Natural Rubber Production Processes

The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimillion dollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic web-thickness profile process control is used via computer, microprocessor control. 

The production process of natural rubber in the tree is not yet fully understood. However, it involves a long series of complex biochemical reactions that do not involve isoprene as a monomer, even though the resulting polymer is 100 percent cis 1,4 polyisoprene. Because the tree makes the product, the rubber production process is really one of recovery. 

Up to the time of World War 11, scrap tires contained only natural rubber. Reclaiming processes were well established, and a reasonable proportion (20%) of reclaim was accepted in compounding of new tires. (Frequently, the percentage was much more in other rubber products.) In 1941 the consumption of reclaim was 32% of the consumption of new rubber. 

Methyl Rubber H, a hard grade suitable for battery boxes and other ebonite-type uses which was made by a low temperature process operated at 30-35°C and which took about 3-4 months. During the war 2350 tons of Methyl Rubber were produced but, since it was far inferior to natural rubber, production ceased at the end of the war. 

Kraton synthetic isoprene rubbers are offered as an alternative to natural rubber products, and provide an option for use in applications requiring no discolouration, odour and a high degree of purity. The benefits are described of two currently available synthetic isoprene processing technologies, - Kraton anionically polymerised IR marketed by Shell and Ziegler-Natta IR, with reference to their ability to reduce problems of discolouration, odour and adverse skin reactions, and to improve the overall quality and performance of finished products without sacrificing the traditional benefits of NR. 2 refs. 

Early rubber products were of limited use because they were sticky in hot weather and stiff in cold weather. In 1839, Charles Goodyear accidentally discovered that by heating a sulfur-rubber mixture, a product could be made that was stronger, more elastic, and more resistant to heat and cold than natural rubber. This process is now called vulcanization (after Vulcan, the Roman god of fire). The purpose of vulcanization is to form cross-links between long polymer chains. An example of a cross-link through two sulfur atoms is shown here ... 

Compared with the natural material, raw SBR is more uniform in a variety of ways. Not only is it more uniform in quality so that compounds are more consistent in both processing and product properties but it is also more uniform in the sense that it usually contains fewer undesired contaminants. In addition, over a period of years it has been generally less subject to large price variations. These differences in uniformity have, however, tended to lessen with the advent of improved grades of natural rubber such as Standard Malaysian Rubber which have appeared in recent years. 

Solid SBR is often prefened to natural rubber because of its better thermal oxidative stability, higher abrasion resistance and easier processability. Solid SBRs are generally grouped into three families according to the production method. 

Natural rubber was the only polymer for elastomer production until the advent of synthetics. Natural rubber, however, continues to maintain its competitive edge due mainly to the gain in properties such as high resilience, low hysteresis, low heat buildup, and excellent tack with mechanical properties achieved through the process of vulcanization [114-115]. The industry is said to be self-sufficient with a good technological base and is expected to compete successfully with synthetics because of the edge in properties mentioned above [116,117]. 

There are some applications for a-sulfo fatty acid esters in the production and processing of synthetic materials or natural rubber. Emulsifiers are needed for the emulsion polymerization, antistatic agents improve the properties of polymers, and wetting agents are needed as parting components for elastomers. 

Emulsion polymerization is the most important process for production of elastic polymers based on butadiene. Copolymers of butadiene with styrene and acrylonitrile have attained particular significance. Polymerized 2-chlorobutadiene is known as chloroprene rubber. Emulsion polymerization provides the advantage of running a low viscosity during the entire time of polymerization. Hence the temperature can easily be controlled. The polymerizate is formed as a latex similar to natural rubber latex. In this way the production of mixed lattices is relieved. The temperature of polymerization is usually 50°C. Low-temperature polymerization is carried out by the help of redox systems at a temperature of 5°C. This kind of polymerization leads to a higher amount of desired trans-1,4 structures instead of cis-1,4 structures. Chloroprene rubber from poly-2-chlorbutadiene is equally formed by emulsion polymerization. Chloroprene polymerizes considerably more rapidly than butadiene and isoprene. Especially in low-temperature polymerization emulsifiers must show good solubility and... 

In 1994, the worldwide consumption of rubber was approximately 14.5 million tons a year, of which about 40% consisted of natural rubber. Natural rubber is produced as latex by tropical rubber trees (Hevea brasiliensis). It is processed locally and therefore the quality of natural rubber fluctuates remarkably [ 140]. Due to increasing demand for rubbers, combined with a decreasing production capacity in Asia and a vast increase in labor costs, the price of natural rubber is still rising sharply. In 1990-1994, the average price of natural rubber was about 0.38 /lb, while in 1996 it was already over 0.80 /lb. The remaining 60% of the articles were manufactured from synthetic petroleum-based rubbers such as isoprene rubber, styrene-butadiene rubber, chloroprene rubber and polyurethanes. The quality of synthetic rubbers is constant, and their price varies between 2 and 5 US per kilogram [137-140]. 

They are not found to any extent in natural products, but are produced in the destructive distillation of complex natural substances, such as coal, and are formed in large amounts in petroleum refining, particularly in the cracking process. The first member of the series is ethylene, C2H4. The dienes contain two double bonds between pairs of carbon atoms in the molecule. They are related to the complex hydrocarbons in natural rubber and are important in the manufacture of synthetic rubber and plastics. The most important members of this series are butadiene, C4H5 and isoprene, CsHg. 

On heating a chemical reaction took place between the rubber and sulphur which resulted in production of tough elastic rubber that retained its moulded shape. Natural rubber is plastic in nature while vulcanised rubber is elastic. This vulcanisation process led to a rapid development of rubber industry. 

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