Mixtures Of Incompatible Polymers Research Articles

Локализация наночастиц в смесях несовместимых полимеров

Локализация наночастиц в смесях несовместимых полимеров

Effects of the phases and the sizes of disperse particles on the elastic moduli of composites based on polymer mixtures

Different methods of calculating the elastic moduli of materials based on incompatible polymer mixtures are analyzed. These materials comprise fine dispersions of one of the polymers in a polymer matrix of another polymer. Different variants were analyzed: a dispersion of a solid polymer in an elastomer, where solid dispersion particles chemically react with the elastomer, or do not chemically interact with the elastomer matrix; a dispersion of a solid amorphous polymer of a particular chemical structure in a solid amorphous matrix of a polymer having a different chemical structure; and a dispersion of a partially crystalline polymer in a solid amorphous polymer. The dependence of the elastic moduli on the molar and volume fractions are defined by the van der Waals volumes of the components, the molecular masses of the repeating units, the densities of the components, the domain volumes, etc. These dependences are associated with the physical states and the phases (a rubber polymer, a crystalline polymer, or a solid amorphous polymer) of the mixed components.

Recycling of blends of acrylonitrile–butadiene–styrene (ABS) and polyamide

AbstractThe aim of this work is to evaluate routes to upgrade recycled engineering plastics, especially mixed plastics with acrylonitrile–butadiene–styrene copolymers (ABS) as the major component. A core‐shell impact modifier was successfully used to improve the impact strength of blends of ABS and ABS/polycarbonate (PC) blends recycled from the automotive industry. However, the presence of other immiscible components like polyamide (PA), even in small amounts, can lead to a deterioration in the overall properties of the blends. A styrene–maleic anhydride (SMA) copolymer and other commercial polymer blends were used to promote the compatibilization of ABS and PA. The core‐shell impact modifier was again found to be an efficient additive with regard to the impact strength of the compatibilized ABS/PA blends. The results obtained with fresh material blends were quite promising. However, in blends of recycled ABS and glass‐fiber‐reinforced PA, the impact strength did not exhibit the desired behavior. The presence of poorly bonded glass fibers in the blend matrix was the probable reason for the poor impact strength compared with that of a blend of recycled ABS and mineral‐filled PA. Although functionalized triblock rubbers (SEBS–MA) can substantially enhance the impact strength of PA, they did not improve the impact strength of ABS/PA blends because the miscibility with ABS is poor. The possibilities of using commercial polymer blends to compatibilize otherwise incompatible polymer mixtures were also explored giving promising results. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2535–2543, 2002

Polymers on Nanoperiodic, Heterogeneous Surfaces

Herein we establish a relationship between controlled nanoscale surface interactions and subsequent macromolecular ordering. Striped surfaces of oxide and metal are generated over large areas, where the stripe width is comparable to the size of a polymer molecule. Homopolymers are found to anisotropically dewet such surfaces, while incompatible polymer mixtures phase separate at the substrate/polymer interface on a molecular level. An orientation of lamellar block copolymer microdomains normal to the surface is found, when substrate and polymer length scales are commensurate.

A study of polycarbonate‐liquid crystal polymer blends

AbstractThe morphology and the thermal and mechanical properties of blends of bisphenol‐A polycarbonate (PC) with a wholly aromatic liquid crystal copolyester‐amide (Vectra‐B of Hoechst‐Celanese) are discussed with reference to the conditions used for their preparation. The blends made by extrusion behave as mixtures of incompatible polymers: the dispersed liquid crystalline phase is more or less oriented in the extrusion direction and acts as a reinforcing filler for the PC matrix. The behaviour of the blends prepared in a batch mixer depends strongly on mixing time. A slight decrease in the mechanical properties (especially tensile strength and elongation) accompanies the morphological changes associated with a progressive improvement in the compatibility of the two polymers, which finally leads to an apparently homogeneous material after 45 min mixing at 290°C and 150 rpm. These effects are interpreted in terms of chemical interactions taking place between the two components of the blends.

Adsorption of polymer mixtures from dilute and semidilute solutions

The adsorption of mixtures of incompatible polymers (polystyrene and polydimethyl siloxane) from solutions in a common solvent (ethyl acetate) in the cross-over region is studied. Adsorption isotherms from particular solutions and their mixtures in the concentration range before and after the critical concentration for overlapping of the polymer coils are given. To explain the isotherms obtained, thermodynamic polymer-solvent interaction parameters, the unperturbed dimensions of the macromolecules in the given solvent, and the dimensions of the polymer aggregates are determined as a function of the concentration of the solution. It is shown that the maximum aggregation is observed in the region before the critical concentration. On attaining critical concentrations the degree of aggregation is sharply decreased because of compression of the polymer coils.

