Jeff Chase, age 10, of Scarborough, Maine, for his question:
How do they make rubber?
The world's first rubber was a present from the plant world. Naturally, the gift was not presented in the form of pencil erasers and bouncing balls. It was a milky sap that oozed from a stately tree. People had to figure out how to make this. basic ingredient into useful rubber items. Later, our clever chemists learned how to create molecules for making synthetic rubbers. But the natural ingredient for making most rubber still comes from those stately tropical trees.
Plants, as we know, tend to ooze sap from their wounds. Most plants of the rubber family ooze tacky sap. The best quality latex comes from the stately hevea tree. Its native home is Brazil, though it grows in other tropical zones where heavy showers fall throughout the year. Nowadays, most of the world's natural rubber comes from plantations in Burma and Borneo, Indonesia and Indo China, Thailand and Ceylon.
The trees are large enough to yield latex when they are six years old. Sharp knives are used to cut shallow sloping grooves in the trunks. This releases the milky sap from the latex cells just below the bark. Pails are placed below to catch it as it drips. In time, the trees become tall tropical evergreens with boughs of huge, oval leaves. The best leave trees yield about 30 pounds of latex each season for 25 years.
In olden times, the people of Brazil dipped their shoes and baskets into latex from wild hevea trees. When the tacky fluid dried, it formed rain proof coatings. They also roiled stretchable, bendable latex into rubber balls. Nowadays, we convert the liquid latex into a product called crude rubber. Then various other processes are used to convert this basic ingredient into rubber for different purposes.
The liquid latex collected from the hevea trees is mixed with water and poured into large troughs. Latex gets its tacky quality from tiny globules of rubbery material floating in liquid. Acid chemicals are added to make these globules clog together. After several hours, a rubbery scum floats to the top. This is crude rubber, the basic ingredient used to make all natural rubber.
The rubbery scum is removed in thin sheets. These must be dried. First they are squeezed through heavy rollers several times. This removes the dripping moisture and creates wrinkled sheets of pale crepe rubber. These are hung up in airy drying sheds and left for several weeks. As a rule, the final drying process includes a week in a smoke house, where the air is filled with smokey fumes.
At last, the crude rubber is fully dried and cured. Most of it is packaged in large bales and shipped here and there around the world. It goes to factories equipped to convert and model it into marketable items. Different recipes are used to give special qualities to tires and inner tubes, erasers and bouncing balls. Most of these qualities can be copied in synthetic rubbers. Some of these man made materials are stronger and more durable than natural rubber.