Vulcanised rubber


Sulphur is used in the manufacture of matches and fireworks, as a dust insecticide and for vulcanising rubber. Most of the world supply of sulphur, however, is used for the manufacture of sulphuric acid (p. 296).  [c.268]

Diselenium dichloride acts as a solvent for selenium. Similarly disulphur dichloride is a solvent for sulphur and also many other covalent compounds, such as iodine. S Clj attacks rubber in such a way that sulphur atoms are introduced into the polymer chains of the rubber, so hardening it. This product is known as vulcanised rubber. The structure of these dichlorides is given below  [c.307]

Vulcanised rubber and thermosetting plastics.  [c.81]

Vulcanised rubber and thermosetting plastics  [c.87]

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts.  [c.276]

In order for a rubbery polymer to realise an effectively high elastic state it is necessary to lightly cross-link the highly flexible polymer molecules to prevent them from slipping past each other on application of a stress. In the rubber industry this process is known as vulcanisation. Ever since the discovery of the process by Charles Goodyear in the USA about 1839 and its exploitation by Thomas Hancock in London from 1843 onwards it has been the usual practice to vulcanise diene polymers with sulphur although alternative systems are occasionally used. The reactions are very involved and appear to be initiated at the a-methylene group rather than at the double bond. Some of the structures that may be present in the vulcanised rubber are indicated schematically in Figure 11.15 as indicated by extensive research into natural rubber vulcanisation.  [c.282]

The detailed structure of ebonite is not known but it is believed that the same structures occur in the rigid material as have been suggested for vulcanised rubber. There will, however, be far more S-containing structures per unit volume and the ratios of the various structures may differ. The curing reaction is highly exothermic.  [c.860]

The other most widely used thermoplastic elastomers are the S-B-S and related materials. These are usually blended with large amounts of a stiffening resin (polystyrene), mineral oils, fillers and even other polymers so that the amount of S-B-S in the finished compound is usually less than 50%. In the area of replacements for commercial vulcanised rubber, the S-B-S compounds are largely used for shoe soling, tubing, sound deadening and flexible automotive parts. The related hydrogenated polymers (S-EB-S) are of particular interest for wire insulation and other applications where enhanced aging and weathering properties are required.  [c.878]

In 1839 Charles Goodyear discovered that raw rubber when mixed with finely divided sulphur and heated to 150°C, changed from a soft deformable substance into a tough resilient material. This reaction was called vulcanisation. Rubber linings have been in use for some 130 years for the protection of substances against chemical attack. In 1855, J. H. Johnson took out a patent for spinning components made from metal covered with rubber, thus combining the strength and durability of the metal with the non liability to oxidation of the rubber. In 1857, Thomas Hancock published his Personal Narrative which included details of the outstanding resistance of natural rubber to chemical compounds. In his summary, Hancock described sheets of a mixture of one part of natural rubber to two parts of pitch for the protection of ships hulls. He listed moulded articles made from hard vulcanisates which were resistant to acids, alkalis and chemical solutions and also mentions vulcanised sheet rubber for use as linings in chemical vessels.  [c.938]

Like sulphur, selenium has been used in the vulcanisation of rubber. It is also used in photoelectric cells.  [c.268]

A mixed polymer of butadiene and acrylonitrile (Perbunan, Hycar, Chemigum) may be vulcanised like rubber and possesses good resistance to oils and solvents in general.  [c.1016]

Rubber chemicals are materials that are added ia minor amounts to mbber formulations in order to improve their properties and make them commercially useful. Raw mbber polymer has very limited practical appHcations because of tackiness, flow, and other undesirable features. Rubber chemicals are added to assist processing, promote cross-linking, and provide longevity to the part in service. Vulcanising adjacent polymer chains together by cross-links prevents flow, increases strength, and provides recovery from deformation. The most widely used method of cross-linking polymer chains is by heating with elemental sulfur (vulcanisation). Accelerators speed up the reaction of sulfur with polymer to improve the economics of manufacture and prevent degradation that would otherwise occur upon prolonged heating. Peptizers and process aids assist flow during the mixing and shaping operations. Antidegradants protect the part in service from heat, oxygen, ozone, and repeated flexing. Other mbber chemicals function as blowing agents, adhesion promoters, and activators or retarders which modify the onset of cross-linking.  [c.219]

Because of the long-range elasticity of soft mbber vulcanisates and the various special conditions under which they are degraded in use, special test methods have been developed which in many respects are unlike those used for wood, metals, and hard plastics. The American Society for Testing Materials (ASTM) through its Committee Dll on Rubber and Rubber-like Materials is constantly developing and promulgating new and improved methods for testing mbber and mbber products.  [c.261]

