Synthetic polyisoprene rubbers applications

Jenke [73] studied the extractabihty of aniline, diphenylguanidine, dedenzyl-amine, and triisopropanolamine from a synthetic polyisoprene rubber similar to the material used in pharmaceutical applications. Rubber samples were autoclaved (121 °C) in contact with water or NaCl 0.9% solution for lh.Table 33 presents the concentration of each compound in solution after the extraction procedure using 2g rubber material. Extraction profiles ranged between 1.64 and 3.73 mg/L, with the exception of diphenylguanidine, whose extraction yield reached 11.76 mg/L. 

Synthetic polyisoprenes are superior to natural rubber in terms of consistency of properties. The are also freer of contaminants, and are preferred for applications that require lighter color, for personal care items and for derivatization to chlorinated and cyclized rubber products that are used in the adhesives and coatings industries. 

Polyisoprene (R = CH3) with a c/s-1,4 configuration is common in nature in different species of piants and is known as natural rubber. Trans-polyisoprene is found in two naturai resins known as gutta-percha and balata. Natural or synthetic polyisoprenes, as well as polybutadiene, are among the most common elastomers with many practical uses. Other elastomers with extensive practical applications are copolymers, many of them using butadiene or isoprene in the starting monomer mixture. 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

A true synthetic natural rubber was introduced in the mid-1960s with the exact same chemical structure as latex tapped from a tree. The difference is that natural rubber comes with a variety of other ingredients in the latex that can both add and detract from performance, while polyisoprene is considered relatively pure. In addition, there are some differences in molecular weight distribution that impact performance. Available in both latex and solid forms, this elastomer can be directly substituted for natural rubber in many applications. Adhesives which are not cured tend to have higher creep values than natural rubber, but also exhibit lower tack and green strength properties. Vulcanized adhesive products perform equal to cured natural rubber adhesive products. 

The simplest technique is to dissolve the polymer in the appropriate solvent add the peroxide initiator, which abstracts a hydrogen radical and generates a radical on the polymer chain and then add fresh monomer for grafting onto this site. This technique has been employed in grafting methylacrylate onto natural rubber and synthetic polyisoprene. In this manner, several commercially useful products such as ABS resins have been prepared however, tire elastomers are not made in this manner because of the generation of micro and macro gel particles, which are detrimental to physical properties. In many cases when latex grafting has been used, the product has usually been targeted toward thermoplastic applications rather than rubber applications. 

Natural Rubber Natural rubber, also called India rubber or caoutchouc, is an elastomer that is derived from latex, a milky colloid mainly extracted from rubber trees (Figure 5.1.35). The purified form of natural rubber is polyisoprene, which can also be produced synthetically. Natural rubber is used extensively in many applications and products, as is synthetic rubber. Today, the global annual production of natural rubber is 10 Mio. tonnes, which is about 40% of the total rubber production (natural and synthetic). The three largest producing countries of natural rubber are Thailand, Indonesia, and Malaysia. 

We will now apply to natural rubber, i.e., NR, biosynthesis what we have learned so far. As mentioned before, in 2005 approximately 10 million tons of NR was produced worldwide for commercial use, from which about 15% was consumed in the United States. While the United States is self-sufficient in S5mthetic mbber production, with substantial export activities, no NR is produced domestically. The development of a U.S.-based supply of NR is recognized in the Critical Agricultural Materials Act of 1984 (Laws 95-592 and 98-284). The Act recognizes that NR latex is a commodity of vital importance to the economy and the defense of the nation. It is important to emphasize that synthetic polyisoprene does not match the performance of imported Hevea NR in several applications, so NR remains irreplaceable. 

Up to the present time, the market for synthetic polyisoprene has been only a small fraction of the total rubber market. The low cost of SBR and the ready availability, up until now, of natural rubber, have rather discouraged developments with this material. It has therefore tended to be used for those applications where the marginal difference in properties between the synthetic material and natural rubber are most significant. It is probably fair to say that in the 1970s the greatest interest in synthetic polyisoprene was in... 

