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CHAPTER 1
INTRODUCTION
Nanotechnology is one of the most popular areas for current
research and development in basically all technical disciplines. The field of
nanoscience has blossomed over the last twenty years, and the importance for
nanotechnology will increase as miniaturization becomes more important in
areas, such as computing, sensors, biomedical and many other applications.
From chemistry to biology, from materials science to electrical engineering,
scientists are creating the tools and developing the expertise to bring
nanotechnology out of the research labs and into the market place.
Nanotechnology can be defined as the design and synthesis of functional
materials within nanometer scale in at least one dimension (up to 100 nm) and
control and exploitation of novel properties and phenomena in physics,
chemistry and biology depending on this length scale. This obviously includes
polymer science and technology and even in this field the investigations cover
a broad range of topics. Nanostructured composite materials, using organic
polymer and inorganic fillers, represent a merger between traditional organic
and inorganic materials, resulting in compositions that are truly hybrid
(Coronado et al 2000).
The incorporation of nanoparticles into polymers is a design
approach that is used in many areas of material science. The concept is
attractive because it enables the creation of materials with new or improved
properties by mixing multiple constituents and exploiting synergistic effects.
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These materials exhibit behavior different from conventional composite
materials with microscale structure, due to the small size of the structural unit
and the high surface to volume ratio. The growing exploration of
nanotechnology has resulted in the identification of many unique properties of
nanocomposites, such as enhanced thermal, optical, electrical, magnetic, and
mechanical properties when compared to conventional formulations of the
same material. Moreover, in recent years, researchers have exhibited an
increased interest in exploring numerous biomedical applications of
nanomaterials (Liu et al 2007).
1.1 POLYMER SCIENCE AND TECHNOLOGY
Polymer science is a multidisciplinary field as it involves the
synthetic polymers, biopolymers, polymer characterization, designing and
fabrication of new innovative products related to safer and sustainable
environment. Recognition of the macromolecular structure of polymers was
the key to enabling the development of polymer science and technology to
occur on sound scientific and engineering bases. Modern polymer science is a
blend of particular aspects of organic chemistry, physical chemistry, material
physics and statistical mathematics, with, to a lesser extent, some aspects of
inorganic chemistry. Polymer technology is even more multifarious,
combining polymer science with aspects of chemical engineering, mechanical
engineering, and rheology, encompassing, for example, reactor design for
polymerization from monomers through blending, extrusion, injection
molding, vacuum forming, reaction injection molding to the production and
use of polymer colloids for drug delivery and adhesives. The
multidisciplinary nature of polymer science and technology and their close
interactions with more traditional disciplines is illustrated in Figure 1.1
(Stepto et al 2003).
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Figure 1.1 Multidisciplinary nature of polymer science and technology
One of the fascinations of polymer science and technology is the
interplay of the various factors related to its constituent disciplines. For
example, the mechanical properties of polymers depend closely on their
chemical structure and on their molecular size or molar mass. The flow
behaviors of polymer melts and the design of processing methods and
machinery are intimately related to molecular size and structure. The
importance in polymer science and technology of the interplay of the various
aspects related to its constituent disciplines arises because polymers are
generally processed and used nearer the limits of their properties. Therefore,
there are more closely defined windows of conditions in which polymers
display the desired properties. Molecular design and control are of paramount
importance.
In short, the 21st century is called the ‘Age of Polymers’ because
the volume of synthetic polymers produced is greater than the volume of
steel. Furthermore, polymer consumptions of developed and developing
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countries increase roughly in proportion to their gross national products.
Conventional plastics account for 88 % of the production of polymers, with 12
% being devoted to high-performance materials. This 12 % is the principal
focus of future research, leading to growth in volume, types of materials, and
applications. Continual development of new polymeric materials is crucial to
sustain and expand the growing interest in this technology and modern polymer
science is highly proficient in tailoring polymers to specific aims in terms of
mechanical and thermal stability.
1.2 POLYMER BLEND
Polymer blending is a proven tool to obtain new types of materials
with a wide diversity of properties intermediate between those of pure
components. This strategy is usually cheaper and less time consuming than
development of new monomers for polymer synthesis. Blending of different
polymers conserves their individual superior properties in the final mixture
while concurrently reducing their poor characteristics. It is an extremely
attractive and inexpensive way of obtaining new structural materials (Zhang et
al 2001).
Polymer blends are defined as physical mixtures of structurally
different homopolymers/copolymers (Figure 1.2) (Tucker and Moldenaers
2002). At thermodynamic equilibrium, a mixture of two polymers in the
amorphous state may exist as a single phase of mixed segments and hence the
blend is said to be homogenous on a microscopic scale and is considered
miscible. When the mixture of two polymers exhibit separate phases
consisting of individual components, the blend is heterogeneous; and on a
microscopic scale, it is immiscible. Multicomponent polymer blends, which
consist of at least three immiscible polymers, are a new emerging area
in the field of polymeric materials. A large range of phase morphology
then becomes available and directly influences the whole set of
properties. The type of morphology and the size of dispersed
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phases in binary or ternary systems are important factors that determine
mechanical properties and rheological behavior of polymeric blends. The type
of morphology and the size of dispersed phases can be affected by
composition, melt viscosity of the components, interfacial interaction, and
processing parameters.
Figure 1.2 Schematic representation of binary polymer blend
When developing suitable polymer blends it is important to
consider a number of different research, development and quality control
issues (Grmela et al 1998). One of the most important issues is blend
compatibility. The properties of the polymer blend depend upon the
compatibility of the individual polymers with each other and the method of
mixing. Compatible polymer blends can avoid undesirable physical and
chemical effects such as:
premature aging
cracking and tearing
break down or disintegration
impermeability to natural elements
chemical attack
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Differential scanning calorimetry (DSC) is a valuable thermal
analysis technique which provides testing laboratories with important
information on the glass transition temperature of polymer blends. Measuring
the glass transition temperature of the desired polymer blends can quickly and
easily determine their compatibility. A considerable amount of works has
been recently conducted to obtain new polymeric blends with enhanced
attributes for specific applications or a better combination of different
properties.
1.3 POLYMER COMPOSITES
Polymer composites mark the beginning of a new era of the
polymer industry towards the sustainable development. Polymer composite
materials contain a strong load-bearing phase, typically in the form of fibers
or fragments of another component which is the reinforcing material or filler,
embedded in a polymer matrix. The reinforcements provide the mechanical
strength and stiffness, and the polymer matrix ensures the transfer of load
between the fillers, and protects them from environmental degradation.
