The Conductivity Of Carbon Fiber/Polypropylene Sandwich Injection Parts

Injection molding conductive polymer composites(IMCPCs) have been widelyused in microelectronics, energy, sensors, electromagnetic shielding fields, etc. thepercolation threshold of IMCPCs is higher than that of compress molded conductivepolymer composites(CMCPCs).This thesis research applied sandwich injectionmolding method to compare the conductivity difference between the sandwichinjection molding parts and the traditional injection molding parts, the dispersioncondition and orientation structure of carbon fiber (CF) was also observed anddiscussed the sandwich injection molding parameters on the influence of theconductivity of sandwich parts. Main works are as follows:(1) A comparative study of electrical conductivity between sandwich injectionmolding and traditional injection molding parts. The sandwich injection skincontaining carbon fiber/polypropylene (CF/PP) composites, core layer is PP, andpre-filled skin volume fraction of the conductive composite materials is50vol%(volume fraction). Results indicated that both the sandwich injection samples and theconventional injection samples showed a nonlinear percolation phenomenon, in thepercolation threshold of the traditional injection sample is about7wt%(massfraction), while the sandwich injection threshold value is about4wt%, compared tothe traditional injection sample, sandwich injection sample showed great superiority,showed its engineering application value.(2) The effect of molding parameters on the conductivity of sandwich injectionmolding parts. Five parameters such as the skin/core injection flow rate, skin melttemperature, mold temperature and pre-filled skin volume fraction were investigatedto evaluate the conductivity influence on the sandwich products. The results showthat the volume resistivity of the sandwich injection parts increases with increasing ofthe skin/core injection flow rate, and skin injection speed is more obvious than theeffect of core layer injection speed; Volume resistivity decreases with the skin melttemperature or mold temperature rise; it is nonlinear relationship between pre-filled skin volume fraction and the conductivity of sandwich injection parts. When thepre-filled skin volume fraction is small, with the increase of skin filling amount,sandwich parts of the volume resistivity decreased more obviously; When pre-filledvolume fraction surpasses50vol%, the influence of pre-filled skin volume fraction onthe sandwich parts of the volume resistivity is more tiny.(3) The relationship of CF dispersion and electrical conductivity of sandwichinjection molding were studied by using the polarizing microscope. The resultsshowed that the CF dispersed evenly and multi-angle orientation is more favorable forthe formation of conductive network in the sandwich injection molding.