Antioxidants, primary role

When acid chelators are combined with one of the phenolic-type antioxidants, they can act synergistically. This type of synergism has been referred to as acid synergism (S). In this case, the primary role of a chelator is to bind metals, or metalloproteins that promote oxidation and thus, allow the antioxidant to perform its function and capture free radicals. In this manner, acid synergism is different than the BHA/BHT system. 

Fatty acids are the integral part of skin and help to maintain a healthy and youthful skin. Topical application of fatty acids, especially polyunsaturated fatty acids (PUFA) has been proved to have potential impact on skin and hair. Primary role of fatty acids in cosmetic composition is its moisturizing function. Fatty acids function as emollients, which on application to skin form a hydrophobic layer and prevent the water loss from skin, eventually reduce the skin dryness and make the skin smooth and soft. Apart from that, PUFA are powerftil antioxidants and can be used to alleviate oxidative damage associated with sun exposure. They were reported to inhibit collagen breakdown and eliminate aging skin symptoms like wrinkles. 

The primary role of antioxidants is to prevent or inhibit degradation induced by free radical reactions. Antioxidants function via the reactions discussed earlier. The two reactions that are most prevalent in antioxidant function are hydrogen abstraction and metal ion assisted electron transfer. 

The base additive packages required for the stabilization of polyolefins usually comprise combinations of phenolic antioxidants (primary antioxidants, radical scavengers), phosphites or phosphonites (secondary antioxidants) and acid scavengers. The co-operative performance of such an additive combination is certainly influenced by the proper choice and concentration of all individual components. Even acid scavengers can play an important role in melt viscosity retention during processing as well as in the long term stability of the final polymer article. 

Role of Other Antioxidants A great deal has been written about the primary antioxidants, which may be used to inhibit development of WOF. Porter (36) has reviewed these compounds, their structures, and probable modes of action so they will not be discussed. The discussion will focus on the other natural antioxidants that may be useful in controlling WOF development. 

While the primary antioxidant serves a critical role, it cannot stop all polymer peroxy radicals from propagating. This is where a second class of antioxidants, called peroxide decomposers, comes in. These molecules catalyze the decomposition of the peroxides to nonradical species, thus breaking the repetitive cycle of radical formation. Phosphites and thioesters commonly serve as secondary antioxidants. Phosphites are commonly used in HIPS resins, but care must be taken to use hydrolysis-resistant molecules to avoid the degradation of these species into black specks that render the final product unacceptable. Phosphites are usually found at levels between 500 and 2000 ppm. 

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