Introduction 1

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Chapter I

INTRODUCTION 1.1 General Introduction The beginning of research on nanotechnology and nanoscience can be traced back over 40 years, first described in a lecture entitled, 'There's Plenty of Room at the Bottom' in 1959 [1]. However, it is during the past decade that nanotechnology went through a variety of disciplines. 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. Nanostructured composite materials, when using organic polymer and inorganic fillers, represent a merger between traditional organic and inorganic materials, resulting in compositions that are truly hybrid. Nature has created many (composite) materials, such as diatoms, radiolarian [2] and bone [3], from which scientists can learn (Fig. 1).

Fig 1.1 Diatoms, like radiolaria, represent the incredible control Nature exerts over the assembly of organic-inorganic materials.

Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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Organic-inorganic composites with nanoscale dimensions are of growing interest because of their unique properties, and numerous potential applications such as enhancement of conductivity [4,5], toughness [6], optical activity [7,8], catalytic activity [9], chemical selectivity [10,11] etc. In these materials, inorganic and organic components are mixed or hybridised at nanometer scale with virtually any composition leading to the formation of hybrid/nanocomposite materials [12-22]. Ceramics are generally known for their hardness and brittleness, along with their resistance to high temperatures and several physical/chemical environments [23, 24]. In addition, many inorganic materials such as silica glass have excellent optical properties such as transparency [25]. For most applications, the brittleness (lack of impact strength) is the major, sometimes fatal, deficiency of ceramics [23]. On the other hand, organic polymers are usually noted for their low density and high toughness. (i.e., high impact strength). They can be tailor-made to exhibit excellent elasticity (e.g., synthetic rubber) or optical transparency (e.g., polymethacrylates or Plexiglas. However, lack of hardness is one of the most significant flaws of polymers in many applications. Associated with the lack of hardness are the problems of low wear and scratch resistance as well as dimensional stability [26]. The developments of conventional composite materials with ceramics as fillers and polymers as matrices are being researched extensively. Important examples of these composite materials are the semi-crystalline polymers mixed with inorganic particles [27]. They consist of an amorphous-crystalline matrix (with a lamella thickness of typical size of 10 to 100 nm) and dispersed nanoparticles. be tailor-made to exhibit excellent elasticity (e.g., synthetic rubber) or optical transparency (e.g., polymethacrylates or Plexiglas. Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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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. The study and exploration of the potential properties of nanocomposites is the motivation of this thesis.

1.2 Why Nanotechnology? What are the potential uses of nanotechnology? In the limited number of years that nanotechnology has been investigated, a plethora of answers to this question have been presented. It seems that nanotechnology could potentially solve almost any problem; thus, a more interesting question is, 'what real problems will nanotechnology solve?' Nanocomposite technology has been described as the next great frontier of material science. For example, polymer resins containing well-dispersed layered organic/inorganic particles are emerging as a new class of nanocomposites. The reason is that by employing minimal addition levels of filler nanoparticles enhance mechanical, thermal, and dimensional and barrier performance properties significantly. It has been said that for every 1 wt% addition, a property increase on the order of 10% (or more) is realized. This loading-to-performance ratio is known as the “nano-effect” [28]. Aliphatic polyamides (nylons) have been subjected to a variety of studies directed to understanding the crystallization behaviour, which contributes to the exceptional mechanical properties of the nylon family [5]. Morphological features such as degree of crystallinity, spherulite size, lamellar thickness and fibre orientation seem to have a pronounced effect on the properties of crystalline thermoplastics and are therefore Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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relevant parameters for prediction of fibre behavior since (mechanical) properties (e.g. toughness) of such materials depend also on crystallinity [14-23]. Nylon-6 is commercially important and usually regarded as a dual-phase system consisting of crystalline and amorphous regions; the former exhibits two structures, namely the α – phase which is most commonly observed at room temperature and the crystallization of pure nylon-6 in melt form monitored by in-situ XRD [24] and the γ -phase [25]. The α and γ -phases have both monoclinic structures where hydrogen bonds are formed between antiparallel chains in the former and (through twisted chains) between parallel chains. In nylon-6, for example, clays are used as synergist giving superior mechanical properties when compared with the pure matrix [26].

