Thermal decomposition kinetics of thermotropic liquid crystalline p-hydroxy benzoic acid/poly(ethylene terephthalate) copolyester

The nonisothermal and isothermal thermogravimetry (TG) in nitrogen and in air of thermotropic liquid crystalline poly(oxybenzoate-co-ethylene terephthalate), a copolyester consisting of 60 mol% of p-hydroxy benzoic acid (HBA) and 40 mol% of poly(ethylene terephthalate) (PET), known as Rodrun LC3000, was performed. The Friedman technique based on a single heating-rate method was used to calculate the kinetic parameters of the nonisothermal degradation and the Flynn technique was employed to calculate the kinetic parameters of isothermal degradation. The nonisothermal degradation of Rodrun LC3000 in nitrogen and in air occurred in two steps. In air, Rodrun LC3000 became degraded leaving very small residues within the range of experimental temperature whereas, in nitrogen, it left some residues which were found to increase in amount with increasing heating rate. The respective activation energy, order and ln(frequency factor) for nonisothermal decomposition of Rodrun LC3000 are 159 kJ/mol, 2.2 and 28 min−1 in nitrogen and 121 kJ/mol, 2.4 and 20 min−1 in air. The respective activation energy, order and ln(frequency factor) for isothermal degradation are found to be 110 kJ/mol, 2.2 and 17.1 min−1 in nitrogen and 103 kJ/mol, 2.3 and 15.9 min−1 in air. The kinetic parameters obtained from the two modes of decomposition indicate that the thermal stability of Rodrun LC3000 is substantially better in nitrogen than in air. The estimated lifetimes at various temperatures suggest a good thermal stability of Rodrun LC3000.