I have determined the activation energy of XLPE material using TGA by iso-conversional method (KAS) at conversion of 5-10% . But now it is very doubtful which value of Ea should be used. Moreover in the formula of ASTM-1877 the doyle approximation value is also troubling.
logt= (2.303/RT + log E/R*heating rate) - a
R= general gas constant
T= Absolute temperature
t= failure time
a= doyle approximation (E/RT)
See the attached file for calculation. I came out with wrong results. Kindly give your suggestion in this regard.