Polybutadiene resilience

The property of polybutadiene of most interest to the mbber compounder is excellent abrasion resistance coupled with excellent resilience. The polymer has very high rebound and low heat generation. With a few exceptions, such as the core of soHd golf balls, the polymer is blended with other polymers to take advantage of its excellent abrasion and rebound. Uses in North America are as follows tires, 500,000 t (74%) plastic modification,... 

Processings and Properties. Polybutadiene is compounded similarly to SBR and vulcanised with sulfur. The high cis-1,4 type crystallizes poorly on stretching so it is not suitable as a "gum" stock but requires carbon black reinforcement. It is generally used for automotive tires in mixtures with SBR and natural mbber. Its low T (—OS " C) makes it an excellent choice for low temperature tire traction, and also leads to a high resilience (better than natural mbber) which ia turn results ia a lower heat build-up. Furthermore, the high i j -polybutadiene also has a high abrasion resistance, a plus for better tire tread wear. 

This lower has a number of ramifications on the properties of polybutadiene. For example, at room temperature polybutadiene compounds generally have a higher resilience than similar natural rubber compounds. In turn this means that the polybutadiene rubbers have a lower heat build-up and this is important in tyre applications. On the other hand, these rubbers have poor tear resistance, poor tack and poor tensile strength. For this reason, the polybutadiene rubbers are seldom used on their own but more commonly in conjunction with other materials. For example, they are blended with natural rubber in the manufacture of truck tyres and, widely, with SBR in the manufacture of passenger car tyres. The rubbers are also widely used in the manufacture of high-impact polystyrene. 

In a block copolymer, a long segment made from one monomer is followed by a segment formed from the other monomer. One example is the block copolymer formed from styrene and butadiene. Pure polystyrene is a transparent, brittle material that is easily broken polybutadiene is a synthetic rubber that is very resilient, but soft and opaque. A block copolymer of the two monomers produces high-impact polystyrene, a material that is a durable, strong, yet transparent plastic. A different formulation of the two polymers produces styrene-butadiene rubber (SBR), which is used mainly for automobile tires and running shoes, but also in chewing gum. 

FIGURE 9.18 (continued) (b) Resilience measurements of elastomers. Samples of chlorobutyl rubber (CIIR), polybutadiene rubber (BR), and cross-linked recombinant resilin. (From Elvin, C.M., Carr, A.G., Huson, M.G., Maxwell, J.M., Pearson, R.D., Vuocolol, T., Liyou, N.E., Wong, D.C.C., Merritt, D.J., and Dixon, N.E., Nature, 437, 999, 2005.)... 

Polybutadiene is produced by solution polymerisation, and one important feature governing the performance of the resultant polymer is the cis 1,4, and 1, 2 vinyl contents. High cis 1,4 polymers (>90%) have a Tg around -90 °C, and hence exhibit excellent low temperature flexibility only exceeded by the phenyl silicones. They also exhibit excellent resilience and abrasion resistance unfortunately the high resilience gives poor wet grip in tyre treads, and hence this rubber finds limited use as the sole base for such compounds. 

Polybutadiene based compounds can be cured by sulphur, sulphur donor systems and peroxides. Less sulphur and a higher level of accelerators are required when compared to NR. The cure of polybutadiene by peroxides is highly efficient in that a large number of crosslinks are produced per free radical, the resultant highly crosslinked rubber exhibiting high resilience this factor is utilised in the manufacture of superballs . 

This ABA block copolymer consists of stiff polystyrene (PS) and resilient polybutadiene blocks. The domains of these TPEs have characteristic Tt values of 100 and —80 C, respectively. The polybutadiene blocks retain their flexibility at low temperatures, and the polystyrene blocks lose their stiffness when the polymer is heated above 110 C. A related thermoplastic is a transparent AB block copolymer of styrene and butadiene (K-resin). 

The major use for polybutadiene is in tires, with over 70 percent of the polymer produced used by the tire industry. Cured polybutadiene has excellent low-temperature properties, high resiliency, and good abrasion resistance due to its low glass transition temperature. However, this same fundamental property also leads to very poor wet skid resistance. For this reason, polybutadiene is blended with other polymers such as natural rubber and... 

There is also a fairly large market for high cis BR in solid core golf balls. In this application, the polymer is compounded with zinc acrylate and the mixture is cured with peroxide.47 This produces an ionically cross-linked compound that has outstanding resilience. The covers are also ionomers with superior cut resistance. In the last few years the golf ball market has been shifting away from the traditional wound ball to these new solid core balls that use polybutadiene. 

Polybutadiene with no substituent groups larger than hydrogen has greater resilience than natural rubber, in which a methyl group is contained in each iso-prcnc repeating unit. Polychloroprenes (neoprenes) have superior oil resistance but lose their elasticity more readily at low temperatures since the substituent is a bulky, polar chlorine atom. (The structures of these monomers are given in Fig. 1-4.)... 

