1.1 Polymer blend

Macroscopically homogeneous mixture of two or more different species of polymer

Blends are homogeneous on scales larger than several times the wavelengths of visible light.

The number of polymeric components which comprises a blend is often designated by an adjective, viz., binary, ternary, quaternary

1. BASIC TERMS IN POLYMER BLENDS AND ALLOYS

1.2 Miscibility

Capability of a mixture to form a single phase over certain ranges of temperature, pressure and composition.

The single phase in a mixture may be confirmed by light scattering, X-ray scattering, and neutron scatteringFor a two-component mixture, a necessary and sufficient condition for stable or metastable equilibrium of a homogeneous single phase is

where mix G is the Gibbs energy of mixing and the composition, where is usually taken as the volume fraction of one of the components. The system is unstable if the above second derivative is negative.

1.3 Miscible polymer blend / homogeneous polymer blend Polymer blend that exhibits miscibility.

For components of chain structures that would be expected to be miscible, miscibility may not occur if molecular architecture is changed, e.g., by crosslinking.

A miscible system can be thermodynamically stable or metastable

For a polymer blend to be miscible, it must satisfy the criteria of miscibility

1.4 Homologous polymer blend Mixture of two or more fractions of the same polymer, each of which has a different molar-mass distribution.

1.5 Isomorphic polymer blend Polymer blend of two or more different semi-crystalline polymers that are miscible in the crystalline state as well as in the molten state. Such a blend exhibits a single, composition-dependent glass-transition temperature, Tg, and a single, composition-dependent melting point, Tm.This behavior is extremely rare; very few cases are known.

1.7 Metastable miscibility

Capability of a mixture to exist for an indefinite period of time as a single phase that is separated by a small or zero energy barrier from a thermodynamically more stable multiphase system.

Mixtures exhibiting metastable miscibility may remain unchanged or they may undergo phase separation, usually by nucleation or spinodal decomposition.

1.8 Metastable miscible polymer blend

Polymer blend that exhibits metastable miscibility.

In polymers, because of the low mobility of polymer chains, particularly in a glassy state, metastable mixtures may exist for indefinite periods of time without phase separation.

1.9 Interpenetrating polymer network (IPN) Polymer comprising two or more polymer networks which are at least partially interlaced on a molecular scale, but not covalently bonded to each other and cannot be separated unless chemical bonds are broken

An IPN may be further described by the process by which it is synthesized. When an IPN is prepared by a process in which the second component network is polymerized following the completion of polymerization of the first component network, the IPN may be referred to as a sequential IPN. When an IPN is prepared by a process in which both component networks are polymerized concurrently, the IPN may be referred to as a simultaneous IPN.

1.10 Semi-interpenetrating polymer network (SIPN)

Polymer comprising one or more polymer network(s) and one or more linear or branched polymer(s) characterized by the penetration on a molecular scale of at least one of the networks by at least some of the linear or branched chains

Semi-interpenetrating polymer networks are different from interpenetrating polymer networks because the constituent linear-chain or branched-chain macromolecule(s) can, in principle, be separated from the constituent polymer network(s) without breaking chemical bonds, and, hence, they are polymer blends.They are also sequential SIPN and simultaneous SIPN.

1.11 ImmiscibilityInability of a mixture to form a single phase.

Immiscibility may be limited to certain ranges of temperature, pressure and composition.Immiscibility depends on the chemical structures, molar-mass distributions, and molecular architectures of the components.

1.12 Immiscible polymer blend/heterogeneous polymer blend

Polymer blend that exhibits immiscibility.

1.13 Composite

Multicomponent material comprising multiple different (nongaseous) phase domains in which at least one type of phase domain is a continuous phase

Foamed substances, which are multiphased materials that consist of a gas dispersed in a liquid or solid, are not normally considered to be composites.

1.14 Polymer composite

Composite in which at least one component is a polymer.

1.15 Nanocomposite Composite in which at least one of the phases has at least nano scale material

1.16 Laminate Material consisting of more than one layer, the layers being distinct in composition, composition profile,or anisotropy of properties.

Laminates may be formed by two or more layers of different polymers.Composite laminates generally consist of one or more layers of a substrate, often fibrous, impregnated with a curable polymer, curable polymers, or liquid reactants.one dimension of the order of nanometers.

1.17 Lamination

Process of forming a laminate.

1.18 Delamination

Process that separates the layers of a laminate by breaking their structure in planes parallel to those layers.

1.19 Impregnation

Penetration of monomeric, oligomeric or polymeric liquids into an assembly of fibers.

