The objective of this experimental study is to obtain some new informa
tion on the plasticization of thermoplastic polymers by water. The eff
ect of moisture on the poly(ethylene terephtalate) (PET) thermal prope
rties has been investigated using differential scanning calorimetry. B
y heating PET film samples at different rates, thermokinetic parameter
s such as the apparent activation energy for glass transition, the app
arent activation energy, Avrami exponent and heating function for crys
tallization, have been determined in relation to the polymer water con
tent.