Research paper Thermal gelation properties of carboxymethyl cellulose and bentonite-carboxymethyl cellulose dispersions: Rheological considerations Abdelhakim Benslimane a, ⁎, Ilies Mohamed Bahlouli b , Karim Bekkour c , Dalila Hammiche d a Laboratoire Mécanique, Matériaux et Energétique, Département de Génie Mécanique, Faculté de Technologie, Université A. Mira-Bejaia, Algeria b Université des Science et de Technologie d'Oran – Mohamed Boudiaf (USTO), Algeria c Laboratoire Icube, Université de Strasbourg, 2 rue Boussingault, Strasbourg 67000, France d Laboratoire des Matériaux Polymères Avancés, Département Génie des Procédés, Faculté de Technologie, Université A. Mira-Bejaia, Algeria abstract article info Article history: Received 16 May 2016 Received in revised form 24 August 2016 Accepted 26 August 2016 Available online xxxx The aim of this work was to study the thermal behavior of carboxymethyl cellulose (CMC) aqueous solutions and bentonite-CMC mixtures, from room temperature to higher temperatures, above gelation, using a rheological analysis. The rheological properties of aqueous CMC solutions and bentonite-CMC dispersions at different mass concentrations of CMC (0.1, 0.5, 1.0 and 2.0 wt%) were investigated at different temperatures (20, 40, 60 and 80 °C) using large deformation rheological measurements. Viscosity measurements show that for both CMC solutions and bentonite-CMC dispersions sudden changes in viscosity occur as the temperature increases. The viscosity is found to decrease below a critical temperature which corresponds to a cloud point or gelation temperature. Above this later, the viscosity increases dramatically with temperature. Hydrophobic interaction is postulated to be the cause of gelation. © 2016 Elsevier B.V. All rights reserved. Keywords: Carboxymethyl cellulose Bentonite Cloud point Gelation temperature Rheological measurements 1. Introduction Many natural polymers and their derivatives form physical gels that are of thermoreversible nature (Sarkar, 1979; Guenet, 1992; Jeong et al., 2002). Particularly, it has been reported that water soluble cellulose de- rivatives such as: methylcellulose (MC) (Sarkar, 1979; Haque and Morris, 1993; Desbrières et al., 2000; Wang and Li, 2005; Bain et al., 2010; Bodvik et al., 2010), hydroxypropylmethylcellulose (HPMC) (Ford, 1999; Fettaka et al., 2011; Silva et al., 2011; Joshi, 2011; Fairclough et al., 2012) and benzylcellulose (Itagaki et al., 1997) show a sol-gel transition by heating and turn back to their state of liquid upon cooling due to the memory effect which might be considered as generic property of materials. During the past two decades, many studies have been carried out to investigate the thermal gelation properties, the mechanism of gelation and structure of the cellulose derivatives gel network using various ex- perimental techniques, that can be found in numerous publications (Chevillard and Axelos, 1997; Desbrières et al., 1998, 2000; Li and Aoki, 1998; Wang and Li, 2005; Allahbash et al., 2015). From a thermodynamic point of view, these materials exhibit a crit- ical temperature called lower critical solution temperature (LCST) also cloud point temperature (CPT) below which the polymer solution is monophasic and the polymer is soluble in the solvent. Otherwise, above the LCST a gel is formed leading to a significant increase in viscos- ity. This phenomenon of thermal gelation is associated with turbidity, indicating phase separation. Therefore, the viscosity of such a polymer solution decreases as the temperature is increased, when the tempera- ture reaches the critical value LCST, a drastic increase in viscosity can be observed leading to the formation of a three dimensional network. There is a certain degree of controversy about the gelling mecha- nism. The main discussions are about the nature of the areas involved in gelation. Savage et al. (1963) suggested that the gel formation ability is a consequence of the presence of areas containing the cellulosic initial structure. Rees (1975) cited in Desbrières et al. (2000), spoke about mi- cellar interactions. Sarkar (1979) postulated that the hydrophobic or micellar interactions are assumed to be the cause of sol-gel transition. The later results were confirmed by Hirrien et al. (1998) for MC solu- tions. Using optical and rheological measurements, the authors show that hydrophobic interactions are the cause of sol-gel transition in MC solutions. They concluded that at low concentrations and low tempera- tures, the methylcellulose is dissolved in water and solutions without aggregates were obtained. Further work showed that the gelation temperature at which phase separation occurs (sol-gel transition), depends on the concentration, molecular weight and chemical structure of the polymer (Hirrien et al., 1998; Sarkar, 1979). Applied Clay Science xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail address: benslimane.ah@gmail.com (A. Benslimane). CLAY-03963; No of Pages 9 http://dx.doi.org/10.1016/j.clay.2016.08.026 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Benslimane, A., et al., Thermal gelation properties of carboxymethyl cellulose and bentonite-carboxymethyl cellulose dispersions: Rheological considerations, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.08.026