The term as defined here is specific to polymer science. An alternative definition of impregnationapplies in some other fields of chemistryImpregnation is usually carried out on a woven fabric or a yarn.

1.20 Prepreg Sheets of a substrate that have been impregnated with a curable polymer, curable polymers or liquid reactants, or a thermoplastic and are ready for fabrication of laminates.

During the impregnation the curable polymer, curable polymers, or liquid reactants may be allowed to react to a certain extent (sometimes termed degree of ripening).

1.21 Intercalation Process by which a substance becomes transferred into pre-existing spaces of molecular dimensions in a second substance.

The term as defined here is specific to polymer science. An alternative definition of intercalation applies in some other fields of chemistry

1.22 Exfoliation Process by which thin layers individually separate from a multilayered structure.In the context of a nanocomposite material, the individual layers are of the order of at most a few nanometers in thickness.

1.23 Wetting Process by which an interface between a solid and a gas is replaced by an interface between the same solid and a liquid.1.24 Adhesion Holding together of two bodies by interfacial forces or mechanical interlocking on a scale of micrometers or less.

1.25 Chemical adhesion

Adhesion in which two bodies are held together at an interface by ionic or covalent bonding between molecules on either side of the interface.

1.26 Interfacial adhesion

Adhesion in which interfaces between phases or components are maintained by intermolecular forces, chain entanglements or both, across the interfaces.

Adhesive strength (symbol: Fa unit: N m2) is the force required to separate one condensed phase domain from another at the interface between the two phase domains divided by the area of the interface.Interfacial tension (recommended symbol: , unit: N m1, J m2) is the change in Gibbs energy per unit change in interfacial area for substances in physical contact.

1.27 Interfacial bonding

Bonding in which the surfaces of two bodies in contact with one another are held together by intermolecular forces.Examples of intermolecular forces include covalent, ionic, van der Waals and hydrogen bonds

1.28 Interfacial fracture

Brittle fracture that takes place at an interface.

1.29 Craze

Crack-like cavity formed when a polymer is stressed in tension that contains load-bearing fibrils spanning the gap between the surfaces of the cavity.Deformation occurs with only minor changes in volume; hence, a craze consists of both fibrils and voids.

1.30 Additive

Substance added to a polymer.The term as defined here is specific to polymer science. An alternative definition of additive applies in some other fields of chemistry An additive is usually a minor component of the mixture formed and usually modifies the properties of the polymer.Examples of additives are antioxidants, plasticizers, flame retardants, processing aids, other polymers, colorants, UV absorbers, and extenders.

1.31 Interfacial agent

Additive that reduces the interfacial energy between phase domains.

1.32 Compatibility

Capability of the individual component substances in either an immiscible polymer blend or a polymer composite to exhibit interfacial adhesion

Use of the term compatibility to describe miscible systems is discouraged.Compatibility is often established by the observation of mechanical integrity under the intended conditions of use of a composite or an immiscible polymer blend.

1.33 Compatibilization Process of modification of the interfacial properties in an immiscible polymer blend that results in the formation of interphases and stabilization of the morphology, leading to the creation of a polymer alloy.

Compatibilization may be achieved by addition of suitable copolymers or by chemical modification of interfaces through physical treatment (i.e., irradiation or thermal) or reactive processing.

1.34 Degree of compatibility Measure of the strength of the interfacial bonding between the component substances of a composite or immiscible polymer blend

Estimates of the degree of compatibility are often based upon the mechanical performance of the composite, the interphase thickness or the sizes of the phase domains present in the composite, relative to the corresponding properties of composites lacking compatibility.The term degree of incompatibility is sometimes used instead of degree of compatibility.

1.35 Compatible polymer blend Immiscible polymer blend that exhibits macroscopically uniform physical properties throughout its whole volume.The macroscopically uniform physical properties are usually caused by sufficiently strong interactions between the component polymers.

1.36 Compatibilizer Polymer or copolymer that, when added to an immiscible polymer blend modifies its interfacial character and stabilizes its morphology.Compatibilizers usually stabilize morphologies over distances of the order of micrometers or less.

1.37 Coupling agent/adhesion promoter Interfacial agent comprised of molecules possessing two or more functional groups, each of which exhibits preferential interactions with the various types of phase domains in a composite. A coupling agent increases adhesion between phase domains. An example of the use of a coupling agent is in a mineral-filled polymer material where one part of the coupling agent molecule can chemically bond to the inorganic mineral while the other part can chemically bond to the polymer.