Generally polymer composites are classified based on the reinforcing material
and is depicted in Figure 1.3 (Mangalgiri 1999). Polymer composites have
replaced a variety of traditional materials in different sectors by virtue of the
desired properties like light weight, durability, heat resistance, reduced wear
and tear, flexibility, chemical resistance and longer shelf life that can be
achieved by making minor alterations in their compositions. They have a wide
array of applications ranging from packaging, spacecrafts and defense
products to textile material and biological implants. Different polymers used
as matrix material to prepare composites with improved mechanical, thermal
and electrical properties includes plastics of different constitution like
polyester, polyamide, etc. The properties of the composites are largely
dependent upon the combination and the relative ratio of the matrix
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and the filler (Matabola et al 2009). By the proper selection of reinforcement
and matrix material, manufacturers can produce properties that can exactly fit
the requirements for a particular purpose. Filled polymers with improved
performance at low loading levels are of great interest, and this has provided
much of the initial motivation for the development of polymer matrices filled
with nanosized particles and the associated hybrid polymer composites.
Therefore, the new formulation of polymers and nanoparticles is opening new
research pathways for engineering flexible composites that exhibit
advantageous electrical, optical or mechanical properties (Njuguna
and Pielichowski 2004).
Figure 1.3 Classification of polymer matrix composites
1.4 POLYMER NANOCOMPOSITES
In the past decade, polymer nanocomposites have emerged as a new
class of materials and attracted considerable interest and investment in
research and development. This is largely due to their new and often much
improved mechanical, thermal, electrical and optical properties as compared
to their macro and micro counterparts. In general, polymer nanocomposites
are made by dispersing inorganic or organic nanoparticles into either a
thermoplastic or thermoset polymer. Nanoparticles can be three-dimensional
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spherical and polyhedral nanoparticles (e.g., colloidal silica), two-dimensional
nanofibers (e.g., nanotubes, whisker) or one-dimensional disc like
nanoparticles (e.g., clay platelet, graphene). Such nanoparticles offer
enormous advantages over traditional macro or micro particles (e.g., talc,
glass, carbon fibers) due to their higher surface area and aspect ratio,
improved adhesion between nanoparticle and polymer, and lower amount of
loading to achieve equivalent properties. While elastomeric composites with
nanoscale spherical fillers have been in use for more than 100 years, in the
last 15 years new fillers have emerged, providing an opportunity for the
development of high-performance multifunctional nanocomposites
(Kawasumi 2004). Thus, the discovery of polymer nanocomposites has
opened a new dimension in the field of material science owing to their unique
properties and numerous potential applications in the automotive, aerospace,
construction, biomedical and electronic industries.
1.5 SURFACE MODIFICATION OF NANOPARTICLES
The dispersion of nanometer-sized particles in the polymer matrix
has a significant impact on the properties of nanocomposites. The main
drawback of hydrophilic inorganic nanofillers in polymer nanocomposites is
its incompatibility with hydrophobic polymer, which often causes
agglomeration of nanofillers in the polymer matrix. Therefore, surface
modification is a feasible and effective means for improving the dispersion of
the nanoparticles. In general, surface modification of nanoparticles is carried
out by either chemical or physical methods. Chemical methods involve
modification either with modifier agents or by grafting polymers. Silane
coupling agents are the most used type of modification agents. Surface
modification based on physical interaction is usually implemented by using of
surfactants or macromolecules adsorbed onto the surface of nanoparticles.
The principle of surfactant treatment is the preferential adsorption of a polar
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group of a surfactant to the surface of nanoparticle by electrostatic interaction.
A surfactant reduces the interaction between the nanoparticles within
agglomerates by reducing the physical attraction and easily incorporated into
polymer matrix. Thus surface modification promotes the surface
hydrophobicity of nanoparticles (Zou et al 2008).
1.6 DIFFERENT TYPES OF NANOCOMPOSITES
1.6.1 Polymer Layered Silicate Nanocomposites
During the last decade, interest in polymer layered silicate
nanocomposites has been rapidly increasing at an unprecedented level, both in
industry and in academia, due to their potential for enhanced physical,
chemical, and mechanical properties compared to conventional filled
composites. Layered silicates used in the synthesis of nanocomposites are
natural or synthetic minerals, consisting of very thin layers that are usually
bound together with counter-ions. Their basic building blocks are tetrahedral
sheets in which silicon is surrounded by four oxygen atoms, and octahedral
sheets in which a metal like aluminum is surrounded by eight oxygen atoms.
Therefore, in 1:1 layered structures a tetrahedral sheet is fused with an
octahedral sheet, thereby the oxygen atoms are shared (Pavlidou and
Papaspyrides 2008). The reason why these materials have received a great
deal of attention recently, as reinforcing materials for polymers, is their
potentially high aspect ratio and the unique intercalation/exfoliation
characteristics. Among the layered silicate nanocomposite precursors,
fluorohectorite is one of the environmentally friendly and readily available
clay mineral with high-aspect ratio and high-surface area. They belong to the
general family of 2:1 layered silicates and their crystal structure consists of
layers made of two silica tetrahedral fused to an edge-shared octahedral sheet
of either aluminum or magnesium hydroxide. Isomorphic substitution within
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the layers generates negative charges that are normally counterbalanced by
cations residing in the interlayer space.
Polymer layered silicate nanocomposites are prepared by
incorporating finely dispersed layered silicate materials in a polymer matrix.
However, the nanolayers are not easily dispersed in most polymers due to the
incompatibility of hydrophilic layered silicate and hydrophobic engineering
plastics. The poor miscibility between the organic and inorganic components
in clay based nanocomposites leads to relatively poor mechanical properties.
Thus, when the polymer is unable to intercalate between the silicate sheets, a
phase separated composite is obtained, whose properties are in same range as
for traditional microcomposites. In order to render hydrophilic clay miscible
with hydrophobic polymer, the alkali counter-ions in the clay is exchanged
with cationic-organic surfactant through ion exchange reactions, as shown in
Figure 1.4 (Stoll et al 2001). The inorganic, relatively small (sodium) ions are
exchanged against more voluminous organic onium cations. This ion-
exchange reaction has two consequences: firstly, the gap between the single
sheets is widened enabling polymer chains to move in between them and
secondly, the surface properties of each single sheet are changed from being
hydrophilic to hydrophobic.
Figure 1.4 Schematic representation of ion-exchange reaction
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It is well established that when layered silicates are uniformly
dispersed in a polymer matrix, the nanocomposite properties can be improved
to a dramatic extent. Depending on the interaction between the clay and the
polymer matrix, two types of nanocomposite morphologies can be obtained:
namely, intercalated and exfoliated (Figure 1.5) (Morgan and Gilman 2003).
Intercalated structures are formed when a single extended polymer chain is
penetrated into the galleries of silicate layers. An exfoliated structure results
when the clay layers are well separated from one another and individually
dispersed in the continuous polymer matrix. The exfoliation configuration is
of particular interest because it maximizes the polymer clay interactions
making the entire surface of layers available for the polymer. This should lead
to the most significant changes in mechanical and physical properties. This
has motivated vigorous research and today efforts are being conducted
globally, using almost all types of polymer matrices.
