Antidegradants antioxidants

Plasticisers in rubbers are usually at high concentrations, and although concentrations of antidegradants (antioxidants and antiozonants) are much lower, they are all very critical in food contact rubber products. 

Antidegradants. Amine-type antioxidants (qv) or antiozonants (qv) such as the phenylenediamines (ppd) can significantly decrease scorch time. This is particulady tme in metal oxide curing of polychloroprene or in cases where the ppd had suffered premature degradation prior to cure. 

Selection of Proper Antidegradant. Because the various antioxidants function by different mechanisms, an antioxidant under one condition may become an oxidation promoter in a different condition. Therefore, an antioxidant should be carefully selected depending on service requirements. Most antioxidants are either amines, phenols, or phosphates. The following are some important properties in the selection of proper antidegradant that should be considered. 

It is difficult to find a single material that meets ah. requirements of a product. Consequently, quite often blends of antioxidants are used. Table 15 provides a summary of characteristics of commercially important antidegradants (39). 

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 above-described issues are the reasons for an increased interest in the synthesis of new antioxidants with the possibility to graft to the polymer backbone or to form polymeric or oligomeric antidegradants. In the last two decades, several approaches have been evaluated in order to develop such new antioxidants ... 

A-l,3-dimethylbutyl-A -phenyl quinone diimine (6QD1) has been introduced as a multifunctional additive for diene rubbers and provides an advantage in mixing characteristics (functions as peptizer and improves scorch safety) as well as improved performance (better antioxidant activity than paraphenylenediamine antidegradants) of the end products [36]. 

Plasticiser/oil in rubber is usually determined by solvent extraction (ISO 1407) and FTIR identification [57] TGA can usually provide good quantifications of plasticiser contents. Antidegradants in rubber compounds may be determined by HS-GC-MS for volatile species (e.g. BHT, IPPD), but usually solvent extraction is required, followed by GC-MS, HPLC, UV or DP-MS analysis. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out. The determination of antioxidants in rubbers by means of HPLC and TLC has been reviewed [58], The TLC technique for antidegradants in rubbers is described in ASTM D 3156 and ISO 4645.2 (1984). Direct probe EIMS was also used to analyse antioxidants (hindered phenols and aromatic amines) in rubber extracts [59]. ISO 11089 (1997) deals with the determination of /V-phenyl-/9-naphthylamine and poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ) as well as other generic types of antiozonants such as IV-alkyl-AL-phenyl-p-phenylenediamines (e.g. IPPD and 6PPD) and A-aryl-AL-aryl-p-phenylenediamines (e.g. DPPD), by means of HPLC. 

Table 2.3 as a completely worked out example using quantitative solvent extraction, ash content determination, TGA, FTIR, XRF, GC-MS, HS-GC-MS, PyFTIR, ICP, and s-NMR. Information on the cure and antidegradant systems was obtained (assigned species/possible origin), as follows cyclohexane thiol/CBS accelerator benzothiazole/MBT, MBTS or CBS accelerators N, A-dimethylformamide/TMTD accelerator phthalim-ide/Santoguard PVI and IV-phenylbenzene amine/possi-bly a diphenyl/acetone amine antioxidant. 

ASTM Standard D 3156-81, Thin-layer Chromatographic Analysis of Antidegradants (Stabilizers, Antioxidants and Antiozonants) in Raw and Vulcanized Rubbers, Annual Book of ASTM Standards, ASTM, Philadelphia, PA (1990). 

Metal deactivation, in antidegradant selection, 22 787 Metal deactivators antioxidants, 3 115 in gasoline, 22 407 for lubricating oil and grease, 15 221 Metaldehyde, 2 103... 

See also Tire compounding antidegradants in, 21 785—790 antioxidants in, 21 789 butyl and halobutyl rubber in, 21 766 elastomers used in, 21 759—772 ethylene-propylene rubber in, 21 765-766... 

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