Michael D. Via

Characterization of exfoliated graphite nanoplatelets/polycarbonate composites: electrical and thermal conductivity, and tensile, flexural, and rheological properties

Exfoliated graphite nanoplatelets (GNP) can be added polymers to produce electrically conductive composites. In this study, varying amounts (2–15 wt%) GNP were added to polycarbonate (PC) and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile, flexural, and rheological properties. The percolation threshold was approximately 4.0 vol% (6.5 wt%) GNP. The addition of GNP to polycarbonate increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 8 wt% (5.0 vol%) GNP in polycarbonate composite had a good combination of properties for electrostatic dissipative applications. The electrical resistivity and thermal conductivity were 4.0 × 107 ohm-cm and 0.37 W/m · K, respectively. The tensile modulus, ultimate tensile strength, and strain at ultimate tensile strength were 3.5 GPa, 58 MPa, and 3.5%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 108 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure polycarbonate and in samples containing up to 8 wt% GNP. PC and GNP/PC composites show shear-thinning behavior. Viscosity of the composite increased as the amount of GNP increased dueto a volume-filling filler effect. The viscosity of the GNP/PC composites are well described by a Kitano-modified Maron-Pierce model.

Effects of Carbon Fillers on Rheology of Polypropylene-based Resins

Varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon nanotubes) are added to polypropylene and the resulting single filler composites are tested for viscosity. In addition, the effects of single fillers and combinations of different carbon fillers are studied via a factorial design. Each single filler and all the combinations of different fillers cause a statistically significant increase in composite viscosity. For synthetic graphite/polypropylene composites, the viscosity increase is due to a volume filling effect. Composites containing carbon black and/or carbon nanotubes show viscosity increases above those containing only synthetic graphite.

Effects of multiple carbon fillers on the electrical and thermal conductivity and tensile and flexural modulus of polycarbonate-based resins

Adding conductive carbon fillers to insulating thermoplastic polymers increases the electrical conductivity of the resulting composite, which could allow them to be used in electrostatic dissipative and semiconductive applications. In this study, three different carbon fillers (carbon black [CB], carbon nanotubes [CNTs], and exfoliated graphite nanoplatelets [GNPs]) were studied via three different combinations of two different fillers (CB/CNT, CB/GNP, and CNT/GNP). These filler combinations were studied via three 32 factorial designs, which considered the following loading levels: CB: 0, 2, 5 wt%; CNT: 0, 1, 5 wt%; and GNP: 0, 2, 5 wt%. These composites were compounded, injection molded, and tested for electrical and thermal conductivity (TC), and tensile and flexural modulus. All of the single fillers caused a statistically significant increase at the 95% confidence level in composite electrical and TC, and tensile and flexural modulus. Many two filler interactions had a statistically significant effect on composite electrical and TC, and tensile and flexural modulus. For example, when CB and CNT are combined into a composite, the composite tensile modulus is higher than what would be expected from the additive effect of each single filler. Five different formulations (four containing two filler combinations) could be used for electrostatic dissipative applications and seven different formulations (six containing two filler combinations) may be used for semiconductive applications.