Vulcanization and curing


Tire Cord. Melamine resins are also used to improve the adhesion of mbber to reinforcing cord in tires. Textile cord is normally coated with a latex dip solution composed of a vinylpyridine—styrene—butadiene latex mbber containing resorcinol—formaldehyde resin.. The dip coat is cured prior to use. The dip coat improves the adhesion of the textile cord to mbber. Further improvement in adhesion is provided by adding resorcinol and hexa(methoxymethyl) melamine [3089-11 -0] (HMMM) to the mbber compound which is in contact with the textile cord. The HMMM resin and resorcinol cross-link during mbber vulcanization and cure to form an interpenetrating polymer within the mbber matrix which strengthens or reinforces the mbber and increases adhesion to the textile cord. Brass-coated steel cord is also widely used in tires for reinforcement. Steel belts and bead wire are common apphcations. Again, HMMM resins and resorcinol [108-46-3] are used in the mbber compound which is in contact with the steel cord to reinforce the mbber and increase the adhesion of the mbber to the steel cord. This use of melamine resins is described in the patent Hterature (49).  [c.331]

Sodium nitrate is also used in formulations of heat-transfer salts for he at-treatment baths for alloys and metals, mbber vulcanization, and petrochemical industries. A mixture of sodium nitrate and potassium nitrate is used to capture solar energy (qv) to transform it into electrical energy. The potential of sodium nitrate in the field of solar salts depends on the commercial development of this process. Other uses of sodium nitrate include water (qv) treatment, ice melting, adhesives (qv), cleaning compounds, pyrotechnics, curing bacons and meats (see Food additives), organics nitration, certain types of pharmaceutical production, refining of some alloys, recovery of lead, and production of uranium.  [c.197]

Vulcanized mbber, phenol—formaldehyde, and cellulose nitrate resins preceded the use of acryflc polymers in prosthetics. Epoxy resins were found unsatisfactory clinically because of handling and curing problems and their dimensional and color instability. Vinyl—acrylics, polystyrene, polycarbonates, and polysulfones can be injection-molded to yield dentures with outstanding toughness, high fatigue strength, and low water sorption. Polycarbonates excel in impact strength, but processing requires high temperature and the use of porcelain teeth, which leads to cra zing in the polymer around the necks of the teeth because of differences in thermal contraction rates.  [c.489]

Compounding. Another important part of the use of polyisoprene mbber is its compounding into formulations that can be utilized to make finished goods and articles. The raw polyisoprene mbber is mixed in a Banbury (internal) mixer or on a mill with ingredients such as fillers (carbon black, clays, or silicates), plasticizers, antioxidants, accelerators, and sulfur. The filler, eg, carbon black, gives durability and reduces cost of the compound. The sulfur functions as a cross-linking agent for the highly unsaturated polyisoprene. The accelerators, eg, sulfenamides, thiazoles, guanidines, thiuram sulfides, and thiocarbamates, help reduce the vulcanization time. The antioxidants (qv), eg, arylamines, hindered phenols, etc, retard the deterioration of the finished article due to aging. Antiozonants (qv), eg, -phenylenediamine, and waxes are also used in tire formulations to retard cracking under stress. The resulting mbber compound is calendered, molded, extmded, or fabricated into the desired shape and vulcanized or cured at around 150°C.  [c.5]

Originally, vulcanization implied heating natural rubber with sulfur, but the term is now also employed for curing polymers. When sulfur is employed, sulfide and disulfide cross-links form between polymer chains. This provides sufficient rigidity to prevent plastic flow. Plastic flow is a process in which coiled polymers slip past each other under an external deforming force when the force is released, the polymer chains do not completely return to their original positions.  [c.1011]

Disulfide interchange also effects the physical properties of the cured polysulftde polymers. Polysulftde polymers undergo stress relaxation in a manner markedly different from conventional mbbers. Stress appHed to stretch a sample of polysulftde mbber rapidly falls to zero. There is no change in the chemical and physical properties of the polymer recovered after the tests. The polysulftde polymer can be repeatedly recycled through the relaxation process. With vulcanized hydrocarbon mbbers, the stress decay takes place much more slowly and the activation energy for the relaxation is higher. Studies have attributed the behavior of the polysulftdes to interchange between the polysulftde linkages of adjacent polymer chains (6). Addition of free sulfur or free thiol groups dramatically increases the rate of relaxation. Small amounts of free thiol can increase the rate several hundredfold (6).  [c.457]

