Prediction of average droplet size in flowing immiscible polymer blends

The paper is focused on calculation of the average droplet size in immiscible blends during their steady flow. Available theoretical and experimental results of studies of the droplet breakup and coalescence are utilized to derive the equations describing dynamic equilibrium between the droplet breakup and coalescence. New expression for the coalescence efficiency, reliably reflecting recent theoretical results, is proposed. The equation for the average steady droplet size, controlled by the stepwise breakup mechanism and coalescence of droplets with not very different sizes, is derived for blends containing up to 10–20 vol % of the droplets. For blends with above approximate 20 vol % of the droplets, the breakup by the Tomotika mechanism and coalescence in highly polydisperse system is modeled. Results of the derived equations are compared with experimental data; qualitative agreement is found for the dependence of the droplet size on the amount of the dispersed phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45250.     

Electroactive polymer blends

The rapid development of two new classes of electrically active polymer materials, electronically conducting and electroactive polymers and ion-conducting polymers respectively, offers new possibilities for application of both classes of material, especially in combination with each other. While some of these combinations have been attempted before, they all met serious problems due to poor interpenetration of the two polymers. The recent availability of solubilized and soluble electroactive and conductive polymers has greatly advanced the possibilities of reducing the interpenetration problem. Some experimental studies using the combination of solubilized electroactive polypyrrole with poly(ethylene oxide) in an electroactive polymer blend electrode for solid-state polymer batteries are discussed. The opportunities for using polymer blends for solid-state electrochemical polymeric devices, and avenues for the development of materials for such devices, are also reviewed.     

On the mechanism of compatibilization of polyolefin/liquid crystalline polymer blends with graft copolymers

The compatibilization mechanism of some compatibilizers for blends of polyolefins with a liquid crystalline polymer (LCP) was studied. Polyethylene (PE) and polypropylene (PP) were blended with a semirigid LCP (SBH) in a batch mixer, either with and without compatibilizers. The latter were two commercially available samples of functionalized polyolefins, that is, a PE‐g‐MA (HDM) and a PP‐g‐AA (Polybond 1001) copolymer and some purposely synthesized PE‐g‐LCP and PP‐g‐LCP copolymers. Microtomed films of the binary and the ternary blends were annealed at 240°C on the hot stage of a polarizing microscope and the changes undergone by their morphology were recorded as a function of time. The results indicate that the compatibilizers lower the interfacial tension, thereby providing an improvement of the minor phase dispersion. In addition to this, the rate of the coalescence caused by the high‐temperature treatment is appreciably reduced in the systems compatibilized with the PE–SBH and PP–SBH graft copolymers. Among the commercial compatibilizers, only Polybond 1001 displayed an effect comparable to that of the above copolymers. HDM improved the morphology of the as‐prepared PE blends, but failed to grant sufficient morphological stabilization against annealing‐induced coarsening. The results are discussed with reference to the chemical structure of the different compatibilizers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3027–3034, 2000     

聚合物共混相容性研究进展

介绍了聚合物共混相容性的热力学理论，讨论了相容性的实验表征方法，包括共混物形态和物性表征等，提出了改善聚合物相容性的重要途径及其进展。     

The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

Influence of compatibilizer addition on particle size and coalescence in TPU/PP blends

The effect of the addition of ethylenic copolymers with different acrylic acid contents on the morphology and coalescence of blends of thermoplastic polyurethane and polypropylene has been investigated. The blends were prepared using a twin-screw extruder. Although the copolymers were immiscible with both blend components and no chemical reaction at the interface could be found, the blend properties were improved. Copolymers that form a stable interfacial layer between the blend components lead to a stabilization of the morphology. Addition of a copolymer containing 4% acrylic acid results in a markedly reduced particle size and improved mechanical properties in addition to the stabilization against coalescence. The copolymer concentration was varied over a wide range. One percent of copolymer was enough to reduce the particle size; about 3 wt % of added copolymer was sufficient to stabilize the morphology against coalescence in quiescent melt and to achieve an optimum in mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2217–2226, 1997     

聚合物共混材料中氢键的研究进展

综述了近年来国内外聚合物共混材料中氢键的研究现状,着重对影响聚合物共混材料氢键强弱的因素、氢键的研究方法、氢键对聚合物共混材料性能的影响以及基于氢键作用制备相容性聚合物共混材料的方法进行总结。指出进一步研究多组分聚合物材料的氢键相互作用,可为制备可控性聚合物共混相容材料、实现功能化材料的构筑提供理论指导。     

