Antioxidants and stabilizers

It will be evident from the above that, in the case of polymers containing a carbon-carbon backbone (PE, PP, polystyrene (PS), polyvinyl chloride (PVC) etc.), oxidation must precede biodegradation [19]. From this it follows that the control of oxidation during exposure of the polymer to the environment may be used to control biodegradation. 

is the usual termination step [16]. However, at low oxygen pressures, for example in a screw extruder where oxygen access is physically restricted, then reactions f and g become important in terminating the chain reaction [16]. 

Hindered amines (Active agent is the corresponding nitroxyl) 

CB-D class (see Table 1.1), whereas nitroxyl radicals (formed in situ from the hindered amines, e.g. Ill), stable phenoxyl radicals (e.g. IV), and quinones (e.g. V) (formed by oxidation of phenols), fall into the second class [20]. However, although CB-D antioxidants terminate the chain reaction, they produce further hydroperoxides in the process which, particularly in the presence of light and transition metal ions or at high temperatures, reinitiate the oxidation cycle, see reaction (1.2). Under these very severe conditions, a complementary class of antioxidants is frequently used. 

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Many hydrazones and azines are colored and useful as dyestuffs. Examples are 2-hydroxynaphthazine, a yellow fluorescent dye (Lumogen LT Bright Yellow), and the pyridon—azino—quinone class of red-violet dyes. Numerous hydrazine derivatives are antioxidants and stabilizers by virtue of their reducing and chelating powers. 

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

Polyvinyl chloride (PVC) Good Yellows. Antioxidants and stabilizers... 

Substituted phenols such as cresols, p-fcrf-butylphenol, / -phcnylphenol, resorcinol, and cardanol (derived from cashew nut shells) have also been used as precursors for phenolic resins. Alkylphenols with at least three carbons in the substituent lead to more hydrophobic phenolic resins that are compatible with many oils, natural resins, and rubbers.7 Such alkylphenolic resins are used as modifying and crosslinking agents for oil varnishes, as coatings and printing inks, and as antioxidants and stabilizers. Bisphenol-A (2,2-p-hydroxyphenylpropane),... 

Parenterais The most important criterion for parenterals is that they have to be sterile for injection or infusion administration. Excipients are added to make parenterals isotonic with blood, improve solubility, and control pH of the solution. The solvent vehicles include water-for-injection, sterile sodium chloride, potassium chloride, or calcium chloride solution, and nonaqueous solvents such as alcohol, glycol, and glycerin. Preservatives, antioxidants, and stabilizers are normally added to enhance the properties of the drug product. 

Applications and Formulation. Pressure-sensitive adhesives are most widely used in the form of adhesive tapes. The general formula for a pressure-sensitive adhesive includes ail elastomeric polymer, a tackifying resin, any necessary fillers, various antioxidants and stabilizers, if needed, and cross-linking agents. 

A very interesting field in membrane bioreactors is the production of cyclodextrins or oligosaccharides. In general, they have applications in food pharmaceutical, cosmetic agricultural, and plastics industries as emulsifiers, antioxidant, and stabilizing agents. In the food industry cyclodextrins are employed for the preparation of cholesterol-free products. The use of enzymatic membrane reactors to produce... 

Al-Malaika S (1989) Effects of antioxidants and stabilizers. In Comprehensive polymer science, Vol 6, Polymer reactions, Eastmond G C, Ledwith A, Russo S and Sigwalt P (Eds), Pergamon Press Oxford, pp 539-578. 

Other Uses for Aniline. Aniline currently is used as a raw material in most of the major groups of rubber-processing chemicals accelerators, antioxidants and stabilizers, and anti-ozonants. The most important of these are the thiazole derivatives and substituted para-phenylenediamines. The demand for aniline in these rubber-processing uses is expected to grow at less than 1 percent/year. In agricultural chemicals, the major use for aniline is as a raw material in the manufacture of amide herbicides for controlling annual... 