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364).  [c.53]

W. A. Wilson and D. C. Grimm, Molecular Structures from Polymerisation and Vulcanisation, Southern Rubber Group, Knoxville, Term., 1994.  [c.501]

Most nitrile mbber is consumed ia appHcatioas utilising vulcanised mbber compouads. Rubber compouads are mixed with a wide variety of iagredieats, including various fillers, plasticizers, processiag aids, stabilizers, and curatives (23). After mixing the mbber compound, various vulcanization techniques, such as compression mol ding, transfer mol ding, and iajection mol ding, can be used to prepare the final cured mbber article. Common appHcations for nitrile mbber take advantage of the chemical resistance of the mbber and are as follows  [c.523]

In Ancient Egypt mummies were wrapped in cloth dipped in a solution of bitumen in oil of lavender which was known variously as Syrian Asphalt or Bitumen of Judea. On exposure to light the product hardened and became insoluble. It would appear that this process involved the action of chemical cross-linking, which in modem times became of great importance in the vulcanisation of rubber and the production of thermosetting plastics. It was also the study of this process that led Niepce to produce the first permanent photograph and to the development of lithography (see Chapter 14).  [c.2]

In extensions of this work on vulcanisation, which normally involved only a few per cent of sulphur, both Goodyear and Hancock found that if rubber was heated with larger quantities of sulphur (about 50 parts per 100 parts of rubber) a hard product was obtained. This subsequently became known variously as ebonite, vulcanite and hard rubber. A patent for producing hard rubber was taken out by Nelson Goodyear in 1851.  [c.3]

The vulcanisation of natural rubber, a long chain polyisoprene, with sulphur involves a similar type of cross-linking.  [c.24]

Reinforcing particulate fillers are effective primarily with elastomers although they can cause an increase in tensile strength with plasticised PVC. Pure gum styrene-butadiene rubber (SBR) vulcanisates have tensile strengths of about 3 MPa. By mixing in 50 phr of a reinforcing carbon black the tensile strength can be increased to over 20 MPa. In a crystalline rubber such as natural rubber such large increases in tensile strength are not observed but as with SBR an increase in modulus, tear resistance and abrasion resistance can be seen. It is often found that a property such as tensile strength usually goes through a maximum value with change in carbon black loading. At first the increase in polymer-black interfacial area is the dominating effect but if the black concentration becomes too high the diminishing volume of rubber in the composite is insufficient to hold the filler particles together. In general reinforcement appears to depend on three factors  [c.127]

Whilst the plastics technologist may incorporate rubber into his resins or plastics materials the rubber technologist often incorporates synthetic resins or plastics into his rubbers. Butadiene-styrene resins containing at least 50% styrene may be blended with rubber to produce compounds for shoe soling and for making car wash brushes. Phenolic resins which have a low viscosity at processing temperatures may enhance the flow and hence processability of rubber compounds but during the vulcanisation of the rubber will simultaneously cross-link, leading to a comparatively rigid product.  [c.128]

Antioxidants may be assessed in a variety of ways. For screening and for fundamental studies the induction period and rate of oxidation of petroleum fractions with and without antioxidants present provide useful model systems. Since the effect of oxidation differs from polymer to polymer it is important to evaluate the efficacy of the antioxidant with respect to some property seriously affected by oxidation. Thus for polyethylene it is common to study changes in flow properties and in power factor in polypropylene, flow properties and tendency to embrittlement in natural rubber vulcanisates, changes in tensile strength and tear strength.  [c.143]

In order to produce thermoset plastics or vulcanised rubbers the process of cross-linking has to occur. Before cross-linking, the polymer may be substantially or completely linear but contain active sites for cross-linking. Such a situation occurs with natural rubber and other diene polymers where the double bond and adjacent alpha-methylene groups provide cross-linking sites. Alternatively the polymer may be a small branched polymer which cross-links by intermolecular combination at the chain ends. The term cross-linking agents is a very general one and covers molecules which bridge two polymer molecules during cross-linking (Figure 7.10(a)), molecules which initiate a cross-linking reaction (Figure 7.10(b)), those which are purely catalytic in their action (Figure 7.10(c) and those which attack the main polymer chain to generate active sites (Figure 7.10(d)).  [c.153]