Connectivity and spacing effects in hydrogen-bonding polymer solutions and blends

In recent experimental work, it was found that the number of hydrogen bonds in polymer mixtures is strongly influenced by chain-connectivity effects and the spacing of functional groups along the chain. In this article, the relationships between the equilibrium constants used to describe the number of hydrogen bonds in mixtures of various types (blends, solutions, random copolymers, etc.) is elucidated and described. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1273–1281, 1998     

Study on morphology of ternary polymer blends. I. Effects of melt viscosity and interfacial interaction

The morphology of some ternary blends was investigated. In all of the blends polypropylene, as the major phase, was blended with two different minor phases, ethylene–propylene–diene terpolymer (EPDM) or ethylene–propylene–rubber (EPR) as the first minor phase and high‐density polyethylene (HDPE) or polystyrene (PS) as the second minor phase. All the blends were investigated in a constant composition of 70/15/15 wt %. Theoretical models predict that the dispersed phase of a multiphase polymer blend will either form an encapsulation‐type phase morphology or phases will remain separately dispersed, depending on which morphology has the lower free energy or positive spreading coefficient. Interfacial interaction between phases was found to play a significant role in determining the type of morphology of these blend systems. A core–shell‐type morphology for HDPE encapsulated by rubber was obtained for PP/rubber/PE ternary blends, whereas PP/rubber/PS blends showed a separately dispersed type of morphology. These results were found to be in good agreement with the theoretical predictions. Steady‐state torque for each component was used to study the effect of melt viscosity ratio on the morphology of the blends. It was found that the torque ratios affect only the size of the dispersed phases and have no appreciable influence on the type of morphology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1129–1137, 2001     

Theory of competition between breakup and coalescence of droplets in flowing polymer blends

The Smoluchowski equation for the breakup and coalescence of dispersed droplets has been solved for flowing polymer blends. A scaling form for the distribution of droplet sized derived and published for a system of clusters with fragmentation and coagualation was used in our dervation. Equations are developed here for the average droplet size and for the characteristic time of transition to steady state flow of blends with a high content of the dispersed phase. Expressions reasonably describing the average size of droplets for all concentrations were obtained by a theory modification. Measured dependences of droplet size on the blend composition can be matched only if simultaneous collisions of three and more droplets are considered. The results of the theory indicate that the mechanism of droplet breakup (formation of pieces with the same or different volumes) has only a small effect on their average size in concentrated systems. The dependence of droplet size on the shear rate in flow is determined by properties of the blend components, and is generally nonmonotonic.     

An application of micro-thermal analysis to polymer blends

Micro-thermal analysis (micro-TA) is a new subsurface thermal analysis technology. The average of the DC signal is a function of the thermal conductivity, and the response to the AC modulation signal is a function of the thermal diffusivity of the subsurface. Using this technique, three images based on topography, thermal conductivity, and thermal diffusivity are obtained simultaneously. Specific areas and domains in these images can then be characterized by simply positioning the probe and performing a localized thermal analysis experiment. The technique has been used to study the phase separation process in a 50:50 (by weight) polystyrene (PS)–poly(vinyl methyl ether) (PVME) blend and natural rubber–nitrile rubber blends. For these polymer blends, considerable contrast between phases is obtained, based on thermal conductivity, whereas optical and electron microscopy would show them as being very similar. For example, it is difficult to image the morphology of natural and nitrile rubber blends by means of transmission electron microscopy, because of their similar chemical structures. Micro-TA gives an excellent image of the morphology of these natural–nitrile rubber blends. This opens a new way for rubber industries to study morphologies of rubber–rubber blends in general. In the 50:50 PS–PVME blend, annealed at 125°C, spinodal decomposition occurred. With increasing time, the domain size and the glass transition temperature of PS-rich domains increased, indicating that the concentration of PVME in the PS-rich phases decreases. The results imply that micro-TA can be used to image the composition in the near-surface or surface regions in multicomponent materials, if the resolution is high enough. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2136–2141, 2001     

