Abstract
M.Sc.
Carbon nanotubes (CNTs) have been of utmost scientific interest since their
discovery in 1991 by a Japanese physicist - Sumio Iijima. This is due to their
extraordinary properties which make them one of the most promising options for
the design of novel ultrahigh strength polymer nanocomposites. It is believed that
the high aspect ratio, mechanical strength, and high electrical and thermal
conductivity of these CNTs will enhance the performance of many polymer / CNT
nanocomposites and open up new applications. However, poor dispersibility and
lack of interfacial adhesion of the CNTs in the polymer matrix have remained a
challenge towards fabrication of these nanocomposites. This has been due to the
atomically smooth surface of the nanotubes and their intrinsic van der Waals
forces which make them chemically inert.
This study was aimed at exploring this concept by using novel phosphorylated
multiwalled carbon nanotubes (p-MWCNTs) and polyvinyl chloride (PVC) polymer.
Phosphorylation of MWCNTs has been successfully achieved in our laboratories,
with the p-MWCNTs showing improvement in thermal stability. PVC on the other
hand, is the world’s second largest thermoplastic material and has physical
properties that are key technical advantages for its use in various and diverse
fields such as building and construction, electronics, food packaging and in
medical applications.
A novel solvent-free method was used to synthesize p-MWCNTs / PVC
nanocomposites. MWCNTs were synthesized by nebulized spray pyrolysis, a
modification of catalytic vapour deposition and purified by soxhlet extraction using
toluene. This method proved to be convenient and economical, producing a high
yield of carbon nanotubes. The MWCNTs were phosphorylated with alkylazido
phosphonate compounds through a 1,3-dipolar cycloaddition reaction between the
phosphonate azides and the C=C bonds of the MWCNTs, with nitrogen loss
occurring upon thermolysis. These p-MWCNTs were then melt compounded with
PVC to form the p-MWCNTs / PVC nanocomposites.
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The phosphorylation of the MWCNTs and their dispersion in the PVC matrix were
characterized by FTIR, SEM, TEM and Raman spectroscopy. Thermal analysis of
the nanocomposites by TGA and DSC showed an enhanced thermal stability
when comparing the nanocomposites with neat PVC. The modulus of the
MWCNTs / PVC nanocomposites increased whilst there was a reduction in their
tensile strength, indicating a decrease in polymer toughness.