As early as the 1960s, the Coca-Cola™ and Pepsi-Cola™ companies were seriously considering the use of plastic bottles for soft drinks, and they began to develop their ideas with major polymer manufacturers in the United States. It soon became apparent that only the polyester and nitrile families of plastics had the necessary physical and chemical characteristics required. Because the nitrile plastics could be made into bottles using existing blow molding equipment, while PET could not because of its inclination to crystallize and go hazy at higher temperatures, early market development work in the 1970s was carried out with nitrile bottles. Coca-Cola successfully launched a 950 mL nitrile bottle in 1975, but the release in 1977 of toxicological data showing that AN monomer could be carcinogenic at high dosage led to the removal of the nitrile bottle from the market (Turtle, 1984). Meanwhile, attempts to successfully manufacture PET bottles using a stretch blow molding process were continuing. In the spring of 1977, the plastic PET bottle for soft drinks was launched by Pepsi-Cola, followed later by Coca-Cola and other beverage producers. It has been described as probably the biggest single development in the soft drinks industry since the introduction of the ring-pull can a decade earlier (Turtle, 1984). Today, the greatest volume of soft drinks is packaged in PET bottles which have achieved their market share mainly at the expense of glass, albeit enlarged total market. The early designs had a round base which necessitated a flat base cup, usually injection molded from high density polyethylene (HDPE) and fixed to the bottle with hot-melt adhesives. The increase of PET recycling schemes accelerated the introduction of the petalloid base, thus obviating the need for a base cup. Although more material is required for a petalloid base, separation of the base cap is not required prior to recycling of the PET bottle. Stress cracking of PET bottles filled with carbonated soft drinks is a complex process that is influenced by a large number of variables, including climate, chemistry, polymer quality and bottle engineering design. There is a growing awareness that “alkalinity,” including naturally occurring water alkalinity, is connected to stress crack failure of PET bottles (see Section 2.3.6.4.1).
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