NATURAL RUBBER/CARBON NANOTUBE NANOCOMPOSITES PREPARED BY ULTRASONICALLY AIDED EXTRUSION

Abstract

ABSTRACT Natural rubber/multiwalled carbon nanotube (MWCNT) nanocomposites at loadings from 2 to 25 phr were prepared by ultrasonically aided extrusion at ultrasonic amplitudes up to 7.5 μm. Die pressure significantly decreased with an increase of ultrasonic amplitude, especially at higher loadings. Power consumption increased with ultrasonic amplitude and was almost insensitive to loadings until an amplitude of 5.0 μm. However, lower values of power consumption were observed at an amplitude of 7.5 μm for loadings of 10 and 15 phr. At these loadings, complex viscosity, storage, and loss moduli of compounds and vulcanizates were unaffected by ultrasonic treatment, whereas at other loadings, these properties were reduced with ultrasonic amplitude, indicating chain scission. Bound rubber in compounds decreased with treatment. The induction time during vulcanization was unaffected by ultrasonic treatment but decreased with loading, with the largest decrease observed at the lowest loading. The maximum torque in curing, cross-link density, and gel fraction of vulcanizates at loadings of 2, 3.5, 5, 7.5, and 25 phr decreased with ultrasonic amplitude, with the largest decrease observed at loading of 25 phr at an amplitude of 7.5 μm. The modulus at 100% and 300% and tensile strength of vulcanizates at loadings up to 15 phr were unaffected by the ultrasonic treatment, but these properties significantly decreased at a loading of 25 phr at an amplitude of 7.5 μm. Atomic force microscope studies of vulcanizates at a loading of 3.5 phr showed a deagglomeration at an amplitude of 7.5 μm, although dispersion analysis from an optical microscope at loadings of 3.5 and 7.5 phr did not show an improvement of dispersion by ultrasonic treatment. Optical microscope and AFM studies of vulcanizates at a loading of 25 phr indicated that ultrasonic treatment at an amplitude of 7.5 μm significantly improved dispersion of MWCNT. Such a behavior led to a strong Payne effect and an increase in hardness of vulcanizates.