Commercially, Evatane^® EVA, poly(ethylene-co-vinyl acetate), is crosslinked with select organic peroxides for use in semi-conductive and low voltage insulation wire & cable, in automotive sound damping crosslinked foam, and in crosslinked athletic, casual, and industrial boot soles [i] , among other uses. Evatane^® EVA is produced by Arkema Inc. and is available in several grades ranging from 18% to 42% vinyl acetate [ii]. Engage^® EOM poly(ethylene-co-octene) is also crosslinked with select organic peroxides and is used in many of the same applications served by EVA. Engage^® is produced by Dow Chemical and is available in a wide range of different compositions and densities.

An 80:20 ratio of EVA and EOM was crosslinked with 1.5 phr of F40P-SP2 and compared with an equal weight of F40KE. (Please refer to Table 9.) F40P-SP2 provides equivalent crosslinking efficiency versus F40KE with a significant 27% increase in ts2 scorch time protection at 175°C (347°F). The ts2 scorch time increased from 0.82 minutes to 1.04 minutes to provide more mold fill, especially for thicker injection molded soles and compression molded foamed slabs. At the 130°C compounding temperature, F40P-SP2 provided a huge 155% increase in the t5 Mooney scorch time from 22.1 minutes to 56.2 minutes.

The use of select coagents with the peroxides and SP2 technology can help to further tailor the level of crosslinking, cure rate and compounding performance. In Table 9 we show data for the evaluation of a blend of 1.0 phr F40P-SP2 and 0.2 phr triallyl cyanurate (TAC). TAC is well known as an efficient coagent for HDPE, LDPE, LLDPE and various polyethylene co- and terpolymers, like EVA, EOM and EPDM. This F40P-SP2 and TAC coagent blend provided a 34% increase in ts2 scorch time at 175°C, versus a 27% increase when using F40P-SP2 without the TAC. Furthermore, there was a desirable 18% decrease in the tc90 cure time at 175°C, from 8.25 minutes to only 6.76 minutes, when using this peroxide and coagent blend. This translates to an 18% improvement in productivity. The t5 Mooney scorch time at 130°C was further increased from 56.2 minutes to 66.6 minutes for the F40P-SP2 and TAC blend, compared to F40P-SP2 without TAC.

By selecting from the well-known [iii] acrylic, methacrylic, allylic, polybutadiene and N,N’-(m-phenylene)bismaleimide [iv] crosslinking coagents and using them in blends with the SP or SP2 peroxide technology, it is possible to tailor the desired level of crosslinking, the cure rate and the scorch time performance, when crosslinking and compounding the various elastomers described above.

In summary, a blend of F40P-SP2 and TAC provides good crosslinking of EVA-EOM, with superior scorch time protection at 175°C for better mold filling and a shorter tc90 cure time, for improved productivity, versus F40KE. We have shown that compounding EVA-EOM at 130°C with this cure system, provides a dramatic 200+% increase in the t5 Mooney scorch time versus F40KE for potential cost savings by reducing the compounding time via a faster mixer speed or by going from a two-pass to a one-pass compounding operation.