Thermal Decomposition Behavior of In Situ Reinforcing Elastomer Composite Based on Thermoplastic Elastomer and Thermotropic Liquid Crystalline Polymer

Abstract

A thermotropic liquid crystalline polymer (TLCP), a copolyester with a 60/40 molar ratio of p-hydroxy benzoic acid (HBA) and poly(ethylene terephthalate) (PET), known as Rodrun LC3000, is melt blended with styrene— (ethylene—butylene)—styrene (SEBS) thermoplastic elastomer using a twin-screw extruder. The nonisothermal and isothermal thermogravimetry (TG) in nitrogen and in air of the neat SEBS and a blend containing 30 wt% Rodrun LC3000 (SEBS-30) are performed. The isoconversional method is employed to study the kinetics of thermal and thermo-oxidative degradation of the neat polymers and its blend. The nonisothermal TG profiles of SEBS and SEBS-30 reveal a single weight loss step in nitrogen and two stages of weight loss in air. For nonisothermal heating, a very small amount of char residues of SEBS are left, whereas the residues of SEBS-30 are left as high as 10 wt% after degradation in nitrogen. The isothermal degradation of SEBS and SEBS-30 in nitrogen becomes relatively more rapid with increasing temperature. A remarkable increase in weight loss rate is observed under isothermal heating in nitrogen above 350°C. By heating isothermally in air, SEBS shows a single weight loss stage and rapid decomposition whereas SEBS-30 exhibits minor and major weight losses in the first step and the second step, respectively. The apparent activation energy (E), ln(frequency factor) (lnA), and decomposition order (n) from nonisothermal and isothermal degradation of SEBS-30 are mostly higher than that of SEBS. The obtained kinetic parameters indicate that the thermal stability in nitrogen is higher than that in air. The estimated lifetimes at different temperatures suggest an enhancement of thermal resistance of SEBS with in situ reinforcing by Rodrun LC3000.