Antidegradent

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. 

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). 

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. 

Report 79 Rubber Compounding Ingredients - Need, Theory and Innovation, Part I Vulcanising Systems, Antidegradants and Particulate Fillers for General Purpose Rubbers, C. Hepburn, University of Ulster. 

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 ... 

Q-Flex QDI Quinone Diimine Antidegradant—Improved Mixing Chemistry Resulting in a Better Balance of Productivity and Performance... 

Two Pass Mixing—Rotor Configurations and Antidegradant in Masterbatch... 492... 

Several studies characterizing the reactions of alkenyl radicals with quinone dumines and quino-neimines were published in the late 1970s. Quinone dumines react with allylic radicals yielding both the reduced PPD and the alkylated product. In these experiments 2-methyl-2-pentene served as a model olefin (model for NR). Samples of the olefin and quinoneimines or quinone diimine were heated to 140°C. Isolation and analysis of products demonstrated that 40%-70% of the imine or diimine was reduced to the corresponding PPD, while 20%-50% was isolated as the alkylated product. This alkylation reaction (via an allylic radical) represents the pathway to the formation of rubber-bound antidegradant. ... 

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. 

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