Rubber, natural prices

Because of the excellent properties of its vulcanisates under conditions not demanding high levels of heat and oil resistance, natural rubber commands a premium price over SBR, with which it vies for top place in the global tonnage... 

Current production of NR is about 5.2 X 10 tonnes. For some years it has enjoyed a premium price over SBR because of its desirable characteristics described above and, compared with other large tonnage polymers, a somewhat restricted supply. Clearly it is difficult to substantially increase the production of such a material in a short period of time and indeed the attractions of other crops such as palm oil as well as the desire to move away from a monoculture economy mitigate against this. The indications are that, unless there is undue intervention of political factors, the future of natural rubber as a major elastomer remains secure. 

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. 

Neoprene, Carothers first practical invention, was made reluctantly, as a kind of side issue to his scientific investigation of polymers. Synthetic rubber was of great commercial interest. The car-happy United States used half the world s natural rubber, and demand had outstripped the supply from wild rubber trees in the Amazon. Price fluctuations on British rubber plantations in Southeast Asia provided further incentive for the development of synthetic substitutes. Du Pont had been trying without success to... 

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]. 

With minor modifications that rubber is still used for passenger cars. It is not suitable for large trucks and bomber tires because of the excess of heat build-up in operation. Before the end of the rubber program, two of the companies, Firestone and Goodrich, had developed processes that produced rubber essentially like natural rubber. Firestone used a lithium catalyst for the polymerization, and Goodrich used a modified Ziegler catalyst. These materials were manufactured for a while until the oil prices became too prohibitive and the natural rubber was again used for heavy-duty tires. 

The balance between natural rubber and SBR is a delicate one. Natural rubber has made a comeback and reversed its downward trend. Developments of rubber farming have raised the yield from 500 Ib/acre/yr to 2,000-3,000. Petrochemical shortages and price increases have hurt SBR. Finally, the trend toward radial-ply tires, which contain a higher proportion of natural rubber, favors this comeback. Fig 18.1 shows the U.S. natural rubber consumption trends vs. U.S. SBR production, where this bounceback of the natural rubber market is very evident from 1980 to the present. The competitive price structure for these two elastomers through the years has been very evident, and their prices are never too far apart. 

Price,C., Allen,G., de Candia,F., Kirkham,M.C., Subramaniam,A. Stress-strain behavior of natural rubber vulcanized in the swollen state. Polymer (London) 11, 486-491 (1970). 

The main reason that this rubber is not used in process industries in place of natural rubber could be that the price of this rubber is much more than that of natural rubber. 

By contrast, cis- 1,4-polyisoprene is produced in limited amounts, since it is not price competitive with natural rubber (owing to the relatively high costs of manufacturing the isoprene monomer). The same applies to trans- 1,4-polyisoprene, which is more expensive than its natural counterparts gutta percha and balata. 

Figure 4-1. Natural rubber prices in the United States during first third of the...

On a global scale, success of rubber plantations in diverse areas such as Malaysia and southern Brazil have drastically altered the price of natural rubber, making extractive rubber production less lucrative... 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

At the end of the 19th century, rubber, with gutta-percha, was used mainly as an electrical insulator on wires and cables. Demand was limited, and the supply of natural rubber at a reasonable price (about 1.00/lb in 1900) was ensured. Some work was done during these years on practical syntheses of isoprene and on the replacement of isoprene by its simpler homolog, butadiene, which had been known since 1863. However, advent of the automobile and accelerated use of electric power rapidly increased the demand for rubber, thus raising its price to about 3.00/lb in 1911. These circumstances focused new attention on the production of a synthetic rubber. S. B. Lebedev polymerized butadiene in 1910, and Carl Dietrich Harries, between 1900 and 1910 established qualitatively the structure of rubber as a 1,A-polyisoprene and synthesized larger quantities of rubberlike materials from isoprene and other dienes. 

Barrier Materials. Polymers are often used as barriers to keep small molecules in or to keep them out. One common example is rubber tubes for tires or more recently the inner liner of tubeless tires. The purpose of such a material is to contain air under pressure to maintain tire inflation. From the data in Table I, it is clear that butyl rubber is a much better material for this purpose than natural rubber. Because of this, butyl rubber has entirely displaced natural rubber from this market. Aside from its prohibitive price, silicone rubber would be totally unsatisfactory for this use because of its high gas permeability. 

SBS production fluctuates or changes according to a number of factors, including market demand, the price of petroleum, and the price of natural rubber. For example, when natural rubber is readily available and inexpensive, the demand for synthetic types of rubber, such as SBS, decreases. Also, when the price of petroleum increases, SBS becomes more expensive to make and production decreases. 

The importance of synthetic rubber industrially is determined by the price at which natural rubber can be bought. At present (March, 1922) the latter sells for such a low price that the synthetic product can not compete with it. 

Natural rubber is obtained from the juice present in various trees and shrubs which grow best in tropical countries. On account of the importance of rubber commercially the trees which yield it are grown systematically on plantations formerly the supply was obtained from natural forests. The intensive cultivation of rubber trees has had a marked effect in lowering the price and insuring a steady supply of rubber. 

Global production and consumption of natural rubber have been growing, although not steadily, during the past decade, as is seen from Table 14.4 [20,21]. The variation in annual growth rate in production is mostly contributed by price and agro-climatic conditions. The growth in consumption also has had its influence on production as is evident from the above table. 

Earlier accounts of the reaction of halogenated products with potassiiun sulfide did not report useful polymeric products [10]. Patrick and Mnookin [11] were the first to report useful polysulfide products that were to become the early basis of the Thiokol Chemical Corp. business. Polysulfides generated interest before and after World War II because natural rubber was difficult to obtain at times and was also high in price [12]. 

Drastic change in the cost of inputs may also result in rapid shifts in technology. Of course, the most familiar example is the recent increase in oil prices which has made past investments predicated on declining prices unattractive. But shifts in the availability of other materials, for example, the loss of natural rubber supplies during World War II, have resulted in major new businesses in the past and may well also in the future. 

As a result of the concurrent progress on the polymerization side, Ludwigshafen and Leverkusen agreed in July 1929 to build a semi-technical works plant for Buna at Knapsack, alongside the carbide works. This plan was blocked by Carl Krauch of Oppau, largely because he wanted to wait until Oppau s methane-to-acetylene electric arc process was ready. A few months later, the Buna program was effectively halted by the onset of the Depression, which soon reduced natural rubber prices to minimal levels. When the production of synthetic rubber was revived in Hitler s Third Reich, the weak Buna, which was a sodium-polymerized polybutadiene, had been displaced by the superior copolymers of butadiene with styrene (Buna S) and acrylonitrile (Buna N or Perbunan). 

American polymer technology was employed in Britain as a result of the 1929 agreement between Du Pont and ICI. Notable, in view of Britain s reliance on natural rubber, was the production, ft-om 1937, by ICI of Du Ponf s synthetic rubber, neoprene The rubber was rather solemnly declared to be incompetitive as regards uses, with natural rubber. The writer has not yet encountered many cases where it would not be extremely competitive. In many instances the price question is no longer important. ... 

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