Antidegradant types

Nonstaining antioxidants This ciass of antioxidants is subdivided into four groups phosphites, hindered phenols, hindered bisphenols, and hydroquinones. Hindered bisphenols such as 4,4 -thiobis(6-r-butyl-m-cresol) are the most persistent of the four classes of material. Because of then-lower molecular weight, hindered phenols tend to be volatile. Phosphites tend to be used as synthetic rubber stabilizers, and hydroquinones such as 2,5-di-re t-amylhydroquinone are used in adhesives  

Staining antioxidants Two classes of staining or discoloring antioxidants find extensive use, polymerized dihydroquinoUnes and diphenylamines  

Dihydroquinolines differ in the degree of polymerization, thus influencing migratory and long-term durability properties. They are good 

Antiozonants pura-Phenylenediamines (PPDs) are the only class of antiozonants used in significant quantities. The general structure is  

They not only serve to protect rubber products from ozone but also improve resistance to fatigue, oxygen, heat, and metal ions. The three general categories of paraphenylenediamines are  

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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). 

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. 

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. 

There are also concerns over amines (particularly aromatic amines) and so reducing their concentration is desirable. In common with nitrosamines, they can originate from accelerators. But they also have a number of other important sources, for example, from amine type curatives and as the breakdown products of the amine class of antidegradants. 

Antidegradant is a generic term for an additive that stops the degradation of the finished plastic product. There are several types of antidegradants. The largest class, by far, is antioxidants, and these are included in their own chapter. The following classes are addressed in this chapter. 

These optimum ratios and fatigue life data should not be considered to be universal values. Different recipes, different types of antidegradants, different... 

Additives used in final products accelerator (MTBS) antidegradants (amine type), antioxidant curing agents (ZnO, Zn stearate) fillers (carbon black and mineral fillers, such as silica, clays, talc, whiting), peroxide (e.g. dicumyl) release agent (metal stearates), retarder (MgO) plasticizers (petroleum based oils), sulfur tackifying resins (phenolic, phenol-formaldehyde, phenol-acetylene, hydrocarbon resins UV stabilizer (carbon black) ... 

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