A mechanism influencing micro injection molded weld lines of hybrid nano filled polypropylene

Abstract

Nano fillers reinforced polymer composites have been widely applied in microsystem technologies. As one popular micro fabrication technology, micro injection molding is playing the key role in manufacturing micro scale parts made of nano thermoplastics composites. As a defect in micro injection molding parts hard to avoid, the weld line causes detrimental mechanical and physical properties, particularly in case of nano filled composites. In this study, the hybrid carbon nanofibers (CNFs)/TiO2 nano particles (1:1) filled polypropylene (PP) was prepared by inner melts mixing process with various weight contents(10, 20, 30 and 35 wt%). Micro tensile samples with weld lines for all composites were formed by micro injection molding process at constant processing conditions. Mechanical properties of micro weld lines were tested by tensile test characterizing method. The results show that comparison with neat PP, the samples with weld lines made of hybrid nano PP composites are showing lower tensile strength and elongation percent, but higher E modulus. As increasing nano filler contents, the tensile strength and elongation of micro weld line samples are decreasing, while the E modulus is improved considerably.