At present, PET (abbreviation for polyethylene terephthalate) as a kind of popular material to make the bottle has already enjoyed huge success in the packaging market, especially for the manufacture of beverage bottle. What's more, it has replaced glass and other types of plastic bottle in countless application.
PET , short for PolyEthylene Terephthalate, belongs to the group of resin named thermoplastic polyester, which can be deformed by the effects of heat
It is a linear thermoplastic resin with a large molecule consisting of chains 100 to 120 repeating unit long, and turns out white with a tint of blue. Unlike simple polyester as polyethylene, PET is not made by a single step process but made from terephalic acid and ethylene glycol through poly-condensation.
PET resins are classified into homopolymer and comopolymer. 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, while 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.
Most bottle grades of PET are copolymers, which means that a few percentage of a modifier has been incorporated into the polymer chain.
With excellent wear resistance, low coefficient of friction, high flexural modulus, and superior dimensional stability, PET becomes a versatile material for fiber, injection molded parts as well as blow molded bottles and jars. Special grades are offered with the required properties for different applications.
As early as the 1950s, PET with its strength, temperature tolerance and wear-resistance came into notice and became an ideal textile material to replace silk, cotton and wool, or addition to those textile material.
Until the 1973 registered patent to make bottle for carbonated drinks using PET, in reply to the marketing need for larger lightweight, unbreakable bottles to pack carbonated drinks, PET became popular among the world wide bottle manufacturers.
PET resin is semi-crystalline thermo-plastic polyester. When the crystalline film is stretched, crystal aligns in the stretch direction, and the film strength increases. PET film' tensile strength is measured up to aluminum film's, and its tensile strength can reach 1/3~1/2 of the steel's to certain degree. It is the toughest thermoplastic film.
However, PET is different than other crystalline materials because it is crystal clear with light transmission like that of glass.
As a kind of transparent, wear-resisting and corrosion-resisting plastics with high strength and smooth finish, PET is widely used for PET bottles of mineral water, juice, edible oil, pharmaceuticals, cosmetics, etc.