Although general-purpose grades are available, as in all walks of life the best results come from a product specifically adapted for its role.The fact that PET Preforms is used for such a variety of packaging items ? from soft drinks to cosmetics ?demonstrates how the qualities of the resin must match the standards needed to keep the product preserved and safe for travel. Not only does the product need to be maintained in good condition, but it also needs to sell. For that reason, the drink or food item and its packaging must be attractive, sensible and convenient. The resin chosen for a certain PET Preforms application has to fulfil the requirements of the end product. Strength, clarity, barrier performance and UV resistance are only a few of the factors to be considered in packaging.Homopolymers and copolymers are both used in PET resins. A homopolymer is PET containing only ethylene glycol and terephthalic acid repeat units which results in the highest melt point and the best strength properties possible. A copolymer is PET containing additional monomers, such as isophthalic acid, to disrupt the polymer chains, resulting in a lower melting point, slower crystallisation and improved clarity particularly in heavy wall applications.Different grades of resins are appropriate for different end uses. Their specific qualities make them ideal for the product which they have been designed to package. What qualities of PET are important? As mentioned above, the qualities that are important depend very much on the product for which the bottles is destined.The resins in PET bottles used to package carbonated soft drinks need very specific qualities. The material must be extremely strong to contain the internal pressures of CO2 without distortion or expansion. This is obtained by using a resin which has high IV and lower copolymer levels.
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