Structure and fracture toughness of thin-wall polypropylene moulded at different injection speeds

Thin-wall injection-moulded parts have received a great deal of attention because of their lighter weight, which offers beneficial environmental and economic savings. However, research on the fracture toughness of thin-wall injection mouldings has been limited. In this study, thin-wall injection-moulded polypropylene (PP) parts were prepared at three injection speeds to reveal the relationship between their internal structures and mechanical properties. These characteristics were investigated by polarized optical microscopy, laser Raman spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering. Fracture toughness was characterized by the essential work of fracture (EWF) method. Overall, the results revealed that the thicker, molecularly oriented skin layer obtained at a low injection speed led to higher fracture toughness in the thin-wall PP moulded specimen.