Formation of dispersed phase in incompatible polymer blends: Interfacial and rheological effects

The formation of dispersed phase in blends of incompatible polymers during melt extrusion with a co-rotating twin screw extruder was studied, using nylon and polyester as the matrix and ethylene-propylene rubbers as the dispersed phase. A master curve is obtained, i.e., Gηmα/γ = 4p^±0.84, where G is the shear rate, γ the particle diameter, η the interfacial tension, η_m the matrix viscosity, η_d the dispersed-drop viscosity, and p = η_d/η_m. The plus (+) sign applies for p > 1, and the minus (?) sign for p < 1. Thus, the dispersed-drop size is directly proportional to the interfacial tension and the ±0.84 power of viscosity ratio. The dispersed drops are the smaller, when the interfacial tension is the lower and the viscosity ratio is the closer to unity. The interfacial tension is largely controlled by the polarities of the two phases, and can be varied over several orders of magnitude by using appropriate dispersants.     

Morphology evolution during cooling of quiescent immiscible polymer blends: matrix crystallization effect on the dispersed phase coalescence

The influence of the matrix crystallization on the coalescence of the dispersed phase particles, in quiescent immiscible polymer blends, is a topic that is scientifically addressed scarcely. The coarsening of the phase structure that is induced by the matrix crystallizing domains was studied using the well-established system comprising a polypropylene and an ethylene–propylene rubber (PP/EPR blends). This subject is of great importance as the effectiveness in the toughening of PP is directly determined by the EPR particle size. Cooling experiments were commenced for resolving the correlation among the imposed cooling conditions, the formed matrix crystalline morphology, and the coalescence of the dispersed phase particles. A confirmation of the profound effect of the PP crystallization on the coalescence of EPR particles was undoubtedly obtained. The contribution of the crystallization to the coalescence of the dispersed phase particles is largest at a finite rate of cooling. A thorough discussion regarding the observed effects, encompassing a potential rejection or an engulfing of the dispersed phase particles by the growing crystallites, was undertaken.     

A polarized light scattering approach for dispersed phase morphology characterization in simulated polymer blends

A light scattering technique using a normal-incidence polarized light beam for the characterization of skin/core simulated polymer blend samples is described. The patterns of reflected, polarized scattered light from an inhomogeneous blend were captured using a video camera. The blend was illuminated from a focused laser source. The simulated samples were constructed by incorporating glass fibers (skin) and glass microspheres (core) in a polymer matrix. Asymmetrical patterns were obtained. They reflect the anisotropic nature of the near-surface morphology. Moreover, the change of the anisotropy ratio of the iso-intensity curves plotted, as a function of distance from the position of the incident laser beam on the sample, gives information about the skin and the core content as well as the skin thickness.     

Morphology development in immiscible polymer blends during crystallization of the dispersed phase under shear flow

Crystallization under shear of dispersed polybutylene terephthalate (PBT) fibers in copolymer polyethylene-methyl acrylate matrix (EMA) was investigated using a hot optical shear device. Crystallization during isotherm and cooling process was studied. Static crystallization experiments were carried out for comprehension purpose. Differential scanning calorimetry (DSC) analysis was performed in order to predict the crystallization behavior of PBT. Shear enhancement of its crystallization was thus demonstrated from rheological experiments. Interfacial tension of EMA/PBT blend was experimentally measured using the hot optical shear device. Theoretical break-up times of PBT fibers were also calculated. Control of the morphology through shear rate and crystallization time balance was demonstrated. Static crystallization experiments show that decreasing crystallization time favor fibrillar morphology. Breaking up of fibers was brought to the fore during dynamic crystallization experiments due to heterogeneous development of the crystallization along the fiber. During the dynamic crystallization, rapid quenching enables fibrillar morphology. Long crystallization times associated with low shear rates allow nodular morphology.     

