Composite and nanocomposite materials

Composite and nanocomposite materials Composite • Composites are materials which consist of a mixture of two or more distinct phases • It consist of matrix (bulk) and dispersed phase (reinforcement) • Matrix is the continuous phase and surrounds the dispersed phase • Composites have combined properties Constituents of composite o Matrix o Dispersed phase/Reinforcement phase o Interface/inter-phase Interface Reinforcement Matrix Composite Constituents of composite o Matrix (Continuous phase) : Continuous or bulk material o Reinforcement (Dispersed Phase) : Added primarily to increase the strength and stiffness of matrix o The reinforcement is generally can be in the form of fibres, particles, whiskers or flakes The most common man made composites can be divided into three main groups based on the matrix Matrix Polymer Ceramic Metal Matrix materials Role of matrix • It binds the fibres together and acts as medium • It transfer the stress to the dispersed phase • It protect the individual fibres from damage Dispersed phase (reinforcement) • Metallic, ceramic, organic materials • Reinforcement form can be fibers, short fibers, Whiskers, flakes, particulates • Depending on the form, volume fraction of reinforcing phase the composite will have isotropic, quasiisotropic and anisotropic properties • Metals, metaloxides, C, B, Mo, W,, SiC, SiO2 Al2O3, TiO2 , ZnO, steel, Talc, fibers of glass, Reinforcement (Dispersed Phase) o The dispersed phase can be any material in the form of fibres, particles, whiskers or flakes Particles Eg Carbon black, talc Flakes Eg Mica Dispersed Phase Fibres Eg Nylon, Sisal Whiskers Eg Graphite, SiC Arrangement of dispersed phase in composites o Metal- matrix composites (MMC) Composite material with at least two constituent parts, one being a metal The other material may be a different metal or another material such as a ceramic or organic compound o Carbide drills are often made from a tough cobalt matrix with hard tungsten carbide particles inside o Modern high-performance sport cars, such as those built by Porsche, use rotors made of carbon fiber within a silicon carbide matrix o Ford offers a Metal Matrix Composite (MMC) driveshaft o The F-16 Fighting Falcon uses monofilament silicon carbide fibres in a titanium matrix for a structural component of the jet's landing gear o MMCs are nearly always more expensive than the more conventional materials they are replacing o As a result, they are found where improved properties and performance can justify the added cost o Today these applications are found most often in aircraft components, space systems and high-end or "boutique" sports equipment Fire retardancy • Generally organic polymers are easily flammable but introduction of nanofillers improve the fire retardancy • Exfoliated clay/polymer (Polyolefins resin/clay) • Graphite, Graphite oxide with polymer, depends on the particle size • CNT materials are highly reflective, hence it absorb little radiation from fire • Ceramic composite are excellent fire retardant materials Fire retardancy • Nano - layered double hydroxides (LDH) acts as self extinguisher in the polymer composite • This is much better than polymer/clay composites LDH with water located between the layers Electrically conductivity • Carbon nano materials improves the electrical conductivity • CNT composite with polymers can improve the conductivity • Depending on the chirality of CNT the electron transport property changes • Chirality shows the way in which the graphene cylinders are twisted • Highly oriented pyroltic graphite shows different resistivity along the perpendicular (2 x 10-4 Ω-m) and along the inplane (2 x 10-7 Ω-m) directions • Intercalation of dopants (alkali, halogen, acids) into the graphitic lattice can make it behave like metals a- Arm chair, b- zig zag, c- Chiral Electrical conductivity • Conductivity depends on extent of percolation of CNT with polymer matrix • Critical concentration of fibers required to make the composite suddenly conductive is called percolation threshold No percolation Percolation and conduction pathway • Electrostatic spray painting process, Charge dissipating materials, Fabrication of electrically conductive components Thermal conductivity • Thermal conductivity of composite can be increased to several orders magnitude using nanofillers • Metal fillers can be used to increase the thermal conductivity – Cu, Ag, Al, steel • Ceramic fillers - SiC, (BN)x, Al2O3 • Carbon – CNT, graphitic carbon fibers • CNT thermal conductivity is three order higher along the tube axis , used to make protective fabrics for clothing • Thermally conductive plastics used in heat sink in electronic devices, microelectronic applications, tubing for heat exchange,heat sensors, switches, enclosures of electrical appliances Thermal conductivity • Acid treated multiwalled carbon nanotubes shows higher thermal conductivity • Acid treatment can introduce surface Hydroxyl, carboxylic, carbonyl groups • Introduction of covalent bonding between CNT and polymer matrix or surface functionalization reduces the thermal resistance • Alignment of fibers or tubes influences the thermal conductivity • Increasing amount of nanofillers increases the thermal conductivity Mechanical properties • Mechanical properties depends on the degree of dispersion of reinforcement phase and interphasial interactions • High tensile strength with increase in interfacial bond strength • Higher the surface