Thermally Induced Shrinkage in Heat Reactive Polymers

Location:

Concepts Shown:

polymers, thermally induced shrinkage, heat reactive polymers

Equipment:

heat shrink tubing (available at most electronics shops) Russell Industries 3000 Lawson Blvd. Oceanside, NY 11572 (516) 536-5000 or (800) 645-2202 a hot iron (clothing iron works well), rod of metal approx. the same diameter as final shrink size.

Procedure:

Construction: Clip off about 1-2 inches of the tubing and place it over the rod. In this state it will be about twice as wide as the bar. Plug the iron in and you are ready. Presentation: When the iron has achieved a temperature of 135 C or more, place the tubing directly against it, using the rod. The tubing will shrink down and will tighten around the rod. You can then pass the rod around to show that the tubing is tight.

Science:

This type of heat shrink tubing is made out of a thermally stable polymer known as polyolefin (a derivative of polyethylene, C2H4). The tubing is supplied in an expanded or stretched form, which is caused by an irradiation by an electron beam. The beam lines up or straightens out the polymer chains which are wrapped around the tube radially. However, if heat is applied to the tube, the chains then return to their original state in which the angles between the mers are smaller. This decrease in angle causes the shrinkage or tightening of the tube. Due to the fact that the mers are lined up radially a 50% shrinkage in the radius occurs, while only a 5% shrinkage occurs longitudinally. Other: 0.5 inch to 0.25 inch in diameter tubing works very well because it is visible in class. also try other colors besides black and clear, they also help with visibility.

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