The next step to discovery was the suggestion that we might lessen the cold flow of BR by adding very short end blocks of polystyrene. Because the chain ends do not contribute appreciably to the vulcanized state, we hoped that the abrasion resistance and resilience of polybutadiene would be little affected by the very low molecular weight end blocks of polystyrene. Processability problems with the polybutadiene led us to use a low molecular weight in the polybutadiene portion. Samples of this type were made for evaluation. 

Polybutadiene is an elastomeric material with good elastic properties and outstanding toughness and resilience. However, it has relatively poor resistance to oils, solvents, oxidation, and abrasion. Polystyrene, on the other hand, is relatively chemically inert and is quite resistant to alkalis, halide acids, and... 

In commercial thermoplastic S-B-S rubber, the end-block phase is present in a smaller proportion with a styrene-to-butadiene (end-block-to-midblock) ratio in the range 15 85 to 40 60 on weight basis. The useful temperature range of S-B-S copolymer lies between the Tg of polybutadiene and polystyrene. Below the Tg of polybutadiene, the elastomeric midblocks become hard and brittle. Above the Tg of polystyrene, the domains soften and cease to act as cross-links for the soft midblocks. Between the Tg of both homopolymers, however, the hard styrene domains prevent the flow of the soft elastomeric butadiene midsegments through a network similar to vulcanized rubber. Therefore, within normal use temperature, S-B-S block copolymer retains the thermoplasticity of styrene blocks and the toughness and resilience of the elastomer units. 

Polybutadiene Higher resilience than similar natural rubber compounds, good low-temperature behavior and adhesion to metals, but poor tear resistance, poor tack, and poor tensile strength Blends with natural rubber and SBR manufacture of high-impact polystyrene... 

Apart from the rather expensive and inferior methyl rubber produced in Germany during World War I, the first industrial production of synthetic rubbers took place in 1932, with polybutadiene being produced in the USSR, from alcohol derived from the fermentation of potatoes, and neoprene (polychloroprene) being produced in the USA from acetylene derived from coal. In 1934 the first American car tyre produced from a synthetic rubber was made from neoprene. In 1937 butyl rubber, based on polyisobutylene, was discovered in the USA. This material has a lower resilience than that of natural rubber but far surpasses it in chemical resistance and in having a low permeability to gases. The chemical structures of these materials are shown in fig. 6.10. 

Very rarely is polybutadiene used by itself. It is generally used as a blend with other elastomers to impart better resiliency, abrasion resistance, and/or low-temperature properties, particularly in the manufacture of automobile tire treads, shoe heels and seals, gaskets, seals, and belting. 

Figure 3 Resilience measurements of cross-linked elastomers chlorobutyl rubber (CNR), polybutadiene rubber (BR), and cross-linked recl-resilin. Reproduced with permission from Elvin, C. M. Carr, A. G. Huson, M. G. etal. Nature 2005,437,999. Copyrighf 2005 Nature Publishing Group.

Thermoplastic rubber is a relatively new class of polymer. It has the solubility and thermoplasticity of polystyrene, while at ambient temperatures it has the toughness and resilience of vulcanized natural rubber or polybutadiene. These rubbers are actually block copolymers. The simplest form consists of a rubbery mid-block with two plastic end blocks (A-B-A), as shown in Figure 5.7. Examples of commercial products are Kraton and Solprene . These materials are often compounded with plasticizers to decrease hardness and modulus, eliminate drawing, enhance pressure-sensitive tack, improve low-temperature flexibility, reduce melt and solution viscosity, decrease cohesive strength or increase plasticity if desired, and substantially lower material costs. Low levels of thermoplastic rubbers are sometimes added to other rubber adhesives. These materials are used as components in the following applications PSAs, hot-melt adhesives, heat-activated-assembly adhesives, contact adhesives, reactive contact adhesives, building construction adhesives, sealants, and binders. Two common varieties of thermoplastic rubber adhesives are styrene-butadiene-styrene (S-B-S) and styrene-isoprene-styrene (S-I-S). ... 

High-impact polystyrene (HIPS) is a graft copolymer. It is a PS backbone with chains of polybutadiene grafted onto the backbone. PS gives the material strength, but the rubbery polybutadiene chains give resilience to make it less brittle. 

An increase in the amount of carbon black in the polybutadiene phase increases the compound tensile strength, tear strength, and resilience. 

Polybutadiene - byu-to- dl- en (1939) n, A synthetic rubber made from 1,3-butadiene (H2C=CH-CH=CH2). The cis type has superior abrasion resistance and resilience, while the trans type is similar to natural rubber See image). 

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