Materials, Methods & Technologies ISSN 1314-7269, Volume 10, 2016 Journal of International Scientific Publications www.scientific-publications.net Page 273 THERMAL EFFECT ON THE UNIAXIAL TENSILE PROPERTIES AND STRUCTURE OF POLY (VINYL ALCOHOL) FILMS Baki Aksakal, Önder Yargi Yildiz Technical University, Department of Physics, Davutpasa Campus, Esenler 34210, Istanbul, Turkey Abstract Influence of heating or annealing at different temperatures from 25 to 140 C on the uniaxial tensile properties of polyvinyl alcohol (PVA) thin films was investigated by using tensile testing method. It was observed that especially the shape of initial part (up to 10% strain) of the stress-strain curve changed significantly which indicates the formation of a transition point at a low strain value of around 1-2% strain with increasing anneal temperature. Besides, initial or Young’s modulus increased from 0.26 GPa to around 1 GPa as the temperature increased from 25 C to around 100 C and then it decreased slightly down to around 0.7 GPa. Ultimate tensile stress increased significantly from around 16 to 39 MPa. Moreover, toughness of the PVA films were improved from around 144*10 4 to 3942*10 4 J/m 3 for the anneal temperatures from 80 to 130 C. By using the FT-IR/ATR spectral results, the increase in tensile strength and toughness is assumed to be due to increase in the degree of crystallization and absorbance ratio of hydrogen bonded OH groups, that is, the increase in the more ordered structural units and reformation and/or breakage of intra- and inter-molecular hydrogen bonds during heating process. Key words: poly (vinyl alcohol), tensile properties, thermal effect, Young’s modulus, hydrogen bond 1. INTRODUCTION Poly vinyl alcohol (PVA) being a water soluble biodegradable synthetic polymer the structure of which has a formula of [CH2CH(OH)]n is commonly used in the food industries as a binding, coating agents, and food packaging (Baker et al. 2012), the textile industries as a sizing and finishing agent (DeMerlis et al. 2003), for paper products manufacturing (DeMerlis et al. 2003), and in the production of polarizer films. Besides, in medical devices, due to its biocompatible, noncarcinogenic, nontoxic, swelling properties, and bioadhesive characteristics, PVA is used as a biomaterial (Hassan et al. 2000). PVA has been also used to treat vascular embolisms (Covey et al. 2005; Tadavarthy et al. 1975) and as tissue adhesion barriers (Weis et al. 2004; Hiraizumi et al. 1995; Lang et al. 2007). It is well known that PVA is widely used to produce nanocomposites with different chemical structures such as graphene oxides, carbon nano tubes, titanium dioxide in order to improve not only optical and electrical properties but also mechanical properties. Although mechanical properties of PVA films having different concentration and composition of different materials such as carbon nanotubes were investigated (Paiva et al. 2004; Xu et al. 2009; Zhan et al, 2014; Ni et al. 2006; Chen et al. 2005; Bahrami et al. 2005), the influence of heating on the uniaxial tensile properties and corresponding changes in the structure of PVA films have not been investigated much. Moreover, the relationship between the changes in the structure and tensile properties of PVA films due to heating was not examined which could be quite important to understand the reasons leading the changes on the stress- strain behaviors and mechanical characteristics of PVA films. In this study, the influence of heating at different temperatures on the uniaxial tensile properties and stress-strain behaviors of PVA films was investigated by using Tensile testing method. The changes in the structure and absorbance values of infrared bands of annealed PVA films were examined by FT- IR/ATR spectroscopy. The relationships between structural changes and mechanical changes in PVA films were tried to set.