As for natural rubber the most important single outlet is in tyre production but benefits may be obtained in the manufacture of products as diverse as elastic bands, bridge bearings, conveyor belts and pharmaceutical goods. Certain specific attributes of synthetic polyisoprenes have made them attractive to manufacturers. For example, the lack of non-rubbers allows higher resistivity values to be reached in electrical applications and the low modulus provides easy extensibility and therefore comfort for items such as respirator masks and bathing hats. 

Other polymeric binders, natural and synthetic, may be found as paints or varnishes in modern artworks and installations. Artists very easily adopt resins developed as industrial coatings or for specialized applications, and use them according to their creative needs. Natural rubber latex is a water dispersion of 1,4-ds-polyisoprene particles where pigments can be added to give coloured paints. By means of Py-GC/MS the presence of these paints can be easily assessed. As shown in Figure 12.13, the principal marker peaks in the pyrogram are those of isoprene, limonene and other cyclic dimers. 

As of this date, there is no lithium or alkyl-lithium catalyzed polyisoprene manufactured by the leading synthetic rubber producers- in the industrial nations. However, there are several rubber producers who manufacture alkyl-lithium catalyzed synthetic polybutadiene and commercialize it under trade names like "Diene Rubber"(Firestone) "Soleprene"(Phillips Petroleum), "Tufdene"(Ashai KASA Japan). In the early stage of development of alkyl-lithium catalyzed poly-butadiene it was felt that a narrow molecular distribution was needed to give it the excellent wear properties of polybutadiene. However, it was found later that its narrow molecular distribution, coupled with the purity of the rubber, made it the choice rubber to be used in the reinforcement of plastics, such as high impact polystyrene. Till the present time, polybutadiene made by alkyl-lithium catalyst is, for many chemical and technological reasons, still the undisputed rubber in the reinforced plastics applications industries. 

All rubbers, glasses, and plastics are polymers. You are probably familiar with natural polymers like cellulose (the building block of plant fibers) and synthetic polymers like polyethylene (plastic milk cartons), polyisoprene (automobile tires), polyethylene terephthalate (soft drink bottles), polymethyl methacrylate (Plexiglas ), polyvinylidene chloride (transparent plastic wrap), polytetrafluoroethylene (Teflon ), and various polyesters (fabrics). Polyvinyl chloride, the polymer shown earlier, is used to make rigid pipes, house siding, and protective coverings for automobile seals and dashboards, among many other applications. 

Chemically, natural rubber is natural ds-polyisoprene. The synthetic form of natural rubber, synthetic ds-polyisoprene, is called isoprene rubber. The physical and mechanical properties of IR are similar to the physical and mechanical properties of natural rubber, the one major difference being that isoprene does not have an odor. This feature permits the use of IR in certain food-handling applications. 

The technology of heterophase polymerization has its model in Nature, with the production of polyisoprene by many plants and also by the Hevea brasiliatsis tree, which serves as the commercial source of natural rabber that, today, is of increasing economic importance [1]. The industrial exploitation of heterophase polymerization began almost 100 years ago, with the first successful production of synthetic rubber in Germany [2]. Today, millions of tons of synthetic polymer dispersions (latexes) are produced via heterogeneous polymerizations for a variety of applications, including commodities and sophisticated specialties [3-5]. 

Natural rubber (NR) is elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloid produced by some plants (Hevea brasiliensis, a member of the spurge family, Euphorbiaceae). The plants are tapped by making an incision in the bark of the tree and collecting the sticky, milk-coloured latex sap, which is refined into usable rubber. The purified form of NR is the chemical polyisoprene, which can also be produced synthetically. NR is used in many applications and products, as is synthetic rubber. It is normally very stretchy and flexible and extremely waterproof. 

Many applications are being found for synthetic rubbers, which are synthetic polymers possessing rubber-like properties. Among those available commercially are butadiene-styrene and butadiene-acrylonitrile (called Buna rubbers), polyisoprene, and polybutadiene. Their properties may be modified considerably more than vulcanized rubbers, particularly with respect to resistance to oxidizing agents, solvents, and oils. Their adhesion to metals, however, is generally poorer. 

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