1.38 Polymer alloy

Polymeric material, exhibiting macroscopically uniform physical properties throughout its whole volume, that comprises a compatible polymer blend, a miscible polymer blend or a multiphase copolymer

1.39 Dispersion Material comprising more than one phase where at least one of the phases consists of finely divided phase domains, often in the colloidal size range, distributed throughout a continuous phase domain.

Particles in the colloidal size range have linear dimensions between 1 nm and 1000 nm.The finely divided domains are called the dispersed or discontinuous phase domainsA dispersion is often further characterized on the basis of the size of the phase domain as a macrodispersion or a microdispersion.

1.40 Dispersing agent/dispersing aid/dispersant

Additive exhibiting surface activity, that is added to a suspending medium to promote uniform and maximum separation of extremely fine solid particles, often of colloidal size

Although dispersing agents achieve results similar to compatibilizers they function differently in that they reduce the attractive forces between fine particles, which allows them to be more easily separated and dispersed.

1.41 Agglomeration/aggregation

Process in which dispersed molecules or particles form clusters rather than remain as isolated single molecules or particles.

1.42 Agglomerate/aggregate Clusters of dispersed molecules or particles that results from agglomeration

1.43 Extender Substance, especially a diluent or modifier, added to a polymer to increase its volume without substantially altering the desirable properties of the polymer.

An extender may be a liquid or a solid.

1.44 FillerSolid extender.

The term as defined here is specific to polymer science. An alternative definition of filler applies in some other fields of chemistry Fillers may be added to modify mechanical, optical, electrical, thermal, flammability properties, or simply to serve as extenders.

1.45 Fill factor

Symbol: fill Maximum volume fraction of a particulate filler that can be added to a polymer while maintaining the polymer as the continuous phase domain.

1.46 Thermoplastic elastomer Melt-processable polymer blend or copolymer in which a continuous elastomeric phase domain is reinforced by dispersed hard (glassy or crystalline) phase domains that act as junction points over a limited range of temperature.

The behavior of the hard phase domains as junction points is thermally reversible.The interfacial interaction between hard and soft phase domains in a thermoplastic elastomer is often the result of covalent bonds between the phases and is sufficient to prevent the flow of the elastomeric phase domain under conditions of use.Examples of thermoplastic elastomers include block copolymers and blends of plastics and rubbers.

2.3 FloryHuggins theory/FloryHuggins Staverman theory

Statistical thermodynamic mean-field theory of polymer solutions, formulated independently by Flory, Huggins and Staverman, in which the thermodynamic quantities of the solution are derived from a simple concept of combinatorial entropy of mixing and a reduced Gibbs-energy parameter, the interaction parameter

The FloryHuggins theory has often been found to have utility for polymer blends; however, there are many equation-of-state theories that provide more accurate descriptions of polymerpolymer interactions.

2.4 interaction parameterSymbol: Interaction parameter, employed in the FloryHuggins theory to account for the contribution of the noncombinatorial entropy of mixing and the enthalpy of mixing to the Gibbs energy of mixing.The definition and the name of the term have been modified from that which appears to reflect its broader use in the context of polymer blends. In its simplest form, the parameter is defined according to the FloryHuggins equation for binary mixtures for a mixture of amounts of

substance n1 and n2 of components denoted 1 and 2, giving volume fractions 1 and 2, with the molecules of component 1 each conceptually consisting of x1 segments whose Gibbs energy of interaction with segments of equal volume in the molecules of component 2 is characterized by the interaction parameter .The interaction parameters characterizing a given system vary with composition, molar mass and temperature.

2.5 Nucleation of phase separation Initiation of phase domain formation through the presence of heterogeneities.In a metastable region of a phase diagram phase separation is initiated only by nucleation.

2.6 Binodal/binodal curve/coexistence curve Curve defining the region of composition and temperature in a phase diagram for a binary mixture across which a transition occurs from miscibility of the components to conditions where single-phase mixtures are metastable or unstableBinodal compositions are defined by pairs of points on the curve of Gibbs energy of mixing vs. composition that have common tangents, corresponding to compositions of equal chemical potentials of each of the two components in two phases.

2.10 Cloud-point curve Curve of temperature vs. composition defined by the cloud points over range of compositions of two substances.

Mixtures are observed to undergo a transition from a single- to a two-phase state upon heating or cooling.

2.11 Cloud-point temperature

Temperature at a cloud point

2.12 Critical point

Point in the isobaric temperature-composition plane for a binary mixture where the compositions of all coexisting phases become identical.

2.13 Lower critical solution temperature

Acronym: LCST

Critical temperature below which a mixture is miscible.