At this point in the process, thermoplastic and chlorosulfonated polyethylene (CSPE) membranes are complete and are ready for packaging. In the case of ethylene—propylene—diene monomer (EPDM), the curing step occurs before the membrane is ready for packaging. The curing process is accomphshed by placing the membrane in a large vulcanizer where the material is heated under pressure to complete the cure.  [c.213]

Zinc oxide is a common activator in mbber formulations. It reacts during vulcanization with most accelerators to form the highly active zinc salt. A preceding reaction with stearic acid forms the hydrocarbon-soluble zinc stearate and Hberates water before the onset of cross-linking (6). In cures at atmospheric pressure, such as continuous extmsions, the prereacted zinc stearate can be used to avoid the evolution of water that would otherwise lead to undesirable porosity. In these appHcations, calcium oxide is also added as a desiccant to remove water from all sources.  [c.225]

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization.  [c.232]

Vulcanization was discovered by Goodyear in 1839 (33). By incorporating elemental sulfur with natural mbber and heating the mass, he found that the resultant compound yielded a tough, elastic material, markedly different from the unvulcanized state. Modem mbber compounding (qv) has come a long way since the discovery of vulcanization, but its explanation stiU remains quite theoretical (34). As a class, SBR is slower curing than natural mbber. This is thought to be caused by the lower unsaturation in SBR.  [c.498]

Dibutyltin and dioctyltin diacetate, dilaurate, and di-(2-ethylhexanoate) are used as catalysts for the curing of room-temperature-vulcanized (RTV) sihcone elastomers to produce flexible siUcone mbbers used as sealing compounds, insulators, and in a wide variety of other appHcations. Diorganotin carboxylates also catalyze the curing of thermosetting siHcone resins, which are widely used in paper-release coatings.  [c.74]

Uses. The uses of zinc oxide can be divided into two groups based on the chemical and physical properties of the compound (47). The largest user, the mbber industry, uses it chemically as a vulcanization activator and accelerator and to slow mbber aging by neutralizing sulfur and organic acids formed by oxidation. Fine oxides are used for fast cures and coarse, sulfated grades for slow cures. Physically, it is a reinforcing agent, a heat conductor, a white pigment, and an absorber of uv light.  [c.423]

Double-Bond Cure Sites. The effectiveness of this kind of reactive site is obvious. It allows vulcanization with conventional organic accelerators and sulfur-based curing systems, besides vulcanization by peroxides. Fast and controllable vulcanizations are expected so double-bond cure sites represent a chance to avoid post-curing. Furthermore, blending with other diene elastomers, such as nitrile mbber [9003-18-3] is gready faciUtated.  [c.476]

New efficient vulcanization systems have been introduced in the market based on quaternary ammonium salts initially developed in Italy (29—33) and later adopted in Japan (34) to vulcanize epoxy/carboxyl cure sites. They have been found effective in chlorine containing ACM dual cure site with carboxyl monomer (43). This accelerator system together with a retarder (or scorch inhibitor) based on stearic acid (43) and/or guanidine (29—33) can eliminate post-curing. More recently (47,48), in the United States a proprietary vulcanization package based on zinc diethyldithiocarbamate [14324-55-1]  [c.477]

Polyisobutylene and isobutylene—isoprene copolymers are considered to have no chronic hazard associated with exposure under normal industrial use. Some grades can be used in chewing-gum base, and are regulated by the PDA in 21 CPR 172.615. Vulcanized products prepared from butyl mbber or halogenated butyl mbber contain small amounts of toxic materials as a result of the particular vulcanization chemistry. Although many vulcanizates are inert, eg, zinc oxide cured chlorobutyl is used extensively in pharmaceutical stoppers, specific recommendations should be sought from suppHers.  [c.487]

