Background

PET (polyethylene terephthalate) plastic bottles must have mechanical strength to resist heat and mechanical shock, and this strength is said to depend on the degree of crystallinity and crystal orientation. As PET is a crystalline polymer, powder XRD can serve as a method to evaluate the degree of crystallinity and crystal orientation. Two-dimensional (2D) diffraction patterns can be easily obtained by directing X-rays at a sample and collecting the diffracted beams with an imaging plate (IP) 2D detector or a 2D semiconductor detector (Fig. 1). If the orientation of the crystals is random, the diffraction image shows a uniform ring pattern. However, if some preferred orientation is present, the image is in the shape of an arc. By analyzing 2D diffraction patterns, information about the preferred orientation of crystals, as well as the degree of orientation, can be obtained.