| dc.description.abstract | Natural rubber (NR)/organoclay nanocomposites were prepared using organomontmorillonite
(OMMT) and organo-sepiolite (OSEP). Both were found to
improve modulus significantly more than equivalent amounts of conventional fillers
such as carbon black for strains up to 100%. OSEP was found to increase modulus
more than OMMT for a given filler content, and NR/OSEP nanocomposites also
had potentially anisotropic physical properties. OMMT had more effect on
vulcanisation than OSEP, although both produced considerable acceleration.
The tensile stress-strain behaviour of NR/OMMT and NR/OSEP nanocomposites
were studied using a number of different micromechanical models.
Some models were found to give a good empirical t with experimental data,
with the best results given by the Halpin-Tsai model. Furthermore, by analysis
of the vulcanisation behaviour using rheometry, and particle morphology using
transmission electron microscopy (TEM), it was possible to accurately estimate
the Young's modulus of a nanocomposite from knowledge of the cure onset time
and the shape factor of the particles.
It was discovered that unmodified montmorillonite and sepiolite clays could
undergo organic modification in situ during mixing into NR following the addition
of a suitable modifier. This resulted in vulcanisates with very similar physical
properties to those found when using pre-modified OMMT or OSEP. TEM and
X-ray diffraction showed that the exfoliation state of the clay modified in situ
was also similar to that of pre-modified organoclay.
Silane coupling agents were also used with NR/OMMT and NR/OSEP nanocomposites,
producing significant increases in modulus. However, the increased
modulus was only observed above 40% strain for OMMT and above 25% for
OSEP. The coupling agents strengthens the rubber-filler interface preventing
interfacial slippage and cavitation in the nanocomposite, and these mechanisms
only begin to operate when the interfacial stress reaches a significant level. The
most effective coupling agent used was bis[triethoxysilylpropyl] tetrasulfide due
to its relatively high reactivity. | en_US |