Effect of the interface with a solid on the thermodynamics of interactions in binary mixtures of incompatible polymers

The thermodynamic interaction parameters χ 23 for a polythylene-polybutyl methacrylate are determined over a wide range of compositions by reverse gas chromatography and also on introduction of aerosil into the mixutre. The sorbate-polymer interaction parameters χ 1 i for mixture components containing different amounts of aerosil are determined simultaneously. Both χ 23 and χ 1 i are inversely related to the concentration of dispersed particles, indicating that the thermodynamic stability of the system has been increased. A model is proposed for a the structure of the polymer mixture interface and the values of the parameter χ 23(b.1.) corresponding to complete transition of the mixture components into the interface state are calculated. A new measure of the thermodynamic activity of the filler is proposed.

Laminar heterogeneous coatings obtained from mixtures of epoxy-oligomer and polymethylphenylsiloxane in binary solvents

Regularities were examined of the layer separation of incompatible polymer mixtures (oligoepoxide and polymethylphenylsiloxane) during evaporation of a general binary solvent from moderately thin layers. A phase diagram was plotted for an oligoepoxide-polymethylphenylsiloxane-acetone-toluene system. As a consequence of nonequilibrium ply separation the structure of laminar heterogeneous coatings depends to a large extent not only on the composition and thermodynamic characteristics of separating phases, but also on solvent volatility, layer thickness and the presence of a hardening agent.

Characterization and control of interfaces in emulsified incompatible polymer blends

AbstractInformation on the interfacial region in incompatible polymer mixtures can be gathered using various techniques including electron microscopy, thermal transition analysis, and more sophisticated methods such as nonradiative energy transfer (NRET). Selected examples are reported here to illustrate the exciting potentialities offered by diblock copolymer emulsifiers in controlling interfacial adhesion and devising high performance polymer blends.

The Rheology of the Fiber-Forming Process in Melts of Incompatible Polymers at Highly Uniform Shear

Abstract As was shown in some works, the morphology of mixtures of incompatible polymers depends on a number of factors, such as composition of the mixture, viscoelastic properties of the components, conditions of their mixing, and surface tension at the interphase. The rheological properties of the components and, consequently, the conditions of their mixing produce a tangible effect on the phase state of the mixture and its microstructure. The morphology, in turn, determines to a great extent the mechanical properties of the products based on mixtures of incompatible polymers. For example, the anisometry of the dispersed phase particles leads to anisotropy of the mechanical properties. In some cases, for instance, when a mixture of polymers is pressed through ducts, the dispersed phase is observed to form a fibrous structure, which results in one polymer being reinforced by the other.

Deformation of melts of mixtures of incompatible polymers in a uniform shear field and the process of their fibrillation

Fibril formation in mixtures of incompatible polymers, in this case polyethylene and polystyrene, has been studied with their melt being deformed in a uniform shear field. It has been found that when polyethylene is present in a smaller amount, it may form very long fibrils 5 to 8 µm in diameter in the deformed mixture. The formation of such fibrils is determined by the relationship between the viscosity ratio of the mixture components and shear stress. Also, just as in the case of a nonuniform shear field in a flow through a duct, fibril formation in melts of mixtures of incompatible polymers in a uniform shear field takes place upon reaching a certain shear stress. The lower the ratio between the viscosities of the fibril-forming polymer and the other component, the lower this shear stress.

Effect of Rheological Properties of Compounds on Fiber Formation in Mixtures of Incompatible Polymers

Abstract Mixtures of linear polyethylene with polystyrene were used in studying the fiber formation pattern of mixtures of incompatible polymers whose melts were forced through dies. Variables included the viscosity of the components, mixture preparation conditions, and shear stress. It has been established that the process of fiber formation occurs within a definite range of shear stresses, dependent on the viscosity ratio of the fiber-forming polymer and the polymer serving as the dispersion medium. When this ratio is equal to or less than unity, mixtures containing the fiber-forming component in the form of a finely dispersed phase yields continuous fibers several micrometers in diameter within a broad range of shear stresses. At greater values of the component viscosity ratio (tens of units), no fiber formation takes place in the mixtures.

Polymer blends—II. The use of solid phase dispersants to improve the properties of binary mixtures of incompatible polymers

The mechanical properties of three binary mixtures of incompatible polymers (LDPE/PP, LDPE/PS and LDPE/PVC) have been studied in the presence of potential solid phase dispersants. The results show that it is possible to achieve an acceptable level of toughness in the composite products for the re-use of the materials in demanding applications. It is suggested that the main factor necessary to achieve good impact resistance and elongation at break of the polymer is the presence of a rubbery interphase between the heterophases. Satisfactory tensile strength on the other hand depends more on the dispersant properties of the third component.

