Why Does Shrink Wrap Plastic Shrink

Polymers: Natural Gold

First, we need to understand something about the natural state of polymers. As you know, polymers are very long molecules. Suppose a molecule is a yarn about 37 feet long. Now let’s take that ball of yarn and give it to a kitty cat. Hell, give them shrink two more pieces of yarn. 

the appearance of the yarn as kitty threads it is the appearance of the individual polymer molecules in the plastic – randomly oriented and tangled: the

Shrink-wrapped plastics look different before shrinkage. The orientation shrink of plastic films, such as polyvinyl chloride (PVC) or polyolefins (e.g. polyethylene), stretches the polymer chains.

Our capricious kitten never managed to roll the yarn into a ball or stretch it out completely. Statistics (and Keaty’s nature) suggest that these yarns will be in a state of disarray. The same is true of polymers: the stretching diagram above is not statistically favorable, 

and nature doesn’t like it, but we’ve forced it into this awkward position anyway. Note that the oriented polymer looks larger and more extended.

Our stretched, oriented polymer film can now be made into bags or wrapped around Christmas baskets. Then a little heat is added and the film shrinks into place: the

During the orientation shrink process, the polymer is locked or frozen into an elongated state. The extra energy increases the movement of the molecules (wouldn’t you move if a fire was set behind you?) . The elongated polymer now recoils or shrinks back to its preferred random disordered conformation.

The size of PVC bags can be reduced by 50%. Their tensile strength also increases. In addition to PVC, shrink wrap uses a variety of polyesters. For large applications, shrink such as wrapping ships or enclosing construction sites, ethylene and vinyl acetate (EVA) copolymers are used.

 This polymer retains some elasticity after shrinkage, does not become brittle in cold weather, and is puncture shrink and flame resistant.