Study on Creep Behavior of PP/CaCO ₃ Molded by Vibration Injection Molding at Different Vibration Frequency and Vibration Pressure

Abstract

Vibration injection molding technology has achieved some good properties, such as high impact strength and high tensile strength. Although many researchers have proved that the short-time mechanical properties of the polymer could be improved by vibration-injection molding technology, the long-time mechanical properties, such as the creep behavior, have not been paid enough attention. In this paper, the creep behavior of the calcium carbonate filled polypropylene (PP/CaCO ₃) prepared at various vibration conditions has been observed. The influences of the vibration pressure and the frequency on the mechanical properties and creep behavior were investigated via creep test and tensile test. Firstly, the tensile fracture strain reached the maximum (11%) at 0.72 Hz. Moreover, with the increasing vibration pressure amplitude, the tensile fracture strain would decrease. The changing tendency of tensile strength is basically contrary with the change of the tensile fracture strain. Secondly, when the vibration frequency reaches the 0.72 Hz, the tensile creep is larger than that of other frequencies samples at 50 MPa; meanwhile, the tensile creep of these PP/CaCO ₃ parts, which has been prepared at 0.48 Hz, decreases with the increasing vibration pressure amplitude. Finally, the dynamic mechanics analysis (DMA) and the wide-angle X-ray diffraction (WAXD) were adopted to analyze the reason of the creep behavior change. The different macromolecular chains mobility caused the different creep behavior.