Tuning gradient microstructures in immiscible polymer blends by viscosity ratio

Bioinspired gradient microstructures provide an attractive template for functional materials with tailored properties. In this study, filaments with gradient microstructures are developed by melt-spinning of immiscible polymer blends. The distribution of the gradient morphology is shown to be controlled by the viscosity ratio of polymers as well as the geometry of the capillary die. Distinct microstructure gradients with long thin fibrils near the surface region and short large droplets near the center region of the filament, as well as the inverse pattern, are formed in systems with different viscosity ratios. The shear flow field in the capillary can elucidate the formation mechanisms of gradient morphologies during processing. The results demonstrate how the features of a gradient microstructure can be tailored by the design of capillary geometry and processing conditions. The viscosity ratio is then introduced as an adjusting tool to control the gradient morphology in a given processing setup. In consequence, this study provides novel design routes for achieving gradient morphologies in immiscible polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48165.     

Effect of the dispersed phase fraction on particle size in blends with high viscosity ratio

It has been reported that for polymer blends with high viscosity ratio (>1), the size of the dispersed particles decreases with increasing volume fraction of the dispersed phase. In order to explain this effect, an equation was derived for the affine deformation of an imaginary plane of the dispersed phase in stratified two‐phase steady, simple, shear flow. The model predicts that for viscosity ratio >1, the deformation rate increases with volume fraction of the dispersed phase, and the shear stress also increases, leading to an increase of the breakup time. Therefore, the total deformation of the dispersed phase, before breakup, increases with increase of volume fraction, resulting in a decrease of the size of the dispersed phase particles. Accordingly, one can expect that in industrial mixers, the particle size of the blends should decrease as the volume fraction increases, if coalescence is suppressed. Experiments were carried out in a Haake batch mixer, using polyethylene/polyamide‐6 blends compatibilized by adding maleic anhydride grafted polyethylene. Particle size decreased up to 20 wt% polyamide‐6, at 100, 150, and 200 RPM, and increased between 20 and 30 wt%. The decrease of the particle size is mainly due to increased deformation of the dispersed phase. The increase of the particle size above 20 wt% is due to coalescence at high fractions.     

Effect of the viscosity ratio on the morphology and properties of PET/HDPE blends with and without compatibilization

The influence of the molecular weight of polyethylene on the morphology and mechanical properties of blends of high‐density polyethylene (HDPE) dispersed as droplets in a poly(ethylene terephthalate) (PET) matrix at various compositions was investigated. The difference of morphologies can be easily explained by the influence of the molecular weight on the viscosity ratio and therefore, on the critical capillary number. The compatibilizing efficiency of copolymers containing glycidyl methacrylate groups was also addressed in relation to their nature, the protocol for their drying and the molecular weight of the HDPE phase. The increase of adhesion between PET and HDPE was found to have a larger influence on tensile properties than the reduction of interfacial tension. The amount of compatibilizer needed for adhesion improvement depends on the interfacial area that is defined by both the interfacial tension and viscosity ratio of the components. A qualitative relation between the optimum amount of compatibilizer and the critical capillary number can be written. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phase continuity detection and phase inversion phenomena in immiscible polypropylene/polystyrene blends with different viscosity ratios

Blends of polypropylene (PP) and polystyrene (PS) were prepared in a twin-screw extruder and studied in a wide range of compositions. Phase continuity was first determined using selective solvent extraction. Subsequently, dynamic stress rheometry and dynamic mechanical analysis were used to detect the co-continuity and phase inversion compositions in the melt and the solid states. It appears that the phase inversion occurs in a domain rather than at a single point. The evaluation of the storage modulus of PP/PS blends in the melt at a constant low frequency gives information about the co-continuity, as far as the onset of co-continuity and phase inversion composition of the PS phase are concerned. The evaluation of the storage modulus and mechanical loss factor at a constant high temperature, or the glass transition temperature intensity allowed to precisely detect the phase inversion composition. The fractionated or bulk crystallization behavior of the crystallizable PP phase in the PP/PS blends can also be used to identify the matrix/dispersed phase or co-continuous phase morphology. Several semi-empirical models using the dynamic viscoelastic properties of blend components have been applied to detect the phase inversion composition. An extensive data set presented, can also be used to guide future modeling.     

