Natural rubber facts for kids
Natural rubber is a stretchy material that comes from plants, mainly the rubber tree. You might also hear it called India rubber or latex. It's made of long chains of a natural chemical called isoprene, along with some other tiny bits and water. Thailand and Indonesia are two of the biggest producers of natural rubber. This type of rubber is known as an elastomer, which means it can stretch a lot and then bounce back to its original shape.
Rubber is mostly collected as a milky, sticky liquid called latex. This liquid comes from rubber trees when workers make small cuts in their bark. This process is called "tapping." The latex drips into cups and is then collected. After collection, the latex is cleaned and prepared to become the rubber we use in many products. Sometimes, the latex is allowed to thicken (or "coagulate") right in the collection cup. These thick lumps are then gathered and dried for sale.
Natural rubber is used in many different products, either by itself or mixed with other materials. It can stretch a lot, is very bouncy, and doesn't let water through.
Types of Rubber Plants
The Amazonian Rubber Tree
The main plant that gives us natural rubber latex is the Amazonian rubber tree (Hevea brasiliensis). It's part of the spurge plant family. This tree is popular for rubber farming because it grows well on plantations. If a tree is cared for properly, it can keep producing latex for many years after being tapped.
Congo Rubber
Long ago, a lot of rubber came from vines in Africa, especially from the Landolphia group of plants. This was known as Congo rubber.
Dandelion Rubber
Did you know that dandelions also have latex in their milky sap? This latex has similar qualities to the rubber from rubber trees. Wild dandelions don't have much latex, and the amount can change a lot. In 2013, scientists in Germany found a way to grow special dandelions that produce enough rubber for commercial use. They are even working with Continental Tires to test this new way of making rubber.
Rubber's Special Features
Rubber has some very unique physical and chemical properties. When you stretch rubber, it behaves in special ways, and it can even form tiny crystals when pulled hard.
Natural rubber can be made stronger and more useful through a process called vulcanization. It can also be affected by ozone cracking, which means it can break down if exposed to ozone gas.
The main liquids that can dissolve rubber are turpentine and naphtha (a type of petroleum). Rubber doesn't dissolve easily, so it's usually shredded into tiny pieces before being put into these liquids.
To stop raw latex from clumping together, a solution of ammonia can be used. Rubber starts to melt at about 180 degrees Celsius (356 degrees Fahrenheit).
How Rubber Stretches
When rubber is relaxed, its tiny chains of molecules are all tangled up. But when you stretch rubber, these chains straighten out. The rubber tries to go back to its original shape because the tangled-up state is more natural for its molecules.
If rubber gets very cold, it becomes stiff and loses its stretchiness. This is because its molecules can't move around easily anymore. This is why rubber parts can fail in very cold conditions. However, this stiffness is temporary; the rubber becomes stretchy again when it warms up.
When stretched rubber is left for a long time, its parallel chains can start to form tiny crystals. This makes the rubber less stretchy. For example, an inflated balloon might seem to shrink after a few days because of this crystallization. If you touch it, the warmth from your hand can melt these crystals, making it shrink more.
Vulcanization is a process that adds special bonds between the rubber chains. These bonds make the rubber stronger, harder, and less likely to stretch out permanently.
How Rubber is Made
In 2017, over 28 million tons of rubber were produced, and about 47% of that was natural rubber. Most of the rest is synthetic rubber, which comes from oil. This means the price of natural rubber can often depend on the price of oil. Asia is the biggest producer of natural rubber, making about 94% of it in 2005. The top three countries that produce natural rubber are Thailand, Indonesia, and Malaysia. Together, they make about 72% of all natural rubber. Natural rubber is not grown much in its original home, South America, because of a plant disease called South American leaf blight.
Growing Rubber Trees
Rubber latex is taken from rubber trees. On farms, rubber trees can produce latex for about 25 years after they grow up. Before that, they spend about 7 years growing without producing much latex.
Rubber trees need certain conditions to grow well:
- The soil should drain water well.
- They need about 250 centimeters (98 inches) of rain each year, spread out evenly, with at least 100 rainy days.
- The temperature should be between 20 to 34 degrees Celsius (68 to 93 degrees Fahrenheit), with an average of 25 to 28 degrees Celsius (77 to 82 degrees Fahrenheit) each month.
- The air should be humid, around 80%.
- They need about 2000 hours of sunshine per year, which is about six hours per day.
- There should not be strong winds.
Farmers have developed special types of rubber trees that can produce more than 2,000 kilograms (4,400 pounds) of dry rubber per year in good conditions.
