Brittle-ductile transitions and the toughening mechanism in paraffin/organo-clay nanocomposites

Tensile properties for paraffin wax and a nanocomposite produced with 2 wt.% Cloisite^® 20A were measured within the temperature range of 10 to 30 °C. Young's modulus and maximum stress are significantly greater at 10 °C for the nanocomposite than those measured for the pure wax. Values for both materials decrease with increasing temperature and converge to where little difference exists as the wax enters a series of plastic crystalline states. Large enhancements in ductility for these nanocomposites reported previously are shown to be a consequence of a decrease in their brittle-ductile transition temperatures. Reduced crystallite size was observed via polarized optical microscopy for the nanocomposite and X-ray diffraction and transmission electron microscopy demonstrate preferred alignments of wax lamellae and organo-clay platelets under strain. Results indicate that a combination of proximity to mesophases and influence of organo-clay on wax morphology and on the fracture mechanism account for the observed high ductility under ambient conditions.