DISPERSION AND CRYSTALLIZATION BEHAVIOR OF POLYPROPYLENE NANCOMPOSITES WITH β NUCLEATING AGENT MODIFIED MULTIWALL CARBON NANOTUBES

Non-colavent modification of multiwall carbon nanotubes (MWCNTs) by arylamides compound beta-nucleating agent (beta-NA) through pi-pi interaction was found to improve the dispersion of MWCNTs in the polypropylene (PP) matrix, increase the crystallinity of PP, decrease the crystal size, and increase the electrical conductivity of their composites. The morphology, crystallization behavior and the electrical conductivity of the nanocomposites were investigated by field emission scanning electron microscopy (FESEM),wide-angle X-ray diffraction (WAXD) and properties test. The characterizaiton of beta-NA-MWCNTs showed that beta-NA was successfully adsorbed on the surfaces of MWCNTs. The incorporation of beta-NA-MWCNTs results in the formation of rich beta-form crystals for PP, higher crystallinity and smaller crystalline sizes. FESEM observation showed that homogeneous compact network structure of beta-NA-MWCNTs was obtained due to the smaller and more uniform crystalline region. Consequently, the PP/beta-NA-MWCNTs nanocomposites possess a high electrical conductivity and a low percolation threshold of 0.3 wt% beta-NA-MWCNTs, which is associated with the homogeneous compact network structure of beta-NA-MWCNTs. The electrical conductivity of PP/beta-NA-MWCNTs (5 wt%) was up to 4.0 x 10(-3) S/cm, which was 3 and 11 orders higher than that of PP/MWCNTs and PP, respectively. The effect of the crystalline size on the electrical conductivity of the nanocomposites was studied by isothermal crystallization method. The electrical conductivity of PP/beta-NA-MWCNTs was increased at first and then decreased with increasing time of isothermal crystallization. And the more MWCNTs added, earlier the maximum conductivity of PP/beta-NA-MWCNTs appeared. At the same content of MWCNTs, the isothermal time for the maximum conductivity at 140 degrees C was longer than that at 130 degrees C. The results imply that high electrical conductivity with optimal MWCNTs network structure can be obtained by controlling the crystallization conditions.