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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.