Collecting Latex
In places like Kerala and Sri Lanka, where coconuts are common, people used coconut shells to collect latex. Now, glazed pottery, aluminum, or plastic cups are more common. These cups hang on a wire around the tree that can stretch as the tree grows. A small metal spout is put into the bark to direct the latex into the cup.
Tapping usually happens early in the morning when the tree's internal pressure is highest. A skilled worker can tap a tree very quickly. Workers often tap between 450 and 650 trees in a day. Trees are usually tapped every other day or every third day.
Workers make a careful cut in the bark with a small hatchet. These cuts allow the latex to flow from special tubes inside the bark. The cuts must be precise so they don't hurt the tree's growth or kill it.
Trees usually drip latex for about four hours. Then, the latex naturally thickens on the cut, blocking the tubes. Workers usually collect the liquid latex around midday after they finish tapping.
Latex Leftovers
There are four types of rubber that are left behind after tapping: "cuplump," "treelace," "smallholders' lump," and "earth scrap." Each type has different qualities.
Cuplump
Cuplump is the rubber that has thickened in the collection cup since the last time it was emptied. It's usually cleaner and more valuable than the other types of leftover rubber.
Tree Lace
Tree lace is the strip of thickened rubber that the worker peels off the old cut before making a new one. It can have more copper and manganese, which can make the rubber weaker over time.
Smallholders' Lump
This type of rubber is made by small farmers who collect rubber from trees far from factories. They might let the latex thicken in any container they have, sometimes even in holes in the ground lined with plastic. They might use acids or fermented fruit juices to help it thicken. This rubber often has twigs, leaves, or bark mixed in, so it's not as clean.
Earth Scrap
Earth scrap is rubber that drips onto the ground around the tree. This can happen if the cup overflows or if rain washes latex out of the cup. It contains dirt and other things, so it's a low-quality rubber. Workers collect it a few times a year.
Preparing Rubber
Latex will thicken if left too long in the cups, so it must be collected quickly. The collected latex is then put into special tanks to be turned into dry rubber. Or, it can be put into airtight containers with ammonia to keep it liquid for longer.
Latex is usually processed into a concentrated liquid form for making things like gloves, or it's made to thicken under clean conditions using formic acid. The thickened latex can then be turned into high-quality rubber blocks or sheets.
Naturally thickened rubber (cuplump) is used to make other types of rubber. This process involves breaking down the rubber and cleaning it to remove dirt before drying it.
The dried rubber is then pressed into large blocks and stacked on pallets for storage and shipping.
Vulcanized Rubber
Natural rubber is often "vulcanized." This is a process where the rubber is heated with sulfur or other chemicals. This makes the rubber much stronger, more elastic, and stops it from breaking down easily. Carbon black is often added to rubber to make it even stronger, especially for car tires. Tires use about 70% of all carbon black produced.
What Rubber is Used For
Rubber that hasn't been vulcanized is used for glues, tapes, and soft crepe rubber for things like footwear. But vulcanized rubber has many more uses!
Because it's strong against wear and tear, softer rubber is great for tire treads and conveyor belts. Hard rubber is used for parts of pumps and pipes that handle rough materials.
Rubber's flexibility makes it useful for hoses, tires, and rollers in machines from clothes wringers to printing presses. Its bounciness makes it good for shock absorbers and special machine parts that reduce shaking.
Since rubber doesn't let gas through easily, it's used for air hoses, balloons, balls, and cushions.
Rubber is also resistant to water and most chemicals. This makes it perfect for rain gear, diving equipment, medical tubes, and as a lining for storage tanks and railroad cars.
Because it doesn't conduct electricity well, soft rubber is used for insulation and protective gloves, shoes, and blankets. Hard rubber is used for things like telephone casings and parts for electrical devices.
Rubber has a high grip on dry surfaces but is slippery on wet ones. This makes it useful for power belts and water-lubricated bearings. Sports balls like lacrosse balls are also made of rubber.
About 25 million tons of rubber are made each year, with 30% being natural rubber. The rest is synthetic rubber, which comes from oil. High-quality natural latex is used for products like surgeon's gloves and balloons. Other natural rubber is used mostly in tires, but also in conveyor belts, boat parts, windshield wipers, and many other items. Natural rubber is very elastic, while synthetic rubbers are often better at resisting things like oils, extreme temperatures, chemicals, and sunlight. "Cured rubber" is rubber that has been treated with the vulcanization process to make it stronger and more durable.
Images for kids
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Pieces of natural vulcanized rubber at Hutchinson's Research and Innovation Center in France.
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Rubber latex elasticity
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Sheets of natural rubber
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Vintage tobacco card, Tapping a Rubber Tree, India, Products of the World series, Player's Cigarettes, 1909
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Compression molding machine for rubber parts
