Comparison of the properties of waterborne polyurethane/multiwalled carbon nanotube and acid-treated multiwalled carbon nanotube composites prepared by in situ polymerization

A series of waterborne polyurethane (WBPU)/multiwalled carbon nanotube (CNT) and WBPU/nitric acid treated multiwalled carbon nanotube (A-CNT) composites were prepared by in situ polymerization in an aqueous medium. The optimum nitric acid treatment time was about 0.5 h. The effects of the CNT and A-CNT contents on the dynamic mechanical thermal properties, mechanical properties, hardness, electrical conductivity, and antistatic properties of the two kinds of composites were compared. The tensile strength and modulus, the glass-transition temperatures of the soft and hard segments (T-gs and T-gh, respectively), and Delta T-g (T-gh - T-gs) of WBPU for both composites increased with increasing CNT and A-CNT contents. However, these properties of the WBPU/A-CNT composites were higher than those of the WBPU/CNT composites with the same CNT content. The electrical conductivities of the WBPU/CNT1.5 and WBPU/A-CNT1.5 composites containing 1.5 wt % CNTs (8.0 x 10(-4) and 1.1 x 10(-3) S/cm) were nearly 8 and 9 orders of magnitude higher than that of WBPU (2.5 x 10(-12) S/cm), respectively. The half-life of the electrostatic charge (tau(1/2)) values of the WBPU/CNT0.1 and WBPU/A-CNT0.1 composites containing 0.1 wt % CNTs were below 10 s, and the composites had good antistatic properties. From these results, A-CNT was found to be a better reinforcer than CNT. These results suggest that WBPU/A-CNT composites prepared by in situ polymerization have high potential as new materials for waterborne coatings with good physical, antistatic, and conductive properties. (c) 2005 Wiley Periodicals, Inc.