Below the LCST and above the UCST if it exists, a single phase exists for all compositions.The LCST depends upon pressure and the molar-mass distributions of the constituent polymer(s).For a mixture containing or consisting of polymeric components, these may be different polymers or species of different molar mass of the same polymer.

2.14 Upper critical solution temperatureAbbreviation: UCSTCritical temperature above which a mixture is miscible.

Above the UCST and below the LCST if it exists, a single phase exists for all compositionsThe UCST depends upon the pressure and molar-mass distributions of the constituent polymer(s).For a mixture containing or consisting of polymeric components, there may be different polymers or species of different molar mass of the same polymer.

2.15 Phase inversion

Process by which an initially continuous phase domain becomes the dispersed phase domain and the initially dispersed phase domains become the continuous phase domain.

2.16 Interdiffusion Process by which homogeneity in a mixture is approached by means of spontaneous mutual molecular diffusion.

2.17 Blooming Process in which one component of a polymer mixture, usually not a polymer, undergoes phase separation and migration to an external surface of the mixture. 2.18 Coalescence Process in which two phase domains of essentially identical composition in contact with one another form a larger phase domain.Coalescence reduces the total interfacial area.The flocculation of a polymer colloid, through the formation of aggregates, may be followed by coalescence.

2.19 Morphology coarsening/phase ripening Process by which phase domains increase in size during the aging of a multiphase material.

In the coarsening at the late stage of phase separation, volumes and compositions of phase domains are conserved.Representative mechanisms for coarsening at the late stage of phase separation are: (1) material flow in domains driven by interfacial tension (observed in a co-continuous morphology), (2) the growth of domain size by evaporation from smaller droplets and condensation into larger droplets, and (3) coalescence (fusion) of more than two droplets. The mechanisms are usually called (1) Siggias mechanism, (2) Ostwald ripening (or the Lifshitz- Slyozov mechanism), and (3) coalescence.Morphology coarsening can be substantially stopped by, for example, vitrification, crosslinking, and pinning, the slowing down of molecular diffusion across domain interfaces.

Many types of morphologies have been reported in the literature of multiphase polymeric materials. It is the intent of this document to define only the most commonly used terms. In addition, some morphologies have historically been described by very imprecise terms that may not have universal meanings. However, if such terms are widely used they are defined here.

3.1 Morphology

Shape, optical appearance or form of phase domains in substances, such as high polymers, polymer blends, composites, and crystals.

For a polymer blend or composite, the morphology describes the structures and shapes observed, often by microscopy or scattering techniques of the different phase domains present within the mixture.

3. DOMAINS AND MORPHOLOGIES

3.2 Phase domain Region of a material that is uniform in chemical composition and physical state.

A phase in a multiphase material can form domains differing in size.The term domain may be qualified by the adjective microscopic or nanoscopic or the prefix micro- or nano- according to the size of the linear dimensions of the domain.The prefixes micro-, and nano- are frequently incorrectly used to qualify the term phase instead of the term domain; hence, microphase domain, and nanophase domain are often used. The correct terminology that should be used is phase microdomain and phase nanodomain.

3.3 Multiphase copolymer Copolymer comprising phase-separated domains.

3.4 Interfacial-region thickness/interphase thickness/interfacial width

Linear extent of the composition gradient in an interfacial region.The width at half the maximum of the composition profile across the interfacial region (see 3.6) or the distance between locations where d/dr (with the composition of a component and r the distance through the interfacial region) has decreased to 1/e are used as measures of the interfacial-region thickness.

3.5 Hard-segment phase domain Phase domain of microscopic or smaller size, usually in a block, graft, or segmented copolymer comprising essentially those segments of the polymer that are rigid and capable of forming strong intermolecular interactions.Hard-segment phase domains are typically of 215 nm linear size.

3.6 Soft-segment phase domain Phase domain of microscopic or smaller size, usually in a block, graft, or segmented copolymer comprising essentially those segments of the polymer that have glass transition temperatures lower than the temperature of use.Soft-segment phase domains are often larger than hard-segment phase domains and are often continuous.

3.7 Segmented copolymer Copolymer containing phase domains of microscopic or smaller size, with the domains constituted principally of single types of structural unit.The types of domain in a segmented copolymer usually comprise hard- and soft-segment phase domains.

3.8 Cylindrical morphology Phase domain morphology, usually comprising two polymers, each in separate phase domains, in which the phase domains of one polymer are of cylindrical shape.Phase domains of the constituent polymers may alternate, which results in many cylindrical layers surrounding a central core domain.Cylindrical morphologies can be observed, for example, in triblock copolymers.

