Vulcanisation peroxide

Oxidative ageing of rubbers is limited by the rate of diffusion of oxygen into the rubber product and is usually confined to the outer 3 mm. Antioxidants are used to protect rubbers from the effects of thermal oxidation and the vast majority of compounds will contain one or more. Peroxide vulcanisates are usually protected with dihydroquinolines. Other antioxidants react adversely with the peroxide inhibiting the crosslinking reaction. 

Dicumyl peroxide vulcanisation of high-cis BR and NR samples at different peroxide levels were investigated by solid-state 13C NMR [42], As the peroxide level increased, decreased signal intensity and peak broadening was observed in the main chain peaks in both BR and NR due to decreased segmental motion. In addition, cis-trans isomerisation was observed during the vulcanisation process in both rubbers. New peaks at 35 and 44 ppm were observed in the BR spectra while peaks at 14.9, 21.4, 30.6, 37.5, and 45.0... 

Network structure and reaction mechanisms in high pressure vulcanisation (HPV) and peroxide vulcanisation of BR was studied by 13C solid-state NMR [43]. Different samples of polybutadiene (51% trans, 38% cis, and 11 % vinyl) were peroxide cured with dicumyl peroxide on a silica carrier and by the HPV conditions of 250 °C and 293 MPa. The 13C NMR spectra from peroxide and HPV cures were compared to a control samples heated to 250 °C for 6 minutes under atmospheric pressure. Although no new isolated strong peaks were detected in either the peroxide or HPV vulcanisations, small increases in both spectra were observed at 29.5, 36.0, 46.5, and 48.0 ppm. These peaks compare favourably with calculated shifts from structures that arise from main chain radical addition to the pendent vinyl groups. These assignments are further reinforced by the observation that the vinyl carbon concentration is substantially reduced during vulcanisation in both peroxide and HPV curing. Two peaks at 39.5 and 42.5 ppm appear only in the peroxide spectrum. Cis-trans isomerisation was absent in both cures. 

Hot Vulcanisation The polymeric materials contain 002-0.05 mol% methylvinyl siloxanes, so that there is one vinyl group for every 500-1000 other groups. Diaroyl peroxides are applied as catalysts, preferably bis(dichlorobenzoyl)peroxide. Vulcanisation proceeds at temperatures of 110-130 °C. A typical composition of initial reactants is 100 wt. pts. of raw rubber, 20-200 wt. pts. of fillers (soot, silica, barite, etc.), 0.5-3 wt. pts. of catalyst, 0.0-5 wt. pts. of pigments. The vulcanisation can also be done in the presence of sulphur (2 wt. % sulphur, 1-4 mol % methylvinyl siloxanes, 150°C). 

In general the moulding of ethylene-propylene based compounds presents few difficulties even when complex moulds are employed. Precautions should be taken with peroxide vulcanisations so as to avoid air being trapped in the mould and causing sticky surfaces. Such precautions consist mainly of supplying suitable vents in the more critical parts of the mould. 

There are a number of advantages, listed below, associated with the peroxide vulcanisation of elastomers ... 

Of the polymers that can be crosslinked, the crosslink efficiency varies considerably. In general the relative efficiency of peroxide vulcanisation of polymers (a.29, a.30) is ... 

Peroxide vulcanisation of EPDM is growing in popularity because of enhanced ageing resistance. A comparison of sulfur and peroxide cure systems for EPDM is shown in Table 32 (381). 

Details are given of the competing chemical reactions involved in the peroxide vulcanisation of elastomers. The effect of various factors including the type of polymer, type and concentration of peroxide, cure temperature, and the presence of additives such as co-agents and antidegradants are discussed. 100 refs. 

Cincinnati, Oh., 17th.-19th. Oct. 2000, paper 79 MONTE CARLO SIMULATION OF THE PEROXIDE VULCANISATION OF ETHYLENE ELASTOMERS... 