Shear-induced fractal morphology of immiscible reactive polymer blends

The origin of shear-induced morphology of two-component immiscible reactive polymer blends is studied by the example of grafting and crosslinking multilayer systems of statistic terpolymer of ethylene, butyl acrylate, and maleic anhydride and statistic copolymers including polyamide and acid groups terminated by acid and/or amine groups. It is found that in contrast to the non-reactive system, the reactive polymer blends display pronounced hydrodynamic instabilities followed by the formation of branched fingers. The observed morphologies are shown to evolve towards the fractal structures. Their fractal dimensions depend on the type of chemical interactions between the blend components resulting either in grafted or crosslinked interfaces. It is shown that the obtained morphologies resemble the Laplacian growth patterns. A simple model of the interface chemical modifications is discussed to explain a physical origin of the observed shear-induced finger instability.     

Transient and steady-state deformations and breakup of dispersed-phase droplets of immiscible polymer blends in steady shear flow

Transient and steady-state deformations and breakup of viscoelastic polystyrene droplets dispersed in viscoelastic high-density polyethylene matrices were observed in a simple steady shear flow between two transparent parallel disks. By separately varying the elasticities of the individual blend components, the matrix shear viscosity, and the viscosity ratio, their effects on the transient deformation, steady-state droplet size, and the breakup sequence were determined. After the startup of a steady shear flow, the viscoelastic droplet initially exhibits oscillations of its length in the flow direction, but eventually stretches preferentially in the vorticity direction. We find that at fixed capillary number, the oscillation amplitude decreases with increasing droplet elasticity, while the oscillation period depends primarily on, and increases with, the viscosity ratio. At steady-state, the droplet length along the vorticity direction increases with increasing capillary number, viscosity ratio, and droplet elasticity. Remarkably, at a viscosity ratio of unity, the droplets remain in a nearly undeformed state as the capillary number is varied between 2 and 8, apparently because under these conditions a tendency for the droplets to widen in the vorticity direction counteracts their tendency to stretch in the flow direction. When a critical capillary number, Ca_c, is exceeded, the droplet finally stretches in the vorticity direction and forms a string which becomes thinner and finally breaks up, provided that the droplet elasticity is sufficiently high. For a fixed matrix shear stress and droplet elasticity, the steady-state deformation along the vorticity direction and the critical capillary number for breakup both increase with increasing viscosity ratio.     

Compatibilizing efficiency of copolymer precursors for immiscible polymer blends

An anhydride‐terminated polystyrene (PS‐b‐Anh) as a block copolymer precursor and a copolymer (PS‐co‐TMI) of styrene (St) and 3‐isopropenyl‐α,α‐dimethylbenzene isocyanate (TMI) as a graft copolymer precursor are chosen to investigate the effect of the type of the copolymer precursor on its compatibilizing and stabilizing efficiency for polymer blends. Results show that during the melt blending of the PS and PA6, the addition of PS‐b‐Anh dramatically decreases the size of the dispersed phase domains, irrespective of its molecular weight. This indicates that a diblock copolymer PS‐block‐PA6 (PS‐b‐PA6) is formed by a reaction between the terminal anhydride moiety of the PS‐b‐Anh and the terminal amine group of the PA6. When PS/PA6 (30/70) blends are annealed at 230°C for 15 min, their morphologies are much more stable in the presence of the PS‐b‐Anh block copolymer precursor than in the presence of the PS‐co‐TMI graft copolymer precursor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of a novel microcompounder for polymer blends and nanocomposite

In this article, we introduce a new type of small scale compounder. The compounder developed is for mixing of polymeric samples of 0.5–10 g. It consists of a heated cylindrical metal having two cylindrical cavities connected through a narrow channel and two cylindrical pistons, which squeeze molten polymers from one cavity to the other cavity through the narrow channel. During mixing procedure, the molten polymers flow from one cavity to the other cavity, repeatedly, and this operation generates the extensional flow in the converging and the diverging geometry. Because the compounder has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. We evaluated the mixing efficiency of the compounder by comparing with the commercialized small‐scale mixers including a cup and rotor batch mixer, an internal batch mixer, and a recirculating conical twin‐screw extruder. It was found that the compounder developed has many advantages over the existing small‐scale mixers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Elongational viscosity for miscible and immiscible polymer blends. I. PMMA and AS with similar elongational viscosity

