Rubber, natural abundance

Figure 15.15 Natural abundance 2H MAS spectra observed in a series of vulcanised natural rubbers with various vulcaniser (sulfur 1 or 3 wt%) and/or filler (carbon black 0 or 40 wt%) contents. The spinning speed is 0.5 kHz. The number of scans is about 300000. Spectra are simulated with two components (a mobile and a rigid one) with various residual quadrupolar interactions...

In addition to plastics materials, many fibres, surface coatings and rubbers are also basically high polymers, whilst in nature itself there is an abundance of polymeric material. Proteins, cellulose, starch, lignin and natural rubber are high polymers. The detailed structures of these materials are complex and highly sophisticated in comparison the synthetic polymers produced by man are crude in the quality of their molecular architecture. 

Rubber is synthesized by plants via a side branch of the isoprenoid pathway by the enzyme rubber transferase (dy-prenyl transferase systematic name poly-dy-polyprenyl-diphosphate isopentenyl-diphosphate polyprenylcistransferase EC 2.5.1.20). Surprisingly, although this process has been studied for decades, due to the labile nature of the rubber transferase and the fact that it is a membrane-associated enzyme present in relatively low abundance, the identification of its protein subunits remain elusive. For some recent reviews on rubber biosynthesis, please refer to [248-251]. 

Xylene is a colorless, sweet-smelling liquid that burns easily. Xylene occurs naturally in petroleum and coal tar. It is used as a solvent in the printing, rubber, and leather industries. It is also used as a cleaner, paint thinner, and as a component of paints and varnishes. Xylene is one of the top 30 most abundant chemicals produced in the United States by volume. 

Natural rubber is obtained from the Heavea brasiliensis tree. This tree is found in abundance in areas with a tropical climate, such as Brazil, Venezuela, Malaysia, India and East Coast African countries. The traditional method of slitting the bark and letting the milk drip to form a solid mass called latex continues to be the sole method of obtaining natural rubber. 

The branched isoprene unit, which is also synthesized from the C, pool, is the basic structure of terpenoids. Less condensed structures are used as volatile pheromones, e.g., jasmonic acid, menthol, or camphor, or as natural rubber material. More condensed structures such as steroids and hopanoids are part of membranes, influencing their fluidity. They are also highly specific to their source organisms. Best known are cholesterol (in animals and plants), ergosterol (in fungi), and brassicasterol (in diatoms). Besides cellulose, hopanoids are the most abundant biomolecules. 

From 1930, ICI undertook research into polyvinylchloride, but despite its popularity in other countries did not embark on manufacture. There was, understandably, no reason to do so, since natural rubber for electrical insulating applications was available in abundance, and calcium carbide, the source of starting acetylene, was, as Herbert... 

Although not a natural product, used automobile tires are certainly abundant in our society. Ground or shredded rubber waste has been employed to remove mercury from aqueous solution (234-236). Many other metals are extracted from solution (235-237), apparently by adsorption on the carbon black contained in the tire material (236), and while this material has not been used analytically, x-ray fluorescence analysis of the adsorbed metals should be possible. 

Short fibres of glass, rayon, aramid, asbestos and cellulose as reinforcing fillers, have been broadly used in rubber industries due to their high modulus, high strength and low creep. In recent years especially, natural fibres such as jute fibre, cellulose fibre, " coir fibre," " sisal fibre," " etc. have been also widely used in NR composites because they are enviromnental friendly, cheap, abundant and renewable. However, natural fibres also have some disadvantages such as moisture absorption, quality variations, low thermal stability and poor compatibility with the hydrophobic polymer matrix. 

Over the next 30 years much data were collected on the absorption of infrared radiation. It became abundantly clear that absorptions could be correlated with certain bonds or groups of atoms. Correlation charts were drawn up which enabled the structural features present in an unknown molecule to be ascertained. Before World War II infrared spectrometers were individually built and therefore the technique was very much a research tool. During the war there was a huge research effort in the United States to find a substitute for natural rubber, as the source of supply in Malaya was cut off by the Japanese. To assist in this search, the first commercial infrared spectrometers appeared, and since that time infrared spectrometry has been widely used in structure elucidation. 

The attempt to blend natural rubber with epoxy resins resulted from the abundance of natural rubber and that it was a renewable resource. Nevertheless, interfacial adhesion between natural rubber and epoxy resins was weak due to the hydrophobic nature of natural rubber. Thus, it was an interesting experiment to blend the toughened epoxy resins with synthetic reactive liquid rubber. In order to achieve an efficient stress transfer between rubber and the... 

Calcium carbonate (CaCOs) has been widely used as a model system for studying the bio-inspired mineralization process due to its abundance in nature and also its important industrial applications in paints, plastics, rubber, and paper [344], Bio-inspired synthesis of CaCOs crystals in the presence of organic templates and/or additives has been intensively investigated and recent reviews show the wealth of resnlts obtained in the last few years [44,45). 

Polymers as made are usually not suitable for industrial use as plashes, so industry uses addihves and modihers to adjust the properties of the as made polymers to make most of the plastics used today. The hrst polymers that became available are natural products like cellulose, natural rubber, or simple chemicals like phenol and formaldehyde that make bakelite. In order to shape cellulose— the most abundant polymer on earth—into useful products, two things must happen. 

Silica, from natural sources, is used as a feedstock to produce very fine particle precipitated, hydrated, amorphous silica, and fumed silica, both commonly used in different ways as reinforcing fillers in rubber technology. Also, silicone rubber, vital to aerospace and medical applications, is ultimately based on silica as a raw material. Because of the abundance of silica in nature, there will never be a shortage of this raw material. 

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