The advantages are outlined of the use of peroxide vulcanising agents in place of sulphur curing for elastomers. The chemistry of both types of vulcanisation systems is explained. Since the chemical mechanisms of each are very different, mbber compounders, experienced in the use of sulphur are reported to often find difficulties in formulating new products which make use of peroxide curatives. An overview is presented of the types of peroxides available and their properties. A description is included of the chemistry by which peroxides vulcanise rubber, followed by a discussion of the potential chemical interferences which may face rubber compounders converting from sulphur vulcanisation to peroxide curing. USA... 

Recent developments in the use of a range of methacrylate coagents to modify the performance of peroxide vulcanised elastomers are summarised. Peroxide vulcanisation has successfully been used in the past to improve heat resistance, but there have been a number of adverse comparisons with sulphur vulcanisation, most notably in tear strength and dynamic performance. The current status is reported, as is the improvement of the adhesion of many elastomers to a range of metals and fibres. 

Sartomer s Saret zinc diacrylate and zinc dimethacrylate coagents were evaluated in the peroxide vulcanisation of EPDM automotive belt and hose compounds. Cure characteristics and effects on mechanical properties, heat and water resistance and adhesion of EPDM to metal and synthetic fibre reinforcements and to other mbbers were investigated. The results of this study and other experiments with Saret coagents in rabber formulations are discussed. 6 refs. 

The advantages and limitations of sulphur and peroxide vulcanisation are discussed. The Luperox range of organic peroxides produced by Elf Atochem and their applications in rubber vulcanisation and as crosslinking agents for polyolefins are reviewed. A number of commercial developments by the Company in this field are examined, and the activities of its plant in Gunzburg in Germany are described. 

A review of the peroxide vulcanisation of elastomers is presented. The generalised mechanism of crosslinking reaction is discussed while network structure is related to vulcanisate properties. Emphasis is placed on elastomers where only the peroxide system is suitable or where it has a comparable advantage over other systems. In addition, the uses of coagents in peroxide vulcanisation... 

The sorption and transport of four aliphatic hydrocarbons (n-hexane, n-heptane, n-octane and n-nonane) into NR crosslinked using conventional, efficient, dicumyl peroxide(DCP) and mixed sulphur/peroxide vulcanisation systems were investigated at temp, of 28 to 60C. The NR vulcanised by DCP exhibited the lowest penetrant uptake of the systems studied. It was observed that the kinetics of liquid sorption in every case deviated from the regular Fickian trend, characteristic of sorption of liquids by rubbers. The diffusion coefficient, activation energy of sorption, enthalpy, entropy and rubber-solvent interaction parameter were evaluated for the four systems from the swelling data. 30 refs. 

Several mechanical properties of carbon black filled EPDM changed drastically by using a strain during the second step of a two-stage peroxide vulcanisation. EB decreased whereas tensile strength increased due to this vulcanisation method. Crosslinked rubbers with the same mechanical properties could be obtained as from a vulcanisation without strain, but with considerably less peroxide. 17 refs. 

Immersion of 1 mm thick sheets of peroxide-vulcanised NR in both liquid and, more surprisingly, powdered solid curing agents was shown to be an adequate method for measuring solubilities. The same experimental method also enabled some diffusion data to be obtained. Solubilities of sulphur, zinc diethyldithiocarbamate and... 

Saret acrylic and methacrylic acid salts (Sartomer) were compared withtriallyl cyanurate as co-curing agents in the peroxide vulcanisation of EPDM compounds for a number... 

Crosslinking elastomers with peroxides has been known for over 50 years. Serious interest in vulcanisation with peroxides began with the commercial introduction of dicumyl peroxide in the late 1950s. The major feature of this peroxide was its higher curing temperature, which has provided scorch time needed for many rubber manufacturing systems. The main features of peroxide vulcanisation are reviewed and the complications that can interfere with crosslinking performance are discussed. USA... 

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