1.3 Nanotechnology: An Emerging Trend in Polymer Technology Nanotechnology is based on the principle that the properties of manufactured products depend on the arrangement of their atoms. To minimize manufacturing costs, it proposes to use replication of processes wherever possible. Nanosize particles, which have been in great attention for a last few decade, have attractive characteristics compared to micro size particles. The surface area is very large and percentage of molecules or atoms on the surface is greatly increased due to very small size. This is expected to have wide applications in various fields. Nanotechnology is recognized as technology development for the 21st century. In the materials industry, the development of ceramic and polymer nanocomposites is a rapidly expanding multidisciplinary research activity.

Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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Recently, according to the development of nanotechnology, there has been a growing interest in the field of nanocomposites due to their special properties (27-31). Nanotechnology is one of the key technologies to solve the accompanying problems. Its pivot is the synthesis of ultrafine particles with dimension in the range between a few nm to a few hundred nm. These nanoparticles are of enormous interest and they are in high demand for various applications such as surface treatment, pigments, for nutritional or pharmaceutical use, in cosmetics, and in transparent polymer composite for gas transport, and in rubber composites. In the past decade, material scientists showed great interest in organic-inorganic nanocomposites as their applications could dramatically improve material properties such as heat resistance, radiation resistance, mechanical and electrical properties, and other properties in engineering plastics, enhanced rubber composites, coatings and adhesives (32-34). If we take into account its incredibly vast and manifold application potentials, we can reasonably predict that over the next decades nanotechnology will become a major strategic research guideline in all industrialized countries. Designing new planning and synthetic strategies, it becomes must in order to allow the approach to versatile production methods for the development of materials. Nanotechnology allows researchers to reduce the gap between pure chemical evaluations of microstructural analysis and to better understand the phenomena, which make energetic work. The commonly used nanoparticles are SiO2, TiO2, ZnO, CaCO3, clay, and layered silicates. (35-39).The research work is carried out on various polymers (40-44) but the work on rubber nanocomposites is rare (45, 46).

Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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1.4 Micron Size Fillers and Importance of Nanofillers for Polymer Composite

Expanding industrial activities create a continual demand for improved materials that satisfy increasing stringent requirements, such as higher strength, modulus ,thermal and electrical conductivity ,heat distortion temperature ,lower thermal expansion coefficient and reduced cost .These requirements ,which often involve a combination of many difficult to attain properties , many dictate the use of composites materials whose constituents will acts synergistically to solve the needs of the application. Fillers have always played an important role in the plastic industry .the commodity plastics such as polyvinyl chloride, polystyrene polyethylene and polypropylene have properties that meet the requirement of high volume pure polymers. In the past few years, however price escalations combined with the sporadic and possible future shortage of polymers and petroleum feed stock, have established an urgent need for widespread utilization of fillers, composite system afford a means of extending the available volume of polymer while improving many of their properties. The improvement in properties are of the associated with economic advantage such as lower raw materials cost , faster molding cycles as result of increased thermal conductivity and fewer rejection of products. Addition of filler is very important to increase the properties and to decrease the cost of a plastic materials, so the research of polymer nanocomposite have it’s own importance. The size of grades of nanoclay is typically in the range of 1- 100 nm while being fully dispersed, the average fulfill dispersed thickness of platelets is around 25 nm , the Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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expected ration is 100 –1000. By adding different series of nanofillers in different series of nanoclay in these different polymers, experimental work on these materials has generally shown that virtually all types and class of nano-composites lead to new and improved properties such as increased stiffness, strength and head resistance and decreased moisture as absorption, flammability and permeability when compared to their macro and micro composites counter parts. Specially commercial available nylon 6 / clay nanocomposites shown that the polymer matrix having layered clay mineral dispersed their in exhibit improved mechanical strength, heat distortion temperature and impermeability to gas and water. In order to prepare the polymer/ clay nanocomposites, the purity of clay is required for the preparation of well-dispersed silicate layer in the polymer matrix.