The melt elasticity of polymer blends: Polystyrene/poly(methyl methacrylate)

Samples of general-purpose polystyrene and poly(methyl methacrylate) were melt blended in a special mixer–extruder over the complete range of compositions from 100% polystyrene to 100% poly(methyl methacrylate). The blends were characterized for their melt rheological characteristics in a melt elasticity tester which measured their stress–strain behavior and strain recovery characteristics as a function of time. In addition, the blends were processed through a laboratory fiber spinning apparatus wherein the spinline tension was measured. Large maxima in the amount of recoverable strain, in the time for the strain recovery to finish, and in the melt tension were observed at a weight percent composition of 40% polystyrene and 60% poly(methyl methacrylate). The melt stress-strain curves showed double yield points at certain compositions. The results are discussed in terms of a model consisting of two interpenetrating continuous phases.     

Rheo-Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior

The phase behavior of polymer blends under simple shear flow has been studied using a custom-designed rheo-optical system consisting of a two-dimensional small-angle light scattering (SALS) device incorporated into a conventional rheometer. Two-dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PVME) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear-induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PVME blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright-streak pattern from a transient dark-streak pattern for a polymer blend system under shear. Rheo-microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a streak pattern by SALS. The relationship between the two phenomena has not yet been established.     

Influence of elasticity on dispersed‐phase droplet size in immiscible polymer blends in simple shearing flow

The influence of elasticity of the blend constituent components on the size and size distribution of dispersed‐phase droplets is investigated for blends of polystyrene and high density polyethylene in a simple shearing flow. The elasticities of the blend components are characterized by their first normal stress differences. The role played by the ratio of drop to matrix elasticity at fixed viscosity ratio was examined by using high molecular weight polymer melts, high density polyethylene and polystyrene, at temperatures at which the viscosity ratios roughly equaled each of three different values: 0.5, 1, and 2. The experiments were conducted by using a cone‐and‐plate rheometer, and the steady‐state number and volume‐mean averages of droplet diameters were determined by optical microscopy. After steady‐state shearing, the viscoelastic drops were larger than the Newtonian drops at the same shearing stress. From the steady‐state dispersed‐phase droplet diameters, the steady‐state capillary number, Ca, defined as the ratio of the viscous shearing stress over the interfacial tension stress, was calculated as a function of the ratio of the first normal stress differences in the droplet and matrix phases. For the blend systems with viscosity ratio 0.5, 1 and 2, the values of steady‐state capillary number were found to increase with the first normal stress difference ratio and followed a power law with scaling exponents between 1.7 and 1.9.     

Nonuniformity of phase structure in immiscible polymer blends

This article is focused on the phase structure development in immiscible polymer blends during melt mixing. Nonuniformity of the phase structure, i.e., the coexistence of areas containing particles with markedly different size distribution, was detected in quenched and compression molded samples of a number of various blends prepared by long and intensive mixing in the chamber of a Plasticorder. The same effect was found also for polystyrene/polyamide blends prepared in a twin‐screw extruder. It was shown that neglecting nonuniformity of the phase structure can lead to considerable error in evaluation of the effect of system parameters on the blend morphology. The reasons for the effect were discussed and it was found that inhomogeneous flow field in mixers is a plausible explanation of the nonuniform phase structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

The effect of the viscosity ratio of dispersed phase to matrix on the rheological,morphological, and mechanical properties of polymer blends containing a LCP

The effect of the viscosity ratio of the dispersed LCP phase to the polystyrene/poly(phenylene oxide) (PS/PPO) thermoplastic matrix on the rheological, morphological, and resultant mechanical properties of the LCP blends was investigated. The viscosity of PS/PPO is largely dependent on the blend composition, so that different levels of viscosity ratios of dispersed LCP phase to PS/PPO thermoplastic matrix are obtained by using PS/PPO premixtures of different blend ratios as a thermoplastic matrix. When the viscosity of the LCP dispersed phase is lower than that of the thermoplastic matrix, finely distributed fibril structure of LCP is obtained. Tensile modulus of injection molded specimens show a positive deviation from the additive rule when the viscosity ratio (η_LCP/η_matrix) is smaller than unity. These improvements in tensile modulus are attributed to the formation of finely distributed LCP fibrils. © 1996 John Wiley & Sons, Inc.     

