The Background, Facts and Properties of Rubber

We use rubber in our everyday lives, whether we acknowledge it or not. It is in our streets as asphalt, under our feet in our pavement and our shoes, in our cars as seals for doors and windows, and even in our apparel. Small rubber parts pervade our lives. But what is rubber, and what are the properties of rubber that make it such a widely-used material? In general rubber is sought out for its elasticity and its potential resilience to extreme conditions. It has protective qualities for anything from people to large industrial machines to workout equipment, making it a material with a very large appeal in a number of different industries. Just like any other substance, rubber has a chemical makeup that determines its own unique properties, as well as influences the applications that it can be used for. This piece will look to provide a helpful outline to understand the history, properties and chemical makeup, and applications of rubber.

History: Rubber is an elastomer that is derived from the latex that is found in the tree Hevea brasiliensis—the Para rubber tree—mostly found in tropic regions such as South America (Brazil) and Southeast Asia (Malaysia, India, Thailand, and Indonesia). When the tree is “wounded,” its natural response is to secrete the latex substance from which we create rubber. Seeds of the Para rubber tree were introduced to Europe from South America by Charles mare de la Condamine in 1736, and later on, Henry Wickham gathered seeds to be planted in England. The Olmecs of Mesoamerica used boiled rubber to create a ball which was used for games, much like basketball or soccer. Currently, the Southeast Asian plantations produce the highest yields of the latex material. These are no longer small rubber plantations!

Chemical Makeup: Rubber is a polymer of isoprene (2-methyl-1, 3-butadiene), written scientifically it appears as such:

CH2=C(CH3)CH=CH2

It has a molecular weight ranging between 100,000 and 1,000,000, and a small percent of its makeup (about 5%) is comprised of other materials such as proteins, fatty acids, and resins. The double bond of each repeating unit which forms the polymer chain makes it susceptible to vulcanization and ozone cracking, but is also the reason for its elasticity. The monomers which form the links of the chain can rotate freely, allowing it to assume a large number of shapes. At room temperature, these chain sections oscillate, causing the substance as a whole to be very pliable. When rubber is frozen, it will lose its elasticity.

The Properties of Rubber: As previously stated, in general rubber is desired for its elastic properties. Rubber’s elastic behavior is caused by bond distortions, where strain energy is stored thermally. It exhibits a stress-strain form of behavior which is what ultimately contributes to its properties. Stretching rubber is in itself an exothermic reaction (releases and produces heat), and allowing rubber to return to its relaxed form is an endothermic reaction (absorbs heat). That is because in its relaxed state, the polymer chain contains a certain amount of kinetic energy which is dispersed when it is stretched; returning it to its relaxed state restores this energy. Rubber hardens below 0C and weakens above 80C, where it can lose strength and become tacky. These undesirable properties can be reduced by the process of vulcanization, the adding of sulfuric bonds between the repeat units of isoprene.

What is rubber but a material that stretches, provides padding, and has a lot of give to it? Because of its elasticity and protective capabilities, it is desired in many industries, and can be found in items such as apparel (any sort of expandable or tight-fitting clothing), in asphalt (making for safer roadways that reduce sound), and is used as flooring and matting in many commercial places, such as kitchens, gyms, pet and animal care facilities, and even playgrounds. Small rubber products are everywhere! The properties of rubber are what make it such a desired commodity; even after it has been used for its initial purpose, it can be recycled and used again to make for a long-lasting product that has many economic and environmental benefits. Now that you know some general rubber facts, you can go out and discover in what ways you currently use rubber in your life and how you can incorporate it into your life even more so!