OUT OF PLANE ORIENTATION AND CRYSTALLINITY OF BIAXIALLY STRETCHED POLYETHYLENE TEREPHTHALATE Sudheer Bandla, Masoud Allahkarami, and Jay C. Hanan School of Mechanical & Aerospace Engineering, Oklahoma State University, Tulsa, OK 74106 Abstract The dependence of polymer properties on their processing history can be used advantageously. Polyethylene terephthalate (PET), a semi-crystalline polymer, exhibits a microstructure reliant on process and thermal history. PET undergoes strain-induced crystallization, making it sensitive to mechanical stretching. As the level of crystallinity in PET governs its mechanical behavior, it is necessary to quantify the effect of crystallinity and molecular orientation for efficient use. The present research is focused on an approach that will aid in correlating the stretch ratio of PET films to the percent crystallinity and mechanical properties. PET films with different local stretch ratios were obtained through bi-axially stretching injection molded cylinders of increasing thickness and weight. Percent crystallinity of the PET films with different stretch ratios was measured using X-ray diffraction. Film samples were marked with respect to the stretch directions for measuring their longitudinal (primary stretch direction) and transverse mechanical properties. Local molecular orientation in the form of pole figures was mapped using the ) 100 ( plane corresponding to the PET lattice. This will help in linking the physical sample directions and processing to the molecular orientation. Associating the mechanical properties with molecular alignment helps in designing production processes that realize the material’s structural potential. Introduction Microstructural information is essential to accurately model a material’s mechanical behavior. For polymers, development of the microstructure is reliant on several elements like chemistry, chain structure, molecular weight distribution, and processing history (Meijer and Govaert, 2005). The above factors can affect the size, shape and the extent of crystal formation in polymers; and makes it more difficult to model their mechanical behavior. Polyethylene Copyright ©JCPDS-International Centre for Diffraction Data 2014 ISSN 1097-0002 66 Advances in X-ray Analysis, Volume 57