Mixtures of Polymers Polymer Blends

Similar to other raw materials, e.g., metals, it is principally possible to vary the properties of macromoiecuiar substances by mixing two or more different polymers. Such systems are generally termed polymer blends. Though, one has to pay attention to the fact that in most cases phase-separated, i.e., heterogeneous products are obtained by mixing macromolecules. Mostly, these polymer blends consist of a continuous phase (matrix) in which a discontinuous (dispersed) phase in the form of more or less regularly shaped particles is included. However, also co-continuous and other complex morphologies are of practical importance. 

If two low-molecular-weight liquids are united they will either mix homogeneously or separate into two phases. Which of the two cases occurs depends on whether the free energy AG increases or decreases during the mixing process  

Therefore, it is only possible to obtain a homogeneous, single-phase mixture of two polymers when the generally slightly positive mixing enthalpy is 

most of the time one obtains phase-separated systems in which the macromolecules of component A are not at all or only to a limited extent miscible with the macromolecules of component B, i.e., polymer A is immiscible or only partially miscible with polymer B. 

Therefore, it is only possible to obtain a homogeneous, single-phase mixture of two polymers when the generally slightly positive mixing enthalpy AH j is sufficiently small or its magnitude is smaller than TAS. However, this is only to be expected for chemically very similar macromolecules. 

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It is clear that the interpolation between the calibration lines cannot be applied to mixtures of polymers (polymer blends). If the calibration lines are different, different molar masses of the homopolymers will elute at the same volume. The universal calibration is also not capable of eliminating the errors which originate from the simultaneous elution of two polymer fractions with the same hydrodynamic volume, but different composition and molar mass. Ogawa [33] has shown by a simulation technique that the molar masses of polymers eluting at the elution volume Ve are given by the corresponding coefficients K and a in the Mark-Houwink equation. 

Melting of Solid Mixtures of Polymer Blend Components... 

Blends of PET and HDPE have been suggested to exploit the availabiUty of these clean recycled polymers. The blends could combine the inherent chemical resistance of HDPE with the processiag characteristics of PET. Siace the two polymers are mutually immiscible, about 5% compatihilizer must be added to the molten mixture (41). The properties of polymer blends containing 80—90% PET/20—10% HDPE have been reported (42). Use of 5—15% compatbiLizer produces polymers more suitable for extmsion blow mol ding than pure PET. 

Ternary Blends. Discussion of polymer blends is typically limited to those containing only two different components. Of course, inclusion of additional components may be useful in formulating commercial products. The recent Hterature describes the theoretical treatment and experimental studies of the phase behavior of ternary blends (10,21). The most commonly studied ternary mixtures are those where two of the binary pairs are miscible, but the third pair is not. There are limited regions where such ternary mixtures exhibit one phase. A few cases have been examined where all three binary pairs are miscible however, theoretically this does not always ensure homogeneous ternary mixtures (10,21). 

Homologous Polymer Blends A subclass of polymer blends limited to mixtures of chemically identical polymers differing in molecular mass. 

Compatible Polymer Blends A term indicating commercially useful materials, mixture of polymers with strong repulsive forces that is homogeneous to the eye. 

Many commercially important polymers are actually mixtures of two or more polymer components that differ from one another in composition (for copolymers) or in microstructure (for homopolymers). Such mixtures may be the deliberate result of polymer blending, polymer synthesis, or the presence of different types of initiators or catalytic sites that produce different polymer chains. The ung spectral data of the whole polymer in such systems would include contributions from all its components, and as such should be treated with care. 

The data of Zink et al. (1998) illustrate the measurement by NRA of near-surface composition profiles in isotopically labelled polymer blends. If a mixture of polymers is adjacent to a phase interface (e.g. a solid or an air surface), often one of the components is preferentially attracted to the surface and will segregate to it, and this phenomenon will influence the tribological behaviour the interface (lubrication, wear and adhesion). 

Certain mixtures of polymers have been shown to form complexes which exhibit substantially higher than expected solution viscosity under low shear conditions. Xanthan gum blends with guar gum (38, 39), sodium poly(styrene sulfonate) (40), polyacrylamide (41), sulfonated guar gum (38), sodium poly(vinylsulfonate) (40), hydrolyzed sodium poly(styrene sulfonate-co-maleic anhydride) (38), and poly(ethylene oxide) (41) and blends of xanthan gum and locust bean gum have exhibited substantially higher than expected solution viscosity (42, 43). 

