Antireversion agents

This section provides some laboratory formulation and test data illustrating the effects of the antireversion agent applied in compounds typical of some industrial rubber products (IRPs) (Table 14.48). A more extensive list of potential applications is given at the end of this section. Details are reported by Datta and Ingham [88]. 

Cure characteristics are shown in Figure 14.15 the antireversion agent has no effect on scorch resistance and time to optimum cure. The beneficial effect becomes apparent when reversion occurs, as observed in the control compound. The compound containing the antireversion agent on the other hand maintains a torque level close to the maximum. 

Compared to the previous example, the engine mount formulation contains a cure package tending to an SEV system this will provide a greater degree of reversion resistance compared to a CV cure system. Nonetheless, the antireversion agent is still able to provide significant, additional benefit. 

The important vulcanizate properties demanded by this application, low heat buildup, and low dynamic set have been determined in the Goodrich Flexometer test. The compound containing the antireversion agent exhibits a marked decrease in heat buildup and dynamic permanent set (Figures 14.21 and 14.22). 

Perkalink 900 is also active in compounds based on blends of NR with the synthetic elastomers SBR and BR. An evaluation in a tank pad formulation has provided evidence of reduced heat buildup on overcure overcure is a common problem in the manufacture of these relatively bulky components. The control and test formulations, in which two levels of the antireversion agent have been evaluated, are fisted in Table 14.52. Cure characteristics are given in Table 14.53. 

Although httle advantage is observed with regard to vulcanizate physical properties (Table 14.54), a benefit is apparent in terms of reduced heat buildup (Figure 14.23). In addition, the antireversion agent provides greater thermal stability in terms of blow-out resistance... 

On extended overcure, which can be considered as an anaerobic aging process, the compound containing the antireversion agent exhibits a higher tensile strength as shown in Table 14.57 together with additional physical properties. 

Addition of bis-(3-triethoxysilylpropyl)-tetrasulphide plus accelerator and sulphur can counter loss of crosslinking. Accelerator systems which respond to this antireversion agent are the thiazoles and the sulphenamides. Thiurams do not respond. For cure state equilibrium to be maintained the proportions of the three constituents (sulphur, accelerator and antireversion agent) are adjusted to give a constant modulus. 

Resistance to compound reversion, particularly of natural rubber compounds, has received more recent attention because of the broad range of requirements including faster processing of compounds in production, processing at higher temperatures, and, perhaps more important, extension of product service life. Three antireversion agents have been used commercially ... 

Precaution May form flamm. dust-air mixts. incompat. with strong oxidizers Hazardous Decomp. Prods. CO, CO2, NOx Uses Antireversion agent for rubber vulcanization... 

Biscitraconimides have been studied in recent years as antireversion agents for S-vulcanized rubbers [297-299]. Reversion causes the loss of cross-linking density and properties. It can be brought about by overcure and/or by high temperature applications. The presence of biscitraconimides minimizes this effect by Diels-Alder reaction with the conjugated polyenes which are formed as a result of reversion [300]. 

This section provides information on the property requirements and the best cure systems in compounds typical of some industrial rubber products (IRP). Examples of industrial rubber products and typical polymers used are shown in Table 50. In a recent study the effect of an antireversion agent (Perkalink 900) was also reported (a.45). 

The above compound (Perkalink 900) was shown to be an effective antireversion agent for sulphur-cured diene elastomers. The performance advantages of using Perkalink 900 in butyl rubber (inner tubes, bladders), halobutyl rubber (iimer liners) and nitrile rubber were demonstrated, the aim being to improve the heat resistance of the compounds. A mechanistic interpretation of the chemistry underlying the crosslinking in butyl rubber and halobutyl rubber was provided. 15 refs. 

---