Mold temperatures vary between 150—200°C, depending on the mol ding methods and part size. Parts can be molded in 1.5—10 min depending on the configuration and thickness of the part, the mold temperature, and the desired state of cure at demolding. Since most ethylene—acryflc parts are postcured, it is sometimes possible to demold partly cured articles and complete vulcanization in the postcuring oven.  [c.500]

Although PPM can only be cross-linked with peroxides, peroxide or sulfur plus accelerators or even other vulcanization systems like resins can be used for EPDM. The choice of chemicals used in an EPDM vulcanizate depends on many factors, such as mixing equipment, mechanical properties, cost, safety, and compatibiUty. In sulfur vulcanization, ENB-containing EPDM is about twice as fast as DCPD-containing EPDM. If peroxide cures are requited for better heat stabiUty, DCPD-containing EPDM gives higher cure states than PPM. The reactivity of ENB—EPDM is lower in peroxide cures. Por peroxide cures of PPM and to a lesser degree of DCPD—EPDM, activators such as sulfur, acrylates, or maleimides are also needed.  [c.504]

Extrusion. Extmsion techniques are used in the preparation of tubing, hose, O-ring cord, preforms and shaped gaskets. Typical extmsion conditions are 70 to 85°C for the barrel temperature and 95 to 110°C for the head temperature. The extmded forms are normally cured in a steam autoclave at 150 to 165°C. Some special grades of peroxide curable fluorocarbon elastomers can be hot air vulcanized.  [c.514]

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]

The duck is glued in thin layers (plies) with a rubber compound and vulcanized (cured). The number of plies used to make a belt and their quality defines the strength of the belt (e.g. 3 ply x 32 or 3 ply x 34, etc.).  [c.204]

Very recently Jeon and Seo used AES depth profiling to determine the effect of curing temperature on adhesion of natural rubber to brass [46]. In their investigation, natural rubber was vulcanized against a thin brass film that was sputtered onto a glass plate. After vulcanization, the rubber was removed from the glass and AES was used to construct depth profiles starting from the brass and proceeding toward the brass/rubber interphase. Fig. 42 shows the copper and sulfur profiles (top) and the zinc and oxygen profiles (bottom) that were obtained for various vulcanization temperatures between 130°C and 190°C. For the samples vulcanized at 130°C, a shoulder appeared near the end of the copper peak. This shoulder coincided with a peak in the sulfur profile, suggesting that a copper sulfide was formed. There was also a peak at the end of the zinc profile that coincided with a peak in the oxygen profile, suggesting formation of zinc oxide. Considering the atomic concentrations detected for the various elements, it was suggested that there was too much sulfur and too much zinc for only copper sulfide and zinc oxide to form. Therefore, it was also suggested that some zinc sulfide also formed at lower temperatures.  [c.293]

This is not an issue when vulcanizing certain sulfur-cured natural rubbers against brass, however. It was known as early as 1862 that coating metal with a layer of electrodeposited brass created strong bonds to rubber vulcanized in contact with the surface [55]. The mechanisms of adhesion are still being actively researched and debated in the literature, but appears related to both chemical bonding due to formation of CutS-Sv-NR bridges [56] and mechanical interlocking with a porous, dendritic sulfide film formed in situ during the vulcanization process [57]. More recent work emphasizes the potential importance of both mechanisms [58]. This process is extremely important in the tire industry for obtaining adhesion of natural rubber compounds to steel tire cords. The brass plating plays a dual role in this instance. The steel in brass plated prior to drawing into wires, and the lubricious nature of the brass surface improves the drawing process considerably. However, adhesion is very sensitive to rubber formulation and the plating process generates large volumes of hazardous waste. These factors limit the utility of brass interlayers for rubber-metal adhesion, and in many applications solvent or water-borne organic primers and adhesives are used.  [c.451]

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.).  [c.573]

Rubber base adhesives can be used without cross-linking. When necessary, essentially all the cross-linking agents normally used in the vulcanization of natural rubber can be used to cross-link elastomers with internal double carbon-carbon bonds. A common system, which requires heat to work, is the combination of sulphur with accelerators (zinc stearate, mercaptobenzothiazole). The use of a sulphur-based cross-linking system with zinc dibutyldithiocarbamate and/or zinc mercaptobenzothiazole allows curing at room temperature. If the formulation is very active, a two-part adhesive is used (sulphur and accelerator are placed in two separate components of the adhesive and mixed just before application).  [c.640]

