Peroxide decomposing process

The second antioxidant mechanism, the peroxidolytic or peroxide decomposing process (PD) removes the hydroperoxides (POOH) that are the main source of initiating radicals by reactions that do not produce free radicals. 

Rubber Chemicals. Sodium nitrite is an important raw material in the manufacture of mbber processing chemicals. Accelerators, retarders, antioxidants (qv), and antiozonants (qv) are the types of compounds made using sodium nitrite. Accelerators, eg, thiuram [137-26-8J, greatly increase the rate of vulcaniza tion and lead to marked improvement in mbber quaUty. Retarders, on the other hand (eg, /V-nitrosodiphenylamine [156-10-5]) delay the onset of vulcanization but do not inhibit the subsequent process rate. Antioxidants and antiozonants, sometimes referred to as antidegradants, serve to slow the rate of oxidation by acting as chain stoppers, transfer agents, and peroxide decomposers. A commonly used antioxidant is A/,AT-disubstituted Nphenylenediamine which can employ sodium nitrite in its manufacture (see Rubber chemicals). 

The thermal decomposition of diacyl peroxides has been the most frequently employed process for the generation of alkyl radicals. The rate and products of the unimolecular decomposition of acetyl peroxide have been the subject of many studies. Acetyl peroxide decomposes at a convenient rate at 70-80°C both in the solution and in the gas... 

The early work of Kennerly and Patterson [16] on catalytic decomposition of hydroperoxides by sulphur-containing compounds formed the basis of the preventive (P) mechanism that complements the chain breaking (CB) process. Preventive antioxidants (sometimes referred to as secondary antioxidants), however, interrupt the second oxidative cycle by preventing or inhibiting the generation of free radicals [17]. The most important preventive mechanism is the nonradical hydroperoxide decomposition, PD. Phosphite esters and sulphur-containing compounds, e.g., AO 13-18, Table la are the most important classes of peroxide decomposers. 

We can also produce direct crosslinks by the action of peroxy radicals, as shown in Fig, 18.8. In this process, we blend an organic peroxide, such as dicumyl peroxide, into molten polyethylene at a temperature below that at which the peroxide decomposes. Once we have formed the molten blend into the required shape, we increase its temperature until the peroxide decomposes into peroxy radicals, as shown in Fig, 18.8 a). The peroxy radicals abstract hydrogen atoms from the polyethylene chains to create free radicals, as shown in Fig. 18.8 b). Crosslinking takes place when two radicals react to form a covalent bond, which is shown in Fig. 18.8 c). 

Peroxide cure systems, in rubber compounding, 22 793-794 Peroxide decomposers, 3 111-114 Peroxide decomposition, 24 279-280 Peroxide formation, by VDC, 25 694. See also Hydrogen peroxide Peroxide initiators, 23 379-380 worldwide producers of, 24 303 Peroxide-ketazine process, 23 582-583 flow sheet for, 23 582 versus Raschig process, 23 583 Peroxide linkages, in VDC polymer degradation, 25 713... 

Scheme 2 Schematic presentation of the cyclical oxidation process and some of the main reactions/products formed from the propagating radicals. The antioxidant mechanisms interrupting the oxidative cycles are also shown. AO antioxidant, CB-A chain breaking acceptor, CB-D chain breaking donor, PD peroxide decomposer, UVA UV-absorber, MD metal deactivator...

New phenolic phosphites prepared from dihydric phenols and phosphorus halides prevent degradation of polypropylene by heat, oxidation, processing, and ultraviolet radiation. These products are active and synergistic with dithiopropionate esters. They seem to function as both free radical scavengers and peroxide decomposers. 

Here we discuss a new class of polypropylene stabilizers—the polymeric phenolic phosphites. These compounds exhibit unique, broad-spectrum activity which may allow simplification of polypropylene stabilizer systems. The most active species are synergistic with thiodipro-pionate esters, are effective processing stabilizers when used alone or with other compounds, and contribute to photostability. Compounds of this type appear to function as both free radical scavengers and peroxide decomposers, and through a mechanism not yet completely understood, allow significant reductions in the concentration of ultraviolet absorbers required to achieve high levels of photostability. 

Although it is evident from the above studies that the dithiocarbamate uv stabilisers function primarily as peroxide decomposers and only to a minor extent at uv absorbers, it is not clear to what extent they act as triplet quenchers. In the case of NlOx, it is known that this is not a hydroperoxide decomposer (37) and this is confirmed in Figure 11 which shows that it does not inhibit thermal oxidation to carbonyl and unlike NiDBC, its main effect in uv degradation is to retard the photo-oxidation process. In order to study the behaviour of these complexes in photo-... 

Decomposes peroxides during processing and reduces acivity of catalyst residues which reduces peroxide formation. Suitable for polyolefins as well as other plastics, elastomers, and adhesives. 

Secondary liquid phosphite antioxidant that functions as a peroxide decomposer and as a processing stabilizer in a wide variety of polymers, including polyolefins and styrenics. 

When a peroxide P is heated to 60°C in an inert solvent it decomposes by a first order process and 20% of the peroxide decomposes in 60 min. A bulk monomer is polymerized using this initiator at 60°C, the initial concentration of the letter being 4.0x10" mol/L. What fractions of the monomer and the initiator should remain unconverted after 10 min At 60°C, the system parameters are k /kt = 22.34 L mol", / = 0.8. 

Finally, peroxide decomposers can decompose hydroperoxides in a nonradical process to interfere with Reaction 4. 

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