Effect of chemical environments on stress cracking of poly(ethylene terephthalate) beverage bottles

The influence of environmental factors on stress cracking in poly(ethylene terephthalate) beverage bottles was evaluated using failure rate data for sets of bottles stored in shallow puddles of aqueous solutions. Humidity and water alkalinity greatly affected bottle failure. Surprisingly, contact of bottles with water having alkalinity greater than that which is found in municipal water sources did not result in failure if evaporation of the water was prevented. During evaporation under conditions of high humidity, aqueous solutions of sodium bicarbonate became more concentrated and lost carbon dioxide to contain more basic and more nucleophilic anions. A mechanism for environmental stress cracking of PET including transformation of bicarbonate anions to carbonate and hydroxide anions during solution evaporation followed by hydrolysis of ester bonds is proposed.