Theoretical Comparison Between Synthetic Rubber and Latex Natural Rubber

Another example is the chemical structure of natural rubber (latex) and synthetic rubber and their pathway from crude oil to rubber.

Natural latex can be extracted from the inner bark of many trees. According to Katz, the white sticky sap of plants such as milkweed and dandelions is also latex, and natural rubber is a polymer of isoprene (2-methyl-l, 3-butadiene) in the form of folded polymeric chains which are joined in a network structure and have a high degree of flexibility (1981). Below is the pathway of synthetic rubber products:

Crude oil —> naphtha —> butadiene + styrene —> synthetic rubber and latex —» tires and rubber products

Carbon and hydrogen are the main atoms in the molecular structure of natural rubber. Natural rubber has a flexible molecular chain due to its amorphous mass of coiled structures that make it too soft to be used for any useful purposes. Therefore, its properties were changed using special processing techniques. The long and flexible chain structure of natural rubber allows it to retain its original shape when it is compressed or stretched. Tensile load can cause changes as the bonds and the chains become elongated. More and more stress can increase the degree of crystallinity, and crystallinity causes greater strength, hardness, and rigidity in rubber.

The natural rubber is soft and degradable. UV light, oxygen, and heat all break down rubbers structure. In order to make natural rubber more strong to meet the basic requirement of a useful material, it can be processed to yield better mechanical strength. Processing means changing the internal structure of materials by adding different materials or by applying different treatment methods to improve or change the properties of the original material. These types of processing are against natural pathways, which reflects the fact that all processing systems, including enriching, concentrating, injecting, or deleting molecules and materials, are anti-nature.

In 1839, Charles Goodyear discovered the process of converting soft natural rubber to a harder, less flexible rubber, called vulcanization. In this process, sulfur, when combined with the natural compounds of rubber, cross-links the molecular chains at their double bonds in order to restrict molecular movement and increase hardness. The sulfur molecule acts as a bridge between rubber molecules and forms a three dimensional network with the assistance of other ingredients. This network assists natural rubber to improve its weaknesses for practical applications. Rubber strands have carbon, hydrogen, and sulfur molecules and are very long. The

Figure 9.33 3D image of rubber structure (Website 8).

cross-linking of sulfur atoms helps rubber products have flexible properties. Generally, the higher the sulfur content is, the higher the resilience and elasticity (Website 8). Here is the point that causes a huge environmental problem in long term.

The discovery of this fact and the industry's need to produce a stronger rubber were the main reasons humans increased the number of sulfur cross-links in the rubber chain, adding more and more sulfur molecules in the rubber structure. This is rare in the environment because nature does it more economically and uses less sulfur in natural rubber. More importantly, the enriching process of rubber has started, and, consequently, rubber has been converted to something unrecognizable by nature called non-degradable. These cross-links in the rubber chain do not allow rubber to enter in natural decay.

Another ambiguity in imitating polymers from natural ones is apparent by considering isomers in polymers. Almost all polymers in nature consist of various numbers of isomers, whereas omitting undesired isomers and producing polymers with desired ones, we are making it unrecognized for natural cycles. Also, changing the molecular structure of each isomer will complete the mistake of the synthetic polymer production process, converting it into something practical in terms of human needs but totally dangerous and toxic for the environment and, consequently, for future generations.

In order to solve the problems that initially rose by way of imitating nature through chemical synthesis in polymers production, it is necessary to figure out how nature does it. The main difference between synthetic and natural processes is apparent in the role of enzymes and catalysts. Enzymes are polypeptides and are crucial to life. Living organisms use enzymes to produce and modify polymers. The enzymatic modification of materials is a suitable approach to explaining the differences of naturally built polymers and synthetically built ones.

Enzymes are catalysts with specific jobs. In fact, oftentimes each enzyme does only one type of job or produces only one kind of molecule. Therefore, there has to be a lot of different enzymes, from different combinations of amino acids joined in unique ways in polypeptides, in order to keep a living organism active (Website 8). Every creature has hundreds or thousands of different types of enzymes. Each enzyme has to be made by other enzymes. This leads to very complicated control mechanisms. However, it is not known how nature manages enzymes' activities and responsibilities.

Materials' properties are dependent upon the internal and external arrangements of atoms and/or the interaction with neighboring atoms. Sometimes atoms, ions, monomers, or the whole molecular structure in both natural and synthetic polymers are the same, but their interactions with neighboring atoms, ions, or monomers are different. As stated above, different kinds of interactions between molecules cause strong characteristics in synthetic polymers that are rare in natural polymers. Therefore, sometimes the molecular structure of materials does not show any difference, but they have different properties and characteristics. The result of this chapter shows that much more study is needed to determine the diverse features of natural polymers.

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