The effects of miscibility and blend ratio on uniaxial elongational viscosity of polymer blends were studied by preparing miscible and immiscible samples at the same composition by using poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-co-styrene) (AS). Miscible polymer blend samples for the elongational viscosity measurement were prepared by using three steps: solvent blends, cast film, and hot press. A phase diagram of blend samples was made by visual observation of cloudiness. Immiscible blend samples were prepared by maintaining the prepared miscible samples at 200°C, which is higher than cloud points using a LCST (lower critical solution temperature) phase diagram. The phase structure of immiscible blends was observed by an optical microscope. The elongational viscosity of all samples was measured at 145°C, which is lower than the cloud-point temperature at all blend ratios. The elongational viscosity of PMMA and AS was similar to each other. The strain-hardening property of miscible blends in the elongational viscosity was only slightly influenced by the blend ratio, and this was also the case with immiscible blends. The strain-hardening property was only slightly influenced, whether it was miscible or immiscible at each blend ratio. Polydispersity in molecular weight for blend samples was not changed by GPC (gel permeation chromatography) analysis. Almost no change in the polydispersity of the molecular weight for blends and the similarity of elongational viscosity between PMMA and AS resulted in little influence of the blend ratio and miscibility on the strain-hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 757–766, 1999     

三元高分子共混体系Spinodal方程的理论推导

将经过改进的Flory状态方程(EOS)理论,引入到三元均聚高分子共混体系,得到三元体系的Flory状态方程。通过对高聚物共混自由能(△G^m)的热力学判据的讨论,得出三元均聚高分子共混体系相容性的临界条件,从而推导出三元均聚高分子共混体系的Spinodal方程。     

Viscoelastic effects in the coalescence of polymer particles

A study was made of the coalescence of linear acrylic resins over a much greater dynamic range than previously investigated. The rate of neck growth between a sphere and a flat slab of the same material was measured in situ by optical microscopy and found to exhibit a number of features typical of polymer viscoelastic response. Results are compared with independent measurements of the melt rheology (torsional creep compliance). An analytic approximation is proposed which allows the neck-growth kinetics to be predicted from the recoverable creep compliance and viscosity of the melt. It predicts qualitative trends consistent with the limited data on molecular weight, structure, and particle size variations. This analysis helps resolve some apparent contradictions among earlier studies and implies a qualitative difference in the coalescence mechanisms for large particles (5 μm) and colloids (<0.5 μm). In either case, the ultimate equilibration to homogeneous bulk mechanical properties requires times on the order of the terminal relaxation time, regardless of particle size. Evidence is presented that, in addition to the recognized effects of chain inter-diffusion, stress relaxation may play a role in the equilibration kinetics.     

Nanostructured polymer blends: Synthesis and structure

Nanostructured polymer blends prepared via anionic ring opening polymerizations of cyclic monomers in the presence of a pre-made polymer melt exhibit a number of special properties over traditional polymer blends and homopolymers. Here, we report on a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP) matrix and a surface-active compatibilizer (i.e. PC grafted onto a mPP backbone generated in situ) to yield a micro- and nanostructured polymer blends consisting of a polycarbonate (PC) minor phase, and a polypropylene (PP) major phase. By varying the processing conditions and concentration of the macrocyclic carbonate it was possible to reduce the size of the PC dispersions to an average minor diameter of 150 nm. NMR and TEM characterizations indicate that the PC dispersions do not influence crystal content in the PP phase. Overall, the results point to a simple strategy and versatile route to new polymeric materials with enhanced benefits.     

Effects of polymer matrix and processing on the conductivity of polymer blends

The influence of different hosts, processing conditions and conducting fillers on the percolation threshold (Φ_c) of the resulting conducting blends was investigated. Results indicate that microscopic properties, such as the dipole moments of the side‐groups, and distribution of these groups on the host polymer backbone govern the strength of host–filler interactions, and to a large extent, the value of Φ_c, rather than macroscopic properties such as surface tension. The grade of carbon black used in this experiment was found to be polar in nature and it resulted in lower values of Φ_c with the polar hosts, contrary to published literature. In general, melt blending has been shown to result in higher values of Φ_c when compared to hot pressing alone. In the latter method the conductive filler was found to be isolated at the grain boundaries of the polymer host, resulting in the formation of continuous conducting pathways at low filler concentration. © 2001 Society of Chemical Industry