1.5 Inorganic Filler Particles Inorganic particles are used in different matrices for specific purposes. For metals, fillers improve high temperature creep properties and hardness when compared with the pure metal. For ceramics, fillers are used to improve their toughness and for polymers for the increase of stiffness, strength, electrical properties and occasionally for toughness. Products such as tennis rackets, golf clubs, or boats abound in our daily lives and can ‘easily’ be manufactured due to the ease with working or shaping polymeric materials because of their low melting points. Compatibility of the matrix and the filler must be considered to prepare a composite and the thermal expansion coefficients must be very close to avoid high thermal stresses that may occur at the filler matrix interface. Fillers that are most commonly added to organic polymers are of an inorganic nature. Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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Unfortunately, the incorporation of fillers in organic polymers can result in a brittle composite material. In addition, the amount of filler that can be incorporated is limited (sometimes the addition of higher amounts of filler does not improve the mechanical properties of the material) and the filler may not be uniformly dispersed in the organic polymer. The efficiency of the filler to modify the properties of the polymer is primarily determined by the degree of dispersion in the polymer matrix. Comparing materials in the micro-size domain with nanosize materials could be useful to realize the importance of these nanosizes.

1.6 Polymer Nanocomposites (PNC) Humen place great importance on materials when talking about the past, from types of manufacturing to even more fundamental conventions of naming specific epochs after the materials used (i.e. Stone Age, Bronze Age, Iron Age) [47,48]. Today’s frontiers of materials technology are most definitely rooted in the combination of various materials to achieve specific goals with the greatest efficiency of properties. Advanced plastics and composites designed for extreme service and environments are blazing a trail for tomorrow’s incredible advances. Incorporation of nano particles like carbon nano tubes, inorganic nanoparticles and MNT clay drastically improves the inherent properties of the polymers [49-55]. Polymer/clay nanocomposites (NCs) have attracted much attention for their excellent properties in mechanics, calories, flame retardation, obstruction, and so forth, which result from their special structure and morphology with respect to conventional composites. Especially, Japanese company reported the synthesis of nylon-6/clay NCs Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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in 1987, this kind of NC has attracted tremendous interest in both academia and industry. At present, the reports about polymer/clay NCs mostly focus on a resin as the matrix, such as polyamide, [56–59] polystyrene, [60, 61] poly(methyl methacrylate) [62] and polypropylene [63–65]. Reports on rubber/clay NCs are, however, very few, and the synthetic methods usually involve the intercalation of rubber macromolecules, such as melt intercalation, [66] solution intercalation, [67–69] and emulsion polymerization [70, 71]. Problems such as weak intercalation power and bad dispersion of montmorillonite occur when those methods are used. In situ polymerization can solve these problems by intercalating molecules into the gallery space and polymerizing in situ; however, this method is rarely used presently. In in-situ method, growth restricts to certain crystalline phases (α andβ ) as compared to large number of phases developed in normal solution precipitation. These restricted phases are responsible for drastic improvement in mechanical properties of polymer nanocomposites. The shape and morphology of nanoparticles are responsible for improvement in the mechanical properties of the nano filled composites, i.e. nano CaCO3 has spherical shape and CaSO4 has needle like structure [72]. Hoffmann et. al. [67-73] reported a correlation between the morphology and rheology of exfoliated PS nanocomposites based on organophillic silicate layers such as flouromicas. Four main crystalline forms (α, δ, γ and β) depend on the thermal history and solution treatment of the preparations [73]. Amongst these crystalline forms present in molten PP; β crystalline form is thermodynamically more stable.