Quantitative prediction of particle size of dispersed phase in elastomer-plastic blends

In investigating the relationship between the particle size of the dispersed phase in a polymer blend and the physical properties of the resulting product, the effects of conditions of blending, viscosity difference, and volume fraction, etc., are usually observed and studied. This approach is uncertain since blending is a complex process. From a theoretical background similar to that of N. Tokita's, but using a different mathematical and experimental treatment, a complex factor composed of shear rate, apparent viscosity of the system, and volume fraction of the dispersed phase is proposed. This factor is found to provide a linear relation with the mean radius of dispersed particles as expressed by where R is the mean particle radius in the dispersed phase; S is shear rate of mixing;, V is apparent viscosity of the system; F is volume fraction of the dispersed phase; B is an experimental constant relating to breaking energy of the dispersed phase and interfacial tension; and A is also a constant relating to interfacial tension and the probability that a collision will result in a coalescence.     

Homogeneous nucleation of the dispersed crystallisable component of immiscible polymer blends

Summary Immiscible melt mixed blends of a crystallisable polyolefin (isotactic polypropylene, PP) and atactic polystyrene (PS) were prepared in a wide composition range. It was found that when PP is the major component in the blend its crystallisation behaviour is not affected by blending it with PS. However if PP is the minor component, it will be dispersed in the immiscible PS matrix, hence the nucleation mechanism changes from predominantly heterogeneous to predominantly homogeneous as long as the size of the dispersed PP droplets is below a critical value (of the order of 1–2 m).     

Entanglement fluctuation during phase separation in polymer blends

For perhaps the first time, the dynamics of liquid-liquid phase separation was studied by time-resolved mechanical spectrometry in order to establish the relationship between blends' properties and the phase structures during spinodal decomposition (SD). The selected system was chlorinated polyethylene (CPE)/ethylene-vinyl acetate copolymer (EVA). It was found that in the early and intermediate stage of SD, the storage modulus (G′) and the loss modulus (G″) increase with time after the initiation of the isothermal phase separation; in the later stage, G′ and G″ decrease as phase separation proceeds. An entanglement fluctuation model was presented to manifest this phenomenon; it was found that the rheological behavior agrees well with the expections of the model in the early stage. For the later stage, the reduction of G′ and G″ can be attributed to the increment of phase-domain size. © 1993 John Wiley & Sons, Inc.     

Filler effect on polymerization kinetics and phase separation in polymer blends formed in situ

The kinetics of formation of a mixture of two polymers [poly(methyl methacrylate) and polyurethane] in situ in the course of two simultaneously proceeding reactions was studied in the presence of various amount of a filler (fumed silica). It was shown that the filler affects the rates of both reactions. In addition, the filler exerts an influence on the phase separation induced by the chemical reaction increasing the amount of a filler increases the time for the onset of phase separation. The effects observed may be explained both by the increase in the viscosity of the reaction system due to introduction of a filler and by selective adsorption of reaction system components at the interface with filler particles. In all cases, phase separation in the early stages of reaction proceeds in a four‐component system (two polymers formed and two initial compounds) and obeys the spinodal mechanism. It is also shown that the final morphology is determined far from the end of the reaction and before establishing the equilibrium state. © 2003 Society of Chemical Industry     

The effect of matrix toughness and dispersed elastomer phase on the brittle-ductile transition in PP/HDPE/SBS blends

In this paper the sbrittle-ductile transition of polypropylene, high density polyethylene, and a styrene-butadiene-styrene triblock copolymer (PP/HDPE/SBS) ternary blends is investigated for fixed compositions and prepared under various conditions. The morphology of the SBS dispersed phase particles and impact strength of the PP ternary blends is closely related to the processing conditions. There is a sharp Brittle-Ductile transition for the ternary blends when interparticle distance T becomes less than the critical interparticle distance T_c. Both the impact strength in general and more specifically, T_c depend upon the toughness of the PP/HDPE composite matrix.     