3.9 Fibrillar morphology Morphology in which phase domains have shapes with one dimension much larger than the other two dimensions.Fibrillar phase domains have the appearance of fibers.

3.10 Lamellar domain morphology Morphology in which phase domains have shapes with two dimensions much larger than the third dimension.Plate-like phase domains have the appearance of extended planes that are often oriented essentially parallel to one another.

3.11 Microdomain morphology Morphology consisting of phase microdomains.Microdomain morphologies are usually observed in block, graft and segmented copolymers.This type of morphology observed depends upon the relative abundance of the different types of structural units and the conditions for the generation of the morphology. The most commonly observed morphologies are spheres, cylinders, and lamellae.

PBT = Poly(butylene terepthalate)

PEO = Poly(ethylene- octene)

EGMA = Poly(ethylene-co-glycidyl methacrylate)DMTA OF TERNARY BLENDS (PBT+PEO+EGMA; 2%)

Blending of immiscible polymers offers attractive opportunities for developing new materials with useful combinations of properties. However, simple blends often have poor mechanical properties and unstable morphologies. Compatibilization of such blends is necessary.

Preformed graft or block copolymers have been traditionally added to act as compatibilizers. Another route, however, is to generate these copolymer compatibilizers in situ during melt blending using functionalized polymers

A variety of reactive polymers that have been utilized in the reactive compatibilization of polymer blends is examined. They are classified into six major categories according to the types of reactive groups they have, namely, maleic anhydride, carboxylic acids, carboxylic acid derivatives, primary and secondary amines, hydroxyl and epoxide, and reactive groups capable of ionic bonding. Their preparation methods and applications and the chemical reactions they undergo during melt blending.There is intense commercial interest in multiphase polymer blends or alloys because of the potential opportunities for combining the attractive features of several materials into one or to improve deficient characteristics of a particular material

Compatibility and adhesion can be improved by the addition of suitable block or graft copolymers that act as interfacial agents. These block or graft copolymers can, in principle, be made separately and then added to polymer blends.

COMPATIBILITY IN POLYMER BLENDSBasic ConceptsThere are two widely useful types of polymer blends: miscible and immiscible. Miscible blends involve thermodynamic solubility and are characterized by the presence of one phase and a single glass transition temperature. Their properties can often be predicted from the composition weighted average of the properties of the individual components. Immiscible blends are phase separated, exhibiting the glass transition temperatures and/or melting temperatures of each blend component. Their overall performance depends upon the properties of the individual components but also depends significantly upon the morphology of the blends and the interfacial properties between the blend phases. Performance is not easily predictable.

To achieve miscibility in polymer blends, a negative free energy of mixing must exist, which in turn requires an exothermic heat of mixing because entropic contributions are negligible. Gmix = Hmix - T Smix

The introduction of specific interactions between blend components. The potentially useful specific interactions range from strong covalent and ionic bonding to nonbonding weak interactions such as hydrogen bonding, ion-dipole, dipole-dipole and donor-acceptor interactions.Few polymer pairs form miscible blends. One of the infrequent examples is the commercially important poly(pheny1ene ether) (PPE)-polystyrene (PS) blend.

Most polymers, however, are immiscible but, immiscibility is not always a bad thing. Blends do not have to be miscible to be useful. High-impact PS (HIPS) and poly(acrylonitri1e-co-butadiene-co-styrene) (ABS) have proven the importance of phase separation.Compatibilized blends are termed compatible blends and characterized by the presence of a finely dispersed phase, good adhesion between blend phases, strong resistance to phase coalescence and technologically desirable properties.

Strategies for Blend Compatibilization

There are several methods of compatibilizing immiscible blends, including compatibilization by the introduction of nonreactive graft or block copolymers, nonbonding specific interactions, low-molecular-weight coupling agents and reactive polymers.

1.Addition of Block and Graft Copolymers

Suitable block and graft copolymers can be used as compatibilizers for polymer blends. A suitable block or graft copolymer contains a segment miscible with one blend component and another segment with the other blend component. Significant amounts of the copolymer are expected to locate at the interface between immiscible blend phases, reducing the interfacial tension between blend components, reducing the resistance to minor phase breakup during melt mixing, thus reducing the size of the dispersed phase, and stabilizing the dispersion against coalescence.

The effects of a copolymer on the morphology of polymer blends, interfacial adhesion between blend phases, and blend properties depend upon such parameters as the type and molecular weight of the copolymer segments, blend compositions, blending conditions, etc.