Cross-linking of a crystalline thermoplastic polymer has, in general, two distinct effects. Firstly it interferes with molecular packing, reducing the level of crystallisation, and consequently the polymer has a lower modulus, hardness and yield strength than the corresponding non-cross-linked material. More importantly, because the network stmcture still exists above the crystalline melting point the material retains a measure of strength, typical of a rubber material. Polyethylene is typical in such behaviour and because of the enhanced heat resistance (in terms of resistance to melt flow), cross-linked or vulcanised polyethylene finds application in the cable industry both as a dielectric and a sheathing material.  [c.239]

Ethylene-vinyl acetate (EVA) polymers with a vinyl acetate content of 10-15 mole % are similar in flexibility to plasticised PVC and are compatible with inert fillers. Both filled and unfilled copolymers have good low-temperature flexibility and toughness and the absence of leachable plasticiser provides a clear advantage over plasticised PVC in some applications. Although slightly stiffer than normal rubber compounds they have the advantage of simpler processing, particularly as vulcanisation is unnecessary. The EVA polymers with about 11 mole % of vinyl acetate may also be used as wax additives for hot melt coatings and adhesives.  [c.276]

Polybutadiene, polyisoprene (both natural and synthetic), SBR and poly-(dimethyl butadiene) (used briefly during the First World War as methyl rubber) being hydrocarbons have limited resistance to hydrocarbon liquids dissolving in the unvulcanised state and swelling extensively when vulcanised. Being unsaturated polymers they are susceptible to attack by such agencies as oxygen, ozone, halogens and hydrohalides. The point of attack is not necessarily at the double bond but may be at the a-methylenic position. The presence of the double bond is nevertheless generally crucial. In addition the activity of these agencies is affected by the nature of the groups attached to the double bond. Thus the methyl group present in the natural rubber molecule and in synthetic polyisoprene increases activity whereas the chlorine atom in polychloroprene reduces it.  [c.282]

Figure 11.15. Typical chemical groupings in a sulphur-vulcanised natural rubber network, (a) Monosulphide cross-link (b) disulphide cross-link (c) polysulphide cross-link (j = 3-6) (d) parallel vicinal cross-link (n = 1-6) attached to adjacent main-chain atoms and which have the same influence as a single cross-link (e) cross-links attached to common or adjacent carbon atom (f) intra-chain cyclic monosulphide (g) intra-chain cyclic disulphide (h) pendent sulphide group terminated by moiety X derived from accelerator (i) conjugated diene (j) conjugated triene (k) extra-network material (1) carbon-carbon cross-links (probably absent) Figure 11.15. Typical chemical groupings in a sulphur-vulcanised natural rubber network, (a) Monosulphide cross-link (b) disulphide cross-link (c) polysulphide cross-link (j = 3-6) (d) parallel vicinal cross-link (n = 1-6) attached to adjacent main-chain atoms and which have the same influence as a single cross-link (e) cross-links attached to common or adjacent carbon atom (f) intra-chain cyclic monosulphide (g) intra-chain cyclic disulphide (h) pendent sulphide group terminated by moiety X derived from accelerator (i) conjugated diene (j) conjugated triene (k) extra-network material (1) carbon-carbon cross-links (probably absent)
In addition to the components of the vulcanising system several other additives are commonly used with diene rubbers. As a general rule rubbers, particularly the diene rubbers, are blended with many more additives than is common for most thermoplastics, with the possible exception of PVC. In addition the considerable interaction between the additives requires the rubber compounder to have an extensive and detailed knowledge concerning the additives that he employs.  [c.283]

Natural rubber is generally vulcanised using accelerated sulphur systems although several alternatives have been used. At the present time there is some limited use of the cold cure process using sulphur chloride in the manufacture of rubber proofings. This process was first discovered by Alexander Parkes in 1846, which was some years before his discovery of Parkesine (see Chapter 1) and this is sometimes known as the Parkes Process. (Another Parkes Process is that of separating silver from lead ) Peroxides are also very occasionally used, particularly where freedom from staining by metals such as copper is important. Nitroso compounds and their derivatives, including the so-called urethane cross-linking systems, may also be employed. The latter in particular give a uniform state of cure to thick sections as well as an improved level of heat resistance compared to conventional sulphur-cured systems.  [c.288]

Because of the excellent properties of its vulcanisates under conditions not demanding high levels of heat and oil resistance, natural rubber commands a premium price over SBR, with which it vies for top place in the global tonnage  [c.288]

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers.  [c.292]

The close structural similarities between polychloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary.  [c.295]

Health hazards now associated with what was one of the most common vulcanising agents for the rubber (ethylenethiourea) have caused problems because of the difficulties of finding an acceptable alternative.  [c.296]

