Elastic Properties of Stretch Film

Stretch film does not get tighter over time.

When an elastic material is deformed due to an external force (example: your hands stretching a rubber band, stretching film), it experiences internal forces that oppose the deformation and restore it to its original state (the rubber band ‘pushing’ back after you slack on stretching it, film ‘relaxing’)  if the external force is no longer applied.

elastic rubber band

 

This is elastic recovery. Elastic recovery exudes constant pressure until the original state of the elastic item is attained.

This pressure is what keeps items tightly bound when it comes to stretch wrapping loads (or binding items with rubber bands). This ability to tightly bind pallets and products is why stretch film is such an effective packaging option.

This constant pressure also means that constant force is also being applied to whatever is halting full elastic recovery.

As seen with tests run on Highlight’s Film Test Stand: Labview Document

If that force is great enough, when applied over time, it can crush particles in items such as boxes, containers, and even watermelons. In the case of stretch wrapping, this is why pre-stretch levels, film force, and containment force are so important: you want enough force to contain your products, but not so much that you damage them.

Crushed load

 

Stretch film (and rubber bands) do not get tighter over time – it is the recovery of the elastic properties that create pressure and force necessary to contain loads. And if the force is too great, this pressure can also crush melons.

 

 

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