Stabilizer also antioxidant

Several CDs applications have been discussed in Chapter 6. Their lack of toxicity forms the basis for their applications in pharmaceutical, agrochemical, and food industries as well as in toiletry and cosmetics [lb, lc]. They are also used or have been proposed to be applied, as sensitizers and stabilizers of dyes in photography, for impregnating paper, as fluorescent and other sensors [28], as corrosion inhibitors and rust proofing materials, UV stabilizers and antioxidants. One of the most spectacular is the prospective use of CDs as biodegradable plastics [29]. The complex of nitroglycerine with p-CDmarketed in Japan was mentioned in Chapter 1 while some other CDs applications have been presented in Chapter 6. 

Used as a thermo/light-stabilizing phenolic antioxidant in the manufacture (compounding and end use) of white, light-colored, and transparent vulcanizates based on natural or synthetic rubber, PS, polyolefins, and pentaplast. Also used in POM and ABS thermoplastics because of its low volatility and migration properties. 

Organotin mercaptide stabilizers also break autoxidation chains, and, compounds of this type are even patented as antioxidants for other plastics. 

EDTA is reported to be effective as the metal ions sequester and is approved for use in the food industry as a stabilizer and antioxidant. It acts also as an inhibitor of Staphylococcus aureus by forming stable chelates in the media with multivalent cations that are essential for cell growth. The effect is largely bacteriostatic and easily reversed by releasing the complexed cations with other cations for which EDTA has higher affinity (Kraniak and Shelef, 1988). 

In the second part of this presentation, we would like to introduce another family of amine stabilizers. Namely, decahydroquinoxalines 3 (R,R =alkyl) which not only show light-stabilizing activity, but also antioxidation properties. 

Other polymerizable ultraviolet stabilizers and antioxidants have also been synthesized and incorporated into polymeric structures. 

Chemical and physical stability also need to be considered. For example, Thoma and Holzmann (1998) showed that dithranol showed a distinct instability in the paraffin base due to light, but was stable when protected from light. In terms of kinetics, Kenley et al. (1987) found that the degradation in a topical cream and in ethanol-water solutions were very similar in the pH range 2-6. This suggested that the degradation of this compound occurred in an aqueous phase or compartment that was undisturbed by the oily cream excipients. If the compound decomposes due to oxidation, then an antioxidant may have to be incorporated. Table 6.8 lists the water soluble and oil soluble antioxidants that can be considered for incorporation into a topical formulation. 

Transparency, in general drops with crystallinity (e.g. polyethylene), and with an increase of crystallite size which causes light scattering. Most fillers, colorants and auxiliary additives lead to opacity. Transmittance depends on the refractive index, so that some fillers may preserve full or partial transparency (translucent). There are also dyes that dissolve in the polymer, so that a colored transparent polymer is produced. It is also possible to find stabilizers (including antioxidants or UV absorbers) that do not affect the polymer transparency. Any chemical change in the polymer like degradation or oxidation, or diffusion of some components, may reduce light transmission. 

Other compounds commonly used in vulcanization, in addition to sulfur and accelerators, are zinc oxide and saturated fatty acids such as stearic or lauric acid. These materials are termed activators (as opposed to accelerators). Zinc oxide serves as an activator, and fatty acids are used to solubilize the zinc into the system. Rubber formulations can also include fillers such as fumed silica and carbon black, and compounds such as stabilizers and antioxidants. Further complicating the situation is the engineering practice of blending various elastomers to obtain the desired properties. 

Automotive tires constitute the classic example of carbon-black reinforced elastomers. The elastomer can be either natural rubber—as typically is the case of truck and aircraft tires, or else a synthetic mbber—as is typical for automobile tires. However, reinforcing fillers constitute only one of many additives. There are also antioxidants, light stabilizers,... 

Absorbers especially 2-hydroxy-4-alkoxy benzophenones Pigments, such as carbon black, also can serve as UV stabilizers. Pheonhc antioxidants, hindered amines, and metal salts are effective in pigmented polyethylene. 

See also antioxidant heat stabilizer ultraviolet stabilizer. 

Cereals are more stable than other foods because they are low in total fat (2-5%) and contain relatively high levels of natural tocopherols (20-50 ppm a-, 13- and /-tocopherols). Cereals are also stabilized by antioxidant products formed during baking by the browning or Maillard reaction. Natural compartmentalization within plant cells and low water activity also contribute to the low susceptibility of cereal lipids to develop rancidity. As in other foods, since flavor deterioration in cereals is caused by minor amounts of lipid decomposition products, the amount of lipid in a product is much less important than its susceptibility to oxidation. 

UV stabilizers are used to prevent or terminate the oxidation of plastics by UV light. They therefore act to protect the moulded product during its life, and are particularly used for building products. They act by absorption of energy, deactivating the by-products of oxidation, and decomposition of by-products (or a combination of these). The action is similar to heat stabilizers and antioxidants, and some types also offer these functions. 

Polymer Stabilizers or Antioxidants. No polychloroprene latex compound is complete without additives that give adequate protection against polymer oxidation. The oxidation studies for dry types also apply to polymers contained in latexes. Hindered phenols are used in many applications. When used at 1-phr,... 

Many sulfur-containing PD antioxidants, especially the metal dithiolates, are very effective long-term thermal stabilizers (also melt and photo antioxidants see later). This versatility in antioxidant action is the direct consequence of their highly effective PD activity (54,105,107,136-140). Moreover, the effectiveness of dithiolate antioxidants, within any one series depends strongly on their solubility in the polymer. For example, in the case of nickel dialkyldithiophosphate (NiDRP, AO 23, Table 3) series, the lower molecular weight members of the series are less soluble, and less effective than the higher members (see Fig. 3) (141). The zinc dialkyl dithiocarbamate (ZnDRC, AO 21) series too show similar behavior (142). 

Since pyrethrins are highly photolytic, antioxidants are often added to preparations to stabilize formulations antioxidants adjoin include pyrocatechol, pyrogal-lol, hydroquinone, and l-benzene-azo-2-naphthol. Practically, all pyrethrins and many pyrethroids are commonly combined to additives (including synergists), some formulations include additional insecticides, insect repellents, or both, and many contain hydrocarbon solvents [3] to enhance their insecticidal activity. Pyrethrin and pyrethroid sprays may also be water based or be alcohol or petroleum based, which increases the overall toxicity. It is known that concomitant use of pyrethrins and pyrethroids with synergists such as piperonyl butoxide, A -octyl bicycloheptene dicarboximide, sulfoxide, sesamin, sesame oil, sesamolin, isosafrole, and organophosphorus compounds or carbamates may increase toxicity by mechanisms involving inhibition of microsomal oxidation [4]. 

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