BACKGROUND: Researchers at Case Western Reserve University are developing a fishing line that changes color when it becomes overstressed and ready to break.
THE PROBLEM: Nylon fishing line is designed to have some natural stretch to it. But if you pull on it too hard -- which happens when fighting to reel in a particularly large fish -- it can stretch so much that its structure is badly weakened.
HOW IT WORKS: The new fishing line contains a type of polymer that fluoresces -- emits light -- when viewed under ultraviolet light. The color of light emitted depends on how much stress the polymer molecule has experienced. When the line is not under stress, the molecules are close together and emit reddish-brown light under a UV lamp. When it stretches, the molecules pull apart and emit green light. A fisherman can check his line under UV light and discard it if it glows green.
A small amount of the polymer is mixed in with a standard plastic blend to make a fishing line. The prototype is not strong enough for bass-fishing, for example, but the same technique should be easily applied to standard nylon fishing line. The same polymer blend used in the fishing line could be used to make tamper-resistant packaging. A barely visible puncture mark from a hypodermic needle would be clearly visible as a green dot under UV light, because the puncture stressed the material at that point. The scientists are also looking at how temperature may affect the polymer's ability to change color.
WHAT ARE POLYMERS: "Polymer" comes from the Greek word polumeres, which means "having many parts." Polymers are large molecules made of repeated chemicals joined together in a long strand, like beads on a string. Most of the plastics we use every day are made of polymers.
The Optical Society of America contributed to the information contained in the TV portion of this report.