Figure 1.5 Formation of intercalated and exfoliated nanocomposite
structures from layered silicate and polymer
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1.6.2 Polymer Graphene Nanocomposites
Carbon-based nanoparticles, in particular carbon nanotubes
(CNTs), offered the potential to combine several properties, such as
mechanical strength, electrical conductivity and thermal stability, among
others. Although significant advances have been made in the use of carbon
nanotubes as reinforcements of polymer matrices, there are still unresolved
issues such as the tendency of nanotubes to agglomerate during processing,
the limited availability of high-quality nanotubes in large quantities and the
high cost of their production. Hence, graphene sheets provide an alternative
option to produce functional nanocomposites due to their excellent properties
and the natural abundance of their precursor, graphite (Stankovich et al 2006).
Graphene is two dimensional carbon nanofiller with a one-atom-
thick planar sheet of sp2 bonded carbon atoms that are densely packed in a
honeycomb crystal lattice (Figure 1.6) (Potts et al 2011). It is regarded as the
“thinnest material in the universe” with tremendous application potential.
Graphene is predicted to have remarkable properties, such as high thermal
conductivity, superior mechanical properties and excellent electronic transport
properties. The superiority of graphene nanoplatelets over carbon nanotubes
in terms of properties is related to their high speci c surface area, wrinkled
(rough) surface, as well as the two-dimensional (planar) geometry of
graphene platelets. These intrinsic properties of graphene have generated
enormous interest for its possible implementation in a myriad of devices.
These include future generations of high speed and radio frequency logic
devices, thermally and electrically conducting reinforced nanocomposites,
ultra-thin carbon films, electronic circuits, sensors, and transparent and
flexible electrodes for displays and solar cells (Park and Rouffs 2009).
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Figure 1.6 Graphene, honey comb lattice of carbon atoms
The most widely used methods to synthesize these high quality,
defect-free graphene sheets have been micromechanical cleavage of graphite
(‘‘Scotch tape’’ or peel off method), and chemical vapour deposition (CVD).
However, their production yield is relatively small and, in the case of the
micromechanical cleavage, time consuming which hinders the effective and
full-exploitation of these materials. An alternative route to produce graphene
and chemically modified graphene is by the exfoliation of graphite or its
derivatives, mainly graphite oxide. The advantage of this approach is that it
enables high yield production and, hence, it is a cost-effective and scalable
process (Wang et al 2009; Inagaki et al 2011).
The superior properties of graphene compared to polymers are also
reflected in polymer/graphene nanocomposites. Polymer/graphene
nanocomposites show superior mechanical, thermal, gas barrier, electrical and
flame retardant properties compared to the neat polymer. It was also reported
that the improvement in mechanical and electrical properties of graphene
based polymer nanocomposites are much better in comparison to other
polymer nanocomposites. Although CNTs show comparable mechanical
properties compared to graphene, still graphene is a better nanofiller than
CNT in certain aspects, such as thermal and electrical conductivity.
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To harnessing the fantastic properties, graphene has been considered to
incorporate into polymers, to prepare graphene filled nanocomposites, which
may offer a novel and intriguing nanostructured materials for various
applications. However, the improvement in the physicochemical properties of
the nanocomposites depends on the distribution of graphene layers in the
polymer matrix as well as interfacial bonding between the graphene layers
and polymer matrix. Interfacial bonding between graphene and the host
polymer dictates the final properties of the graphene reinforced polymer
nanocomposite. Pristine graphene is not compatible with organic polymers
and does not form homogeneous composites. The surface modification of
graphene is an essential step for obtaining a molecular level dispersion of
individual graphene in a polymer matrix (Lin et al 2011).
1.6.3 Polymer Hydroxyapatite Nanocomposites
Calcium phosphates serve a common interest among various fields
such as biology, chemistry, dentistry and medicine. They are known for their
structural and compositional resemblance to natural tissues such as bone and
teeth. This makes them an ideal biomaterial for applications such as bone
grafts, coatings for bone prostheses, cements, composites and scaffolds for
hard tissue regeneration and in dentistry. They are biocompatible, bioactive as
well as offer variable resorbability based on their composition. They induce
direct bone bonding and help bone cell adhesion, growth and proliferation
(Cao et al 2010). Calcium phosphates have various forms and phases with the
calcium to phosphorous (Ca/P) molar ratios between 0.5 and 2.0. The
different phases of calcium phosphates are monocalcium phosphate
monohydrate and monocalcium phosphate anhydrous, dicalcium phosphate
dihydrate/brushite, dicalcium phosphate anhydrous/monetite, hydroxyapatite
(HA), calcium-deficient hydroxyapatite, octacalcium phosphate, fluorapatite,
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chlorapatite, tricalcium phosphate, amorphous calcium phosphate and
tetracalcium phosphate (Thamaraiselvi and Rajeswari 2004).
Hydroxyapatite (HA), fluorapatite, and chlorapatite belong to the
apatite family of minerals that share the general formula A10(PO4)6(OH, F,
Cl)2. The A cation could be barium, strontium or magnesium besides calcium.
The chemical formula for HA is Ca10(PO4)6(OH)2. HA belongs to hexagonal
crystal system. The crystal form of chemically pure HA is monoclinic with
four units in each cell. A transformation from monoclinic to hexagonal form
has been observed at higher temperatures. The hexagonal form is more stable
form of HA which has some substituted hydroxide or phosphate groups as
shown in Figure 1.7 (Damien and Revell 2004). HA can be made in various
forms like porous scaffolds, granules, powder and as dense bodies by
sintering (Oh et al 2006).
Figure 1.7 Hexagonal crystal structure of hydroxyapatite
Recent enhancements of surgical techniques together with
increasing expectations regarding the quality of life and the aging of the
world’s population have resulted in a rapid growth of the number of skeletal
reconstruction surgeries. The number of bone-grafting procedure reached an
estimated 1.3 million per year in 2002 worldwide and this figure is likely to
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reach 4 million interventions in 2011. Most of the bone grafts used today is
natural bone harvested on the same patient (autograft) or taken from a bone
bank (allograft). These procedures present good clinical results but come with
clinical complications and are in limited supply. An alternative to natural
bone graft is synthetic bone substitute. Recently, reconstruction of bone tissue
using polymer nanocomposite bone grafts, having structure, composition,
physicochemical, biomechanical, and biological features is similar to natural
bone is gaining much interest owing to their sophisticated functional
properties. Nanocomposite bone graft made of nano hydroxyapatite (n-HA)
and polymer facilitates greater osteoconduction and related functions than
conventional bone grafts. These new materials, with the incorporation of
bioceramic particles, could induce or enhance the formation of tissue adjacent
to them and finally establish a strong bond with the newly formed tissue
(Wang 2003). The nanocomposite formulation also produced better
mechanical properties to the implant material making it more favorable for
load bearing application (Suchanek and Yoshimura 1998).
The successful clinical use of bioactive nanocomposites has paved the
way for further developing this type of biomaterials for various applications.
