Heat shrink tubing gets longer when heated.

[George Herold]

OK this is hardly an electronics question.
Does anyone know the physics of heat shrink tubing.
Why it only shrinks in one dimension and gets a little longer in the other.

 

[whit3rd]

On Friday, January 30, 2015 at 12:30:31 PM UTC-8, George Herold wrote:

OK this is hardly an electronics question.
Does anyone know the physics of heat shrink tubing.
Why it only shrinks in one dimension and gets a little longer in the other.

Long-chain molecules, tangled together (like a felt fabric). When
stretched, the material becomes anisotropic. When heated, the
material 'relaxes' to isotropic, because that has higher entropy.

Cool example: a rubber band has heat capacity according to three
dimensions of thermal excitation. Stretch it, and the transverse
modes remain, but the longitudinal modes are too high energy for
room temperature excitation. So the heat capacity drops, and the
stretched rubber band is hotter than ambient temperature.
Let it cool while stretched, then release the tension. Heat capacity
rises, so the relaxed rubber band cools below room temperature.

 

[Jasen Betts]

On 2015-01-30, George Herold <gherold@teachspin.com> wrote:

OK this is hardly an electronics question.
Does anyone know the physics of heat shrink tubing.
Why it only shrinks in one dimension and gets a little longer in the other.

It's made in the shrunk state and then stretched while warm and cooled
into the unshrunk size, when heated it relaxes to the shrunk size.

it can be heated and re-stretched.

polyethylene film will also shrink when heated.

--
umop apisdn

 

[Cydrome Leader]

Jasen Betts <jasen@xnet.co.nz> wrote:

On 2015-01-30, George Herold <gherold@teachspin.com> wrote:
OK this is hardly an electronics question.
Does anyone know the physics of heat shrink tubing.
Why it only shrinks in one dimension and gets a little longer in the other.

It's made in the shrunk state and then stretched while warm and cooled
into the unshrunk size, when heated it relaxes to the shrunk size.

I keep thinking they do something with an electron beam or type of
radiation to make heatshrink tubing.

A quick check dug up this good explanation-

http://www.symmetrymagazine.org/article/april-2010/accelerator-apps-heat-shrink-tubing