Evaluation of the Hydrolysis Behavior of Polyethylene Terephthalate Yarns

A laboratory investigation as to the hydrolysis behavior of polyethylene terephthalate (PET) yarns is the subject of this ongoing study. The project stems from an earlier specification which was developed based on the results of an independent durability study. The specification requires PET yams that are used for reinforcement applications to have a maximum carboxyl end group (CEG) value of 30 mmol/kg, and a minimum molecular weight of 25,000 kg/mol. In this study, eight PET yarns with various CEG and molecular weight values were evaluated for their hydrolysis property under pH = 7 water at temperatures 45, 55 and 65°C. The duration of the study was 4 years. The hydrolysis behavior was monitored using tensile strength properties which were found to be quite sensitive to the material changes. The decrease of tensile strength increases with incubation temperatures. For PET yarns with CEG values of 30 mmol/kg, a 60% drop in tensile strength resulted after 4 years at 65°C. Using this data, the extrapolated strength loss at 20°C is 11% after 100 years. In terms of a long term chemical reduction factor for design purposes this is equivalent to a value of 1.12.