Synthesis and charactirezation of surface-activated multiwalled carbon nanotubes-polymer composite electrospun nanofiber

Abstract

The major problem in the development of polymer nanofiber composites with the infusion of multiwalled carbon nanotubes (MWCNTs) is to ensure good dispersion of the MWCNTs within the polymer matrix. This study reports an effective approach to activate the surface of MWCNTs by a non-covalent binding strategy, and incorporation of MWCNTs in poly (L-lactide-co-e-caprolactone) (PLCL) using electrospinning process. The debundling of the MWCNTs aggregates through the non-covalent surfactant attachment on their outer layers was studied using surfactants with different ionic characters, which were sodium dodecyl sulphate (anionic, SDS), cetyltrimethyl ammonium bromide (cationic, CTAB), and polysorbate 80 (non-ionic, Tween-80) surfactants. Results obtained from the Atomic Force Microscopy (AFM) analysis of surface roughness of the surfactant-MWCNTs aggregates show different contours which were assigned to the size of the aggregates, distribution and orientation of the deposited surfactants on the surfaces of MWCNTs. The dispersion behavior of the respective surfactant molecules studied showed that the non-ionic surfactant molecules of Tween-80 have better adsorption coverage on MWCNTs surface due to the hydrophobic interactions between the liquid-solid interfaces, rather than the ionic surfactants of SDS and CTAB. The orientation of the adsorbed surfactants on the surfaces of MWCNTs was found to be strongly associated with the surfactant affinity, which was contributed by the surfactants head groups ionization. The surface morphology of each adsorbed surfactant molecule onto MWCNTs surface was determined by the Field Emission Scanning Electron Microscopy (FESEM) analysis. Furthermore, the infusion of the Tween-80-MWCNTs usability as the nanofiller component to produce electrospun polymer nanofiber composites was conducted using a customized electrospinning reactor system. The inclusion of Tween-80-MWCNTs resulted in superior electrospun MWCNTs-PLCL nanofiber composite with tensile stress value of 5.82-15.95 MPa, with the incorporation of MWCNTs ranging from 0.1wt% to 1.0wt%. Characterization by Transmission Electron Microscopy (TEM) depicted the homogenous distribution of MWCNTs within the polymer matrix. The manipulation of the electrospinning operational parameters in producing different structural features of the polymer nanofibers from PLCL was successful in producing both solid and porous structured nanofibers through the variation of solvent composition used. The solid PLCL nanofibers were formulated from the optimized polymer solution of 11wt% (w/v) of PLCL in dichloromethane/ dimethyl formamide (DCM/DMF) (70:30) at an applied voltage of 14kV with spinning solution flow rate of 1.0 mL/hr. While the porous PLCL nanofibers were formulated from the optimized polymer solution of 11wt% (w/v) of PLCL in DCM/acetone (70:30) at an applied voltage of 14kV with spinning solution flow rate of 1.0 mL/hr. The substitution of DMF to acetone in binary solvent system has resulted in highly-porous PLCL nanofibers. The AFM characterization revealed the differences in the surface roughness and pore depths of both dense and porous PLCL electrospun nanofibers fabricated.