Rubber grades commercial

Several partially cross-linked butyl rubbers are commercially available. The more tightly cross-linked grades are designed for butyl tapes. On the other hand, various depolymerized butyl rubbers and butyl/plasticizers blends are also available. 

For the preparation of filler reinforced elastomer composites, most frequently commercial rubber grades with variable microstructure and broad molar mass distribution are applied. The typical rubber grades, considered in the present review, are as follows ... 

In addition to the commercial rubber grades, model polymers with variable molar mass and narrow molecular weight distribution are often used for studying reinforcement mechanisms. (In Sect. 4.3 we consider a special S-SBR type with 29 vol.% vinyl and 25 vol.% styrene units Mw/Mn=l.l). 

Anionic Polymerization. The oldest process, no longer carried out commercially, uses sodium as initiator. It was described as early as 1910 in an English patent, and was also published shortly afterward by Harries. For better distribution, the sodium is added as a suspension in paraffin oil or hexane and the polymerization is carried out in bulk in a kneader or screw extruder. During the process, about 70% of 1,2 structures are formed in the polymer. The products found application in Germany as buna rubbers [butadiene-natrium (sodium) polymerizate], classified by numbers, and in the USSR as SK sowjetischer kautschuk (soviet rubber)] grades. The Russian products carry the letters SKA when the butadiene is derived from petroleum and SKB when it is produced from alcohol. Numbered buna production ended as early as 1939 in Germany, with the exception of buna 85, which was used in the production of hard rubber. 

FIGURE 1.3 Structural units in the polychloroprene chain (typical commercial rubber grade)... 

The butadiene-acrylonitrile rubbers were first prepared about 1930 about five years after the initial development of free-radical-initiated emulsion polymerisation. Commercial production commenced in Germany in 1937, with the product being known as Buna N. By the late 1980s there were about 350 grades marketed by some 20 producers and by the early 1990s world production was of the order of 250000 tonnes per annum, thus classifying it as a major special purpose rubber. 

A somewhat different approach to the production of thermoplastic polyolefin rubbers has been adopted by Allied Chemical with their ET polymers. With these materials butyl rubber is grafted on to polyethylene chains using a phenolic material such as brominated hydroxymethyl phenol. The initial grades of these polymers, which were introduced commercially towards the end of the 1970s, had polyethylene butyl rubber ratios of 50 50 and 75 25. Both low-density and high-density polyethylene-based varieties were produced. 

During the next few years PVC was steadily developed in the United States and in Germany. Both countries were producing the material commercially before World War II. In Great Britain, ICI in 1942 and the Distillers Company in 1943 also commenced pilot-plant production of PVC, a material then in demand as a rubber substitute for cable insulation. Paste-forming grades suitable for the production of leathercloth also became available soon afterwards. 

In the preceding sections, our discussion has been limited to softer grade elastomer-plastic vulcanizates. Commercial interest, however, also centers on another major family of polymer blends, semi-rigid impact resistant polyolefins. Thus, we report some of our findings on PRP triblock copolymer and EVA rubber blends without... 

Acrylated rubber These are based on styrene butadiene and have become commercially available only relatively recently. They are manufactured in several grades but most have the advantage over other materials in this class of being based on white spirit solvent rather than the stronger and more obnoxious xylol. In other respects, they are similar to chlorinated rubber and cost approximately the same, although they are easier to airless spray and the dried film contains less pores. They are considered to have superior weather resistance to chlorinated rubber and vinyl. 

Silicone rubber as a shaft seal and backing material has a number of special applications. It can be used over a temperature range of —60°C to 260°C (—76°F to 500°F) in air or suitable fluids. Its abrasion resistance is good with hard shafts having a 0.000254 mm RMS surface finish. Commercial grades of silicone rubber are compatible with most industrial chemicals up to 260°C (500°F). In lubricating oils, the limiting temperature is 120°C (250°F), but special types have been developed for use up to 200°C (392°F). 

Researchers at Goodyear 121 have successfully exploited route 1 above to produce antioxidant-modified SBR and NBR for example, Chemlgum HR 665, is a commercial grade of nitrile rubber containing a... 

The polymerisation of butadiene results in a polymer with a narrow molecular weight distribution which can be difficult to process. Indeed, commercially available grades present a compromise between processibility and performance. Most polybutadiene rubbers are inherently difficult to break down during mixing and milling, have low inherent tack, and the inherent elasticity of the polymer gives poor extrudability. Peptisers can be used to facilitate breakdown and hence aid processing. 

Commercial grades of HR (butyl rubber) are prepared by copolymerising small amounts of isoprene with polyisobutylene. The isoprene content of the copolymer is normally quoted as the mole percent unsaturation , and it influences the rate of cure with sulphur, and the resistance of the copolymer to attack by oxygen, ozone and UV light. The polyisobutylene, being saturated, however, naturally confers on the polymer an increased level of resistance to these agencies when compared to natural rubber. Commercial butyl rubbers typically contain 0.5-3.0% mole unsaturation. 

The first type was produced from ethylene dichloride and sodium polysulphide. A high molecular weight polymer is obtained with predominantly hydroxyl end groups on the polymer chain. This type of polysulphide rubber was the first commercial grade but has, to a large extent, been superseded. 

The FTIR spectra of Figure 3 comparing a commercial grade rubber (Alloprene CR-20 from ICI) with guayule CR shows the two materials to be essentially identical. Absorption bands characteristic of CR appear near 780 cm" and 736 cm" and represent the secondary C-Cl and the CI rocking... 

Figure 6 Gel permeation Chromatograms of Chlorinated Rubber (a) Guayule CR prepared with AIBN, Ecess Chlorine (b) Guayule CR prepared with AIBN (Cl - 63.7%) (c) Commercial grade CR-5 (Cl - 64-65%)...

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