Modem floor finishes contain mixtures of ingredients that when applied as a liquid dry to give a clear, durable film coating. Most floor finishes are combinations of polymers blended to provide unique and desirable characteristics such as durability, gloss retention, resistance to scuffing, fast-drying, and ease of removal. Polymers made up of more than one monomer or repeating unit are called copolymers. 

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Note 1 The definition and the name of the term have been modified from that which appears in ref. [5] to reflect its broader use in the context of polymer blends. In its simplest form, the %. parameter is defined according to the Flory-Huggins equation for binary mixtures... 

Blends are physical mixtures of polymers. Depending on the extent and type of blend the properties may be characteristic of each blend member or may be some blend of properties. Immiscible blends are phase-separated with the phases sometimes chemically connected. They are generally composed of a continuous and discontinuous phase. HIPS is an example of an immiscible blend. Miscible blends occur when the two blended materials are compatible. Often the properties are a mixture of the two blended materials. The plastic automotive panels and bumpers are generally made from a miscible blend of PE and a copolymer of PE and PP. 

ABS Three-component copolymer of acrylonitrile, butadiene, and styrene, alloy Rubber-toughened materials in which the matrix can be a mixture of polymer tyrpes. alternation copolymer Ordered copolymer in which every other building is a different mer. azeotropic copolymer Copolymer in which the feet and composition of the copolymer are the same, blends Mixtures of different polymers on a molecular level may exist in one or two phases, block copolymer Copolymer that contains long sequences or runs of one mer or both mers. 

Equation (5.80) implies that the tensile strength of a mixture of polymer components (blend or alloy) can be related to the weight average of the component tensile strengths,... 

A polymer composition and a polymer film, which protects thermoplastics from chemical attacks by various polymer foam blowing agents is made of a blend or mixture of polymers and copolymers comprising (29) ... 

Flory-Huggins Theory. The simplest quantitative model for AGmx that includes the most essential elements needed for polymer blends is the Flory-Huggins theory, originally developed for polymer solutions (3,4). It assumes the only contribution to the entropy of mixing is combinatorial in origin and is given by equation 3, for a unit volume of a mixture of polymers A. and B. Here, pt and... 

A number of classes of polymer blends containing block copolymers have been studied. Namely, binary blends of a block copolymer with a homopolymer, ternary mixtures of a block copolymer with two homopolymers and blends of two block copolymers. Experimental and theoretical studies of all these mixtures are the subject of Chapter 6. 

Compared to bulk polymer mixtures, the interfacial behaviour of polymer blends is essentially different [341]. The demixing process in thin films is strongly affected by the thin film confinement and the interfacial interactions of the blend components with the confining phases (e.g., substrate and air). Even in the one-phase region of the phase diagram, preferential segregation of the components at one of the interfaces leads to a certain composition profile as a function of the distance from the free surfaces and the substrate plane [342,343]. In the... 

Compared to binary mixtures of low molecular fluids, the critical behavior of polymer blends has been much less explored so far. However, a number of interesting static and dynamic critical phenomena in polymer blends attract increasing attention [4, 5], Neutron, X-ray, and static light scattering experiments belong to the major techniques for characterizing the static properties of polymer blends. Photon correlation spectroscopy (PCS) has traditionally been the method of choice for the investigation of the dynamics of critical [6-9] and noncritical [10-12] polymer blends. 

First we treat diffusion processes within the homogeneous phase. The presence of a temperature gradient in binary fluid mixtures and polymer blends requires an extension of Fick s diffusion laws, since the mass is not only driven by a concentration but also by a temperature gradient [76] ... 

H.C. Park, R.M. Meertens, M.H.V. Mulder, C.A. Smolders, Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol), J. Membr. Sci. 90 (1994) 265-274. 

Polymers of different structures do not form homogeneous blends. Mixture of polymers that differ in structure and polarity are compatible with one another only to a very limited extent. They separate in the melt or at the latest after cooling in the solid state, as a result of weak interfaces between the components and local stress concentrations. Therefore, they cannot be... 

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