2. Utilization of Nonbonding Specific InteractionNonbonding specific interactions like hydrogen bonding, ion-dipole, dipole-dipole, donor- acceptor and r-electron interactions are useful for enhancing the compatibility of polymer blends.Typical examples that illustrate the importance of specific interactions in enhancing compatibility in polymer blends include hydrogen bonding interactions in the blends of

a) Poly(ethy1ene-co-vinyl acetate-co-carbonmonoxide), poly(alky1ene oxide), polyacrylates, poly(viny1 acetate), or polyesters with poly(viny1 chloride) (PVC);

b ) poly(alky1ene oxide) with poly(acry1ic acid); ion-dipole interactions in PS ionomer/ poly(alkylene oxide); c) dipole-dipole interactions in the blends of poly(viny1 acetate) or polyacrylates with poly(viny1idene fluoride); d) and donor-acceptor interactions in the blend of poly[w-(3,5-dinitrobenzoyl)- hydroxy-alkylmethacrylate] with poly[2-(N-carbazolyl)ethylmethacrylate].3.Addition of Low-Molecular- Weight Coupling AgentsAddition of low-molecular-weight reactive compounds may serve the purpose of compatibilization of polymer blends through copolymer formation. Recent examples of interest in this category include the compatibilization of poly(styrene-co-maleic anhydride) (SMAn)- brominated butyl rubber blends by dimethylaminomethanol, 22

PS-linear low-density polyethylene (LLDPE) blends by peroxide and a small amount of poly(styrene-co-vinyl benzaldehyde),and PPE-polyamide (PA)6,6 blends by organosilanes.

4. Reactive Compatibilization

Graft or block copolymers acting as compatibilizers for polymer blends can be formed in situ through covalent or ionic bonding during the melt blending of suitably functionalized polymer. The in-situ formed copolymer compatibilizers are located preferentially at the interface where they are most needed, reducing the size of the dispersed phase and improving the interfacial adhesion between blend phases and the physical properties of the blends.

A required reactive group can be incorporated into a polymer by: (a) incorporation into the backbone, side chain &/or at chain ends as a natural result of polymerization; (b) copolymerization of monomers containing the desired reactive groups; and (c) chemical modification of a preformed polymer through a variety of chemical reactions

Chemical modification of preformed polymers particularly in the melt is a more attractive technique for its apparent simplicity and cost effectiveness.

Some common reactions used in the preparation of reactive polymers for polymer blend applications include the following.

Addition reactions: (a) catalyzed grafting, e.g., free radical catalyzed grafting of maleic anhydride (MA) onto PE; (b) concerted ene addition of MA onto double bond, a well-known phenomenon, with MA-grafted natural rubber being an industrial product.Substitution reactions: (a) sulfonation and bromination of PS and other polymers containing phenyl groups; (b) hydrolysis of poly(viny1 acetate) into poly(viny1 alcohol), a well-known industrial process; (c) ring opening of side or end cyclic groups; (d) terminal substitution on condensation polymers

Reasons for rapid development low costs, easy production,variable properties,possibility for valuation of waste Estimation approximately polymers and elastomers are blends

Polymers Don't Mix !

It has to do with that old culprit entropy. First Thermodynamic Law Second Thermodynamic Law

One of the biggest reasons two compounds will ever mix together is that they are more disordered mixed together than they are separate. So, mixing is favored by the second law of thermodynamics. But an amorphous polymer is so disordered as it is, that it really doesn't gain that much entropy when it's blended with another polymer. So mixing is disfavored.

First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy.

Two polymers that do actually mix are polystyrene and poly(phenylene oxide).

polystyrene poly(phenylene oxide) There are a few other examples of polymer pairs which will blend. Here is a list of a few:

poly(ethylene terephthalate) with poly(butylene terephthalate)poly(methyl methacrylate) with poly(vinylidene fluoride)

poly(butylene terephthalate) poly(vinylidene fluoride)

The first way is to dissolve two polymers in the same solvent and then wait for the solvent to evaporate.

When the solvent has all gone away, you'll be left with a blend at the bottom of your beaker, presuming your two polymers are miscible. (laboratory way)

Making blends in large amounts, it means heat the two polymers together until you're above the glass transition temperatures of both polymers. At this point they will be nice, and you can mix them together. This is such as extruders. When the material cools, a nice blend appears, again, presuming two polymers are miscible.

Take for example the glass transition temperature, or Tg for short. If we take polymer A and blend it with polymer B, the Tg will depend on the ratio of polymer A to polymer B in the blend. You can see this in the graph below.