α crystalline form can also be

transformed into β crystalline form at higher temperatures by isothermal melt crystallization. Though, isothermal crystallization of polymers was extensively studied by Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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several researchers [74,75] using DSC, but practically non-isothermal crystallization is of great interest as industrial processes work on non-isothermal crystallization principles. Depending on the functionality, packing density and shape of the filler, nano fillers can optimize their compatibility with a given polymer and polymeric foam [76-78]. Owing to dimensional aspects, nano filler posses larger surface area, which makes strong interaction with the matrix. The effect of the amount and size of nano particles on the properties of single-phase polyurethane was investigated [78]. In this case singlephase polyurethane consists of polyols and diisocyante was crosslinked. Such system has considerably lower strength than the two phase segmented polyurethane. The much higher strength of the later attributes the existance of hard domains that act as trap propagation stoppers [79-81]. Present study has mainly focused on the compressive and insulation properties of polyurethane cellular nano CaSO4 composites. The particle distance also plays an important role in enhancing the interaction of filler. Essential work energy of fracture and yield stress models are used to study the effect of temperature on the fracture energy for the material breaks in ductile manner. Like wise the critical strain energy release rate (GIC) and critical stress intensity factor (KIC) models are used to interpret the fracture energies and failure stress as functions of temperature for the samples fail in brittle manner. Nano fillers may be used as effective strategy for either increasing or reducing heat transfer rates of composite materials. Keblinski et al [57] and Eastman et al [58] reported their ideas on possible mechanisms of enhancing thermal conductivity, and suggested that the effect of particle size, clustering of nanoparticles and the surface adsorption could be the major reason of enhancement. While, the Brownian motion of nanoparticles contributes much less than other factors. Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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1.7 Applications of Nano Structural Polymer Composites Conceptually, uniform nanomaterials will have enormous potential in near future. They are also unique tools for learning about the electrical, magnetic, optical and biological behaviors of nanosize matters. The ability to make nanoparticles structure in polymers and other materials, is now reaching a high level of sophistication and applications are becoming increasingly exciting. Potential applications currently being envisaged include nanoelectronics, antimicrobe nanocomposite, fire-suppression agents, fire retarding materials novel optoelectronics devices sensors, ultra soft magnets, advance healthcare diagnostic and therapeutic materials, single site catalyst and other nanodevices which have considerable applications. Nanocomposites are being rapidly commercialized for different applications. Nylon- 6 and PP nanocomposite find the use for packing and injection molded articles. Semi crystalline nylon nanocomposites are used for barrier films, containers and fuel tanks and other automobile applications layered silicate promote rapid crystallization, hence better clarity is obtained as compared to pristine polymers, which makes them ideal for film applications. Polymer clay nanocomposites, being stiff and tough, are now being considered for lightweight structure required for transportation vehicles in the defense sector.

1.8 Rheology of Nanocomposites Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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The flow behavior of polymer melts is having great importance in polymer manufacturing. Therefore, the description of flow phenomena by rheological studies is highly desirable to assist in the materials (industrial) processability [82, 83]. Polymers melt flow behavior are strongly affected by the presence of filler particles including its morphology, surface chemistry and concentration. Melt polymers filled with fine particles have shown yield stress [84,85] i.e. a stress below which there is no flow or the appearance of a plateau in the storage modulus at low frequencies in a dynamic deformation experiment. Some materials will not flow until a critical yield stress σ y is exceeded (Bingham behaviour). Density and strength formed by the interaction between the filler particles is associated with the existence of this behavior. For shear-thinning materials the general shape of the curve shows a first Newtonian region (low shear rate or stresses with constant viscosity) and a second Newtonian region also referred as zero-shear viscosity (high shear rate or stresses with constant viscosity). It has been reported [86] that non-linear viscoelastic properties of nano-filled polymer melts are similar to those observed in filled rubbers. However, the three dimensional network of rubber particles has been found to be different than that of the silica network. Alternatively, the molecular weight of the matrix, entanglement characteristics of the polymer and trapping of polymer chain loops at the filler surface appear to be the primary factors determining the non-linear viscoelasticity [86]. Adsorption of polymer chains on the silica surface of spherical particles (3 μm) has been an explanation for the rheological behavior of polybutadiene chains filled with rigid spheres. Tethering of polymer chains to (clay) particles has been used as explanation for its elastic behavior. If the polymer chains are not tethered, the slopes G’ and G” are similar to that of the Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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neat polymer. In the case of nanoparticles, aggregation in clusters has been observed which led to the formation of a percolation-like filler network [89]. Therefore it is expected to be of high elasticity and viscosity and according to [87,88] high yield stress. Nevertheless, the mechanisms for reinforcement and non-linearity remain controversial. Constitutive equations often apply over limited parts of the flow curve. For example, the Bingham equation describes the shear stress/shear rate behavior of many shearthinning materials at low shear rates, but only over a one-decade range (approximately) of shear rate [87]. Strong interaction between particles, tethering of polymer chains to the filler or network formation on elasticity are responsible mechanisms for the elasticity of a filled polymer. In this chapter, rheological measurements at low shear rates are performed to get additional information of the effect of the silica dispersed in PA6. The