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     

Development of dispersed phase size and its dependence on processing parameters

Through measurement of phase dimension via laser scattering, phase morphology development in immiscible blends of polyamide 12/poly(ethylene glycol) (PEG) with an extremely high viscosity ratio was investigated. The blends were prepared by melt blending in a batch mixer. The objective was to examine the influence of mixing time, rotor speed, as well as blending temperature on the size distribution of the minor phase. It is of interest that the breakup process of the dispersed PA 12 phase was observed for the blend systems even for extremely high viscosity ratios of ≤ 10²–10³. Mixing time had a significant effect on the development of dispersed phase size distribution. It was found that the bulk of particle size reduction took place very early in the mixing process, and very small droplets with a diameter of 0.1–10 μm were produced. The number of small particles then decreased, resulting in a larger average particle size. With further prolonged mixing, the particle size levels off. The particle size and its distribution were also found to be sensitive to the rotor speed. The average particle size decreased with increased rotor speed. The effect of blending temperature on size and size distribution, which has seldom been studied, was also examined in this work. When the blending temperature altered from 190°C to 220°C, the size and its distribution of the dispersed phase varied considerably, and the change of viscosity ratio was found to be the key factor affecting the dispersed phase size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3201–3211, 2006     

Morphological study of two‐phase polymer blends during compounding in a novel compounder on the basis of elongational flows

A new laboratory‐scale mixing device based on an original concept was built and tested. This device has important technical features such as tightness to liquids and gases, the possibility of direct specimen molding after mixing, and easy handling of reactive systems. In comparison with existing laboratory mixers, the flow in this mixer is characterized by a high contribution from elongational flow. Morphological data on model polystyrene/poly(methyl methacrylate) blend systems have proved the high distributive and dispersive mixing efficiency in comparison with a classical rotational batch mixer. The influence of different experimental parameters such as the flow rate, mixing time, mixing element geometry, and viscosity ratio of blends is characterized and discussed. Much finer dispersions have been obtained with this new device versus those obtained with a conventional mixer with equivalent specific energy input. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of the viscosity ratio on polyolefin ternary blends

Polyolefin binary and ternary blends were prepared from polypropylene (PP), an ethylene–α‐olefin copolymer (mPE), and high‐density polyethylene (HDPE) on the basis of the viscosity ratio of the dispersed phase to the continuous phase. In PP/mPE/HDPE blends, fibrils were observed when the dispersed‐phase (mPE/HDPE) viscosity was less than that of PP, or when the viscosity of mPE was less than that of PP, although the viscosity of mPE/HDPE was greater than that of PP. The notched impact strength and mechanical properties such as the yield strength, flexural modulus, and hardness of PP/mPE binary blends further increased with the addition of HDPE according to the type of HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4027–4036, 2004     

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.     

Influence of rubber particle size on mechanical properties of polypropylene–SEBS blends

Isotactic polypropylene blends with 0–20 vol % thermoplastic elastomers were prepared to study the influence of elastomer particle size on mechanical properties. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) was used as thermoplastic elastomer. SEBS particle size, determined by means of transmission electron and atomic force microscopy, was varied by using polypropylene and SEBS of different molecular weight. With increasing polypropylene molecular weight and, consequently, melt viscosity and decreasing SEBS molecular weight, SEBS particle size decreases. Impact strength of pure polypropylene is almost independent of molecular weight, whereas impact strength of polypropylene blends increases strongly with increasing polypropylene molecular weight. The observed sharp brittle–tough transition is caused by micromechanical processes, mostly shear yielding, especially occurring below a critical interparticle distance. The interparticle distance is decreasing with decreasing SEBS particle size and increasing volume fraction. If the polypropylene matrix ligament between the SEBS particles is thinner than 0.27 μm, the blends become ductile. Stiffness and yield stress of polypropylene and polypropylene blends increase with increasing polypropylene molecular weight in the same extent, and are consequently only dependent on matrix properties and not on SEBS particle size. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1891–1901, 1998     

The viscosity of immiscible polymer blends: influences of the interphase and deformability

The viscosity of immiscible polymer blends has been studied via application of certain aspects of rheology. A symmetric mixture rule was derived, and the deviations from the ‘additivity rule’ have been associated, essentially, with the properties of the interphase, with its influence on the effective volumes of the two polymers constituting the blend and with the deformability of both the interphase and the disperse phase. The rule predicts a positive deviation for a mixture with a disperse-phase viscosity (η_d) greater than that (η_m) of the continuous medium, and a much higher-viscosity interphase, i.e. η_i å η_d ≥ η_m. Negative deviation is to be expected when the interphase has a much lower viscosity than those of the two pure polymers (η_d, η_m å η_i) in the blend. The viscosity and strength of the interphase depend mostly on the specific thermodynamic interactions that led to its creation.     

