Molecular morphology of petaloid bases of PET bottles: A small-angle X-ray scattering study

Small-angle X-ray scattering (SAXS) studies were undertaken to explore possible morphological explanations for poor mechanical strength in the petaloid bases of poly(ethylene terephthalate) (PET) bottles. The bottles were manufactured using a two-stage injection stretch blow molding process. Splitting of PET bottle bases under load is both inconvenient and expensive. In this study, SAXS data were collected with a 100 mu m square X-ray beam to establish the molecular morphology as a function of position across the base topology. An amorphous region was identified in the base center (i.e., close to the injection gate of the preform) with biaxially orientated, semicrystalline regions in the feet and valleys of the bottle bases. For bottles that had split under load, the transition between these two regions displayed uniaxial orientation that would lead to reduced mechanical strength in the circumferential direction. Reasons for this effect are explored. (c) 2006 Wiley Periodicals, Inc.