Residual organic peroxides

GC is extensively used to determine phenolic and amine antioxidants, UV light absorbers, stabilisers and organic peroxide residues, in particular in polyolefins, polystyrene and rubbers (cf. Table 61 of Crompton [158]). Ostromow [159] has described the quantitative determination of stabilisers and AOs in acetone or methanol extracts of rubbers and elastomers by means of GC. The method is restricted to analytes which volatilise between 160 °C and 300 °C without decomposition. A selection of 47 reports on GC analysis of AOs in elastomers (period 1959-1982) has been published... 

Applications As the basic process of electron transfer at an electrode is a fundamental electrochemical principle, polarography can widely be applied. Polarography can be used to determine electroreductible substances such as monomers, organic peroxides, accelerators and antioxidants in solvent extracts of polymers. Residual amounts of monomers remain in manufactured batches of (co)polymers. For food-packaging applications, it is necessary to ensure that the content of such monomers is below regulated level. Polarography has been used for a variety of monomers (styrene, a-methylstyrene, acrylic acid, acrylamide, acrylonitrile, methylmethacrylate) in... 

The hydrogen peroxide is extracted with water and concentrated, and the quinone is recycled for reconversion to the hydroquinone. A second organic process uses isopropyl alcohol, which is oxidized at moderate temperatures and pressures to hydrogen peroxide and acetone. After distillation of the acetone and unreacted alcohol, the residual hydrogen peroxide is concentrated. 

For peroxide cross-linking, organic peroxides, such as dicumyl, di-t-butyl, and benzoyl peroxides, are used in amounts 1 to 3 phr (parts per hundred parts of rubber). Typical cure cycles are 5 to 10 min at temperatures 115 to 170°C (239 to 338°F), depending on the type of peroxide used. Each peroxide has a specific use. A postcure is recommended to complete the cross-linking reaction and to remove the residues from the decomposition of peroxide. This improves the long-term heat aging properties.62... 

The subsequent oxidation proceeds with air at 30 to 80°C and pressures up to 5 bar, if necessary after catalyst separation and a precautionary filtration. It can be carried out in CO- or countercurrent mode, in a single step or multistep process. The hydrogen peroxide formed during the oxidation is extracted from the reaction mixture with water e.g. in pulsating packed towers. The extraction yield is ca. 98%. The hydrogen pieroxide solutions obtained are 15 to 35% by weight and must be freed from residual organic compounds before they can be concentrated by distillation. 

Organic peroxides and peroxodisulfates as well as some azo compounds and carbon-carbon compounds are mainly used as initiators in radical polymerization. The production volume of these initiators exceeds 250,000 metric tons. More than 50% of all polymers are made industrially by radical polymerization. Considering that the annual worldwide production of polymers is in the range of 200 Mio metric tons, it indicates that initiators have fundamental importance. The quantity of initiator used varies in a range from 0.01- 5% depending on the process and polymer applied (Fig. 1). Their decomposition products become incorporated or remain as a residue in this large volume of polymers (Fig. 2). 

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