Effect of viscosity variation with temperature on the compounding behavior of immiscible blends

Morphology development in the compounding of immiscible blends depends on a number of material properties and process conditions. In this work, different model blend systems are considered to outline the effects of the relative transition temperatures and viscosities of the blend components. We focus on the evolution of blend morphology, specifically phase continuity. A framework based on these factors is presented for analyzing the compounding behavior of immiscible blend systems. With the minor component at 10 wt%, it was found that phase inversion during compounding occurred in blends with a viscosity ratio of less than 0.2, independent of the relative transition temperatures. It was shown that in these constant mixer temperature runs, the torque trace was not a completely reliable indicator of phase inversion. When a temperature ramping program was used, the lower melting point component formed the continuous phase initially, independent of the viscosity ratio. Quantitative measures of the amount of minor component which was continuous at different mixing times were made using selective extraction in a Soxhlet apparatus. Results from compounding runs of polycarbonate/ polyethylene, an amorphous copolyester/polyethylene and polybutylene/polycaprolactone blends are presented.     

Effect of crosslinking on polyamide 11/butadiene-acrylonitrile copolymer blends

The effect of crosslinking of polyamide 11 and butadiene-acrylonitrile copolymer (nitrile rubber) was studied. The effect of static and dynamic crosslinking on blending are described. Static and dynamic crosslinking do not significantly improve impact strength of low-rubber-content PA11/NBR blends. For blends with dynamic crosslinking and high rubber contents, mechanical properties including impact strength improve. Thermal behavior of crosslinked PA11/NBR blends were studied by DSC and DMA. SEM was used for investigation of the effect of crosslinking on particle size and particle size distribution, phase morphology, and fracture surface morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1605–1611, 1997     

Effect of composition on the linear viscoelastic behavior and morphology of PMMA/PS and PMMA/PP blends

Here, the effect of concentration on the morphology and dynamic behavior of polymethylmethacrylate/polystyrene (PMMA/PS), for PS with two different molecular weight, and polymethylmethacrylate/polypropylene (PMMA/PP) blends was studied. The blends concentrations ranged from 5% to 30% of the dispersed phase (PS or PP). The dynamic data were analyzed to study the possibility of inferring the interfacial tension between the components of the blend from their rheological behavior using Palierne [Palierne JF. Rheol Acta 1990;29:204-14] [1] and Bousmina [Bousmina M. Acta 1999;38:73-83] [2] emulsion models. The relaxation spectrum of the blends was also studied. The dynamic behavior of 85/15 PS/PMMA blend were studied as a function of temperature. It was possible to fit both Palierne and Bousmina's emulsion models to the dynamic data of PMMA/PS blends, to obtain the interfacial tension of the blend. This was not the case for PMMA/PP. The relaxation spectrum of both blends was used to obtain the interfacial tension between the components of the blends. The values of interfacial tension calculated were shown to decrease when the concentration of the blends increased. It was shown using morphological analysis that this phenomenon can be attributed to the coalescence of the dispersed phase during dynamic measurements that occurs for large dispersed phase concentration. When the ‘coalesced’ morphology is taken into account in the calculations the interfacial tension inferred from rheological measurement did not depend on the concentration of the blend used. The values of interfacial tension found analyzing the dynamic behavior of one of the PMMA/PS blend were shown to decrease with temperature.     

Compatibilized iPP/aPS blends: The effect of the viscosity ratio of the components on the blends morphology

More than 25 PP/PS/SEP blends, where PP is isotactic polypropylene, PS is atactic polystyrene, and SEP is poly(styrene‐block‐ethylene‐co‐propylene), were prepared. The main objective of this study was to investigate the influence of PP/PS viscosity ratio, λ_TM, on the blends' morphology. It was shown that λ_TM strongly influenced not only the overall morphology of the blends, but also the morphology of SEP, which exhibited as many as five different types of structure when blended with PP and/or PS. SEP was found an efficient compatibilizer of PP/PS blends as it decreased the average particle size in all studied systems. An interesting “by‐product” of this work was the discovery of a brand‐new type of polymer morphology, which was called morel structure. The characteristic feature of the morel structure was PS matrix compartmentalized by SEP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2236–2249, 2006     

On modeling the composition dependence of the bulk viscosity of immiscible polymer blends

