Antidegradants antiozonants

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. 

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). 

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. 

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). 

Over half of the remaining market for products used in the processing of rubber is made up of antioxidants, antiozonants and stabilizers, either amino compounds or phenols. Aniline is used to manufacture vulcanization accelerators, antioxidants and antidegradants. Of the latter, several are A-substituted derivatives of p-phenylenediamine and octyl dipheny-lamine. Diphenylamines terminate free-radical reactions by donating the amino hydrogen, and are used to protect a wide range of polymers and elastomers. Many synthetic rubbers incorporate alkylated diphenylamine antioxidants. Other antioxidants include aryl amine resinous products from, e.g. condensation of aniline and acetone in the presence of... 

Vulcanised rubber has for many decades, been stabilised by p-phenylene diamines (PPD), as antioxidant and antiozonant. However, traditional PPD tend to migrate to the surface and discolour non-carbon black vulcanisates, as they are capable of extraction from the rubber and volatile. In general, all amine antidegradants are soluble in water and need special precautions and environmental labelling. 

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. 

Solubility Low solubility of an antidegradant will cause the material to bloom to the surface, with consequent loss of protection of the product. Therefore, solubility of antidegradants, particularly antiozonants, controls... 

Concentration Most antidegradants have an optimum concentration for maximum effectiveness after which the materiai soiubiiity becomes a iimiting factor./jura-Phenyienediamines offer good oxidation resistance at a ioading of 0.5-i.0 phr and antiozonant protection in the range of 2.0-5.0 phr. Above 5.0 phr /jura-phenyienediamines tend to bioom. 

Solubility Low solubility of an antidegradant will cause the material to bloom to the surface, with consequent loss of protection of the product. Therefore, solubility of antidegradants, particularly antiozonants, controls their effectiveness. The materials must be soluble up to 2.0phr, must be able to migrate to the surface, but must not be soluble in water or other solvents such as hydraulic fluid so as to prevent extraction of the protectant from the rubber. 

The PPD class of antidegradants provides by far the best antiozonant protection (for a review of antiozonants, see Reference 82). PPDs inhibit ozone degradation of rubber by multiple mechanisms (76,83-85) ... 

Antidegradants including waxes, antiozonants, antioxidants, and prevulcanisation inhibitors are also necessary for good processability and performance of rubbery parts. Unfortunately, these materials are also had for adhesion because they can also migrate to the rubber surface and interfere with crosshridging reactions. The lowest possible amount of these materials necessary to get acceptable part performance without causing blooming to the surface of the rubber is preferred. 

N,N -Dibutylthiourea is a nitrosamine free accelerator, antidegradant, and corrosion inhibitor. Ultra-accelerator for mercaptan-modified CR. It is slightly safer than DETU. It is also used as a secondary accelerator for NR and synthetic rubbers. It disperses easily in rubber. It is non-staining and does not bloom. It is practically odorless. Antioxidant for NR, antiozonant for NR and SR, particularly SBR. 

Halobutyl rubbers with almost completely saturated backbones usually do not require extra antioxidants or antiozonants the rubber producer adds traces of stabilizers. For severe service circumstances, particularly in blends with unsaturated rubbers, the addition of some antidegradant may be necessary. In the selection of any antidegradant care should be exercized, particularly regarding amine derivatives that may interfere in the crosslinking process, but with proper technology vulcanizates with enhanced stability may be obtained [103]. Ozone resistance and weathering behavior of halobutyl rubber vulcanizates are also dependent on the curing system, on the nature and amount of fillers and plasticizers. 

In rubber compounding the term antidegradant is commonly used for any substance that is added to retard the deterioration of the vulcanized compound under service conditions. This deterioration, most often a result of chemical attack, results in a progressive loss of functional properties and a decrease in service lifetime of a rubber article. The three principal agents attacking rubber and causing its deterioration are oxygen (O2), ozone (O3), and ultraviolet radiation. Virtually all antiozonants used in rubber also act as antioxidants however, many antioxidants do not act as antiozonants. 

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. 

Antiozonants are a very large part of the rubber antidegradant market. Many times antiozonants are used together with antioxidants in rubber compounds to achieve the best synergistic protection from oxidative degradation while the rubber product is in use. Virtually all chemical antiozonants can act, at least to some extent, as antioxidants. 

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