Introduction Acrylonitrile–butadiene–styrene (ABS) is an impor- tant engineering terpolymer. Due to its superior me- chanical properties, chemical resistance, ease of pro- cessing and recycling ability is widely used in the industry. Those properties are directly related to the polar nature of the acrylonitrile component. Typi- cally, ABS consists of a styrene/acrylonitrile continu- ous phase (SAN matrix) partially grafted to a dis- persed butadiene phase, which acts as impact modifier, giving excellent mechanical properties to the polymer. ABS has various application, e.g. in ar- chitecture and construction, personal care products, toys, computer and business equipments, medical de- vices and in automotive interior components. ABS is also used with fiber-reinforcement to enhance the me- chanical properties such as tensile strength, flexural modulus and hardness [1, 2]. Another reason to use ABS is its price that is between the lower priced commodity thermoplastics and the more expensive high performance engineering plastics [2]. Thermogravimetric analysis (TG) and differen- tial thermal analysis (DTA) are commonly used meth- ods to investigate the thermal stability of polymers and composites [3]. With proper experimental proce- dures, information on the degradation kinetics of de- composition can be obtained. There are several re- ports on the thermal analysis (TG, DTA, FTIR, DSC) of ABS as well its individual components under vari- ous conditions (purging gases, heating rates, etc.) [3–15]. Degradation of ABS is a radical process where end-chain and random scission occurs. Based on different characterizing conditions the degradation of ABS took place either in one step or two steps with different kinetic parameters (degradation starting temperature, ending temperature, peak temperature, reaction order, pre-exponential factor and activation energy) by assuming different kinetic models [14]. M. Yang [3] reported that the activation energy for ABS is 175.8 kJ mol –1 (using Flynn–Wall approach, dy- namic method, 5, 10, 20 and 40°C min –1 heating rates and N 2 atmosphere) by using Freeman and Carroll isothermal approach from 350 to 450°C in N 2 atmosphere, the acti- vation energy is 134.0 kJ mol –1 . A similar value was found by S. Yang et al. [14], the activation energy was 134.4 kJ mol –1 , using also Freeman and Carroll ap- proach, in an isothermal method at 370 to 560°C, while in another work [15] at 10% conversion, N 2 atmosphere and at 0.5, 1, 2, 5 and 10°C min –1 heating rates, an activation energy of 190.0 kJ mol –1 was reported by Day [15]. Un- der dynamic circumstances (nitrogen atmosphere and heating rates between 5–30°C min –1 ) by assuming an autocatalytic model [16] the activation energy is varied between 140–160 kJ mol –1 as determinate by Balart [16]. Experimental The degradation process of three different commer- cial ABS: GP, an ABS for general-purpose use; HI, an ABS high impact; and HH, an ABS high heat resis- tance was studied. The ABS samples were produced by addition of styrene and acrylonitrile to poly- butadiene latex; the resultant is a material with polybutadiene grafted with acrylonitrile and styrene (a SAN matrix) that is essential to obtain the required properties of the desired polymer. 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2009 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 95 (2009) 1, 131–134 DEGRADATION BEHAVIOR AND KINETIC STUDY OF ABS POLYMER H. Polli 1* , L. A. M. Pontes 1 , A. S. Araujo 2 , Joana M. F. Barros 2 and V. J. Fernandes Jr. 2 1 UNIFACS – Department of Chemical Engineering, Av. Cardeal da Silva, 132, 40.220-141 Salvador, BA, Brazil 2 Federal University of Rio Grande do Norte, Department of Chemistry, CP 1662, 59078-970 Natal, RN, Brazil The degradation kinetics of the ABS terpolymer (acrylonitrile–butadiene–styrene) was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere applying three different heating rates: 5, 10 and 20°C min –1 . The Vyazovkin model-free kinetic method was used to calculate the activation energy (E) of the degradation process as a function of conversion and temperature. Between 20 and 80% of conversion, E was calculated and the figures were : for ABS GP, E is 204.5±11.5 kJ mol –1 (medium value); for ABS HI, E is 239.0±9.8 kJ mol –1 ; for ABS HH, E is 242.4±5.4 kJ mol –1 . Keywords: acrylonitrile–butadiene–styrene (ABS), model-free kinetics, thermal degradation, thermogravimetry * Author for correspondence: polli@unifacs.br