energies of the dispersed phase in better molecular adsorption with matrix ( nanostructured materials) • Nano clay ( exfoliated, organic modified), Layered double hydroxides (LDH), nanosized fillers ( TiO2, SiO2, ZrP, Talc, CNT, Nanofibers as dispersed phase increases the modulus, impact strength and fatigue resistance Biocompatibility - Biomedical Applications of Polymer Composites o Biomaterials in the form of implants like sutures, bone plates, joint replacement ligaments, vascular grafts, heart valves, intraocular lenses, dental implants etc and medical devices like pacemakers, bio sensors, artificial hearts and blood tubes are widely used to improve the quality of life of the patients o Bio compatibility is measured to indicate the biological performance of materials o Optimal interaction between biomaterial and host is reached when both the surface and the structural compatibilities are met o A large number of polymers are used in various biomedical applications o Ceramics are known for their good bio compatibility, corrosion resistance and high compression resistance o Since the fiber reinforced polymers exhibit low elastic modulus and high strength, they are used in several orthopedic applications Composites in biomedical applications o The composite materials offer several advantages over metals and alloys in biomedical applications such as: a) The radio transparency can be adjusted by adding contrast medium to the polymer b) The polymer composite materials are fully compatible with the modern diagnostic methods such as computer tomography and magnetic resonance imaging as they are non-magnetic o The applications include: a) Hard tissue applications b) Bone cement c) Synthetic bone graft materials Hard Tissue applications o During the external fixation of bones in case of fractures, casting material used includes fabrics of glass and polyester fibers o However, plaster of Paris has many disadvantages like heaviness, bulkiness, and low fatigue strength radio opaque and long setting time o Casts made of glass or polyester fiber fabrics and water activated polyurethanes are gaining popularity because of - ease of handling - light weight - comfortable to anatomical shape - strong and stiff - water proof - radiolucent - easy to remove - permeable to ventilation (to avoid the patient’s skin getting scorched or weakened) Fixations using nanocomposites o External fixation made of stainless steel designs are being used which are heavy and cause discomfort to the patients o External fixations made using polymer composite materials are gaining acceptance because of their light weight yet sufficient strength and stiffness o In the internal fixation approach bone fragments are held together by different ways using these nanocomposite implants because of their flexibility and bio-compatibility Bone Cement o The most widely used bone cement is based on PMMA, also called acrylic bone cement o It is self polymerizing and contains solid PMMA powder and liquid MMA monomer o Fiber reinforcement with metal also reduces the peak temperature during polymerization of the cement and thus reducing tissue necrosis o The reinforced cement possesses higher fracture toughness, fatigue resistance and damage energy absorption capabilities than the unreinforced cement o In another approach, bone particles or surface reactive glass powders are mixed with PMMA bone cement to achieve immediate mechanical fixation of PMMA with chemical bonding of bone particles or surface reactive glass powder with the bone o Formation of this chemical bond makes it possible for mechanical stresses to be transferred across the cement/bone interface o For developing new bone cements the requirements are that it can be shaped, moulded or injected to conform to complex internal cavities in bone and it must harden in situ Synthetic bone graft materials o The bone graft material must be sufficiently strong and stiff and also capable of bonding to the residual bones o Polyethylene is considered biocompatible for satisfactory usage in hip and knee joint replacement for many years o For load bearing applications, properties of polyethylene need to be enhanced o In order to improve the mechanical properties polyethylene is reinforced with hydroxyapatite to get a composite material Advantages/disadvantages of advanced composites: S No Advantages Disadvantages Weight reduction High strength or stiffness to weight ratio Cost of raw materials and fabrication Tailorable properties Can tailor strength or stiffness to be in the load direction Transverse properties may be weak Redundant load paths (fiber to fiber) Matrix is weak, low toughness Longer life (no corrosion) Reuse and disposal may be difficult Lower manufacturing costs because of less part count Difficult to attach Inherent damping Analysis is difficult Increased (or decreased) thermal or electrical conductivity Matrix subject to environmental degradation Some typical Applications and reasons for using composites Reason for use Material selected Application Lighter, Stiffer and stronger Boron, all carbon/ graphites, some aramid Military aircraft, better performance Commercial aircraft, operating costs Lower inertia, faster startups, less deflection High strength carbon/graphite, epoxy Industrial rolls, for paper, films Very high modulus Lightweight, damage tolerance High strength carbon/graphite, fiberglass, (hybrids), epoxy CNG tanks for ’green’ cars, trucks and busses to reduce environmental pollution More reproducible complex surfaces High strength or high modulus carbon graphite/ epoxy High-speed aircraft Metal skins cannot be formed accurately Less pain and fatigue Carbon/graphite/epoxy Tennis, squash and racquetball Racquets Metallic racquets are no longer available Tailorability of bending and twisting response Carbon/graphite-epoxy Golf shafts, fishing rods Transparency to radiation Carbon/ graphite-epoxy X-ray tables Crashworthiness Carbon/ graphite-epoxy Racing cars Higher natural frequency, lighter Carbon/ graphite-epoxy Automotive and industrial drive shafts Water resistance Fiberglass (woven fabric), polyester or isopolyester Commercial boats Ease of field application Carbon/graphite, fiberglass - epoxy, tape and fabric Freeway support structure repair after earthquake [...]