Preparation and properties of acid-treated multiwalled carbon nanotube/waterborne polyurethane nanocomposites

Nitric acid treated multiwalled carbon nanotubes (A-CNTs) were dispersed in a waterborne polyurethane (WBPU) matrix to obtain WBPU/A-CNT nanocomposite films (99.99/0.01-98.5/1.5) with enhanced thermal, mechanical, and electrical properties. By X-ray photoelectron spectroscopy (XPS), the oxygen content of the carbon nanotube (CNT) surface was found to increase with increasing acid treatment time. With increasing acid treatment time, the contact angle of the CNT surface was significantly decreased from 15 to 0degrees. The mean particle sizes of the raw CNT and A-CNT aqueous solutions were 404.2 and 17.2 nm, respectively, indicating that the acid treatment led to a reduced agglomeration of CNTs. The electrical conductivity of raw CNT was 23 S/cm, and that of A-CNT significantly increased with increasing acid treatment time up to 30 min and then decreased a little. By dynamic mechanical thermal analysis, the storage modulus and loss tangent peak temperature (the glass-transition temperature) of the WBPU/A-CNT nanocomposites were found to increase with increasing A-CNT content. The initial tensile moduli and tensile strengths of the nanocomposite film with 1.5 wt % loading of A-CNT were enhanced by about 19 and 12%, respectively, compared to the corresponding values for the original WBPU film. The WBPU/A-CNT1.5 nanocomposite film containing 1.5 wt % of A-CNT exhibited a conductivity of 1.2 x 10(-4) S/cm, which was nearly eight orders of magnitude higher that of the WBPU film (2.5 x 10(-12) S/cm). The antistatic half-life (tau(1/2)) of the WBPU film was about 110 s, indicating that pure the WBPU film was a typical electrostatic material. However, those of the WBPU/A-CNT nanocomposites decreased exponentially with increasing A-CNT content. The WBPU/A-CNT1.5 sample, containing 1.5 wt % of A-CNT and with a tau(1/2) of 1 s, had good antistatic properties. (C) 2005 Wiley Periodicals, Inc.