Vulcanisation chemistry

A. B. Sullivan, C. J. Harm, and G. H. Kuhls, "Vulcanisation Chemistry— Fate of Elemental Sulfur and Accelerator during Scorch Delay as Studied by Modem HPLC", Paper No. 9, presented at the MGS Tubber Division Meeting Toronto, Canada, May 21 —24, 1991, American Chemical Society, Washington, D.C., 1991. 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

Therefore most progress towards the understanding of sulfur-vulcanisation chemistry was originally made by vulcanising low-molecular-weight model olefins. Numerous... 

Similar vulcanisation chemistry is observed with the N- -butyl-2-benzothiazole sulfenimide (TBSI) accelerated sulfur-vulcanisation of HR [26] compared to the TBBS accelerated systems... 

The effect of the accelerator to sulfur ratio on the vulcanisation chemistry was also investigated by comparing the vulcanisation products from conventional, SEV and EV formulation systems. With increase in accelerator to sulfur ratio (from conventional to EV) there is a lowering in the sulfur rank. Also, the cis-to-trans isomerisation increases with the amount of accelerator. 

Chemical structure of rubbery materials Chapters 1, 2, 3, 4, 5, 6, 9 and 11, describe applications of (multi) hyphenated TGA techniques, optical and high-resolution NMR spectroscopes for the analysis of chain microstructures and conformations, chemical composition of components, additives and volatiles in rubbery materials, vulcanisation chemistry, functional groups analysis and chemical modification of rubbery materials. 

Sulfur reacts very slowly with rubber, and so is compounded with rubber in the presence of accelerators and activators. Typical accelerators are thia-zoles and a typical activator is a mixture of zinc oxide and a fatty acid. The chemistry of the vulcanisation reactions is complicated, but generates a three-dimensional network in which rubber molecules are connected by short chains of sulfur atoms, with an average of about five atoms in each chain. 

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Scheme 5.4 Structural formulae of some vulcanisation accelerators (I) FDMPTD, (II) FDMPTM, (III) FZMPC and (IV) OFPBG. After Kelm and Gross [252]. Reprinted with permission from Rubber Chemistry and Technology. Copyright (1985), Rubber Division, American Chemical Society, Inc.

Macromolecular chemistry covers a particularly wide field which includes natural polymeric material, such as proteins, cellulose, gums and natural rubber industrial derivatives of natural polymers, such as sodium carboxymethyl cellulose, rayon and vulcanised rubber and the purely synthetic polymers, such as polythene (polyethylene), Teflon (polytetrafluoroethylene), polystyrene, Perspex (poly (methyl... 

The technology of sulfur vulcanisation of unsaturated elastomers has evolved since Goodyear s invention in 1839. Scientific studies into the chemistry of sulfur vulcanisation started to appear in the late 1950s (for reviews see References [14-18]). Two experimental approaches can be distinguished the analysis of rubber vulcanisates themselves and the so-called low-molecular-weight model studies. 

In general, most of the problems encountered in the study of the chemistry of the sulfur vulcanisation of elastomers are also encountered in the study of peroxide-curing. In comparison with sulfur vulcanisation only a limited number of spectroscopic studies on peroxide-curing have been published. 

The mechanism of the accelerated sulfur vulcanisation of EPDM is probably similar to that of the highly unsaturated polydiene rubbers. The vulcanisation of EPDM has been studied with emphasis on the cure behaviour and mechanical and elastic properties of the crosslinked EPDM. Hardly any spectroscopic studies on the crosslinking chemistry of EPDM have been published, not only because of the problems discussed in Section 6.1.3 but also because of the low amount of unsaturation of EPDM relative to the sensitivity of the analytical techniques. For instance, high-temperature magic-angle spinning solid-state 13C NMR spectroscopy of crosslinked EPDM just allows the identification of the rubber type, but spectroscopic evidence for the presence of crosslinks is not found [72]. 

Accelerated sulfur formulations are the most common vulcanisation systems used in commercial and industrial applications. Therefore, research on both the fundamental and applied aspects of accelerated sulfur vulcanisation is ongoing. Several reviews of the chemistry and/or physics of accelerated sulfur-vulcanisation of elastomers have been published [13, 14, 22, 23]. 

Charles Goodyear [1], an American scientist, worked with gutta-percha, a gum from natural tropical trees, and Thomas Hancock, a British scientist who simultaneously and independently developed a process for the vulcanisation of rubber (1839) by reacting it with sulphur and heat, are credited with the first deliberate attempt to chemically modify a natural polymer to produce a moulding material. Gutta-percha was used to protect and insulate the first submarine telegraph cables. The combined and independent efforts of these men helped to lay the foundation for the manufacture of synthetic materials using chemistry. 

Kauffman, George B. (1989). Charles Goodyear— Inventor of Vulcanisation. Education in Chemistry 26(6) 167-170. 

Figure 1.14 Laser desorption mass spectrum of Compound 2, the carbon-black filled vulcanised rubber compound, obtained using the LAMMA 1000 spectrometer Reproduced with permission from Waddell and co-workers. Rubber Chemistry and...

Vulcanisation conditions vary enormously according to the process used and chemistry selected, but may be optimised to provide limited control over product strength. A full discussion of these parameters is outside the scope of this chapter. 

Some more specific polymer chemistry applications for TG-FTIR are solvent and water retention, curing and vulcanisation reactions, isothermal ageing, product stability, identification of base polymer type and additives (plasticisers, mould lubricants, blowing agents, antioxidants, flame retardants, processing aids, etc.) and safety concerns (processing, product safety, product liability, fire hazards) [357]. A wide variety of polymers and elastomers has been studied by TG-FTIR [353,358,359]. The potential applications of an integrated TG-FTIR system were discussed by various authors [346,357]. 

Rubber surfaces were characterised directly by ToF LMMS, LD-FTMS and TD-FTMS [201, 202]. The surface chemistry of the antiozonant N-(l,3-dimethylbutyl)-lV -phenyl-p-phenylenediamine (HPPD) in vulcanised natural rubber compounds was explored by ToF LMMS in order to investigate the mechanism of rubber-surface ozone ageing... 

Elastomeric properties are obtained by flghdy cross-flnking the polymer chains. There are two types of rubber material room temperature vulcanised (RTV) and high temperature vulcanised (HTV) polymers. The chemistry used to produce these elastomers is shghtly different. For the RTV the cross-links are created by the reaction of the polymer with a reactive cross-linking agent, usually a hydro-lysable tetrafunctional silane (Figure 7.18). 

Some of these chemical agents (e.g., the amine/thiol mixtures) were used in the chemical probe rubber chemistry research work being undertaken at TARRC in the 1950s and 1960s to establish the chemical nature and processes involved during the sulfur vulcanisation of diene rubbers, such as NR. 

Injection moulding is different from extrusion in that it involves a crosslinking reaction. Therefore, the rate and the mechanisms of crosslinking is an integral part of the process. However, in this chapter, chemistry of vulcanisation is not included. 

Workers at Port Elizabeth University have produced an important series of papers addressing the fundamental chemistry involved in the vulcanisation of different types of rubber compounds. DSC has been used extensively in this body of work to study the behaviour of accelerators and other essential cure ingredients in isolation [94] and in the presence of rubber molecules [95]. 

Brief details are given of the chemistry involved in the vulcanisation of elastomers and plastics using peroxides as an alternative to sulphur. Data are presented for the peroxide curing of EPDM. 

Cincinnati, Oh., 17th.-19th. Oct. 2000, paper 75 CHEMISTRY OF VULCANISATION OF RUBBER... 

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... 

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