Antidegradant use

Rubber processed in latex form accounts for about 10% of new mbber consumption. Rubber latex is a Hquid, oil-in-water emulsion which is used to make foam or thin-walled mbber articles. The same accelerators and antidegradants used in dry mbber are used in latex, with longer-chain versions preferred for greater oil solubiHty. To prepare these and other additives for addition to latex, they must be predispersed in water and the surface of the powder or oil droplet coated with a surface-active agent to prevent destabilization (coagulation) of the latex. 

The unit power to mix can be generally described as a function of the rotor surface area, the RPM used during mixing, the time required to reach dump temperature for the first pass mix, and a treatment for the type of antidegradant used. Again the discrete variable of antidegradant was treated continuously by assigning the values of 0, 1, and 2 to the conditions of Ctrl, PPD, and QDI. 

A03038 An investigation of the breakdown products of curatives and antidegradants used to produce food contact elastomers. 

Table 15. Representative Amine Antidegradants Used in Rubber... 

Antiozonants are special antidegradants used by the rubber industry to protect cured rubber articles from attack by atmospheric ozone, which can be particularly potent if the rubber is unprotected. Those elastomers (NR, SBR, BR, and so on) with carbon-carbon double bonds in the polymer chain are the most susceptible to ozone attack. Ozone attack is more acute with rubber articles that in service are undergoing rapid and repeated deformation (flexing). This attack is worst when the deformation is elongation, and it manifests itself in the formation of surface cracks in the rubber. In service, these cracks will progressively grow and finally result in premature failure of the rubber article. Though observed and suffered for more than a century, this problem was only understood and remedied in the mid-twentieth century. 

Aniline can react with hydrogen chloride to form an aniline hydrochloride intermediate that is used to produce diphenylamine, the base feedstock for production of ADPA, octylated diphenylamine, 6PPD, and DOPD antidegradant used by the rubber industry. These are some of the highest volume AOs used by the rubber industry. 

Polymer compoimds invariably contain antidegradents. These are generally further divided into antioxidants and anti-ozonants. The major group of antidegradents used in elastomers is composed of phenylene diamines, which have the structure ... 

For polyolefins, the primary antidegradents used are again alkylarylamines, and hindered phenols [156]. 

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). 

As with almost all mbbers, the final properties are deterrnined by compounding and subsequent vulcanization or cross-linking. Various fillers, processing aids, plasticizers, tackifiers, cure systems, and antidegradants are used. 

Several of the commonly used rubber chemicals tike accelerators, retarders, antidegradants, etc. are classified as hazardous on account of values of LD50 (lethal dose 50%) [6]. Many of the guanidine... 

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. 

Any substance used to prevent premature coagulation of rubber latex the commonest are ammonia, sodium sulphite and formaldehyde. Antidegradant... 

Gas chromatography-mass spectroscopy is used to obtain extensive compositional information on rubbers. It can identify minor components of the sample such as the breakdown products of the cure system and the antidegradants. 

Antidegradants known to be suitable for use in combination with peroxide crosslinking systems are thiophosphatcs. / -phenylenediamines and modified triazines. 

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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