Treatments of PET materials with a saturated solution of calcium hydroxide (pH=
12.5) have shown the great sensitivity of PET to alkalis under extreme conditions. In nature,
however, a soil having a pH higher than 10 is rarely found. Therefore, it is more important
for geotextile applications to know the resistance of PET at pH = 10 instead of the
resistance at pH= 12. In an extensive program we have treated PET yarns (Diolen 164 s, Akzo)
with a solution of Ca(OH) 2 at pH = 10 at SO, 70, and 90° c. The rate of hydrolysis was
directly compared w.Lth the rate of degradation of PET at pH= 7 as a reference. ·’ . From the experiments the conclusion can be drawn that at a moderate temperature {T S0 ° C)
and a pH S 10 the hydrolysis of PET yarns is brought about by the reaction of PET with water – . molecules and not by a reaction with OH ions. Below 50 ° C the hydrolysis is not dependent on
the pH in the region 7
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