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A study of the morphology-property relationships of polymer-layered silicate nanocomposites
Author(s)
Mbanjwa, Khangelani Methuli
Date Issued
2007
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The continuous development of new materials and the improvement of existing ones ensure a
balance between technological growth and environmental sustainability. With the above
trade-offs, the quality of life for humankind is continually being improved. Polymeric
materials are some of our most valued commodities in our everyday lives. They continue to be
developed and improved in a variety of ways; one of which is to improve their properties by
preparing nanocomposites. Polymer-based nanocomposites (PNCs) is a way of getting novel
properties and enhancing existing one in polymer matrices, by incorporating additives on a
nano-scale. The most significant advantage of PNCs is the potential to design and tailor
properties for a specific application, since the control of the structure can be done at the
molecular level. Therefore, a fundamental understanding of the relationships between the
structure and the properties of PNCs is of utmost importance. Amongst the most studied and
researched PNC materials, polymer-layered silicate nanocomposites (PLSNs) have recently
enjoyed attention from academia and industry.
In the current study structure-property relationships of PLSNs were investigated. Polystyrene
(PS) was chosen as the base polymer due to its wide use in many articles such as in
packaging. It was also a material of choice based on its poor mechanical properties in its
natural state (unfilled), so as to contribute in its property improvement. Montmorillonite
(MMT) was a layered silicate (clay) of choice, as much research has been done on it, and it is
available worldwide, as a main component in Bentonite (a natural material).
Clays are composed of sheet-like, layered particles, which, when in a suitable environment,
can delaminate into single, nano-sized sheets. The sheets are held together by van der Waals
forces and between the sheets are exchangeable cations. The clays are hydrophilic in nature
and cannot readily delaminate in a hydrophobic polymer matrix due to the differences in
surface energies. A MMT surface was functionalized to be hydrophobic by conducting an ion
exchange reaction with alkyl ammonium surface active agents (surfactants). Polymerizable
surfactants (surfmers) were used to enhance the interfacial interaction between the PS matrix
and MMT silicate layers. The organically modified clays (organoclays) were used in synthesizing polystyrene-layered
silicate nanocomposites (PS-LSN) by an in-situ intercalative polymerization method. The
polymerization of the nanocomposites was conducted in bulk. The morphologies of the
nanocomposites were characterized using small-angle X-ray scattering (SAXS), transmission
electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and gel
permeation chromatography (Ope).
The study was further expanded to the investigation of the effects of the nanocomposite
structure, type of organic modifier, and amount of clay loading on the properties of the
materials. The properties were studied by dynamic mechanical analysis (DMA),
thermomechanical analysis (TMA) and dielectric analysis (DEA). The properties were
dependent on the interfacial processes between the clay layers and the polymer matrix. The
changes in properties compared to the PS homopolymer showed time and temperature
dependent effects, as determined by DEA. Even though the dynamics of the interfacial
interactions are still not fully understood, the nanocomposites showed improvements in
properties compared to the homopolymers.
balance between technological growth and environmental sustainability. With the above
trade-offs, the quality of life for humankind is continually being improved. Polymeric
materials are some of our most valued commodities in our everyday lives. They continue to be
developed and improved in a variety of ways; one of which is to improve their properties by
preparing nanocomposites. Polymer-based nanocomposites (PNCs) is a way of getting novel
properties and enhancing existing one in polymer matrices, by incorporating additives on a
nano-scale. The most significant advantage of PNCs is the potential to design and tailor
properties for a specific application, since the control of the structure can be done at the
molecular level. Therefore, a fundamental understanding of the relationships between the
structure and the properties of PNCs is of utmost importance. Amongst the most studied and
researched PNC materials, polymer-layered silicate nanocomposites (PLSNs) have recently
enjoyed attention from academia and industry.
In the current study structure-property relationships of PLSNs were investigated. Polystyrene
(PS) was chosen as the base polymer due to its wide use in many articles such as in
packaging. It was also a material of choice based on its poor mechanical properties in its
natural state (unfilled), so as to contribute in its property improvement. Montmorillonite
(MMT) was a layered silicate (clay) of choice, as much research has been done on it, and it is
available worldwide, as a main component in Bentonite (a natural material).
Clays are composed of sheet-like, layered particles, which, when in a suitable environment,
can delaminate into single, nano-sized sheets. The sheets are held together by van der Waals
forces and between the sheets are exchangeable cations. The clays are hydrophilic in nature
and cannot readily delaminate in a hydrophobic polymer matrix due to the differences in
surface energies. A MMT surface was functionalized to be hydrophobic by conducting an ion
exchange reaction with alkyl ammonium surface active agents (surfactants). Polymerizable
surfactants (surfmers) were used to enhance the interfacial interaction between the PS matrix
and MMT silicate layers. The organically modified clays (organoclays) were used in synthesizing polystyrene-layered
silicate nanocomposites (PS-LSN) by an in-situ intercalative polymerization method. The
polymerization of the nanocomposites was conducted in bulk. The morphologies of the
nanocomposites were characterized using small-angle X-ray scattering (SAXS), transmission
electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and gel
permeation chromatography (Ope).
The study was further expanded to the investigation of the effects of the nanocomposite
structure, type of organic modifier, and amount of clay loading on the properties of the
materials. The properties were studied by dynamic mechanical analysis (DMA),
thermomechanical analysis (TMA) and dielectric analysis (DEA). The properties were
dependent on the interfacial processes between the clay layers and the polymer matrix. The
changes in properties compared to the PS homopolymer showed time and temperature
dependent effects, as determined by DEA. Even though the dynamics of the interfacial
interactions are still not fully understood, the nanocomposites showed improvements in
properties compared to the homopolymers.
Additional information
Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2007
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