Why does PVC heat shrinkable film shrink when

Why does PVC heat shrink film shrink when exposed to heat? Are you also puzzled? Many people think that it is due to thermal expansion and contraction. In fact, it is not. Many people don't understand the real reason. So let's explain why PVC heat shrinkable film shrinks due to heat?

In fact, the shrinkage of PVC heat shrinkable film after heating is a physical phenomenon, which requires certain physical knowledge to explain. In short, it is the thermal movement of the molecules that causes the shrinkage of the PVC heat shrinkable film.

The macromolecules of ordinary plastic film are in a natural curl state and will not shrink when exposed to heat. The PVC heat shrinkable film is different. Its film formation has two steps. After the raw material is melted, the film is stretched under the specified temperature and external force, and the macromolecules cannot slide with each other and are frozen in an unnatural state.

Under normal temperature, the activity of plastic macromolecules is very poor, so we cannot rely on the movement of molecules to eliminate this unnatural state, which is why PVC heat shrinkable film does not shrink at normal temperature.

However, this is only a superficial phenomenon. In fact, there are unstable factors hidden inside this seemingly stable PVC heat shrinkable film. When the PVC heat shrinkable film is reheated to a certain temperature, the frozen macromolecules start to move again and return to the natural state from the unnatural state, thus shrinking.

The above is the reason why the PVC heat shrinkable film shrinks after heating. In fact, the phenomenon that the PVC heat shrinkable film shrinks after heating is essentially the same as the elasticity and rebound of the rubber band. The heated PVC heat When the temperature drops, the shrink film will return to its original state.