Cross-linking vulcanization

When the temperamre is lowered, rubbers become stiff and brittle. All rubbers eventually stiffen to a rigid, amorphous glass at the glass transition temperature (Tg). This temperature also indicates the low-temperature service limit of the rubber. Tg values are dependent on the structure, degree of cross-linking (vulcanization) and isomeric composition of the rubber. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic mbbers (TRs). SBS contains butadiene—soft and elastic—and styrene— hard and tough—domains. Because the styrene domains act as cross-links, vulcanization is not necessary to provide dimensional stability. TRs generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. Due to their nature, TR soles show low surface energy, and to reach proper adhesion a surface modification is always needed. 

Identical to chemically cross-linked (vulcanized) elastomers, the modulus of radiation cured gum elastomers depends on the concentration of elastically effective network strands and temperature. ... 

In 2004, Berstorff introduced a combined rubber extruder/gear pump, patent pending, for the production of dynamically cross-linked vulcanized thermoplastic elastomers (TPE-V) (DE 101340701 Al). A short rubber extruder, with a gear pump connected downstream,... 

In cross-linking studies it is sometimes useful to adopt an exactly opposite approach to cross-link ( vulcanize ) previously prepared linear chains. This process is applied in practice many different ways, mostly in the rubber industry. For study purposes, reversible cross-linking is most suitable because the network can subsequently be destroyed, for example by hydrolysis. Reactions of suitable macromolecules with chelating compounds are interesting from this point of view. 

Hexadiene is utilized as a third co-monomer in ethylene/propylene elastomers. While the terminal double bond is incorporated into the polymeric chain, the internal one is not and can be cross-linked (vulcanized) to confer... 

Network polymers can also be made by chemically linking linear or branched polymers. The process whereby such a preformed polymer is converted to a network structure is called cross-linking. Vulcanization is an equivalent term that is used mainly for rubbers. The rubber in a tire is cross-linked to form a network. The molecular weight of the polymer is not really infinite even if all the rubber in the tire is part of a single molecule (this is possible, at least in theory), since the size of the tire is finite. Its molecular weight is infinite, however, on the scale applied in polymer measurements, which require the sample to be soluble in a solvent. 

Cross-linking, vulcanization, and grafting are some of the polymer reactions that take place on functional or reactive groups located in the polymer main chain. We have already discussed some of these reactions in the preceding sections. We now discuss other examples of modification of polymers based on reactive monomers, oligomers, or polymers. 

The dispersed elastomer particles are uncross-linked (TPE-O or TPO), but may also be cross-linked (TPE-V). The cross-linking (vulcanization) occurs during compounding in closed mixers (batchwise) or with twin-screw extruders (continuous). 

Elastomers are also sometimes known as rubbers. They are also irreversibly cross-linked by covalent bonds. The elastomer raw materials (rubber base) generally have higher molar masses than the thermoset raw materials. In addition, the cross-linked network produced by cross-linking (vulcanization, hardening) is not so densely cross-linked as in the case of the thermosets. For this reason, elastomers have a high segmental mobility above the glass transition temperature. They deform readily under stress above this temperature, but because of their cross-linked structure, they rapidly return to their initial state when the stress is released because the initial state corresponds to the state of maximum conformational entropy. 

The first elastomeric adhesive was prepared by the end of eighteenth century and was composed of naphtha solutions of natural rubber. Such adhesives are stUl in nse in the production of temporary joints in textile, art material and footwear (where they are called cement adhesives). One of the early apphcations of the natural rubber adhesives was the laminating of textile products to impart waterproof resistance. For this application, cross-linking (vulcanization) after application of adhesive was necessary. 

Several types of reactions involving polymers themselves have been studied using VS, including cross-linking, vulcanization, and degradation. The same methods are used for these processes as are used to study polymerization reactions. 

Swelling has consequential implications for the apphcations of polymers, particularly elastomers where solvent contact is likely. For example, olefinic thermoplastic elastomers are not affected by water or aqueous solutions of chemicals and resist acids and bases. Hydrocarbon solvents tend to swell and soften TPO products. This effect is much more pronounced for softer grades. Cross-linking (vulcanization) is used to improve mechanical properties, to reduce swelling in oils and solvents, and to... 

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