Meaning
Resistance to further deformation caused by the uncoiling of molecular chains provides a self stabilizing mechanism during the stretching of heated polymer preforms. entropic strain hardening prevents localized thinning by increasing the stiffness of the material as it is stretched. This phenomenon is a result of the chains moving from a disordered state to a more ordered, aligned state.
Chain Extension
The transition from a random coil to a straight line requires an input of energy that results in an increase in force on the stretching equipment. As the chains reach their limit of extension, the material becomes significantly harder to pull. This hardening ensures that the stretch is distributed to thicker, less oriented areas of the part.
Wall Thickness
In blow moulding, this property allows for the production of containers with very thin but uniform walls. The material naturally stops stretching in areas that have already reached the target orientation, forcing the remaining air pressure to act on the rest of the preform. Without this effect, the plastic would simply burst at the thinnest point.
Processing Limit
Finite amount of orientation can be accommodated before the chains begin to break. Selection of a resin with a matching hardening profile prevents failure during the blowing stage.
