Properties of polyetherimide/graphite composites prepared using ultrasonic twin-screw extrusion

Abstract

The dispersion of various graphites in polymers is a challenging problem limiting their potential use. To solve this problem, an ultrasound assisted twin-screw extruder was developed and utilized to compound polyetherimide (PEI) with untreated nature graphite (UG), modified graphite (MG) and expanded graphite (EG) at concentrations up to 10 wt %. The effect of ultrasonic amplitude on rheological, mechanical and electrical properties of the PEI composites was investigated. Ultrasonic treatment of PEI/UG composites showed little effect on these properties. In contrast, ultrasonic treatment of PEI/MG and PEI/EG composites led to an increase of the storage (G′), loss (G″) moduli and complex viscosity and to a decrease of the damping characteristics. In particular, the PEI/5 wt %EG composite ultrasonically treated at an amplitude of 10 μm showed a 45% higher complex viscosity than the untreated composite at a frequency of 0.5 rad/s. Also, the PEI/5 wt % EG composite treated at an amplitude of 10 μm showed a reduction in the electrical volume resistivity by almost three orders of magnitude leading to a lower percolation threshold. The untreated and treated PEI/UG and PEI/MG composites did not show any percolation within all graphite concentrations studied, due to large size of particles of UG and MG and their strong agglomeration. The ultrasonic treatment showed slight effect on mechanical properties of all these composites.