Process and properties of micro-ultrasonic powder molding with polypropylene

Aimed at microplastic parts molding, we use a novel method of micro-ultrasonic powder molding (micro-UPM) on polypropylene (PP) microplastic parts and investigate the experimental process in detail. Firstly, the experimental results show that the temperature is maximum on the top outer edges of plastic parts and minimum on the bottom center. Then, the effects of experimental process parameters on plastic flashes are studied. The results show that under the same pressure, the flash thickness gradually thins with increased ultrasonic time. The ultrasonic time for the flashes to be automatically separated from the matrix of microplastic parts is obviously shortens with increased pressure. Finally, the tests on thermal properties, morphology, and mechanical properties of microplastic parts are also conducted. The results show that the melting point and crystallinity of microplastic parts produced by micro-UPM are higher than those of raw materials. The organizational structure shows no obvious “skin–core” structure, and its crystal form is α crystal form, which is the most common type of polypropylene. With increased ultrasonic time, the tensile strength and elongation at break of samples both have a trend of rise followed by drop before and after annealing. An ultrasonic time that is too long can lead to the degradation of materials.