Experimental and Modeling Studies on the Solubility of Sub- and Supercritical Carbon Dioxide (scCO 2 ) in Potato Starch and Derivatives Henky Muljana, Francesco Picchioni, Hero J. Heeres, Leon P.B.M. Janssen Department of Chemical Engineering, University of Groningen, Groningen 9747AG, The Netherlands The solubility of CO 2 in native potato starch (NPS) and potato starch acetate (SA) at two different temperatures (508C and 1208C) and various pressures (up to 25 MPa) was determined using a magnetic suspension balance. Within the experimental window, a maximum solubility of 31 mg CO 2 /g sample for NPS and 79.4 mg CO 2 /g sample for SA was obtained. The CO 2 sorption behavior is highly depending on the temperature and pressure. The solu- bility data were modeled with the Sanchez Lacombe equation of state (S-L EOS). The swelling (S w ) values, as predicted using the S-L EOS, were relatively small and a maximum value of 6.1% was obtained for SA at 25 MPa and 1208C. POLYM. ENG. SCI., 51:28–36, 2011. ª 2010 Society of Plastics Engineers INTRODUCTION The unique properties of supercritical fluids (e.g., gas- like diffusivity and liquid-like density) have rendered supercritical technology a very attractive alternative for conventional ones and have led to a boost in research activ- ities [1]. Among the supercritical solvents, supercritical CO 2 (scCO 2 ) has been used in a broad range of applications including the use as an alternative solvent and processing aid in polymerization reactions and polymer processing [2, 3]. ScCO 2 , obtainable at relatively mild critical condition (T c ¼ 318C, P c ¼ 7.38 MPa), is considered to be ‘‘green,’’ it is nonflammable, relatively nontoxic and inert. Another advantage is the ease of separation of the product from the solvent by depressurization [4–6]. Recent publications have also shown the potential use of scCO 2 for the chemical and physical modification of polysaccharides such as chitin, cellulose, and starch [7–10]. In recent work from our group, the use of scCO 2 for the acetylation of potato starch was investigated, and good results were obtained with respect to the degree of substitution (DS) and reaction selectivity [10]. When using scCO 2 as a solvent for starch modifica- tions, the extent of the physical and chemical reactions is expected to be affected by the amount of dissolved CO 2 in the starch matrix [3, 11–14]. Therefore, fundamental knowledge on the solubility of CO 2 in native starch is required not only to explain the observed trends of pro- cess conditions on important output variables such as the DS but also to develop reactor engineering models and to aid in further process development activities. Despite the importance of solubility data, experimen- tally determined solubilities of CO 2 in native starch sam- ples for a wide range of conditions are limited. To the best of our knowledge, the work of Hoshino et al. [15], Singh et al. [16], and Chen and Rizvi [17] are the only articles concerning to the solubility of CO 2 in the starch. Hoshino et al. [15] studied the adsorption of CO 2 in dried corn starch (water content of 3.8% wt/wt) at two different temperatures (40–508C) and of dried potato starch (water content of 4.3% wt/wt) at a temperature of 408C in a pressure range of 0–29.4 MPa by a gravimetric method. The authors reported a decrease in the solubility with temperatures and observed a maximum solubility near the critical region of CO 2 followed by a sharp decrease at higher pressures [15]. Chen and Rizvi [17] measured the solubility of CO 2 in pregelatinized-corn starch (water con- tent of 40% wt/wt) at a temperature of 508C and various pressures (up to 16 MPa) by a pressure decay method. In their work, the swelling of the starch samples was pre- dicted with the Sanchez-Lacombe equation of state (S-L EOS), and it was shown that both the CO 2 solubility and the sample swelling increase with pressure [17]. The same pressure trends were also reported by Singh et al. [16]. These authors observed an increase of the solubility of CO 2 in the gelatinized corn starch irrespective of the water content at elevated pressure (up to 11.7 MPa) [16]. Thus, experimental data for the solubility of CO 2 in potato starch are only reported for dried potato starch at 408C and are absent for native potato starch (NPS) in a larger temperature window. In addition, the sorption of CO 2 in important starch derivatives such as potato starch acetate (SA) is unknown. This information is of vital importance to elucidate the role of scCO 2 in important starch modification reactions such as the base-catalyzed acetylation of starch using acetic anhydride in scCO 2 [10]. Correspondence to: Hero J. Heeres; e-mail: H.J.Heeres@rug.nl DOI 10.1002/pen.21786 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2010 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2011