This research aimed to develop technology and processes to further beneficiate two southern
African bentonites for applications in polymer/clay nanotechnology. The bentonites were
from the Koppies mine in South Africa, and the Boane mine in Mozambique. The work was
divided into two parts: (i) preparation of organomodified nanoparticulate smectite clays, and
(ii) preparation of their poly(ethylene-co-vinylacetate) nanocomposites.
Nanoparticulate organobentonites were prepared using purified bentonites. The conventional
organomodification process uses a very low concentration of bentonites at 80 oC. In this
study, a novel method was developed: concentrated slurries of naturally occurring
Ca-bentonite partially activated with soda ash in the presence of a proprietary dispersant were
contacted at ambient temperature with quaternary ammonium surfactants. A known amount
of bentonite dispersion was placed in a planetary mixer before the mixture. Likewise, a
known amount of surfactant, up to 50% excess, based on the estimated cation exchange
capacity (CEC) of the bentonites, was added while mixing the dispersion. The surfactants
added were either in solution or in powdered form. The intercalated bentonite was recovered
by centrifugation and washed repeatedly with water until halide ions could not be detected
using a 1M silver nitrate solution. The solids were dried at ambient temperature and humidity,
and then crushed and milled into a fine powder using a mortar and pestle.
Several instrumental techniques were used to characterise and examine the properties of the
bentonite samples before and after organic treatment.The X-ray diffraction (XRD) results were
consistent with: (i) paraffin-type extended chain intercalation; and (ii) interdigitated monolayer
intercalation of the C12 and C14 single-chain alkyl surfactants and bilayer intercalation of the
single-chain C16 surfactant and the surfactants with double alkyl chains. Fourier transform
infrared (FTIR) spectroscopy analysis of the organobentonite powders confirmed disordered
chain conformations. XRD also detected significant amounts of cristobalite in the samples of
Boane bentonite (from Mozambique). This impurity could not be removed cost-effectively.
The onset decomposition temperature ofthe present organobentonites was around 200 ºC, which
is within the typical range of polymer/organoclay processing temperatures. The thermal stability
of the organobentonites was independent of both the number of alkyl chain substituents and
their length, and also independent of the degree of clay intercalation.
SURFACTANT INTERCALATED KOPPIES AND BOANE BENTONITES FOR POLYMER NANOTECHNOLOGY
ii
Poly(ethylene-co-vinylacetate) nanocomposites were prepared with South African Koppies
bentonite, organomodified with single-chain C12 (and polar 2-hydroxyethyl side chain) and
double-chains C18 alkyl ammonium cationic surfactants. The later surfactant was intercalated
both below and above the clay CEC. Nanocomposites were prepared by twin-screw melt
compounding. Transmission electron microscopy (TEM) indicated the presence of mixed nanoand
micron-sized clay morphologies. XRD studies revealed that the crystallinity of the particles
improved and that the d-spacing values increased on incorporation of the modified bentonites in
the polymer matrix. It is postulated that, rather than indicating polymer co-intercalation, this was
caused by further intercalation of either excess surfactants or surfactant residues that were released
by shear delamination of the clays during compounding. Improved mechanical properties were
realised, especially when using the bentonite containing the longer double-chains surfactant
intercalated at levels in excess of the CEC of the clay. The nanocomposites showed improved
tensile modulus and elongation at break values at the expense of a reduction in impact
strength, while tensile strength was about the same as for the neat polymer. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/40227 |
| Date | January 2013 |
| Creators | Massinga, Pedro Horacio |
| Contributors | Focke, Walter Wilhelm, massingajr@uem.mt |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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