Compounding Hierarchy. In designing or making the selection of ingredients for use in a mbber compound the compounder rehes on experience, education, training, and various information sources such as suppHer data and technical reports. Ingredients are generally selected in the following order (/) polymer (natural or synthetic mbber), (2) vulcanization system (curing agent, accelerator(s), or coagent), (J) reinforcing agent and fillers, (4) plasticizers or oil, (5) antioxidant and antiozonant, (6) bonding agent or adhesive, and (7) tackifer if needed.  [c.230]

Butyl and Halobutyl Rubber. Butyl mbber is made by the polymerization of isobutylene a small amount of isoprene is added to provide sites for curing. It is designated HR because of these monomers. Halogenation of butyl mbber with bromine or chlorine increases the reaction rate for vulcanization and laminates or blends of halobutyl are feasible for production of mbber goods. It is estimated that of the - 100 million kg of butyl (UR) and halobutyl (HIIR) mbber in North America, over 90% is used in tire apphcations. The halogenated polymer is used in the innerliner of tubeless tires. Butyl mbber is used to make innertubes and curing bladders. The two major suppHers of butyl and halobutyl polymers in North America are Exxon and Bayer (see ELASTOLffiRS,SYNTHETIC-BUTYLrubber).  [c.232]

A mbber-based adhesive can be a very complex mixture of iagredients. The main component is an elastomer from which the adhesive derives most of its strength. Tackifters are often added both to provide tack and to increase the autohesion or knitting characteristics plasticizers are often added to make the adhesive more permanently soft and pigments and fillers are used to change color, control viscosity, and reduce cost. Solvents, a key portion of solvent-based adhesives, reduce viscosity to allow appHcation and modify the green strength or knitting characteristics. Curing systems, which can build heat resistance and increase the shear strength of the material, are often added also. Metal oxides are frequently used because they participate in the cure in the normal sense of vulcanization of elastomers. These oxides can act as acid acceptors when the base resin is a Neoprene polymer. Antioxidants can also be added in order to provide stabiHty.  [c.235]

Extruded Latex Thread. In the manufacture of extmded latex thread, a concentrated (up to ca 50% soHds) natural mbber latex is blended with aqueous dispersions of vulcanising agents, stabilizers, and white pigments. This compounded latex is held under controlled temperature conditions until partial vulcanization occurs. This has the effect of increasing wet strength and thus the processibiUty of the extmded threads. The matured latex is extmded at constant pressure through precision-bore glass capillaries into a 15—55% acetic 2Lcid[64-19-7] bath where coagulation into thread form occurs. Threads are removed from the coagulation bath by transfer rollers, washed free of excess acid with water, and conducted through a dryer, after which a sihcone oil-based finish is appHed and the threads are formed into multiend ribbons. The ribbons are then vulcanized by multiple passes on a conveyer belt through an oven that can increase curing temperature in stages up to about 150°C. After vulcanization the multiend ribbons are packed without support in boxes for shipment to the customer. A typical extmded latex thread production line is shown in Figure 3. Latex thread production rates vary with thread size and equipment but, owing to hydrodynamic drag and the weak nature of the coagulating thread, maximum line take-up speeds are about 30 m /min.  [c.306]

In 1839, Charles Goodyear developed a technique for vulcanizing rubber. He blended natural rubber with sulfur and placed it on his wood stove, then noticed that the heat from the stove had cured the mbber into a water-impermeable sheet on one of his failed mailbags (1). In 1844, Goodyear appHed for and received a patent for his invention. Because of the shortage of natural mbber at that time, a mhher-red aiming process, based on steam pressure to devulcanize used mbber, was developed in 1858 (1). The cured ground mbber was subjected to steam pressure for 48 hours. High cost siUcone mbber polymers are reclaimed in much the same way in the 1990s, although most synthetic polymers requite more compHcated techniques.  [c.12]

