid phase at long-term use temperatures.In modern applications, synthetic antioxidants are slowly being replaced by products obtained from renewable resources, mostly of plant origin. This conversion in the area of cosmetics, medicine, pharmacy, food additives, and food protection is very advanced. In polymer processing, application of natural antioxidants is still on the development stage.Considering the importance of antioxidants in medicine, cosmetics, pharmacy, food processing, this book gives the selection of both important synthetic and natural products, stressing on the commercially viable additives and most recent interest in the application and use of natural products.The antioxidants included in this book belong to many groups of chemical products including acids and their esters, amines, anthocyanidines, ascorbates, benzofuranones, benzoimidazoles, benzoquinones, biopolyphenols, carotenoids, coumarines, enzymes, flavonoids, hydrazide metal deactivators, hydroquinidines, hydroquinones, hydroxylamines, isoflavones, lignanamides, liposomes, peptides, phenolics, phosphites, phospholipides, polyphenols, polysaccharides, sterically hindered phenolics, sulfur-containing compounds, tannin derivatives, terpenoids, thioethers, tocopherols, and quinolines.