With new knowledge being gained of natural tissues and the human body and
the advancement of composite science and technology, newer and better
nanocomposite materials will become available as a new class of synthetic
bone grafts. Apart from the biomedical applications, incorporation of calcium
phosphate nanoparticles into polymer matrix improves the mechanical,
thermal and barrier properties, which elucidate its industrial applications
(Thomas et al 2009).
1.7 PREPARATION OF NANOCOMPOSITES
The key to the successful development of polymer nanocomposites
is to achieve homogeneous dispersion of nanofillers in the polymer matrix.
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Creating one universal technique for making polymer nanocomposites is
difficult due to the physical and chemical differences between each system
and various types of equipment available to researchers. Each polymer system
requires a special set of processing conditions to be formed, based on the
processing efficiency and desired product properties. The different processing
techniques in general do not yield equivalent results. There are several
processes to make polymer nanocomposites, including in-situ polymerization,
solution casting and melt blending. As shown in Figure 1.8 (Sorrentino et al
2006), each technique consists of several steps to achieve polymer
nanocomposites. The formation of polymer nanocomposites is driven by
different forces depending on the techniques used, and each technique has its
advantages and disadvantages. These methods are discussed below.
Figure 1.8 Flow chart of processing techniques for polymernanocomposites: (a) in-situ polymerization, (b) solutioncasting and (c) melt blending
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1.7.1 In situ Polymerization
In this method, the nanofillers are mixed with the monomers or pre-
polymers, sometimes in the presence of a solvent, and then the polymerization
reaction proceeds by adjusting parameters such as temperature and time.
Research on in situ polymerized nanocomposites not only analyzes the effect
of the nanofillers in the polymer matrix morphology and final properties, but
also in the polymerization reaction or curing reaction. The advantages of this
strategy are twofold: first, it provides a strong interaction between the
incorporated particles and the polymer matrix, facilitating stress transfer, and
second, it enables an outstanding and homogeneous dispersion. However, it is
usually accompanied by a viscosity increase that hinders manipulation and
loading fraction.
1.7.2 Solution Casting
Solution casting is a liquid-state powder processing method that
brings about a good molecular level of mixing and is widely used in material
preparation and processing. In this method, the nanofillers are dispersed in the
solvent in which the polymer is soluble. The polymer after swelling in the
solvent is then added to the nanofiller suspension and mixed well. The last
step is the removal of solvent by evaporation usually under vacuum.
1.7.3 Melt Blending Method
Melt blending is much commercially attractive than the other two
methods, as both solvent casting and in situ polymerization are less
environmental friendly. This method involves direct inclusion of nanofillers
into the molten polymer using a twin-screw extruder and adjusting parameters
such as screw speed, temperature and time. It is compatible with current
industrial process, such as extrusion and injection molding. The melt blending
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method allows the use of polymers which were previously not suitable for in
situ polymerization or solution casting (Kim 2009).
1.8 PROPERTIES OF NANOCOMPOSITES
Nanocomposites consisting of a polymer and nanofiller possess
unique properties, typically not shared by their more conventional
microscopic counterparts, which are attributed to their nanometer size features
and the extraordinarily high surface area. In fact, it is well established that
dramatic improvements in physical properties, such as tensile strength and
modulus, heat distortion temperature and gas permeability, can be achieved
by adding just a small fraction of nanofiller to a polymer matrix, without
impairing the optical homogeneity of the material. These unique properties
make the nanocomposites ideal materials for products ranging from high
barrier packaging for food and electronics to strong, heat resistant automotive
components. The main reason for these improved properties in
nanocomposites is the strong interfacial interaction between the matrix and
nanofiller. The following section will cover up some of the important areas of
nanocomposite properties.
1.8.1 Mechanical Properties
The major requirement of polymer nanocomposites is to optimize
the balance between the strength/stiffness and the toughness as much as
possible. Therefore, it is usually necessary to characterize the mechanical
properties of the nanocomposites from different viewpoints. Tensile test is the
most widely used method to evaluate the mechanical properties of the
resultant nanocomposites, and accordingly Young’s modulus, tensile strength,
and the elongation at break are three main parameters obtained.
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The Young’s modulus of the nanocomposites tends to increase with
the volume fraction of the inclusions in every case (Hasegawa et al 1998). In
some systems, there is a critical volume at which aggregation occurs and the
modulus goes down. In general, there is also an increase in modulus as the
size of the particle decreases. For polymer systems capable of having a higher
degree of crystallinity, the increase in modulus with decreasing particle size is
found to be greater in systems with poor interactions between filler and matrix
as opposed to those with good interaction. However, the overall trend of the
modulus of polymer nanocomposites is not found to be greatly dependent
upon the nature of matrix or the interaction between the filler and matrix
(Mishra et al 2004). The modulus of the nanocomposites increases with
increasing filler content, whereas the tensile strength and elongation at break
shows a decreasing trend. The nanocomposites containing low filler content
has good dispersion and interfacial adhesion, so when under tensile stress, the
force is transferred to nanoparticles through the interphase and the
nanoparticles became the receptor of the tensile force. The decrease in tensile
strength and elongation at break beyond critical value is mainly due to the
agglomeration of nanoparticles.
1.8.2 Thermal Stability
Thermal stability of polymer nanocomposites is estimated from the
weight loss upon heating which results in the formation of volatile products.
Thermogravimetric analysis demonstrates the thermal stability of the
nanocomposites, while differential scanning calorimeter determines the
thermal transition behavior. The degradation behavior of polymers is
commonly evaluated in terms of three parameters: (1) the onset temperature
considered as the temperature at which the system starts to degrade, (2) the
degradation temperature, considered as the temperature at which maximum
degradation rate occurs, and (3) the degradation rate, seen in the derivative
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weight loss as a function of temperature curve. Generally, the incorporation of
nanometer-sized inorganic particles into the polymer matrix enhances thermal
stability by acting as a superior insulator and mass transport barrier to the
volatile products generated during decomposition (Gilman et al 1999).
Dabrowski et al showed that protective barriers are formed during thermal
degradation of polyamide 6/clay nanocomposite, which slow down the rate of
degradation via diffusion process (hindering the escape of volatiles)
(Dabrowski et al 2000). In fact, despite the general improvement of thermal
stability, decreases in the thermal stability of polymers upon nanocomposite
formation have been reported, and various mechanisms have been put forward
to explain the results. It has been argued that after early stages of
decomposition the stacked silicate layers could hold accumulated heat, acting
as a heat source to accelerate the decomposition process, in conjunction with
the heat flow supplied by the outside heat source. Moreover, the clay itself
can also catalyze the degradation of polymer matrices. Thus, it becomes
obvious that the organoclay may have two opposing functions in thermal
stability of nanocomposites: a barrier effect, which should improve the
thermal stability and a catalytic effect on the degradation of polymer matrix,
which should decrease the thermal stability. Thus, when a low clay fraction is
added to the polymer, the clay disperses well and the barrier effect is
predominant, but with increase in loading, the catalyzing effect rapidly
increases and becomes dominant, so that the thermal stability of the
nanocomposite decreases (Pavlidou and Papaspyrides 2008).
