Evaluation of the Hydrolysis Behavior of Polyethylene Terephthalate Yarns

摘要

A laboratory investigation as to the hydrolysis behavior of polyethylene terephthalatern(PET) yarns is the subject of this ongoing study. The project stems from an earlierrnspecification which was developed based on the results of an independent durabilityrnstudy. The specification requires PET yarns that are used for reinforcementrnapplications to have a maximum carboxyl end group (CEG) value of 30 mmol/kg,rnand a minimum molecular weight of 25,000 kg/mol. In this study, eight PET yarnsrnwith various CEG and molecular weight values were evaluated for their hydrolysisrnproperty under pH = 7 water at temperatures 45, 55 and 65℃. The duration of thernstudy was 4 years. The hydrolysis behavior was monitored using tensile strengthrnproperties which were found to be quite sensitive to the material changes. Therndecrease of tensile strength increases with incubation temperatures. For PET yarnsrnwith CEG values of 30 mmol/kg, a 60% drop in tensile strength resulted after 4 yearsrnat 65℃. Using this data, the extrapolated strength loss at 20℃ 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.