Polymeric rubber is prized for its stretchability and resilience, which makes it useful in everything from automobile tyres to protective gloves. Unlike most other common materials such as metals, plastics and wood, rubber can recover its shape after being stretched or deformed. This ability to rebound is due to a preponderance of wrinkled chains rather than linear ones, which are much less elastic. The elasticity of rubber can be modulated by varying the amount of chemical cross-links, known as vulcanization.
Vulcanization is a chemical reaction that produces di- and polysulfide bonds between chain ends, restricting the degrees of freedom for the chains and thus making them tighter at a given strain. This results in a higher elastic force constant, which also increases the resiliency of the material. The addition of vulcanizing agents also lowers the crystallization temperature to about 25 degC, which allows the material to be processed further before it can be cured to the final solid form.
The Science Behind Polymeric Rubber: Unraveling Its Properties and Applications
Natural rubber (cis-1,4-polyisoprene) is a polymer derived from the monomer isoprene, which can be obtained in its natural form as the milky latex of hevea tree sap. It is commonly found in a number of physical forms, including sponges, sheets, and blocks.
Synthetic elastomers are produced by the controlled polymerization of monomers such as butadiene, styrene and ethylene. The most common are the cis-polyisoprene (NR), cis-butadiene rubber (BR) and styrene-butadiene rubber (SBR). Another type of synthetic elastomer is the ethylene-propylene monomer (EPM), which is produced in a similar way to SBR but has the advantage of being a solid at room temperature.