Role of surfactant molecular weight on morphology and properties of functionalized graphite oxide filled polypropylene nanocomposites

Abstract

Various surfactants of different molecular weights, including alkylamine, poly(oxypropylene) diamine (POP), and maleic anhydride grafted polypropylene (PPgMA) oligomers, were used for simultaneous funtionalization and reduc- tion of graphite oxide (fGO). In this study, the effect of molecular weight and compatibility of the surfactants on the mor- phology and properties of the nanocomposites are reported. Wide-angle X-ray diffraction (WAXD) exhibited a definite interlayer thickness for GOA (alkylamine intercalated GO), however, the diffraction peaks were nearly suppressed for fGOs combining ODA with either POP (GOAP) or PPgMA (GOAE). The uniform dispersion of the fGO flakes in the polypropy- lene matrix resulted in the significant increase in both the degradation temperature and the crystallization temperature. A single characteristic melting peak of monoclinic (!) crystalline phase was observed from DSC traces, which was consistent with WAXD results. Dynamic mechanical analysis clearly indicated increase in both the storage modulus and the glass tran- sition temperature of the nanocomposites due to the enhanced affinity between fGO and the polypropylene matrix. How- ever, GOAP composite showed lower E and Tg than GOAE because POP is less compatible with the matrix than PPgMA oligomer. Dielectric analysis also showed significant increase in both dielectric permittivity and dielectric loss at low fre- quency regimes with GOAE showing maximum dielectric properties. The finely dispersed GOAE and its compatibility with polymer matrix manifested the interfacial polarization, which gave rise to much greater # and #$ than other nanocom- posites.