1.8.3 Flame Retardant Properties
Fire retardants are used to make materials harder to ignite by
slowing decomposition and increasing the ignition temperature. It functions
by a variety of methods such as absorbing energy away from the fire or
preventing oxygen from reaching the fuel. The flammability behavior of
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polymer nanocomposite is defined on the basis of several processes or
parameters, such as burning rates, spread rates, ignition characteristics, etc.
The addition of nanoparticles reduced the peak heat release rate of the
polymer nanocomposite compared to pure polymer. The flame-retardant
mechanism of the addition nanoparticles to polymer was inferred to be the
coagulation of the particles and the accumulation of loose, granular particles
near the sample surface to form a protective layer as a heat insulation and
barrier for evolved degradation products.
1.8.4 Barrier Properties
The incorporation of inert and nonporous fillers into a polymer
nanocomposites results in an increase in barrier property because filler
particles lowers both solvent solubility and diffusivity within the polymer.
Solvent transport in nanocomposites proceeds by a solution-diffusion
mechanism in which the permeability (p) is given by S × D, where S and D
denote the solubility and diffusivity of the permeating species, respectively.
The solubility provides a measure of interaction between the polymer matrix
and penetrant molecules, whereas the diffusivity describes molecule mobility,
which is normally governed by the size of the penetrant molecule as it winds
its way through the permanent and transient voids afforded by the free volume
of the nanocomposites. Therefore, barrier property is to be strongly dependent
on the amount of free volume in the polymer matrix (Patel et al 2004).
Nanofillers are believed to increase the barrier by creating a ‘tortuous path’
that retards the progress of penetrant molecules through the matrix.
Messersmith and Giannelis studied the permeability of liquids and gases in
nanocomposites and they observed that water permeability in
polycaprolactum (PCL) nanocomposites reduced dramatically compared to
the unfilled polymer. The decrease in permeability is much pronounced in the
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nanocomposites compared to conventionally filled polymers with higher filler
content (Messersmith and Giannelis 2001).
1.8.5 Optical Properties
The most important optical properties of a material are its
transparency and refractive index. Transparency is the physical property of
allowing the transmission of light through the material. It is important for
many practical applications of polymer nanocomposites (Schmidt and
Maltwitz 2003). Microsized particles used as reinforcing agents scatter light,
thus reducing light transmittance and optical clarity. On the other hand,
layered silicate platelets, even though their micro lateral size, are just 1 nm
thick. Thus, when single layers are dispersed in a polymer matrix, the
resulting nanocomposite is optically clear in the visible region, whereas, there
is a loss of intensity in the UV region mostly due to scattering by the layered
silicates. To remain transparent, nanoparticles should disperse in the
composite at a very fine scale to allow light to transmit easily. For
quantitative analysis, transmittance of the film is measured by UV-vis
spectroscopy. The refractive index is the ratio of speed of the light in vacuum
to the speed of light in the medium. It is the most important property of
optical systems that use refraction, and its can be measured by a
refractometer.
1.8.6 Biodegradability
Another interesting and exciting property is the significantly
improved biodegradability of nanocomposites made from nanofillers. The
first reported studies on the biodegradability of nanocomposites based on
PCL, showed an improved biodegradability over pure PCL. Such an improved
biodegradability of PCL in clay based nanocomposites is attributed to the
catalytic role of organoclay in the biodegradation mechanism. The
24
biodegradability is also attributed to the presence of terminal hydroxylated
edge groups in the clay layers (Lee et al 2002).
1.9 APPLICATIONS OF POLYMER NANOCOMPOSITES
Polymer nanocomposites represent an exciting and promising
alternative to conventional composites owing to the dispersion of nano
particles and their markedly improved performance in mechanical, thermal,
barrier, optical, electrical and other physical and chemical properties. Thus,
many industries have taken a strong interest and invested in developing
nanoprecursors and polymer nanocomposites as illustrated in Figure 1.9
(Godovsky 2000). Polymer nanocomposites offer higher performance with
significant weight reduction and affordable materials for transport industries
such as automotive and aerospace. The excellent barrier properties of clay
based nanocomposites would result in considerable enhancement of shelf-life
for many types of packaged food. Meanwhile, the optical transparency of
polymer nanocomposite film is generally similar to their pristine counterparts,
which is impossible for conventional polymer composites. Therefore, the
above property advantages would make them acceptable widely in packaging
industries as wrapping films and beverage containers, such as processed meat,
cheese, confectionery, cereals, fruit juice and dairy products. The property
enhancement, especially on the thermal responsivity, swelling-deswelling rate
and molecular diffusion of some stimuli responsive hydrogels by
incorporating nanoparticles extend its applications as artificial muscles and
rapid actuators. The integration of inorganic nanoparticles into the organic
polymeric matrices, as a coating layer, enhances the corrosion protection
effect of steel and aluminum in comparison to pristine polymers. The nano
inclusions employed to effectively increase the length of the diffusion
pathways for oxygen and water and decrease the permeability of the coating
and lead to corrosion receptivity of coating.
25
Figure 1.9 Schematic representation of application of polymer
nanocomposites in various fields
Another area that nanocomposites are likely to shine is in provision
enabling them to reduce a high applied voltage (up to 20 kV) to a level where
damage is not caused. This must be in a short enough time to prevent
spontaneous discharge or arcing and overheating. In all filled polymers, direct
particle-particle contacts are rare, since each particle is surrounded by
polymer. Therefore, electrical conduction in filled polymers is a combination
of ohmic and quantum mechanism which facilitated nanocomposites tailoring
at molecular level. An immediate application of this behavior is receiving
considerable interest in its field-emission flat-panel displays, energy-storage
batteries, and supercapacitor electrodes, lubrication and hydrogen storage
(Njuguna and Pielichowski 2004). Organic polymers with uniformly
dispersed nanoscale inorganic precursors enable polymeric materials to with
stand the harsh space environment and used as critical weight-reduction
materials on current and future space systems. Nanocomposite materials also
26
offer the unique opportunity for improved coefficient of thermal expansion
which would be especially useful in constructing large aperture telescopes and
antennas using inflatable membranes.
The applicability of polymer nanotechnology and nanocomposites
to biomedical/biotechnological applications is a rapidly emerging area of
development. One area of intense research involves electrospinning for
producing bioresorbable nanofiber scaffolds for tissue engineering
applications. Another area also involving nanofibers is the utilization of
electrically conducting nanofibers based on conjugated polymers for
regeneration of nerve growth in a biological living system. Polymer matrix
nanocomposites have been proposed for drug delivery/release applications.
The addition of nanoparticles provide an impediment to drug release allowing
slower and more controlled release, and reduced swelling and improved
mechanical integrity (Haraguchi et al 2006).