The purpose of this article is to clear the confusion in the literature on the following two issues: (1) determination of the bulk viscosity of immiscible polymer blends using a plunger‐type capillary viscometer and (2) modeling the composition dependence of the bulk viscosity of immiscible polymer blends. Related to the first issue, it is pointed out that measurement of the total pressure drop across the entire length of a capillary die, while using a plunger‐type viscometer, to determine the bulk viscosity of an immiscible polymer blend is not justified. This is because the morphology (the state of dispersion) of an immiscible polymer blend varies along the axis of a capillary die. Related to the second issue, it is pointed out that the use of such empirical expressions as inverse additivity or logarithmic additivity relationships is of no rheological significance to determine the composition dependence of the bulk viscosity of immiscible polymer blends. This is because such empirical expressions do not contain terms describing the state of dispersion of an immiscible polymer blend. A computational approach is suggested, though formidable but not insurmountable, which will lead to establishing rheology–morphology–processing relationships in immiscible polymer blends. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Influence of composition on the linear viscoelastic behavior and morphology of PP/HDPE blends

In this paper the influence of temperature and composition on the dynamic behavior and morphology of polypropylene (PP)/high-density polyethylene (HDPE) blends were studied. The blend composition ranged from 5 to 30 wt% of dispersed phase (HDPE) and the temperatures ranged from 180 to 220 °C. The interfacial tension between PP and HDPE at temperatures of 180, 200 and 220 °C was obtained from fitting Palierne's emulsion model [1] to the experimental data of PP/HDPE blends with different compositions and from the weighted relaxation spectra of PP/HDPE blends with different compositions, following Gramespacher and Meissner [2] analysis. The interfacial tension between PP and HDPE as inferred from the rheological measurements was shown to depend on PP/HDPE blend composition. However, the results indicated that there is a range of PP/HDPE blend composition for which interfacial tension between PP and HDPE is constant. Considering these values, it was shown that interfacial tension between PP and HDPE decreases linearly with increasing temperature.     

On the steady-state drop size distribution in stirred vessels. Part II: Effect of continuous phase viscosity

In Part I, we used silicon oils with viscosities across six orders of magnitude to investigate the effect of the dispersed phase viscosity on the droplet size distribution of dilute emulsions. In this study, we extended Part I by using three glucose aqueous solutions to thicken the continuous phases, approximately an order of magnitude while keeping the Power number constant. It was found that increasing the continuous phase viscosity decreases the maximum drop size despite having drops well above the Kolmogorov lengthscale. Our results are in disagreement with the mechanistic models for the turbulent inertia regime. The results were explained using the full turbulent energy spectrum proposed by Pope instead of the Kolmogorov −5/3 spectrum. Our analysis revealed that most of the steady-state drop sizes do not fall in the isotropic turbulence size range.     

Emulsification of a viscous monomer mix: Particle size and size distribution

A non-Newtonian mixture of monomers, their copolymer and pigment was dispersed into water with emulsifier by a rotor-stator homogenizer (Brinkmann Polytron). Volume median diameters d₅₀ of the droplets, measured by Coulter Counter or optical microscopy, were typically 4–20 μm; d₅₀ was about inversely proportional to monomer fraction (0.2 to 1.0), or to rotor speed (4000 to 11000 rpm). Increasing the emulsifier from 0.1 % to 3% roughly halved d₅₀; volume fraction of organic phase had little effect. Turbulent dispersion theory (Calabrese et al., 1986a, b), adapted to non-Newtonian drops, represented the data but with different numerical constants. A high geometric standard deviation, around 1.7 but increasing slightly as monomer fraction decreased, may be due to non-uniform turbulence and to the complexity of breakup at high viscosity.     

Preparation of aqueous dispersible polyurethane: Effect of acetone on the particle size and storage stability of polyurethane emulsion

An aqueous dispersible polyurethane was prepared by the reaction of hydroxyl‐terminated poly(ethylene adipate), dimethylol propionic acid, 4,4′‐diphenylmethane diisocyanate, and ethylene glycol. Formation of the dispersion was achieved by phase inversion of an acetone solution of the polyurethane with water, utilizing carboxylate anion groups as the internal emulsifying sites. The amount of acetone added has a large effect on the particle diameter (0.08 to 8.61 μm) and particle size distribution of the polyurethane emulsion. The storage stability was evaluated in terms of particle size distribution breadth. The aqueous emulsion obtained with no use of acetone was sufficiently stable in storage for at least 6 months. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3455–3461, 2004