Thermochimica Acta 419 (2004) 51–58 Analytical expressions of specific heat capacities for aqueous solutions of CMC and CPE N. Semmar, J.L. Tanguier ∗ , M.O. Rigo Laboratoire d’Etude et de Recherche sur le Matériau Bois, UMR INRA 1093, Université Henri Poincaré, Boulevard des Aiguillettes, BP 239, F 54506 Vandoeuvre Les Nancy Cedex, France Accepted 12 January 2004 Available online 12 March 2004 Abstract As previously reported, the influence of temperature and mass concentration on the specific heat capacity of two highly viscous solutions has been measured using adiabatic calorimetry. The absolute measurements were automated to operate steadily over the temperature range 290–360 K with an average heating rate of 8 × 10 -4 Ks -1 . For both solutions of carboxy-methyl-cellulose (CMC) and carboxy-poly-ethylene (CPE), the evolution of specific heat capacities with temperature is compared with that of pure water. With CPE solutions, the increase of the temperature translated into an evolution of the C p is comparable to the pure water with a value that varies with concentration. For CMC solutions, we observe the same temperature behaviour for a concentration of 83 g l -1 . For weaker concentrations, the influence of the temperature is different. To account for the influence of temperature and concentration parameters, we propose a correlation that facilitates the utilisation of these results corresponding to a relative error inferior to 2%. © 2004 Elsevier B.V. All rights reserved. Keywords: Adiabatic calorimeter; Specific heat capacity; Complex fluids; Polynomial correlations; Polymeric aqueous solutions 1. Introduction Polymeric aqueous solutions, such as carboxy-methyl- cellulose (CMC) and carboxy-poly-ethylene (CPE), are widely used to simulate the rheological behaviour of highly viscous liquids. Their apparent viscosity is 10 3 to 10 4 times higher than that of water, even for very dilute solutions (1–83 g l -1 ). Coupling both thermal and rheological studies requires the knowledge of thermophysical properties and particularly reliable specific heat capacities (C p ). But, these are not always available and are rarely reported in data bases. As indicated in Refs. [1,2], in some earlier works, authors have simply identified the C p of this aqueous solution type to that of pure water. In more recent works [3,4], experimen- tal and sophisticated numerical methods have been used to determine C p values indirectly. Nevertheless, their accuracy was estimated at less than 10%. ∗ Corresponding author. Tel.: +33-83-68-48-48; fax: +33-83-68-48-53. E-mail address: tanguier@lermab.uhp-nancy.fr (J.L. Tanguier). Thus, to achieve direct, absolute and more accurate mea- surements, adiabatic calorimetry was adapted to the study of CMC (18, 35, 83 g l -1 ) and CPE (1.5, 3, 10 g l -1 ) [5]. A second order polynomial expression allows us to link our experimental values to the temperature for each solution. From the analysis of coefficients thus obtained, we have es- tablished a more general relationship that takes into account the influence of the temperature and the concentration with a relative error inferior to 2%. 2. Apparatus performance The spherical calorimeter used in this study was designed for solid samples at low temperatures [6], and adapted to viscous samples in the temperature range from 290 to 360 K [7]. Some details about the calorimetric device are briefly described in order to explain its performance. The cell (Fig. 1) is centred inside a spherical shield. Its differential temperature change is controlled by a differential “T” thermocouple connected to a PID controller. Throughout 0040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2004.01.030