The simulation of phase diagrams for polymer blends at various pressures

A procedure is described for the simultaneous prediction of the binodal and spinodal curves of polymer mixtures at various pressures using a form of the equation-of-state theory of Flory and co-workers. The results of the calculation are compared with experimental results for the effect of pressure on the cloud points of both oligomer mixtures showing upper critical behavior and polymer mixtures showing lower critical behavior. The procedure successfully predicts the sign of the effect and its magnitude within the experimental and theoretical uncertainties for the systems studied.     

Compatibilizing effects of block copolymer mixed with immiscible polymer blends by solid-state shear pulverization: stabilizing the dispersed phase to static coarsening

A continuous, industrially scalable process called solid-state shear pulverization (SSSP) leads to compatibilization of polystyrene (PS)/high-density polyethylene (HDPE) blends by addition of a commercially available styrene/ethylene-butylene/styrene (SEBS) triblock copolymer. Partial or full compatibilization is characterized by a reduction or elimination of coarsening of the dispersed-phase domains during high-temperature (190 °C), static annealing. In the case of a 90/10 wt% PS/HDPE blend, processing with 3.5 wt% SEBS block copolymer by SSSP yields a coarsening rate that is reduced by a factor of 10 (six) relative to a melt-mixed blend without copolymer (with 3.5 wt% SEBS block copolymer). Addition of 5.0 wt% SEBS block copolymer to the 90/10 wt% PS/HDPE blend during SSSP yields a reduction in coarsening rate by a factor of thirty relative to a melt-mixed blend without copolymer. With an 80/20 wt% PS/HDPE blend, pulverization with 10 wt% SEBS block copolymer yields cessation of coarsening when the average dispersed-phase domain diameter reaches 1.6-1.7 μm. The implications of these results for developing a new, technologically attractive method for achieving compatibilization of immiscible polymer blends are discussed.     

Prediction of dispersed phase hold-up in pulsed perforated-plate extraction columns

Published experimental results for the dispersed phase hold-up in pulsed perforated-plate extraction columns are considered. Based on 1574 data points in the absence of solute transfer for 14 liquid-liquid systems a single empirical correlation is developed which predicts the hold-up in the mixer-settler, transition and emulsion regions of operation to within 17% from the physical properties and operating variables. The same correlation with modified constants (but unchanged indices) can be used when solute transfer occurs in either direction. Futhermore, this correlation also predicts the boundary between mixer-settler and transition regions of operation.     

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.     

Prediction of the gas permeability of heterogeneous polymer blends

A recently introduced predictive scheme is used to calculate the permeability of various types of heterogeneous polymer blends, which are characterized by the ratio of the permeability of constituents in the range 10–10,000. The scheme combines a two‐parameter equivalent box model and the data on the continuity of constituting phases acquired by modifying equations proposed by the percolation theory; it takes into account the permeability of components and the interval of phase duality (co‐continuity) delimited by the critical volume fractions of components v_1cr and v_2cr. The scheme can be used in two ways: (i) permeability of blends predicted by using the “theoretical” value of parameters v_1cr = v_2cr = 0.16 should be regarded as a first approximation which may not well approximate experimental data due to the fact that real v_1cr and v_2cr are affected by relative viscosities of the components, interfacial energy, conditions of blend mixing, phase structure coarsening, etc.; (ii) conversely, by fitting experimental data, it is possible to determine v_1cr and v_2cr for the studied system; thus the scheme can be alternatively viewed as an efficient tool for phase structure analysis of polymer blends.     

Prediction of drop diameter,hold-up and backmixing coefficients in liquid-liquid spray columns

The available literature data for the drop diameter, hold-up and backmixing coefficients were tested experimentally in a pilot plant size spray column. For all these parameters correlations were found which gave results in agreement with the experimental data so that reasonable prediction is possible. Different equations were compared and the ones giving the best fit are recommended.