1.10 POLYSULFONE BASED BLENDS, COMPOSITES AND
NANOCOMPOSITES
Polysulfone (PSf) is an amorphous polymer that has properties
matching those of light metals. The structural unit of PSf composed of
phenylene units linked by three different chemical groups such as
isopropylidene, ether, and sulfone each contributing specific properties to the
polymer (Figure 1.10). The complex repeating structure imparts inherent
properties to the polymer that conventionally are gained only by the use of
stabilizers or other modifiers.
27
CH3
CH3
O S
O
O
O
n=50-80
Figure 1.10 Chemical structure of polysulfone
The most distinctive feature of the backbone chain is the diphenylene
sulfone group (Figure 1.11). The influence of diphenylene sulfone on the
properties of resins has been the subject of intense investigation since the
early 1960s. The contributions of this group become evident upon
examination of its electronic characteristics. The sulfur atom (in each group)
is in its highest state of oxidation. Furthermore, the sulfone group tends to
draw electrons from the adjacent benzene rings, making them electron-
deficient. Thermal stability is also provided by the highly resonant structure
of the diphenylene sulfone group.
S
O
O
Figure 1.11 Diphenylene sulfone group in polysulfone structure
In the literature, few articles about PSf blends, composites and
nanocomposites are presented. A brief look into the reports available in
literature about PSf blends, composites and nanocomposites are listed in
Table 1.1.
28
Table 1.1 Overview of polysulfone blends, composites and
nanocomposites
Nanocomposites/Composites Procedure Application
PSf/ MMT nanocomposite Solution dispersion Membrane
PSf/OMMT nanocomposite Solution dispersion Corrosion prevention
PSf/ OMMT nanocomposite Solution dispersion High performance
PSf/ silver nanocomposite Wet phase inversion Membrane
PSf/cyanate ester/OMMT Solution dispersion High performance
PSf/cellulose nanocrystals Solution dispersion Membrane
PSf/silica nanocomposite Solution dispersion Membrane
PSf/fullerene nanocomposite Solution dispersion Membrane
PSf/CNT nanocomposite Solution dispersion Membrane
PSf/CNT nanocomposite Phase inversion Electrochemical sensing
PSf/HA composite Melt blending Tissue replacement
PSf/ bioactive glasscomposite
Injection moulding Tissue replacement
PSf/Poly(isobutylene-alt-maleicanhydride)composite
Diffusion inducedphase separation
Membrane
PSf/Polyaniline composite Phase inversion byimmersionprecipitation
Membrane
PSf /Polyamide11 composite Solution dispersion High performance
PSf /Polypyrrole composite Solution dispersion Membrane
29
1.11 LITERATURE REVIEW
PSf is a high performance amorphous engineering thermoplastic,
having excellent mechanical properties even at high temperature due to its
high glass transition temperature. It has tremendous applications especially in
medical, food processing equipment, electrical and electronics components
due to its excellent properties, such as high mechanical strength, high Tg,
flexibility and excellent thermal stability.
Nayak et al (2012) developed carbon based PSf nanocomposites
successfully by solution mixing technique to explore the effect of state of
dispersion and wt% loading of carbon nanofibers on thermal and electrical
properties of PSf. In order to enhance the interfacial adhesion between carbon
nanofibers and PSf, carbon nanofibers were functionalized by air oxidation.
Thermal properties were characterized by using thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC). The state of dispersion of
carbon nanofibers throughout the PSf matrix and matrix-filler interaction
were confirmed using and high resolution transmission electron microscopy
(HRTEM) study. The electrical properties of nanocomposites were studied
from direct current and alternating current resistivity measurement. Dielectric
constant and dissipation factor of nanocomposites were significantly
increased with increase in carbon nanofibers content in nanocomposites. The
enhancement in these properties suggests a great potential application of the
resulting nanocomposites as multifunctional materials in various electronics
industries.
Sur et al (2001) prepared PSf/organoclay nanocomposites by solution
casting technique, and were characterized by X-ray diffraction (XRD),
transmission electron microscopy (TEM), stress-strain measurement in
elongation, and thermogravimetric analysis. The XRD and TEM results
demonstrated that at least at some compositions, the technique employed was
30
successful in exfoliation and widely dispersing the clay platelets. The other
measurements demonstrated considerable improvements in strength and
modulus and thermal stability
Yeh et al (2003) prepared a series of polymer/organoclay
nanocomposite materials containing PSf and layered montmorillonite (MMT)
clay via a solution casting technique for anticorrosion applications. The
prepared nanocomposite coatings with low clay loading (1 wt%) on
cold-rolled steel were found to be superior in corrosion prevention to those of
bulk PSf, based on a series of electrochemical measurements of corrosion
potential, polarization resistance, corrosion current and electrochemical
impedance spectroscopy in 5 wt% aqueous NaCl electrolyte. The effects of
material composition on the barrier, mechanical and optical properties of PSf
and nanocomposites, in the form of films, were also studied.
Gao et al (2008) studied the thermal, mechanical and solvent
resistance properties of organo-montmorillonite (OMMT)/fluoroelastomer
nanocomposites prepared by melt intercalation method. When the
montmorillonite content was low, the nanocomposites exhibited excellent
mechanical properties, thermal stability and solvent resistance which were
attributed to the nanometer scale dispersion and the higher aspect ratio of the
clay mineral layers. The decrease of properties with increasing clay content
was explained due to the decreased exfoliation.
Maiti et al (2006) has used AFM as an effective tool to analyze the
morphology of the fluoroelastomer/clay nanocomposites, dispersion of the
nanoclay in the rubber matrix, interface thickness, and interaction forces. The
phase images of the filled nanocomposites revealed the presence of clay
fillers as the bright features in the dark rubber matrix. The changes in surface
topography of nanocomposites were determined quantitatively by the root
mean square (RMS) roughness calculation. This study was helpful in a range
31
of applications particularly where the surfaces involved show a degree of
randomness.
Pavlidou and Papaspyrides (2008) reported a review on polymer
layered silicate nanocomposites. The recent advances in the field of polymer-
layered silicate nanocomposites were discussed. The polymer-layered silicate
nanocomposites attracted both academic and industrial attention because they
exhibited dramatic improvement in properties at very low filler contents.
Herein, the structure preparation and properties of the polymer-layered
silicate nanocomposites were discussed.
The role of the aspect ratio of the layered silicate platelets on the
mechanical and oxygen permeation properties of hydrogenated nitrile
rubber/organophilic layered silicate nanocomposites was investigated by
Gatos and Kocsis (2007). The dispersion of montmorillonite (MMT) and
fluorohectorite (FH) bearing the same type of intercalant (i.e.,
octadecylamine; ODA), was assessed by X-ray diffraction and transmission
electron microscopy, respectively. The mechanical and permeation properties
were measured and modeled by varying the volume fraction in the
nanocomposite and the best performance of hydrogenated nitrile rubber/
organomodified FH nanocomposite was explained by its high aspect ratio of
FH platelets.
