Meaning
Polyethylene terephthalate resins engineered with high molecular weight and specific melt characteristics support the production of clear, pressurized containers. Standard bottle grade pet typically exhibits an intrinsic viscosity between 0.76 and 0.86 deciliters per gram. Selection of these grades depends on the balance between cycle time and the final toughness of the preform.
Polymer Grade
Molecular weight determines the primary classification of these resins within the polyester family. When processing bottle grade pet, the material undergoes solid state polymerization to reach a higher viscosity than standard textile chips. This elevation prevents sagging during blow moulding.
Crystallinity Control
Thermal behavior dictates how the resin transforms from a molten state into a transparent finished part. Fast cooling in the injection mould prevents the formation of large spherulites that would otherwise cause haze in bottle grade pet. Monitoring the cooling rate at the gate ensures the preform remains amorphous.
Gas Permeability
Small molecules like oxygen and carbon dioxide move through the molecular lattice at rates determined by the polymer structure. Long chain orientation during the stretch blow moulding of bottle grade pet improves the gas barrier properties of the final container. This mechanical stretching aligns the molecules to create a more tortuous path for diffusing gases.
Increased orientation directly extends the shelf life of the beverage inside.
