Sorption of n-Hexane in Amorphous Polystyrene Ashish Kadam, 1 Thomas Karbowiak, 1 Andree Voilley, 1 Jean-Pierre Bellat, 2 Olivier Vitrac, 3 Frederic Debeaufort 1,4 1 UMR A 02.102 PAM, Equipe PAPC, Universit e de Bourgogne-AgroSupDijon, 1 Esplanade Erasme, 21000 Dijon, France 2 ICB, UMR 6303 CNRS-Universit e de Bourgogne, 9 avenue Alain Savary, 21078 Dijon, France 3 UMR 1145, Groupe IMMC, AgroParisTech-INRA, 1, avenue des Olympiades, 91300 Massy, France 4 IUT-Dijon, D epartement G enie Biologique, BP 17867, 21078 Dijon, France Correspondence to: F. Debeaufort (E- mail: frederic.debeaufort@u-bourgogne.fr) Received 30 April 2014; revised 8 July 2014; accepted 9 July 2014; published online 26 July 2014 DOI: 10.1002/polb.23557 ABSTRACT: Sorption properties of pure n-hexane vapor in amorphous polystyrene (PS) were studied at 298 K by ther- mogravimetry under controlled vapor pressure. Two sorption– desorption cycles were performed by varying the relative pres- sure between 0 and 0.91. Mixing of PS with n-hexane resulted in a strong plasticization, which was evidenced by quite signifi- cant depression in the glass transition temperature of the poly- mer as shown by differential scanning calorimetry. Maximum quantity of n-hexane sorbed in the PS at 298 K and at a pres- sure close to saturation was about 12.4 wt %. The thermog- ravimetry yielded an isotherm with a strong hysteresis loop, explanation of which was hypothesized with the help of (a) Flory–Huggins sorption model extended by Vrentas, (b) analy- sis in terms of modification in the glass transition temperature of the n-hexane/PS system as a function of sorbed quantity, and (c) change in total volume of the system. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1252–1258 KEYWORDS: amorphous; Glassy Polystyrene; sorption hysteresis; structure; swelling INTRODUCTION The sorption of gases in polymers presents a widespread concern in the field of polymer processing. The maximum quantity of a gas sorbed and the rate of diffusion in a polymer are important aspects. 1 Knowing sorption prop- erties of polymers has been a subject of interest for many decades for scientific and industrial fields such as polymer manufacturing, purification of gases, packaging, and so forth. Certain applications of polymers require their contact with volatile and/or nonvolatile compounds. A lot of sorption data are available on several polymeric packaging materials, but very few studies have been per- formed concerning transport of low molar weight com- pounds through amorphous packaging polymers such as polystyrene (PS) or polyamide (PA) due to longer equilibra- tion times and complexities in data interpretations due to the polymer plasticization by the sorbate. 2 Sorbate/amor- phous polymer mixtures normally exhibit different sorption behaviors, above and below the glass transition of the mix- ture. At low sorbate concentrations, the glassy polymers show a sorption isotherm of a shape corresponding to that of a glassy polymer and at relatively high sorbate concentra- tions, their sorption isotherm is shaped as that of a rubbery polymer. 3 The sorbate concentration in rubbery polymers can be determined using Henry’s law for low penetrant con- centrations, and at the concentrations high enough the devia- tions from Henry’s law are observed. 3–6 As a glassy polymer is nonequilibrium, the sorption data below the glass transi- tion temperature (T g ) of the sorbate/polymer mixture is often difficult to interpret. The sorption of gases in glassy polymers is often described using the dual mode sorption model, which is based on the hypothesis of two co-existing populations of the sorbate, one dissolved in the polymer and the other situated in microvoids of the polymer. Among a few sorption studies done in amorphous PS are the sorption of toluene in PS by Kruger (magnetic suspension balance), 2 nitrogen, argon, methane, and carbon dioxide (CO 2 ) by Vieth (pressure decay apparatus), 7 n-pentane by Baird (quartz helical spring balance), 8 propane, methane, and chlorodifluoromethane by Barrie (electronic vacuum microbalance), 9 cyclohexane, toluene, carbon tetrachloride, benzene, chloroform by Saeki (piezoelectric sorption appara- tus), 10 n-hexane, toluene, benzene by Tihminlioglu (inverse gas chromatography), 11 and n-hexane by Kang (quartz helical spring balance). 12 Most of these data are obtained below the polymer’s T g . Moreover, consideration is rarely given to the alteration in the polymer’s T g due to sorption. During V C 2014 Wiley Periodicals, Inc. 1252 JOURNAL OF POLYMER SCIENCE, PART B: POLYMER PHYSICS 2014, 52, 1252–1258 FULL PAPER WWW.POLYMERPHYSICS.ORG JOURNAL OF POLYMER SCIENCE