Hydroxy-4-n-octoxybenzophenone is an effective photostabilizer for a variety of plastic systems. It may be used in food packaging materials as an antioxidant and stabilizer and in addition may be used as a stabilizer in petroleum wax. When used in packaging materials, it prevents UV-radiation from reaching the stored product and increases the stability of the container. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Flexzone [Uniroyal]. TM for a series of an-tiozonants, antioxidants, and stabilizers based on p-phenylenedi amine. 

HALS exhibit a complex behavior when present in combination with other antioxidants and stabilizers. Effective synergism in both melt and thermal stabilization has been achieved when secondary and tertiary HALS were used in combination with both aromatic and aliphatic phosphites the synergistic optimum depends on the structure of the phosphite. HALS also synergize the action of UV-absorbers, e.g., benzo-triazoles, in different polymers such as polypropylene, polystyrene, and ABS. " ... 

Antioxidants and stabilizers are generally used in the chemical processing industry for the protection and preservation of properties of materials, including food, with the aim of prolonging and extending their shelf life. They are essential ingredients for the long-term durability of many polymers, such as... 

Antioxidants and stabilizers are chosen for target applications on the basis of chemical, physical, toxicological, and economic factors. The final selection of an antioxidant package must take into consideration the performance requirements of the end-use polymer article including toxicity, compatibility, appearance, and color. Issues of efficacy and safety have been the driving force behind much of the recent progress made in the areas of biological, reactive, and macromole-cular antioxidants. 

Scott, G. Mechanochemical modification of polymers by antioxidants and stabilizers. In Developments in Polymer Stabilisation Scott, G., Ed. Elsevier Applied Science London, 1987 Vol. 8, 209-238. 

Effects of Antioxidants and Stabilizers on Dehydrochlorination of Chemically Crosslinked CPE at 150°C in Nitrogen. 

Since the dehydrochlorlnation was conducted in nitrogen, the antioxidant system alone had no effect on the dehydrochlorlnation rate. However, the combined antioxidant and stabilizer system had an appreciable effect on peroxide crosslinked CPE, giving rise to an induction period of 105 hours when Dicup was used for crosslinking and 90 hours when Dlcup emd TMPT were combined to crosslink the polymer. The muimum rate of dehydrochlorlnation was also appreciably reduced from 55x10 to 3.1x10 mg. eq. HCl/g. polymer-hour due to the incorporation of the stcd>lllzer... 

The reasons for the present interest in polymer-bound antioxidants is discussed, and some of the more important approaches to the chemical attachment of antioxidants and stabilizers to polymer molecules are briefly reviewed. 

Other areas where physical loss of additives from polymers is increasing in importance is in food contact applications and in medical uses of polymers. In Europe, legislation is steadily moving toward the situation where loss of any additives, irrespective of their toxicity, may be prohibitive above a certain level. It is, therefore, no longer an academic exercise to retain antioxidants and stabilizers in polymers merely to satisfy unrealistic accelerated tests. It is a practical necessity to improve the substantivity of antioxidants and stabilizers for a variety of quite different practical reasons. 

A hybrid antioxidant of new generation - ichfan is suggested for the therapy of membrane-pathologies associated with neurodegenerative diseases. It was shown that the compound applied in a wide range of concentrations modifies the properties of erythrocyte membranes and cells of Ehrlich ascitic carcinoma and changes the functional state of cells. Incorporated in the lipid phase and near-protein lipids of membranes, the antioxidant affects the structural state of the lipid bilayer, the structure and functional activity of proteins, in particular, the functions of ionic channels. Recommendations were made as to the compound doses responsible for the pronounced antioxidant and stabilizing effects and the absence of unfavorable side-effects. 

Boskou, D. (1999) Non-nutrient antioxidants and stability of frying oils, in Frying of Food (eds D. Boskou and I. Elmadfa) Technomic Publishing Co, Inc., Lancaster, pp. 183-204. 

Addition of Stabilizers Such as Antioxidants and Stabilization through the Use of Packaging... 

Ethanox . [Ediyl] Antioxidant and stabilizer for plastic, resin, rubber, adhesives, petroleum oil, and wax. 

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