The most important of these is ebonite, which may be considered as the world s earlier thermosetting plastics material. It is obtained by vulcanising (natural) rubber with large quantities of sulphur. Whereas ordinary vulcanised rubber as used in tyres contains normally only 2-3% of sulphur a typical rubber/ sulphur ratio for ebonite is 68 32. Compared with ordinary vulcanisates, ebonite is more rigid, shows less swelling in hydrocarbon solvents and has a higher density. These factors indicate a fairly high degree of cross-linking. As the vulcanisation reaction proceeds it is observed that the non-extractable sulphur content steadily increases to reach a maximum of 32% and at this point the unsaturation of the composition falls to zero. The sulphur content is in accord with the empirical formula CsHgS so that in effect for each atom of sulphur combined there is a loss of one double bond.  [c.860]

Hard products may also be made by vulcanising rubber (natural or synthetic) using only about two parts of sulphur per 100 parts of rubber. In these cases either the so-called high-styrene resins or phenolie rubber compounding resins are ineorporated into the formulation. These compounds are processed using the methods of rubber technology but, like those of ebonite, the produets are more akin to plastics than to rubbers. Examples of the usage of these materials are to be found in battery boxes, shoe heels and ear washer brushes.  [c.863]

If polypropylene is too hard for the purpose envisaged, then the user should consider, progressively, polyethylene, ethylene-vinyl acetate and plasticised PVC. If more rubberiness is required, then a vulcanising rubber such as natural rubber or SBR or a thermoplastic polyolefin elastomer may be considered. If the material requires to be rubbery and oil and/or heat resistant, vulcanising rubbers such as the polychloroprenes, nitrile rubbers, acrylic rubbers or hydrin rubbers or a thermoplastic elastomer such as a thermoplastic polyester elastomer, thermoplastic polyurethane elastomer or thermoplastic polyamide elastomer may be considered. Where it is important that the elastomer remain rubbery at very low temperatures, then NR, SBR, BR or TPO rubbers may be considered where oil resistance is not a consideration. If, however, oil resistance is important, a polypropylene oxide or hydrin rubber may be preferred. Where a wide temperature service range is paramount, a silicone rubber may be indicated. The selection of rubbery materials has been dealt with by the author elsewhere.  [c.896]

Copper and silver tarnish readily in sulphide atmospheres, and copper in contact with sulphur-vulcanised rubber will sometimes react with the sulphur, devulcanising it in the process. The growth of conducting sulphide whiskers on silver is noteworthy as these whiskers may give rise to short circuits across silver-plated contacts. Ammonia has little effect on most metals, but traces will tarnish many copper alloys and cause stress-corrosion cracking of certain stressed brasses.  [c.955]

Historically latex was the milky Hquid drawn from any of 200 plants, most notably the Hevea brasiliensis tree of South America (1). Early appHcations of natural mbber, 93—95% <7j -l-4-isoprene, included waterproofing and strengthening of other materials (see Isoprene Rubber, natural). Vulcanisation and the automobile increased natural mbber demand through the end of the nineteenth century (2). Large mbber plantations in Malaya, Ceylon, Indonesia, and Indochina increased the world s natural mbber production to 200,000 metric tons by 1920. Enhanced supply led to rapid growth of natural mbber products and improvements in latex processing. The AUied blockade of Germany during World War I led to the first process for making synthetic latex (3). Soon thereafter United States companies began to produce commercial synthetic latices Buna S (butadiene—styrene copolymer), also known as Government Rubber—Styrene or GR—S mbber Neoprene (polychloroprene) (4) andThiokol (polysulfides) (see Polymers containing sulfur Styrene—butadiene rubber). Japan s seizure of the Southeast Asia mbber plantations during World War II led to intensive research in synthetic mbber production (5). Synthetic latex production accounts for 65% of the 15 x 10 — t total mbber market (6). Worldwide concern over the AIDS epidemic has sharply increased the demand for latex used in the preparation of mbber gloves and similar dipped goods. Estimates are for a 5—7% annual growth rate in this market.  [c.23]

As in dry rubber compounding, neoprenes require sulfur and an accelerator for vulcanisation, but sine oxide can also be used to accelerate the cure and to function as an acid acceptor. Unlike dry neoprene compounding, no magnesium salt is used because of its destabilising effect on the latex. Organic accelerators are used to improve the physical properties of neoprene latex films but their effect is not generally as great as when used with other polymers. The most effective accelerators in neoprene latex are thiocarbanilide (yy -diphenylthiourea) used either alone or in combination with DPG, or combinations ofTETD and SBUD.  [c.256]

C. S. L. Baker, Vulcanisation with Urethane Reagents, NR Technical Bulletin, Malaysian Rubber Pioduceis Research Association, Biickendonbeiiy, U.K, 1978.  [c.276]