... polystyrene nanocomposites synthesized with this reactive nanoclay at a clay concentration of 20 wt % Synthesis of PS nanocomposites o Polystyrene clay nanocomposites were synthesized in both intercalated and exfoliated structures o To prepare the nanocomposites, organo-nanoclay particles are pre-mixed with PS and then mechanically blended in single or twin screw extruders o The formation of nanocomposites... manufacturing like aerospace industry Nanocomposites Polymer nanocomposites o Polymer nanocomposites find importance sine incorporation of these materials into polymer matrices give property improvement remarkably o These can be incorporated into plastic foams to improve their inferior mechanical strength, poor surface quality and low thermal and dimensional stability o Nanocomposite foams based on the combination... nanoparticles and super-critical fluid forming technology may lead to a new class of materials that are light weight, high strength and multifunctional o Polymer composites are widely used in automotive, aerospace, constructions and electronic industries because of their improved mechanical properties and physical properties over pure polymers Types of polymer nanocomposites o Polymer nanocomposites... improve the compatibility of polypropylene and clay o Polymers and carbon nanofibers, nanocomposites are also synthesized through this method o Shear stress is needs to be controlled at an appropriate level to disintegrate and disperse nanoparticles Synthesis of nanocomposites c) In situ polymerization: o Only viable method for most thermoset polymer to prepare nanocomposites [ o By tailoring the interactions... On mixing resin with glass and carbon, materials of exceptional properties are obtained o The resin matrix spreads the load applied to the composite between each of the individual fibers and also protects the fibers from damage caused by abrasive o High strength and stiffness, ease of moulding complex shapes and high environmental resistance and low densities make these composites superior to even... textiles, gaskets, sports applications, shock and sound attenuation and shoes • Polymer foams can be classified as macro cellulose (> 100 μm), micro cellulose (1 - 100 μm), ultra micro cellulose (0.1 - 1 μm) and nano cellulose ( 0.1 – 100 nm) Synthesis of nanocomposite foams o The aim of synthesis of nanocomposites is to achieve controlled nanoparticle dispersion and distribution in a polymer matrix - The... been used to prepare PS nanocomposites o By using reactive surfactants, the copolymerization of the interlayer surfactant and styrene monomer provides the driving force for delamination of clay crystallite Synthesis of PVC nanocomposites 1) By melt blending: o Used to prepare exfoliated nanocomposites of PVC o Particles used include clay, calcium carbonate hydrosulphite, copper and antimony trioxide... polymer o Process eliminates the use of solvent o Economically attractive route in fabricating polymer nanocomposites - Nylon 6, polystyrene and polypropylene composites are manufactured by this method o This melt intercalation gives a simple way of preparing nanocomposites o Polar interactions of polymer and clay surface play a critical role in achieving particle dispersion o For non polar polymers (polypropylene)... important matrix materials and are used in more than 95% of the composite products in use today Polymer Resin Thermosets Elastomer Thermoplastic Polymer matrix composites  Thermoplastic polymer matrices- Thermoplastics are incorporated in the composite system by melting and solidifying by cooling - The physical reaction being reversible in nature - Thermoplastics have low creep resistance and low thermal... are divided into two general types: a) Intercalated nanocomposites consisting of a regular penetration of the polymer in between the clay layers b) Delaminated/exfoliated nanocomposites where thick layers of the matrix forming a monolithic structure on the microscale INTERCALATED nanofillers are dispersed in the EXFOLIATED Types of nanocomposites o Nanomaterials are usually divided as: a) Platelet like ... processes and material forms o The higher properties are associated with higher technology manufacturing like aerospace industry Nanocomposites Polymer nanocomposites o Polymer nanocomposites... properties over pure polymers Types of polymer nanocomposites o Polymer nanocomposites are divided into two general types: a) Intercalated nanocomposites consisting of a regular penetration of... cellulose (0.1 - μm) and nano cellulose ( 0.1 – 100 nm) Synthesis of nanocomposite foams o The aim of synthesis of nanocomposites is to achieve controlled nanoparticle dispersion and distribution