2. Bi-orientation phenomenon
Molecular orientation is linked to an ordered rearrangement of macromolecular chains, usually achieved by stretching the polymer at an appropriate temperature. As a result of this macromolecular rearrangement, certain mechanical properties of the transformed object (tensile strength, Young's modulus, impact resistance, etc.) are improved in the direction of stretching. In particular, creep and stress crack resistance are significantly improved. This macromolecular rearrangement reduces gas permeability, hence the use of this process to manufacture bottles for carbonated beverages.
During the manufacture of hollow bodies by extrusion blow molding with two-drawing or injection blow molding with two-drawing, the preforms, which are significantly smaller than the final object, are stretched axially and radially, resulting in a two-dimensional orientation of the molecular...
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Bi-orientation phenomenon
PET (polyethylene terephthalate) and blow-molding applications
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