EPDM reclaimed rubber is a kind of rubber processed from EPDM scrap rubber and waste EPDM rubber. It can replace EPDM rubber to produce EPDM rubber products and reduce raw material costs. When using EPDM reclaimed rubber to produce rubber products, in addition to the traditional sulfur curing system, many rubber product manufacturers also choose peroxide as the vulcanizing agent of the vulcanization system. The vulcanization process, reaction mechanism, formula design, and performance characteristics of vulcanizates with peroxide-cured EPDM reclaimed rubber are quite different from sulfur-vulcanized EPDM reclaimed rubber.
1. Vulcanization process and vulcanization mechanism
EPDM reclaimed rubber is usually subjected to peroxide cure three processes: peroxide under the action of heat split to form two alkoxy radicals; alkoxy radicals from the polymer chain to take hydrogen Atoms form macromolecular radicals; adjacent two large molecules are radically coupled to form CC crosslinks. When peroxide-vulcanized EPDM rubber compound is used to regenerate the rubber compound, the peroxygen bond in the peroxide is split to form active free radicals, and other reactions are completed in a very short time. The speed and amount of decomposition directly determine the cure rate of EPDM reclaimed rubber.
2, peroxide curing system formula design
Dicumyl peroxide (DCP), benzoyl peroxide (BPO), BPMC, DBPMH, and BIPB are common peroxide vulcanizing agents. Among them, DCP has good storage stability, high activity, and low price. It is a rubber product. The most commonly used curing system. When DCP vulcanized EPDM reclaimed rubber is used, a small amount of co-crosslinking agent such as TAIC can be added to further increase the rubber density of EPDM vulcanizate. The most commonly used reinforcing agent for EPDM rubber/reclaimed rubber products is carbon black. , BPO, DCPB activity is too high, not suitable for the use of carbon black reinforced rubber, so it is not common in EPDM rubber products.
The peroxide-vulcanized EPDM reclaimed rubber vulcanizates have lower tensile strength and wear resistance than sulfur-vulcanized rubbers. Therefore, in the peroxide vulcanization system, it is necessary to use appropriate amounts of multiple bonds or The double bond active agents, such as TAC, TAIC, TATM, etc., further improve the compression set, tensile stress, hardness, tensile strength, heat resistance, etc. of the EPDM vulcanizate, and attention should be paid to such active agents. The amount should not be too much, otherwise it will cause EPDM vulcanizate elongation at break, tear strength decreased, hot tearing properties, scorch safety worse; peroxide curing EPDM regeneration When the glue is easy to produce scorch, adding 0.2-0.3% of the anti-caustic agent BHT peroxide amount can increase the material scorch time and curing rate.
3, peroxide curing system factors
When EPDM recycled rubber products are peroxide-cured, there are many factors that affect the peroxide cure process. Peroxide is very sensitive to acids, and the use of acidic channel acids, such as channel black, white carbon, hard clay, etc., can easily cause cracks or ionic decomposition under the action of acid, inhibit the formation of active radicals, and reduce Oxide cross-linking efficiency; active hydrogen atoms contained in phenolic antioxidants and amine antioxidants will preferentially consume active free radicals. Excessive amounts will affect the formation of macromolecular radicals and reduce peroxide cross-linking efficiency. The problem of insufficient cross-linking of EPDM vulcanizates, especially the antioxidant 4010NA, is commonly selected in peroxide-cured ethylene-propylene rubber formulations for antioxidants RD; benzyl in naphthenic or aromatic process oils Base and allyl hydrogen in the high content of the yard, these hydrogen atoms are more likely to react with alkoxy radicals, severely affect the degree of EPDM curing, so the amount should not be too much, the best control in less than 30, or avoid the use of aromatic oils to manipulate oil Paraffin oil substitute.
The oxygen in EPDM recycled rubber production process will also affect the degree of peroxide cure. In addition to the above issues, there are also attention to the problem of blooming. The use of peroxide cure systems for EPDM reclaimed rubber products is very different from that of vulcanization and sulphur vulcanization. Both have their own advantages and disadvantages. The rubber product manufacturers can also choose the sulphur/peroxide vulcanization system to cure the ternary vulcanization. Ethylene-propylene reclaimed rubber improves the vulcanization process and improves the overall performance of rubber products.