Nonsulfur Vulcanizing Agents. Many high performance specialty elastomers do not contain diene moieties ia their molecular stmcture and therefore caimot be sulfur-cured. These elastomers require cross-linking agents capable of reacting with the specific functional group(s) contained by the specific elastomer. Some common nonsulfur curatives iaclude peroxides, dihmctioaal resias, and metal oxides.  [c.236]

There are three generally recognized classifications for sulfur vulcanization conventional, efficient (EV) cures, and semiefficient (semi-EV) cures. These differ primarily ki the type of sulfur cross-links that form, which ki turn significantly influences the vulcanizate properties (Eig. 8) (21). The term efficient refers to the number of sulfur atoms per cross-link an efficiency factor (E) has been proposed (20).  [c.238]

Vulcanizing Agents. Tire compounds are almost exclusively cured (cross-linked) with sulfur. Sulfenamides, thiazoles, thiurams, guanidine, and carbamates are the most popular choices to accelerate curing. Efficient vulcanization (EV), semiefficient (semi-EV), and the conventional curing systems are all used, sometimes in the same tire for different compounds/components. They are also varied depending on the mbber or mbber combinations used within a given compound, ie, a compound using a blend of NR and SBR uses a more efficient system than the NR alone may require.  [c.251]

Silicone Room Temperature Vulcanizing Gross-Linking. Condensation-cured polydimethylsiloxanes contain terminal silanol groups which condense with the silanols produced by ambient moisture hydrolysis of acyloxysilanes. Methyltriacetoxysilane, ethyltriacetoxysilane, and tetraacetoxysdane are the most commonly used cross-linking agents.  [c.40]

Reaction of TYZOR DC and 1,3-propanediol gives titanium 1,3-propylenedioxide bis(ethyl acetoacetate) [36497-11-7J, which can be used as a noncorrosive curing catalyst for room-temperature-vulcanizing siUcone mbber compositions (99). Similar stmctures could be made, starting with titanium bis-acetylacetonates, such as that shown in stmcture (9).  [c.147]

The salts of the 0-esters of carbonodithioic acids and the corresponding 0,i -diesters are xanthates. The free acids decompose on standing. Potassium ethyl xanthate was first prepared ia 1822 by W. C. Zeise from potassium hydroxide, carbon disulfide, and ethanol. Most alcohols, including cellulose, undergo this reaction to form xanthates, but normally phenols do not (see Fibers, regenerated cellulosics). Potassium phenyl xanthate was prepared ia 1960 from potassium phenoxide and carbon disulfide ia dimethylformamide (1). The preparation of phenoHc xanthates has been expanded by the use of dialkyl ethers of mono- or polyethylene glycols or sulfolane (2). Xanthates remained a laboratory curiosity until the turn of the twentieth century when the mbber iadustry developed a use for them ia the curing and vulcanization of mbber (see Rubber chemicals Rubber compounding). Comehus Keller s iavention of xanthates as flotation collectors for the nonferrous metal sulfides ia 1927 (3) ranks as the chemical iavention that had the greatest impact ia flotation (4) (see Flotation). This is the principal use for the nonceUulose xanthates several of the alkah metal xanthates are commercially available.  [c.359]

The polyamines also are used in several ways in the manufacture and processing of elastomers, polymers, and related materials. A significant volume of ethyleneamines is used in the coagulation of SBR and other synthetic mbber latexes (370—373) (see Elastomers, styrene-butadiene rubber Latex technology). They also are used in vulcanization processes for various mbbers including thiodiethanol (374), vinyl acetate copolymer (375), ethylene copolymer (376), EPDM terpolymer (377—379), SBR (380), modified diene (381,382), chloroprene telomer (383), and urethane (384). Ethyleneamines and certain of their derivatives are also used in a variety of urethane systems as curing agents, catalysts, polyol precursors, stabilizers, and internal parting agents—even in the recycling of rigid polyurethane waste. EDA also finds use as a curing catalyst for phenoHc resins (qv), a stabilizer for urea resins, an antistatic treatment for polystyrene foam, and as a polymerization inhibitor for isoprene. EDA is a key component of the polymer in spandex fiber (see Eibers, elastomers). TETA is a popular curing agent for furfural resin binders for molded graphite stmctures and foundry molds and EDA finds use in systems for etching polyimide Aims. EDA reacts with haloalkylalkoxysilanes and phthalocyaninatosilanols to make agents that improve the adhesion between inorganic surfaces and polymers. Scmbber solvents containing TETA are used to remove acrylate and other monomer vapors from exhaust streams generated during handling and processing operations, such as latex paint vehicle manufacturing. The bisamide made by reaction of 1 mole of EDA with 2 moles of stearic acid, [ethylenebis(stearamide)], is used as an external lubricant for ABS resin and PVC, parting material, viscosity regulator, preservative, and surface gloss enhancer. It is also useflil as a defoamer in paper mill operations and certain detergent formulations (see Amides, fatty acid).  [c.49]

