Peroxide crosslinker

W.C. Endstra and C.T.J. Wressmann, Peroxide Crosslinking of EPDM Rubbers, in Elastomer Technology Handbook, N.P. Cheremisinoff and Pn. Cheremisinoff, Eds., CRC Press, New Jersey, 1993. 

Figure 18,8 Peroxide crosslinking of polyethylene a) decomposition of dlcumyl peroxide, b abstraction of hydrogen from polyethylene chain, and c) formation of covalent C-C crosslink...

Ethylene-propylene and silicone rubbers are crosslinked by compounding with a peroxide such as dicumyl peroxide or di-t-butyl peroxide and then heating the mixture. Peroxide cross-linking involves the formation of polymer radicals via hydrogen abstraction by the peroxy radicals formed from the decomposition of the peroxide. Crosslinks are formed by coupling of the polymer radicals... 

Fig. 8. Gel formation of peroxide crosslinked poly(HAMCL), based on coconut fatty acids (COFA), oleic acid (OA), tall oil fatty acids (TOFA) or linseed oil fatty acids (LOFA)...

However, butyl rubber and epichlorohydrin rubber cannot be peroxide-crosslinked. 

Antidegradants known to be suitable for use in combination with peroxide crosslinking systems are thiophosphatcs. / -phenylenediamines and modified triazines. 

Extending oils for compounds crosslinked with peroxides have to be carefully selected. Synthetic ester plasticisers such as phthalates, sebacates and oleates may be used in combination with crosslinking peroxides without affecting the crosslinking reaction. Some derivatives of alkylated benzenes are also known for their very low consumption of free radicals, which is clearly desirable. Mineral oil with double bonds, tertiary carbon atoms or containing heterocyclic aromatic structure may react with radicals paraffinic mineral oils are more effective than naphthenic types, which usually require extra treatment in order to guarantee optimum results when used in peroxide crosslinked blends. 

This method is the only anaerobic non-pressurised system which is suitable for vulcanisation of peroxide crosslinked systems. 

CROSSLINKING OF POLYOLEFIN FOAMS. I. EFFECT OF TRIALLYL CYANURATE ON DICUMYL PEROXIDE CROSSLINKING OF LOW-DENSITY POLYETHYLENE... 

Peroxide crosslinking of the copolymer is more efficient than that of the homopolymer (Table 9-1). The process becomes a chain reaction (but with short kinetic chain length) involving polymerization of the pendant vinyl groups on the polysiloxane chains in combination with coupling of polymeric radicals. The crosslinking of EPDM rubbers is similarly more efficient when compared to EPM rubbers since the former contain double bonds in the polymer chain. 

Fig. 34 WAXD patterns of 5 phr organoclay-filled peroxide-crosslinked NBR in the presence of different vulcanizing ingredients...

Very recently, attempts have been made to develop PP/EOC TP Vs. In order to make TPVs based on PP/EOC blend systems, phenolic resin is ineffective because the latter needs the presence of a double bond to form a crosslinked network structure. Peroxides can crosslink both saturated and unsaturated polymers without any reversion characteristics. The formation of strong C-C bonds provides substantial heat resistance and good compression set properties without any discoloration. However, the activity of peroxide depends on the type of polymer and the presence of other ingredients in the system. It has been well established that PP exhibits a (3-chain scission reaction (degradation) with the addition of peroxide. Hence, the use of peroxide only is limited to the preparation of PP-based TPVs. Lai et al. [45] and Li et al. [46] studied the fracture and failure mechanism of a PP-metallocene based EOC based TPV prepared by a peroxide crosslinking system. Rajesh et al. 

Endstra WC, Wreesmann CTJ (1993) Peroxide crosslinking of EPDM rubbers. In Cheremi-sinoff NP (ed) Elastomer technology handbook. CRC, Boca Raton... 

The new absorptions in the spectra of crosslinked rubber are assigned on the basis of 13C solution NMR chemical shifts for a variety of model compounds, such as pentenes and mono-, di- and tri-sulfidic compounds, by using the 13C chemical shift substituent effect. From the calculated values for particular structural units, the experimental spectra of a sulfur vulcanized natural rubber 194,195,106), natural rubber cured by accelerated sulfur vulcanization 197 y-irradiation crosslinked natural rubber198 and peroxide crosslinked natural rubber and cis-polybutadiene 193 1991 are assigned. 

The fact that these graft copolymers contain polyethylene chains makes them crosslinkable by organic peroxides. One of them has already found industrial application as a peroxide crosslinkable material in cable insulation. 

Dynamic viscoelastic and stress-optical measurements are reported for blends of crosslinked random copolymers of butadiene and styrene prepared by anionic polymerization. Binary blends in which the components differ in composition by at least 20 percentage units give 2 resolvable loss maxima, indicative of a two-phase domain structure. Multiple transitions are also observed in multicomponent blends. AU blends display an elevation of the stress-optical coefficient relative to simple copolymers of equivalent over-all composition. This elevation is shown to be consistent with a multiphase structure in which the domains have different elastic moduli. The different moduli arise from increased reactivity of the peroxide crosslinking agent used toward components of higher butadiene content. 

The variation in modulus appears to be caused by increased reactivity of the dicumyl peroxide crosslinking agent toward butadiene-rich polymers. 

The aim of this chapter is to review optical spectroscopy studies on sulfur and peroxide crosslinking of polydiene rubbers, such as NR and BR (Sections 6.2.1 and 6.3.1, respectively), and to discuss in detail recent FT-Raman and FT-IR spectroscopy studies into the sulfur and peroxide crosslinking of EPDM (Sections 6.2.2 and 6.3.2, respectively). The results of optical spectroscopy studies will also be discussed in the light of results obtained with other techniques. Finally, the elucidation of the chemical structures of the crosslinks formed will allow enhanced understanding of the mechanisms of crosslinking and some preliminary insight into the structure/property relationships of crosslinked rubber. 

The mechanism of peroxide crosslinking of elastomers is much less intricate than that of sulfur vulcanisation. Crosslinking is initiated by the thermal decomposition of a peroxide, which is the overall cure rate determining step. Next, the active radicals thus formed abstract hydrogen from elastomer chains to form macroradicals. Finally, crosslinking results either from the combination of two macroradicals or from the addition of a macroradical to an unsaturated moiety of another primary elastomer chain. 

Optical spectroscopy (IR/NMR/Raman) has been extremely useful in the study of the sulfur and peroxide crosslinking chemistry of elastomers, especially that of EPDM. The... 

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