Mechanical properties, resistance to chemicals, radiation, or heat; they all generally plot the same way as the Tg does with respect to the relative amounts of each polymer in the blend.

Enter polystyrene. Polystyrene and PPO- poly(propylenoxide) blend nicely with each other. Since polystyrene has a Tg about 100 oC, blending polystyrene with PPO drops the Tg of the blend down to temperatures which make the blend much more processable than straight PPO.

To Blend or Not to Blend ? There will be a range of compositions for which the two polymers won't mix. For example, let's say we have two polymers, polymer A and polymer B. Let's also say they are miscible when we have less than 30% polymer B, that they are miscible when there is more than 70% polymer B. But between 30 and 70% polymer B, the blend phase-separates into two phases.

In this material, PET and PVA separate into sheet like layers called lamellae. The resulting arrangement lamellar morphology. This particular immiscible blend is used to make plastic bottles for carbonated beverages. Carbon dioxide can't pass through PVA.

Morphology The shape made by the two phases, and the arrangement of the two phases is called morphology. The biggest thing one can do to affect the morphology of an immiscible blend is to control the relative amounts of the two polymers one is using.

One unusual property of immiscible blends - one made from two amorphous polymers has two glass transition temperatures Tg The mechanical properties of this immiscible blend are going to depend on those of polymer A (major component) , because the polymer A phase is absorbing all the stress and energy when the material is under load.

So why make immiscible blends then, if separate materials are stronger? These rods act like the fibers of a reinforced composite material. They make the material stronger in the direction of the rods.

Another way to make a strong immiscible blend is to use more equal amounts of the two polymersPolymer A and polymer B - roughly equal amounts of two co-continuous phases. This means both phases will be bearing the load of any stress on the material, so it will be stronger.

So what is a compatibilizer?

Often times a compatibilizer is a block copolymer of the two components of the immiscible blend.

These graft copolymers allow stress to be transferred from the polystyrene phase to the polybutadiene phase. Compatibilizer lowers the energy of the phase boundary when a compatibilizer is used, spheres don't need to be as big (polystyrene spheres were about 5-10 mm in diameter) When enough of a polystyrene-polyethylene block copolymer (enough being 9%) is added to the immiscible blend, the size of the polystyrene spheres drops to about 1 mm.

In almost all cases, good distribution AND good dispersion are required.

Distributive mixing can be achieved by providing convoluted flow paths that split and reorient the flow repeatedly

Dispersive mixing can be achieved by passing the mixture through small regions of intense deformation.

Distributive mixing involves stretching, dividing and reorienting the flow of the polymer melt compound in order to eliminate local variations in material distribution and produce a more homogeneous mixture.

Distributive mixers must impose high strain on the material together with splitting and reorienting the flow.Achieved by introducing barriers with large clearances that generate a long, convoluted flow path.

Dispersive mixing involves generating high stresses (shear and elongational) in the material to break down dispersed particles. These particles may be insoluble fillers (composites) or a second polymer melt (blend).

Dispersive mixers force the material to flow over barriers that form narrow clearances between mixing elements (i.e. between extruder wall and a screw element).

Mixers can be classified into two categories:

Batch mixers: They are the oldest type of mixing equipment and are still widely used. They are versatile units, because operating conditions and the time at which the additives are incorporated can be varied during a cycle to achieve optimum mixing.

Continuous mixers: They include single and twin-screw extruders and modified variants. Continuous mixing offers higher throughputs, reduced manpower requirements and greater product uniformity, leading to easier quality control. Disadvantages include less processing flexibility, requirement for expensive feeding equipment and generally lower dispersive mixing quality

A two-roll mill consists of a parallel pair of counter-rotating, heated metal rolls that turn at a slightly different rate (roll ratio) and provide an adjustable gap (or nip) between them.

The shear stresses generated in the gap are substantial and provide further compound mixing while shapingthe compound into a sheet.

Temperature control is more easily affected in a mill, when compared to aBanbury-type mixer that completely encloses the compound.

Internal mixers are high intensity mixers that work especially well in the dispersion of solid particle agglomerates.

The dispersion of agglomerates depends strongly on mixing time, rotor speed, temperature and rotor blade geometry.

The tangential rotor design, or Banbury isshown here, but several variations exist, includingthe interlocking rotor design known asthe Intermix type.

Single Screw Extruders:The SSE is a relatively poor mixing device and specialized screw sections are needed to improve the mixing efficiency of this apparatus.Distributive mixing can be improved using static mixers or mixing heads such as the pineapple configuration shown here.Pineapple Mixing SectionKenics Static Mixer

Dispersive mixing is more difficult, as it requires that high shear stresses be generated. There are numerous designs for mixing sections, which can improve dispersive mixing

These devices force the melt to flow over barriers, which form narrow clearances between the screw and the barrel, thus improving dispersive mixing.