Thomas et al (2009) conducted contact angle studies of
polystyrene/calcium phosphate nanocomposites with water and methylene
iodide to know surface properties of the nanocomposites. Various contact
angle parameters such as total solid surface free energy, work of adhesion,
interfacial free energy and spreading coefficient were analyzed. The
interaction parameter between the polymer and the liquids has been calculated
using the Girifalco-Good’s equation. The solid surface free energy of the
composites decreased and thereby increases the work of adhesion. The
32
interaction between the liquid and solid surface became high compared to the
neat polymer.
Thomas et al (2009) prepared poly (ethylene-co-vinyl
acetate)/calcium phosphate nanocomposites by melt mixing method.
Mechanical properties of the composites showed improvement by the addition
of 3 wt% of nanofillers due to the better filler dispersion. The particle
agglomeration in the higher loadings caused decrease in the mechanical
properties. Onset of thermal degradation of the nanocomposites showed a
positive shift, which indicate good thermal stability by the addition of very
low amount of nanofillers. Oxygen gas permeability of the composites
decreased considerably due to tortuous path created by the nanofillers. The
permeability data is very important for the end use applications of the
nanocomposites and a potential application in the healthcare devices will be
taken up after preclinical and related studies.
The impact of nanocomposites in the field of bone grafting and the
recent trends in orthopedic research and developments was reviewed by
Murugan and Ramakrishna (2003). This article provides an overview of the
nanocomposite strategy of bone, bone grafting, synthetic approaches to bone
structure, development of nanocomposites from the conventional monolithic
biomaterials, and recently developed processing conditions for making
nanocomposites. The state-of-the-art of nanocomposites as a new class of
synthetic bone grafts fulfills the great challenge to design an ideal bone graft
that emulates nature’s own structure.
Fang et al (2007) developed nano-sized hydroxyapatite (n-HA)
particles reinforced ultrahigh molecular weight polyethylene nanocomposite
by combined swelling/twin-screw extrusion, compression molding, and then
hot drawing, for biomedical applications. Morphological characterization
revealed that HA nano-particles were homogeneously dispersed in polymer
33
and formed an inter-penetrated network structure. Addition of filler enhances
the mechanical properties of the polymer such as Young’s modulus and
tensile strength, which was comparable to that of cortical bone. The
composite also exhibited great ability of inducing calcium phosphate
precipitates on its surface in simulated body fluid, which was promising to be
used for load bearing bone substitutes.
Orefice et al (2006) prepared PSf/bioactive glass composites to
combine bioactive properties of bioceramics with the superior mechanical
properties of engineering plastics. Mechanical tests performed on
PSf/bioactive glass composites demonstrated that they have properties with
values within the range reported for cortical bone. The values obtained for
elastic modulus were within the range predicted by models used in the
literature to relate this property to the volume fraction of particulate. In vitro
tests showed that hydroxy-carbonate-apatite can be deposited on the surface
of a composite as early as 20 h in a simulated body fluid. Moreover, a
physical model based on dynamical mechanical tests showed evidences that
the interface of the composite was aiding in the stress transfer process.
Leonar et al (2003) studied high-resolution and in situ imaging of
the formation of an apatite layer on the surface of composite composed of
biodegradable starch-based polymeric matrix and hydroxyapatite fillers, by
means of AFM for the first time. The results of in situ AFM observation
agreed with those of standard in vitro bioactivity tests in combination with
SEM observations. Furthermore, the formation of the apatite layer on the
surface of the composites confirms that the composites exhibit a strong in
vitro bioactivity that is supported by the polymer’s water-uptake capability.
These results suggest the great potential of the composite for a range of
temporary applications in which bone-bonding ability is a desired property,
when implanted in vivo.
34
Rabe et al (2011) reviewed protein adsorption on solid surfaces
which has scientific relevance in various problems encountered in research
areas such as designing biocompatible materials, tracing biological events that
trigger or prevent diseases, improving analytical devices, or control fouling
processes. In this review recent achievements and new perspectives on protein
adsorption processes are comprehensively discussed. The main focus is put on
commonly postulated mechanistic aspects and their translation into
mathematical concepts and model descriptions. Relevant experimental and
computational strategies to practically approach the field of protein adsorption
mechanisms and their impact on current successes are outlined.
Recent developments in polymer/n-HA materials for bone tissue
regeneration and reconstruction was reviewed by Pielichowska and Blazewicz
(2010). Since most polymers are not compatible with bone tissue, an
appropriate modification of their structure and properties by incorporation of
n-HA, to obtain materials that mimic the structural and morphological
organization of bone was suggested. Specific topics associated with
polymer/n-HA composition, molecular orientation and morphology, surface
modifications, the interactions between the components, and their biological
behaviors are described. Finally, the challenges facing this emerging field of
research are outlined. New possibilities for the creation of the next generation
biomaterials with well-defined nanotopography which can elicit the desired
cellular and tissue response were also discussed.
Ramanathan et al (2008) reported the creation of poly
(acrylonitrile) nanocomposites with functionalized graphene sheets, which
overcome the obstacles remain to achieve polymer-particle interactions. Good
dispersion of the nanosheet filler and strong interaction with the matrix
35
polymer result in a substantial improvement in the thermal and mechanical
properties.
Potts et al (2011) presented a survey of the literature on polymer
nanocomposites with graphene-based fillers including recent work using
graphite nanoplatelet fillers. A variety of routes used to produce graphene-
based materials are reviewed, along with methods for dispersing these
materials in various polymer matrices. The rheological, electrical, mechanical,
thermal, and barrier properties of these composites, and how each of these
composite properties is dependent upon the intrinsic properties of graphene-
based materials and their state of dispersion in the matrix were discussed. An
overview of potential applications for these composites and current challenges
in the field are provided for perspective and to potentially guide future
progress on the development of these promising materials.
Pramoda et al (2010) reported a new route to covalently bonded
polymer/graphene nanocomposites and the subsequent enhancement in
thermal and mechanical properties of the resultant nanocomposites. The ODA
functionalized graphite oxides are reacted with methacryloyl chloride to
incorporate polymerizable -C=C- functionality at the nanographene platelet
surfaces, which were subsequently employed in situ polymerization of
methylmethacrylate to obtain covalently bonded poly(methyl methacrylate)/
graphene nanocomposites. The obtained nanocomposites show significant
enhancement in thermal and mechanical properties compared with neat
polymer.
The modification of graphene/graphene oxide and the utilization of
these materials in the fabrication of nanocomposites with different polymer
matrixes were reviewed by Kuilla et al (2010). Different organic polymers
36
have been used to fabricate graphene filled polymer nanocomposites by a
range of methods. In the case of modified graphene-based polymer
nanocomposites, the percolation threshold can be achieved at a very lower
filler loading. Herein, the structure, preparation and properties of
polymer/graphene nanocomposites are discussed in general along with
detailed examples drawn from the scientific literature.
