Density, Refractive Index, Apparent Specific Volume, and Electrical Conductivity of Aqueous Solutions of Poly(ethylene glycol) 1500 at Different Temperatures Bernardo de Sa ́ Costa, †,‡ Edwin Elard Garcia-Rojas, ‡ Jane Se ́ lia dos Reis Coimbra,* ,† Jose ́ Antônio Teixeira, § and Javier Telis-Romero ⊥ † Departamento de Tecnologia de Alimentos (DTA), Universidade Federal de Viç osa (UFV), Campus Universita ́ rio, s/n, CEP 36570-000, Viç osa, MG, Brazil ‡ Departamento de Engenharia de Agronegó cios, Universidade Federal Fluminense (UFF), Avenida dos Trabalhadores, 420, CEP 27225-250, Volta Redonda, RJ, Brazil § Centro de Engenharia Bioló gica, Universidade do Minho (UMinho), Campus de Gualtar, 47710-057, Braga, Portugal ⊥ Departamento de Tecnologia e Engenharia de Alimentos, Instituto de Biociê ncias, Letras e Ciê ncias Exatas, Universidade Estadual Paulista “Julio de Mesquita Filho”, CEP 15054-000, Sã o Jose ́ do Rio Preto, SP, Brazil ABSTRACT: Thermophysical properties of aqueous solutions of poly(ethylene glycol) 1500 g·mol -1 were measured as a function of polymer concentration w = (0.05, 0.10, 0.15, 0.20 and 0.25) and temperature T/K = (288, 293, 298, 303 and 308). Aqueous systems composed of poly(ethylene glycol) are frequently used in processes involving the separation of biological compounds. The density of the solutions varied from (1001.68 to 1042.65) kg·m -3 , the refractive index ranged from (1.3377 to 1.3681), the apparent specific volume was between (0.8336 and 0.8528) g·cm -3 , and the electrical conductivity varied between (66.22 and 170.29) 10 -3 mS·cm -1 . Polynomial models for the properties as a function of temperature and poly(ethylene glycol) 1500 g·mol -1 concentration were fitted to the experimental data. Models accounting for combined effects between variables are particularly useful in industrial applications in which physical parameters must be promptly and accurately calculated. 1. INTRODUCTION The synthetic polymer known as poly(ethylene glycol) is frequently used in processes involving the separation, concen- tration, isolation, and purification of biological compounds. 1-8 For this reason, accurate prediction of the physicochemical properties of aqueous solutions of poly(ethylene glycol) (PEG) is becoming increasingly important. 9-14 PEG is a neutral polyether composed of repeating ethylene glycol units and is also referred to as poly(ethylene oxide) (PEO) or the IUPAC name poly(oxyethylene) (POE). 15 The material is approved by the U.S. Food and Drug Administration (FDA) as a food ingredient, is nontoxic, weakly immunogenic, and is efficient in the exclusion of other polymers when present in an aqueous environment. 16-18 Extraction systems composed of poly(ethylene glycol) 1500 g· mol -1 (PEG1500), salt, and water are classified as aqueous two- phase systems (ATPS). These systems are widely used in the separation of biomolecules 19-21 due to their mild conditions and greater selectivity, larger difference in density, lower viscosity, and lower cost than ATPS formed from PEG1500 and other polymers such as dextran or maltodextrin. 22 The solute partitioning in ATPS systems is affected by factors such as the nature and size of the biocompound, the structure and chain size of the polymer, type of salt, pH, initial composition of the system, and temperature. Consequently, information concerning the dynamic behavior of aqueous PEG1500 solutions is required for the design of biotechnological processes in which this polymer is used. Data on thermophysical properties of aqueous solutions containing PEG have been reported in the literature, such as for viscosity, 7-13,22-31 density, 7-14,22-30 electrical conductivity, 25,28 apparent specific volume, 32 and refractive index. 25,28,33 However, less accurate equipment and limited temperature ranges still being used to measure thermophysical properties of ATPS. Therefore, we determined the density, refractive index, apparent specific volume and electrical conductivity of aqueous PEG1500 solutions at several concentrations and temperatures. In addition, viscosity data obtained in previous experiments 23 were used to develop predictive models for the systems. 2. EXPERIMENTAL SECTION 2.1. Materials. Poly(ethylene glycol) [HO-(CH 2 - CH 2 O) n -CH 2 OH] with an average molar mass of 1500 g· mol -1 (PEG1500) and sodium hydroxide (NaOH; mass purity >0.99) were purchased from Vetec Qui ́ mica Fina (Brazil). Received: September 6, 2013 Accepted: January 7, 2014 Published: January 13, 2014 Article pubs.acs.org/jced © 2014 American Chemical Society 339 dx.doi.org/10.1021/je400802t | J. Chem. Eng. Data 2014, 59, 339-345