The principal commercial uses of sulfur monochloride are in the manufacture of lubricant additives and vulcanising agents for mbber (147,154,155) (see Lubrication AND lubricants Rubber chemicals). The preparation of additives for wear and load-bearing improvement of lubricating oils is generally carried out in two steps and the technology is described in numerous patents (155) (see Sulfurization and sulfchlorination).  [c.139]

Standard Test Method for Adhesion Between Steel Tire Cords and Rubber. Steel cords are vulcanised into a block of mbber and the force necessary to pull the cords linearly out of the mbber is measured as adhesive force. ASTM method D2229-93a can be used for evaluating mbber compound performance with respect to adhesion to steel cord. The property measured by this test method indicates whether the adhesion of the steel cord to the mbber is greater than the cohesion of the mbber, ie, complete mbber coverage of the steel cord or less than the cohesion of mbber (lack of mbber coverage).  [c.90]

So people have tried to improve on nature. First, they tried to extract natural polymers, and reshape them to their purpose. Cellulose (Table 21.4), extracted from wood shavings and treated with acids, allows the replacement of the —OF side group by —COOCIT3 to give cellulose acetate, familiar as rayon (used to reinforce car tyres) and as transparent acetate film. Replacement by —NO3 instead gives cellulose nitrate, the celluloid of the film industry and a component of many lacquers. Natural latex from the rubber tree is vulcanised to give rubbers, and filled (with carbon black, for instance) to make it resistant to sunlight. But the range of polymers obtained in this way is limited.  [c.254]

The coagulated rubber was a highly elastic material and could not be shaped by moulding or extrusion. In 1820 an Englishman, Thomas Hancock, discovered that if the rubber was highly sheared or masticated, it became plastic and hence capable of flow. This is now known to be due to severe reduction in molecular weight on mastication. In 1839 an American, Charles Goodyear, found that rubber heated with sulphur retained its elasticity over a wider range of temperature than the raw material and that it had greater resistance to solvents. Thomas Hancock also subsequently found that the plastic masticated rubber could be regenerated into an elastic material by heating with molten sulphur. The rubber-sulphur reaction was termed vulcanisation by William Brockendon, a friend of Hancock. Although the work of Hancock was subsequent to, and to some extent a consequence of, that of Goodyear, the former patented the discovery in 1843 in England whilst Goodyear s first (American) patent was taken out in 1844.  [c.3]

Because of its highly regular structure natural rubber is capable of crystallisation. Quoted figures for are in the range 15-50°C which means that for an unfilled unvulcanised material there is some level of crystallinity at room temperature. (Chemical cross-linking and the presence of fillers will impede crystallinity.) The extent of crystallisation is substantially increased by stretching of the rubber causing molecular alignment. This crystallisation has a reinforcing effect giving, in contrast to SBR, strong gum stock (i.e unfilled) vulcanisates. It also has a marked influence on many other mechanical properties. As already mentioned in the previous section, the ability of natural rubber to crystallise also has an important influence on natural tack, a property of great importance in tyrebuilding operations.  [c.288]

The proximity of the methyl group to the double bond in natural rubber results in the polymer being more reactive at both the double bond and at the a-methylenic position than polybutadiene, SBR and, particularly, polychlor-oprene. Consequently natural rubber is more subject to oxidation, and as in this case (c.f. polybutadiene and SBR) this leads to chain scission the rubber becomes softer and weaker. As already stated the oxidation reaction is considerably affected by the type of vulcanisation as well as by the use of antioxidants.  [c.288]

Whereas natural rubber is crystalline with a of about 50°C, SBR with its irregular molecular structure is amorphous. Although the crystallinity in natural rubber is reduced by the presence of cross-links and by fillers and other additives it still crystallises on extension and normal ambient temperatures to give a good tensile strength even with gum (i.e. unfilled) stocks. Gum vulcanisates of SBR on the other hand are weak and it is essential to use reinforcing fillers such as fine carbon blacks to obtain products of high strength. Black-reinforced SBR compounds do, however, exhibit a very good abrasion resistance and are commonly superior to corresponding black-reinforced NR vulcanisates at temperatures above 14°C. Against this the SBR vulcanisates have lower resilience and resistance to tearing and cut growth. It is largely the deficiency in these properties together with the lack of green strength and natural tack which has led to the natural material recovering some of the market for tyre rubbers, particularly since the change over from crossply to radial tyres.  [c.293]


See pages that mention the term Vulcanised rubber : [c.393]    [c.283]    [c.292]   
Plastics materials (1999) -- [ c.81 ]