Aug. 5, 2003 Dinosaurs like the manual typewriter and its annoying correction tape have long since given way to the P.C., but as kids go back to school this fall one vestige of a simpler time has survived. The trusty old eraser, with pencil or without: Where would students be if they didn't have one to help them through a math test?
The story of the chemistry behind these under-appreciated "graphite grabbers," as some people in the industry like to call them, begins with the history of the pencil. Chemical & Engineering News, the weekly newsmagazine published by the American Chemical Society, the world's largest scientific society, reports that this history goes back to the 1560s, when people started writing with graphite sticks. The sticks later evolved into crude pencils.
C&EN notes that writers erased the first unwanted pencil marks with a ball of moist bread. Nearly 200 years later, in 1752, the French Academy of Sciences concluded that caoutchouc (condensed latex), obtained from the rubber tree, could be used to remove the marks. The first scientific description of caoutchouc had surfaced during a French geographic expedition to South Africa in 1735. In 1770, British-American chemist Joseph Priestly coined the word "rubber" to describe the product, since it was used to rub out pencil marks, the newsmagazine says.
There were two problems with the first erasers and all rubber products. First, rubber products softened during warm weather and hardened in cold weather. Second, rubber took on an unpleasant odor as it started to degrade. It took a while, but in 1839 hardware merchant-turned-chemical engineer Charles Goodyear developed the vulcanization process to cure rubber, according to C&EN.
In this process, sulfur is added to the rubber and the mixture is heated under pressure to form sulfur cross-links between the rubber's polymer chains. The cross-links increase the strength, stability and elasticity of the rubber.
After Goodyear's discovery, rubber became widely used for many items, including erasers. The first patent on a combined pencil and eraser was granted in the United States in 1858. Most pencils made outside the United States today still don't have erasers attached, however.
To make pencil erasers, cylindrical ribbons of rubber are cut into short pieces called plugs, C&EN explains. The plugs are placed in a rotating hopper that lines them up on a conveyor belt, which carries them to be joined with a pencil. A band of metal called a ferrule is glued onto the end of the pencil where a recess has been cut, while at the same time a plunger presses an eraser plug into the ferrule. When the glue dries, voila!
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To access the C&EN story on erasers, which appeared in the Dec. 12, 2002, issue as part of the "What's That Stuff" series, go to: http://pubs.acs.org/cen/whatstuff/stuff/8050erasers.html
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