Viscosity of solutions of incompatible polymer mixtures

Experiments were carried out to determine the viscosity of toluene solutions of polyisoprene rubber mixed with PS of varying MW, with polymethylphenylsiloxane and with low molecular PE. A theoretical analysis has brought to light relations between the viscosity of these incompatible polymer systems and the fraction of a new phase. It was found that the new phase concentration is influenced by the concentration and composition of a system and by MW. These relations are described by an equation derived for the viscosity of incompatible polymer solutions.

The applicability of the concept of free volume to processes of glass transition in incompatible polymer mixtures

A study was made of the behaviour at different temperatures of incompatible polymer mixtures by dynamic dilatometry and isothermal compression. Both homopolymers and polymer mixtures were examined. This study seeks to verify the applicability of the concept of free volume to incompatible polymer mixtures.

Morphological evaluation of changes in the supercrystallite structure of two component polymer mixture obtained from melt

An investigating the morphology of incompatible polymer mixtures it was shown that the homogeneity of supermolecular structures observed using the electron microscope, is not evidence of compatibility on a supermolecular level, but is merely the result of a weak optical contrast. Individual morphological structures can be detected in these systems by transfer to the oriented state. Separation into two clearly expressed phases in this case distinctly indicates the absence of compatible supermolecular structures. When an intermediate layer is formed at the interface, this is a typical sign of morphologically incompatible polymers.

Effect of graft-copolymer on the structure and behaviour of solid mixtures of cellulose acetate and polyacrylonitrile

Mixtures of polymers may be used effectively to modify the properties of high molecular weight materials. This method is based on the theoretical possibility of controlling the properties of these materials by modifying their chemical compositions and molecular structures by means of the appropriate selection of miscible polymers. The properties of polymer mixtures largely depend on the effect of the components on one another, i.e. on their compatibility [1–3]. Molecular mixtures of compatible polymers are really materials with completely new properties, and articles made from them may possess good mechanical properties. However, compatible polymer systems are by no means commonly found. Mixtures of incompatible polymers generally have a coarse type of structure which is reflected in poor mechanical properties. If on the other hand it is somehow found possible to obtain a highly dispersed mixture from incompatible polymers, the fabricated articles may combine the properties of the miscible components so that the strength properties will be superior to those of any of the components taken separately. One method of increasing the homogeneity and stability of mixtures of incompatible polymers is by introducing a graft-copolymer into the system [1, 4]. In previous investigations [4, 5] we showed that if we take a mixture of cellulose acetate (CA) and polyacrylonitrile (PAN), which are incompatible, and then add CA-PAN graft-copolymer to this mixture, considerable improvements in the homogeneity and stability of mixtures of the solutions are obtainable, although the introduction of the graft-copolymer does not prevent the separation of CA and PAN, i.e. it creates kinetic compatibility. This tends to enhance the mechanical properties of the fibre obtained from the mixture. It may be assumed that the condition of the initial solution that is to be modified by the graft-copolymer will largely be reflected in the structure of the resulting fibre, and this will provide the possibility of modifying the mechanical properties of the material. In this paper we are reporting on a study of the structure of mixtures of CA and PAN in the condensed state to determine the particular changes it may undergo owing to the introduction of the graft-copolymer. The structure is investigated in relation to certain mechanical properties of the products.

The adsorption behavior of polymer mixtures

AbstractThe interfacial behavior of several mixtures of incompatible polymers has been examined at 24°C using finely divided silica as the adsorbent and trichloroethylene as the solvent. Displacement experiments have shown that poly (ethylene‐vinyl acetate) (EVA) (20.4% by wt. vinyl acetate) completely displaces polystyrene (PS) from silica within 1 hr. while poly (vinyl acetate) (PVAc) displaces ethyl cellulose (EC) within 3 hrs. A given EVA copolymer displaces one of lower vinyl acetate content; EVA (44.2% vinyl acetate) is displaced by EC. EC tends to displace poly (methyl methacrylate) (PMMA), but the process is slow and incomplete. The fraction of adsorbed polymer segments attached directly to silica, as determined by infrared spectroscopy, can be correlated with the displacement results. Experiments with PS/PVAc, PS/PMMA, and polydimethylsiloxane/EVA (20.4% vinyl acetate) mixtures have shown that adsorbance values of the preferentially adsorbed PVAc, PMMA, and EVA are increased by the second polymer, when polymer concentrations which cause phase separation are approached. Increases in adsorbance are accompanied by lower infrared bound fraction values, implying formation of a more extended adsorbed layer.