effect

of

organically

modified

montmorillonite

(OMMT)

on

polyamide

nanocomposites was studied.OMMT/polyamide nanocomposites were prepared through direct melt compounding on a conventional twin screw extruder. With increasing the loading of OMMT, the Young modulus, elongation at break and tensile strength increased. 1mass% loading of OMMT/polyamide resulted in 11% increase of the elongation at break compared to virgin polymer, while 4% loading showed 13%. Rheological data like torque, fusion time, viscosity and shear rate were also recorded on Brabender plasticorder and were correlated with M=CSa and τ=K(γ)n. The value nb1 indicated pseudo-plastic nature of the polyamide/OMMT. The torque decreased with increased loading due to soft nature of OMMT, which acts as a lubricating agent. This improvement in mechanical properties with increase in amount of OMMT loading was also indicated by the reduction in shear viscosity and torque. Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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1.9 Applications in Polyamide Nanocomposites

Products based on polyamides, such as PA6, are used in a broad range of applications in the automotive [1], electrical [2], and other industries [3]. The future success of nylon as thermoplastic (new types or reinforced) rests upon continuous innovation to meet the demands in cost, quality and competition in properties with others plastics. The technical and business aspects of nylon indicate a capacity for change, which will enable the nylon industry to overcome the challenges ahead [4]. All the nylons currently known nylon-6-, -7-, -8-, -9-, -11-, and 12 have been manufactured on an industrial scale. Of these, nylon-6 is the best known, the most widely used, and the most studied [5,6]. The tensile strength of the nylons-4 is half of that of 6-, 8-, and nylon-12. The Young modulus of nylon-4 filaments is, however, comparable with the Young modulus of nylon-6 fibers [5,6]. While nylon-6 competes mostly on the basis of price, good friction and wear characteristics [7- 10], nylon-11 and nylon-12 both contain very small amount of residual monomer, absorb only small amount of moisture from the environment, and maintain elasticity and ductility at lower temperatures than nylon-6. The low moisture absorption results in higher strength retention, electric resistance and stability than nylon-6 upon going from the dry to the wet state. Therefore these polyamides can also lead to interesting materials and properties [11-13].

1.10 Motivation Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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The possibility of forming a nanocomposite through homogeneously dispersed inorganic fillers in a technically interesting polymer has been investigated since the early 1980’s where the advantages of nano- over microstructured particles in polymer matrices was reported [29]. Thermoplastics such as nylon (a polyamide) and polypropylene (PP) have found widespread applications in diverse areas such as household, automobile and electrical industries. These polymers derive their usefulness and versatility from their inherent toughness, chemical resistance, and good mechanical and electrical properties. Recently, interest in rigid particle-strengthened thermoplastics has developed. With the growth of nanocomposite materials research, additional unique mechanical and shaping properties can now be realized not previously accessible with traditional composites. For example, in 1998, a nylon/silica nanocomposite was obtained through a novel method, In-situ polymerisation, by first suspending agglomerated 100 nm (solid) silica particles in caproamide and then polymerising the mixture at high temperature under N2 atmosphere [30]. Surprising was the fact that upon addition of 5 wt % of silica nanoparticles, the mechanical properties such as impact strength, tensile strength and elongation at break of the nanocomposites showed a tendency to increase. For normal polymers it is known that stiffness, impact resistance and hardness never appear in combination in which all have favourable attributes. Silica sol and caprolactam were mixed into a reactor achieving a good dispersion of the nanoparticles .50 nm [31]. The most striking result obtained from that study was the evidence of a filler size effect on the filler dispersion (within the limited particle size studied). The surface treatment of SiO2 using silane coupling agent was reported Liu et al improved the strength and toughness of the polyamide up to some extent [32]. Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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96:6, 2005

Ph.D Thesis, Mr. Shriram S. Sonawane, UDCT, North Maharashtra University, Jalgaon

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