Why does PVC heat shrink film experience thermal shrinkage?

whyPVC heat shrink filmShrink upon exposure to heat? Do you also feel confused? Many people believe that it is due to thermal expansion and contraction, but in fact, the real reason is not well understood. So, Coating Home will answer why PVC heat shrink film undergoes thermal shrinkage?

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

The large molecules of ordinary plastic film are in a naturally curled state and will not shrink when exposed to heat. But PVC heat shrink film is different. Its film formation has two steps. After the raw materials are melted, the thin film is stretched under the specified temperature and external force, and the large molecules cannot slide against each other, and are frozen in an unnatural state.

At normal temperatures, the activity of plastic macromolecules is poor, so we cannot rely on molecular motion to eliminate this unnatural state. This is why PVC heat shrink film does not shrink at normal temperatures.

However, this is only a surface phenomenon, and there are actually unstable factors hidden inside this seemingly stable PVC heat shrink film. When the PVC heat shrink film is reheated to a certain temperature, the frozen macromolecules start to move again, returning to their natural state from an unnatural state, thus causing shrinkage.

That's whyPVC heat shrink filmThe reason for the shrinkage of PVC heat shrink film after heating is essentially the same as the stretching and rebound of rubber bands. When the temperature drops, the heated PVC heat shrink film will return to its original state.