Deimede et al (2000) prepared nylon 11/sulfonated PSf blends by
solution casting from dimethyl formamide (DMF). FT-IR and FT-Raman
spectroscopic techniques have been used to confirm the nature of the specific
interactions involved. Differential scanning calorimetry has shown a melting
point depression of the equilibrium melting point of nylon 11. Dynamical
mechanical analysis revealed a non single-phase system at lower
temperatures, although the glass transition temperature (Tg) of nylon 11 phase
is shifted to higher temperatures.
Polypyrrole-polysulfone composites were prepared by Bhattacharya
et al (2008) using diffusive chemical oxidative polymerization technique.
FTIR, TGA and AFM studies have been carried out to provide evidence for
incorporation of pyrrole moiety as well as to characterize the composites.
Padaki et al (2011) reported the synthesis of a new composite of
poly (isobutylene-alt-maleic anhydride) with polysulfone using diffusion
induced phase separation method. Composites were characterized by FT-IR,
SEM and DSC studies. Thermal properties showed that, higher the
composition of the polysulfone, higher was the Tg value. The contact angle
measurements showed that, as the poly (isobutylene-alt-maleic anhydride)
increases contact angle of the composite decreases.
37
1.12 SCOPE OF THE PRESENT INVESTIGATION
Recent research and development in the field of polymer
nanocomposites has led to the production of materials with high performance
characteristics i.e., thermal stability, mechanical strength, dielectric behavior,
barrier property, hydrophobicity, bioactivity etc. Polysulfone is an
engineering thermoplastic with good mechanical properties. Favorable
properties of polysulfone like high strength and stiffness, resistance to
oxidation, excellent resistance to hydrolysis and stability in aqueous inorganic
acids, alkalis and salt solutions, makes it a suitable candidate for wide range
of industrial applications. Furthermore, high resistance to , , IR and X ray
radiations and bioinertness of PSf extends its application to bone
implantation.
Though polysulfone exhibit a better range of characteristic
properties, still some more improvements is needed in properties, such as
toughness, tensile strength, hydrophobicity, solvent resistance, bioactivity, to
enable them to find a place in high performance engineering and biomedical
applications. The incorporation of nanoprecursors is expected to improve
mechanical, thermal, barrier and hydrophobic properties. Therefore, PSf
nanocomposites with organomodified fluorohectorite clay and chemically
modified graphene nanoplatelets have been developed, and characterized to
investigate the improvement in material properties. PSf nanocomposites using
stearic acid modified hydroxyapatite have been prepared to obtain cost
effective bone implants with improved biocompatibility and thermo-
mechanical properties. Further, PSf blends were developed with poly (ether
imide ester), in the form of thin films using solution casting method. Hence,
the present work has got potential applications towards industrial as well as in
biomedical point of view.
38
With this in view, the present work is proposed
To develop organomodified fluorohectorite clay reinforced
polysulfone nanocomposite by solution casting method.
To study morphological, mechanical, thermal, hydrophobic,
dielectric and barrier properties of polysulfone/organoclay
nanocomposites.
To synthesize and characterize stearic acid modified
hydroxyapatite nanoparticles using XRD, ATR-FTIR and TEM.
To prepare organomodified hydroxyapatite incorporated
polysulfone nanocomposites for tissue replacement application.
To ascertain the effect of organomodified hydroxyapatite
nanofiller addition on thermo-mechanical, aging as well as
surface behavior of nanocomposites.
To evaluate the bioactivity of PSf/organomodified
hydroxyapatite as a bone implant by monitoring the
concomitant formation of apatite on the material surface after
soaking them in simulated body fluid at 37°C.
To assess the qualitative and quantitative protein adsorption
onto the PSf nanocomposites by incubating in the phosphate
buffered saline (PBS, pH 7.4) solution containing 10 % fetal
bovine serum albumin (BSA).
To synthesize organomodified graphene nanoplatelets and
characterize them using XRD, ATR-FTIR and TEM.
To fabricate organomodified graphene nanoplatelets reinforced
polysulfone nanocomposite by solution casting method.
39
To investigate morphological, thermo-mechanical, hydrophobic
dielectric and aging properties of organomodified graphene
nanoplatelets incorporated PSf nanocomposites.
To synthesize poly (ether imide ester)s (PEIE).
To prepare PSf/PEIE blends and study their morphological,
hydrophilic, mechanical and thermal properties.
All these narrate the content of the thesis, which is divided into
seven chapters. Chapter one presents a detailed review on the current status of
polymer science and technology, polymer nanocomposites, various
nanoparticles, preparation, properties and applications of polymer
nanocomposites, polysulfone blends and nanocomposites, and scope of the
present investigation.
Chapter two describes the preparation and characterization of
organomodified fluorohectorite clay, stearic acid modified
nanohydroxyapatite, organomodified graphene and poly (ether imide ester).
The formulations used for the preparation of PSf blends and nanocomposites
and characterization procedure such as ATR-FTIR, 1H and 13C NMR, XRD,
AFM, TEM, contact angle, mechanical, thermal, dielectric and aging studies
are also discussed. Theory and calculation of the various surface energy
parameters of the nanocomposite films such as interfacial free energy, surface
free energy, work of adhesion and spreading co-efficient formulated from
Newman method are also included in this chapter.
Chapter three studies the results and discussions of organomodified
fluorohectorite clay reinforced polysulfone nanocomposites prepared by
solution casting method. The characterization of the resulting
nanocomposites, morphology by ATR-FTIR, XRD, AFM and TEM,
hydrophobicity by Goniometer, mechanical properties by Universal Testing
40
Machine, thermal properties by TGA and DSC are carried out. Further, the
dielectric behavior by means of impedance analysis and aging property are
also included in this chapter.
Chapter four focuses on the preparation and characterization of
stearic acid modified nanohydroxyapatite filled PSf nanocomposites for bone
tissue engineering applications. The bioactivity of the nanocomposites
evaluated using simulated body fluid test and protein adsorption test are
discussed. The effect of nanohydroxyapatite incorporation on mechanical,
thermal, hydrophobic and aging properties of nanocomposites are also
included in this chapter.
Chapter five deals with the results and discussions of
organomodified graphene reinforced polysulfone nanocomposites prepared by
solution dispersion method. The morphology, mechanical, hydrophobic,
thermal, dielectric and aging properties of the prepared nanocomposites are
presented in this chapter. Attempts have been made to correlate
nanocomposite performance with the changes in morphology and the results
are discussed in detail.
Chapter six explains the preparation and characterization of the
PSf/PEIE binary blends. The effect of blend ratio on the morphology,
hydrophilicity, mechanical and thermal properties of the resultant blends are
presented in this chapter.
Chapter seven presents the summary and conclusions including the
utility of PSf nanocomposites and PSf/PEIE blends for high performance
applications.