Twin Screw Extruders:TSEs have two screws within the barrel and can be co-rotating or counter-rotating, intermeshing or non-intermeshing. They are favoured forMixing and compoundingChemical reactions / reactive extrusionDevolatilization

Our research group has been active in the development of polyethylene-based clay and silica nanocompositesOur objective is to distribute and DISPERSE inorganic fillers of nanoscale dimension by melt compoundingAnticipated benefits include improvements in material stiffness (as per rubber compounds) and impermeability

Sounds easy?Polyethylene is non-polar and interacts weakly with high energy fillers such as precipitated silica (glass).Clay minerals are large-scale layered structures of charged platelets that must be exfoliated

Figure. FT-IR spectral changes in hydroxyl region of polychromatic irradiated E-P blends.

Figure. FT-IR spectral changes in carbonyl region of polychromatic irradiated E-P blends.

Ammonium carboxylate formation at 1555 cm-1:. Changes in carboxylate ion concentration of 200 hours thermalphotooxidized E-P blend films after ammonia treatment

Hydroxyl absorptions generates acyl fluorides at 1840-1848 cm-1 After exposure to SF4 gas, the oxidized PP chain absorbs at 1841 cm-1 PE at 1848 cm-1

The NO-treated oxidized PE films : A symmetrical nitrate absorption at 1276 cm-1 from secondary hydroperoxide and a small secondary nitrite peak at 778 cm-1 from secondary alcohol The oxidized PP prominent absorptions at 1302 and 1290 cm-1 with small absorptions at 760 and 778 cm-1.

FT-IR spectral changes upon thermal photooxidization (200 hours), then SF4, treated and the corresponding non oxidized E-P blend films subtracted.

. FT-IR spectral changes of thermal-photooxidized (150 hours) E-P blend films. Spectral substraction of oxidized film from corresponding oxidized and NO treated

Transmission electron microscopy (TEM) images of 13 wt% SiO2/PE-g-PA 5 wt% SiO2/HDPE

(scale bars correspond to 200 nanometres).

Transmission electron microscopy (TEM) images of 40 wt% NR4+-MM/PE-g-PA5 wt% NR4+-MM/HDPE (scale bars correspond to 200 nanometres).

Idea to locate fillers preferentially in one phase, to selectively reinforce it.

This can be accomplished by adding functional groups having better affinity with the filler, so that it will migrate and exfoliate to the preferred phase.

Blending two or more polymers is a common approach to develop new polymeric materials with customized properties. Generally, these systems are composed of two or more immiscible polymers and display a matrix /dispersed phase morphology.

Interfacial tension between two polymers can be controlled by the (FloryHuggins) interaction parameter. Most of the papers on multiphase blends showed that the morphology of ternary blends is strongly affected by the wettability as the driving force of encapsulation and can be predicted through the knowledge of interfacial tension between the components of the blends

Figure 1. Possible morphology formation in ternary polymer blends: (a) stacked formation; (b) capsule formation; (c) isolated formationFigure 2. (a) TMAFM topographical surface images of (1) 80% HDPE/20% PS, (2) 80% HDPE/20% PMMA and (3) 80% HDPE/10% PS/10% PMMA

three-dimensional view of the blend structure, showing the thin PS layer at the HDPE/PMMA interface;section showing the relative position of the different phases.

(a) no copolymer; (b) A-B; (c) A-B-A; and (d) B-A-B. The white color indicates a continuous phase made of B and copolymer, and the black color shows the dispersed phase made of A.

1. Fayt, R., Hadjiandreou, P. and Teyssie, P., J. Polym. Sci. Polym. Chem. Ed., 1985, 23, 337.2. Ikawa, T.; Abe, K.; Honda, K.; and Tsuchida, E.; J. Polym. Sci., Polym. Chem. Ed., 1975, 13, 1505. 2. Ting, E. P.; Pearce, E. M. and Kwei, T. K., J. Polym. Sci. Polym. Lett. Ed., 1980, 18, 201.3. Pearce, E. M.; Kwei, T. K. and Min, B. Y., J. Macromol. Sci. Chem., 1984, 21, 1181.4. Coleman, M. M., Graf, J. F. and Painter, P. et al., Specific Interactions and the Miscibility of Polymer Blends, Technomic, 1991, p.20.5. http://www.pslc.ws/macrog/maindir.htmReferences:

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