Chemically modified nitrile mbbers are also produced commercially with the objective of changing thek chemistry in such a way that specific properties are enhanced (8). The oldest of the chemically modified NBRs are the carboxylated varieties, made by copolymerizing methacrylic or acryUc acid with the butadiene and acrylonitrile. The resultant products, which typically contain 2—6% by weight of the acid monomer, can be vulcanized with polyvalent metals in addition to the normal sulfur or peroxide cure systems (9). The most outstanding result of this modification is a large improvement in abrasion resistance. Another chemical modification currently in use is the copolymerization of a monomer which causes an antioxidant stmcture to be attached to the polymer (10). The result is improved resistance to oxidation, particularly after the mbber has been exposed to a hydrocarbon fluid that would normally extract a conventional antioxidant from the polymer, leaving it unprotected. The most recent and potentially the most important chemical modification is hydrogenation of the polymer so that Httle of the unsaturation remains (11—15). This results in a product with much improved resistance to oxidation and weathering, but with Httle or no sacrifice in other useful properties. The usual procedure is to hydrogenate in a solution process until just enough unsaturation is left to provide sites for curing, using catalysts based on mthenium, rhodium, or palladium. A latex reduction process has been reported using hydrazine and an oxidizer such as hydrogen peroxide (16,17). Other chemical modifications such as attachment of isocyanate or hydroxyl functionahty have been reported (18), but have not become commercially significant.  [c.516]

Curing Systems. The most commonly used vulcanizing agent for the polyethers not containing AGE, that is, ECH and ECH—EO, is 2-mercaptoimidazoline, also called ethylenethiourea [96-45-7]. Other commercially appHed curing agents include derivatives of 2,5-dimercapto-l,3,4-thiadiazole, trithiocyanuric acid and derivatives, bisphenols, diamines, and other substituted thioureas.  [c.557]

In addition to the vulcanizing agent, an acid scavenger that acts as an activator is required. Eor most of the curatives, a lead-containing compound, such as red lead oxide, Htharge, lead phthalate, and lead phosphite, is used most commonly. However, lead-containing materials cause mold fouhng during mol ding operations. This has led to the use of other activators, such as calcium oxide or hydroxide and magnesium oxide for the thiourea curatives. These, and weaker bases such as calcium carbonate and barium carbonate, are used with the dinucleophilic curatives, the dimercaptothiadiazoles and derivatives and trithiocyanuric acid and derivatives. The function of these activators during curing is to scavenge HCl to drive the cross-linking reaction and prevent the HCl from causing backbone cleavage of the polymer.  [c.557]

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing  [c.475]

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator.  [c.638]

Peroxides. Peroxides cure by decomposing on heating into peroxy radicals which abstract a hydrogen from the elastomer and generate a polymer radical. Most of these radicals immediately combine to form cross-links. Peroxides offer the advantage of curing both saturated and unsaturated rubbers and produce quite thermally stable carbon-carbon cross-links. However, the peroxide curing has some disadvantages because of the poor tensile and tear strengths obtained, many antioxidants cannot be used, and it has higher cost than sulphur vulcanization.  [c.639]


See pages that mention the term Vulcanization and curing : [c.1005]    [c.1011]    [c.428]    [c.65]    [c.188]    [c.455]    [c.576]    [c.650]   
Langes handbook of chemistry (1999) -- [ c.7 , c.10 ]