Peroxide Cure Systems

Peroxide curing systems Peroxide decomposers Peroxide initiators Peroxides... 

Heat resistance is iafluenced by both the type and extent of cure. The greater the strength of the chemical bonds ia the cross-link, the better is the compound s heat resistance. Peroxide cure systems, which result ia carbon—carbon bonds, result ia a range of sulfur cross-links varyiag from 1 to > 30 sulfur atoms per cross-link, and heat resistance improves as the number of more thermally stable short cross-links predominates. This is an important factor ia designing the desired cure system. 

Peroxide curing systems are generally the same for CSM as for other elastomers but large amounts of acid acceptor must be present to complete the cure. A small amount of a polyfunctional alcohol, ie, pentaerythritol (PER) in the compound significantly reduces the amount of base required by acting as a solubiHzer. TriaHyl cyanurate [101-37-17 is an additional cure promoter and leads to higher cross-link density. 

Bromine- and iodine-containing fluoroolefins have been copolymerized with the above monomers in order to allow peroxide cure (14—21). The peroxide cure system does not requite dehydrofluorination of the polymer backbone, resulting in an elastomer that shows improved properties after heat and fluid aging. 

Internal mixing is widely used with fluorocarbon elastomers. Gumstocks and compounds that are particularly successful fall in the viscosity ranges discussed earlier, and use both incorporated bisphenol-type and peroxide cure systems. A typical internal mix cycle mns 6—8 min with a drop temperature of 90—120°C. The typical formulations in Tables 4 and 7 are readily mixed in an internal mixer. 

There are no known practical peroxide cure systems for the PO—AGE polymers. Apparentiy the peroxide attacks the polymer backbone at a rate that is unfavorably competitive with the cross-linking rate. A typical sulfur cure system consists of zinc oxide [1314-13-2] tetramethylthiuram mono sulfide (TMTM), 2-2-mercaptobenzothiazole [149-30-4] (MBT), and sulfur. A sulfur donor cure system is zinc oxide, di-o-tolylguanidine [97-39-2] (DOTG) and tetramethylthiuram hexasulftde. 

Interestingly, later grades of Vamac to become available did not employ the cure site monomer, using instead a peroxide-curing system. Some of these copolymers also contained higher levels of methyl acrylate (up to 69%) to enhance the oil resistance. 

Figure 8 shows the SEM images with a low level of strain (50%). It is clear that even with a low-strain level defects are initiated in the sulfur cured system with the formation of large cracks at the boundary layer between the two phases. However, in the peroxide cured system the mechanism of crack initiation is very different. In the latter case the NR-LDPE interface is not the site for crack initiation. In this case, stress due to externally applied strains is distributed throughout the matrix by formation of fine crazes. Furthermore, such crazes are developed in the continuous rubber matrix in a direction... 

Elastomeric composition for dynamic application of cross-linked E-plastomers has been made with filer-reinforced systems which contain a metal salt (typically zinc) of an alpha, beta unsaturated acid. These additives improve the tensile and tear strength of the elastomer and are cured with a peroxide cure system. These cross-linked articles are suitable for dynamic loading applications such as belting, including power transmission and flat belting. 

Peroxides vulcanization of EPDM is growing in popularity because of enhanced aging resistance. A comparison of sulfur- and peroxide-cure system is shown in Table 14.31 [53]. 

The tensile strength of NR compounds in the presence of cross-link promoters such as dichlorobenzene is increased as compared to the sulfur-accelerator and peroxide-curing systems. The retention of the maximum tensile strength at elevated temperamres is greater for radiation cured than for chemically vulcanized NR [326,327]. Also reported are a higher abrasion resistance [328] and a lower flex life in the case of radiation-cured system. Effect of phenoxy ethyl acrylate (PEA)... 

Crosslinking time is directly dependent on the rate of decomposition of the peroxide. The effectiveness of the overall crosslinking reaction is thus dependent on the type of peroxide and polymer radicals produced during the process. Cure time and temperature can, in a peroxide cure system, be determined solely from knowledge of the rate of peroxide thermal decomposition. 

Peroxide cure systems, in rubber compounding, 22 793-794 Peroxide decomposers, 3 111-114 Peroxide decomposition, 24 279-280 Peroxide formation, by VDC, 25 694. See also Hydrogen peroxide Peroxide initiators, 23 379-380 worldwide producers of, 24 303 Peroxide-ketazine process, 23 582-583 flow sheet for, 23 582 versus Raschig process, 23 583 Peroxide linkages, in VDC polymer degradation, 25 713... 

Peroxidic cure systems are applicable only to fluorocarbon elastomers with cure sites that can generate new stable bonds. Although peroxide-cured fluorocarbon elastomers have superior heat resistance, their difficult processing has been an obstacle to their wider use for years. Only recent improvements in chemistry and polymerization are offering more opportunities for this class of elastomers.32... 

NR/modified EPDM, in which EPDM was modified by pendant sulfur, exhibited improved endurance to repeated stress over that of covulcanized EPDM-NR mbber blends (68). The effects of ethylene and diene contents in EPDM, blend ratio, dicumyl peroxide curing system on the physical properties, interfacial adhesion force, and dynamic crack growth were examined (69). As the ethylene and diene contents in EPDM increased, the physical properties, such as dynamic cut growth, adhesion to other component were also increased. The mechanical properties of the blends are compared to those of the pure components in Table 15.3 (56). The ultimate tensile strength of noncompatibilized blends is lower than that of pure NR, as expected since these blends are incompatible. 

The polyester alkyd molding compositions are also based on a polyester resin similar to those used for laminating. (The term alkyd is derived from alcohol and acid.) They are prepared by blending the resin with cellulose pulp, mineral filler, pigments, lubricants, and peroxide curing systems on hot mills to the desired flow properties. The mix is then removed, cooled, crushed, and ground. 

Uses Curing agent for radiation and peroxide cure systems incl. acrylics, adhesives (pressure sensitive, structural), coatings (glass, metal, optical, paper, PVC floor, release, textile, wood), concrete polymers, flooring, electronics (conformal, photoresists, solder masks), inks (flexo, gravure, litho, screen), paints, photopolymers Trade Names SR 454 SR 454HP... 

---