Eudragit S (Methyl Methacrylate Methacrylic Acid Copolymer)/Fatty Acid Blends as Form-Stable Phase Change Material for Latent Heat Thermal Energy Storage Ahmet Sari, 1 Cemil Alkan, 1 Ugur Kolemen, 2 Orhan Uzun 2 1 Department of Chemistry, Gaziosmanpas ˛a University, 60240 Tokat, Turkey 2 Department of Physics, Gaziosmanpas ˛a University, 60240 Tokat, Turkey Received 4 August 2005; accepted 8 October 2005 DOI 10.1002/app.23478 Published online 27 April 2006 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: By composing (Eudragit S) with fatty acids (stearic acid (SA), palmitic acid (PA), and myristic acid (MA)), form-stable phase change materials (PCMs), which can retain the same shape in a solid state even when the temperature of the PCMs is over the melting points of the fatty acids, are prepared. The compatibility of fatty acids with the Eudragit S is proved by microscopic investigation and infrared (FTIR) spectroscopy. The melting and crystal- lization temperatures and the latent heats of melting and crystallization of the form-stable PCMs are measured by Differential Scanning Calorimetry (DSC) method. The max- imum mass percentage of all fatty acids in the form-stable PCMs is found as 70%, and no leakage of fatty acid is observed at the temperature range of 50 –70°C for several heating cycles. Thermal properties obtained from the DSC analysis indicate that the Eudragit S/fatty acid blends as form-stable PCM have great potential for passive solar latent heat thermal energy storage (LHTES) applications in terms of their satisfactory thermal properties and utility advan- tage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1402–1406, 2006 Key words: form-stable; Eudragit S; myristic; palmitic and stearic acids; LHTES; polymer-based PCM; DSC analysis; FTIR spectroscopy INTRODUCTION Thermal energy can be stored as a change in internal energy of a material as sensible heat, latent heat, and thermochemical heat, or as a combination of these. Latent heat thermal energy storage (LHTES) is based on the heat absorption or release when a storage ma- terial undergoes a phase change from solid to liquid or liquid to gas or vice versa. Solid–liquid transition of phase change materials (PCMs) has proved to be eco- nomically attractive for use in thermal energy storage systems. PCMs themselves cannot serve as a heat transfer medium. Heat transfer mediums with a heat exchanger are required to transfer energy from the source to the PCM and from the PCM to the load. Therefore, designing of the heat exchanger is an im- portant part for improving heat transfer in latent heat storage systems. PCMs also have positive volumetric expansion on melting, so, volume design of the con- tainers is also necessary, which should be compatible with the PCM used. 1–3 A great variety of PCMs such as salt hydrates, par- affins, nonparaffin organic compounds and their mix- tures for latent heat thermal energy storage systems have been investigated. 1–5 The fatty acids in the class of nonparaffin organic compounds have superior properties over the other PCM groups, such as con- gruent melting and cooling, high latent heat of fusion, self-nucleating behavior, ready availability, nontoxic- ity, nonflammability, noncorrosive, small expansivity during solid–liquid phase change, and good thermal and chemical stability after a large number of acceler- ated thermal (melt/freeze) cycles. 4–8 However, the fatty acids cost more than the other PCMs on a bulk basis, but they are cheaper to package, so the final module costs are comparable. In recent years, there has been growing interest in developing the polymer-based PCMs as new type of latent heat thermal energy storage materials for pas- sive solar LHTES systems. Advantages the of poly- mer-based PCMs are as follows: (1) such a type of PCM can retain the similar shape in a solid state even when the temperature of the blend is over the melting point of the PCM; therefore, it is called as form-stable PCM; (2) they do not require any capsulation; thus, not only the encapsulation problem of PCM is solved, but also heat resistance caused by capsule shell of PCM is disappeared by using this kind of form-stable PCM; (3) because they contact with the heat transfer medium in a LHTES system directly, they are cost- effective; (4) they are easily prepared with desirable Correspondence to: C. Alkan (cemilalkan@gop.edu.tr). Journal of Applied Polymer Science, Vol. 101, 1402–1406 (2006) © 2006 Wiley Periodicals, Inc.