Stabilizer inherent chemical efficiency

Physical mixtures of stabilizers or bifunctional stabilizers represent a very successful exploitation of the knowledge of the inherent chemical efficiency of stabilizers in both intermolecularly and intramolecularly cooperating systems. Moreover, there are data available dealing with the exploitation of transformation products of stabilizes in supporting mechanisms [24]. 

A very limited amount of information deals with the efficiency of polycondensate antioxidants. It was reported [158] that the efficiency of linear phenol-formaldehyde condensates drops in systems containing more than three phenolic nuclei. Similarly, an optimum AO effect was observed with 4-methoxyphenol-formal-dehyde condensates having a molecular weight of 1000 as a maximum [160]. Both reported data [158, 160] deal more or less with the inherent chemical efficiency of stabilizers. The physical persistency was not particularly considered in this case. 

High inherent chemical efficiency of phenolics is a prerequisite for the successful protection of plastics against degradation. It is controlled by the architecture of the stabilizer molecule. Steric hindrance of the phenohc moiety is one of the factors governing antioxidant efficiency. Most hindered phenols contain one tertiary butyl group combined with a methyl group or two tertiary butyls in positions 2 and 6 [3]. Compounds I and II are typical representatives of broad-spectrum antioxidants for plastics. Some phenolic antioxidants have one of the ortho positions (relative to the HO group) unsubstituted. Compounds III-V are examples. 

The general drawbacks are sensitivity to heat, UV, light and weathering, requiring efficient protection for outdoor exposure (stabilized grades are marketed) inherent easy combustion, but FR grades are marketed cost (but justified by the performances) creep when the temperature rises sensitivity to attack by some chemicals. 

Anisidine Value. Anisidine value is a measure of secondary oxidation or the past history of an oil. It is useful in determining the quahty of crude oils and the efficiency of processing procedures, but it is not suitable for the detection of oil oxidation or the evaluation of an oil that has been hydrogenated. AOCS Method Cd 18-90 has been standardized for anisidine value analysis (103). The analysis is based on the color reaction of anisidine and unsaturated aldehydes. An anisidine value of less than ten has been recommended for oils upon receipt and after processing (94). Inherent Oxidative Stability. The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction that occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds contained in the unsaturated fatty acids are the sites of this chemical activity. An oil s oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (C18 3), with three double bonds, is more susceptible to oxidation than linoleic (C18 2), with only two double bonds, but it is ten times as susceptible as oleic (C18 l), with only one double bond. The relative reaction rates with oxygen for the three most prevelent unsaturated fatty acids in edible oils are ... 

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