Effect of supercritical carbon dioxide on morphology development during polymer blending

Supercritical carbon dioxide (scCO₂) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO₂ in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s^?1. However, further compounding led to coalescence of the dispersed phase. Adding scCO₂ did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO₂ venting. The reduction in size of the PMMA phase was lost after CO₂ venting. The resulting morphology was similar to that without the addition of CO₂. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO₂ was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s^?1, the addition of scCO₂ only slightly reduced the domain size of the minor phase.     

Model experiments concerning morphology development during the initial stages of polymer blending

Summary In order to investigate the mechanisms of morphology development in polymerpolymer blending, a model experiment is developed which allows the matrix to be dissolved away so that the dispersed phase may be observed directly using scanning electron microscopy (SEM). The dispersed phase for the model experiments is an amorphous nylon. The matrix phase is a polystyrene. These model experiments dramatically reveal the primary modes of particle deformation and the nature of the morphologies at short mixing times. The initial mechanism of morphology development involves the dragging of a large particle of the dispersed phase along a hot surface such as the mixer walls. This dragging action results in the formation of sheets or ribbons of the dispersed phase. These sheets or ribbons become unstable due to the effects of shear and interfacial tension. Holes develop in the ribbons which grow in size and concentration until a fragile lace structure is formed. This lace structure breaks into irregularly shaped particles which are then broken up into nearly spherical particles.     

Phase continuity and inversion in polymer blends and simultaneous interpenetrating networks

A semi-empirical expression for predicting phase continuity and inversion in polymer blends and simultaneous interpenetrating networks (SINs) was developed and examined experimentally. A rheological model based on the volume fraction, ?, and viscosity, η, led to the equation as the criteria for dual phase continuity for phases 1 and 2. This relation was evaluated for two systems: a castor oil polyester-urethane/polystyrene SIN, and a mechanical blend of polystyrene and polybutadiene. Literature data was also examined. A gradual phase inversion was found, with a region of dual phase continuity in between. While predictions of phase continuity were confirmed for the mechanical blends, they were not confirmed for the SIN system. This was probably due to rapid gelation at the point of phase inversion.     

The development of laminar morphology during extrusion of polymer blends

Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-induced morphology to generate discontinuous overlapping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high density polyethylene and polyamide-6 (HDPE/PA-6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems.     

Morphology and continuity development in highly reactive nanoscale polymer blends

This work examines the effect of the extent of reaction on morphology, continuity development and cocontinuity in highly reactive nanoscale blends of brominated poly(isobutylene-co-p-methylstyrene) (BIMSM) and polyamide (PA) containing different amounts of plasticizer. The reactive melt blending protocol used is shown to be very effective in generating fine droplets in the 50-80 nm range scale, as observed by atomic force microscopy, and producing high amounts (about 46%) of graft copolymer. The amount is even higher (about 57%) for plasticized blends. It can be seen that the reaction between the elastomer and PA shifts the percolation thresholds and overall continuity development in the system to higher concentrations, but no effect is observed on the concentration region of dual-phase continuity.When a plasticizer is added to the PA, and it is the matrix phase, elastomer continuity development and cocontinuity shifts to higher concentrations. This is a result of both the increased extent of reaction in the presence of a plasticizer and the lower viscosity of the PA phase. When plasticized PA is the dispersed phase, however, these two phenomena oppose each other. The increased extent of reaction shifts plasticized PA continuity development to even higher concentrations in the blend, but the lower viscosity of the plasticized PA phase shifts the continuity development to lower PA phase concentrations. The net effect is that no change is observed on PA phase continuity with addition of plasticizer in an elastomer matrix.It is found, overall, that the dominant factor in controlling the dispersion of higher concentrations of elastomer into the PA phase is the extent of reaction between BIMSM and polyamide.     

Development of phase morphology in incompatible polymer blends during mixing and its variation in extrusion

An experimental study of the development of phase morphology in incompatible polymer melt blends of polyethylene/polystyrene (PE/PS), polyethylene/polycarbonate (PE/PC), and polyethylene/nylon-6 (PE/N6) is presented. Different temperatures (180°C, 240°C) of mixing and polyethylene molecular- weight levels were used in the PE/PS studies. Little variation in the cross-sectional phase morphology of the PE/PS extrudates was observed with these variables, though the morphology became finer with increased shear rate/stress in capillary die flow. Variations in the longitudinal morphology are observed with continuous filaments of dispersed phase only arising when the dispersed phase has an equal or lower viscosity than the continuous phase. The PE/N6 and PE/PC, especially the former, give coarser morphologies when the N6 and PC are the continuous phases. This was attributed to larger inter-facial tensions. The effect of viscoelasticity was also discussed.     

Fast determination of phase inversion in polymer blends using ultrasonic technique

Ultrasonic attenuation and velocity, together with SEM observation were used to investigate the morphology of some polymer blends. For miscible polymer blends of PVC/NBR, because there is no phase inversion but a homogeneous system a linear change (without discontinuity) of ultrasonic velocity and attenuation was observed in a whole composition ranges. For immiscible polymer blends, namely, PP/PS, PS/EPDM and PS/SBS system, the non-linear variation of ultrasonic velocity with composition indicates the immiscibility. On the other hand, the intensity of scattering attenuation changed from system to system depending on the size of dispersed phase, but a discontinuity of scattering attenuation was always observed as the phase inversion occurred. Our result suggests the sensitivity of ultrasonic attention vs phase inversion and may be served as a useful method to fast determine the phase inversion for immiscible polymer blends.     

Scale effects upon morphology development during mix melting of multiphase polymer blends in ZSK extruders

Replicate experiments were performed on ZSK-30 and ZSK-40 split barrel extruders concerning structure developments from PS-PE pellet blends during the melting process. PS is the minor phase. PE grades were choosen to accommodate viscous and thin matrix phase viscosities. The large extruder displays a more diverse cross channel structure and retarded phase development for some blends. Inferior dispersion is especially obvious in the larger extruder when processing low viscosity matrix blends. Similar phase development occurs in the extruders for high viscosity matrix blends.     

Studies of polymer morphology with 13C inversion recovery cross polarization NMR

Summary Inversion recovery cross polarization (IRCP) NMR was used to study the solid state morphologies of plasticized and neat poly(vinyl butyral-co-vinyl alcohol) (PVB), of polyether polyurethane elastomers (PU), and of low density polyethylene (LDPE). IRCP decay data for these polymers were best fit to a biexponential two-component model modulated by T₁H relaxation. These results clearly display the two-phase nature of these polymers, as well as the potential applicability of the IRCP technique.     

Evidence for mechanical coupling effects in binary polymer blends: Relationships with morphology

The viscoelastic properties of binary thermoset and thermoplastic polymer blends were investigated in connection with blend morphologies. Christensen and Lo's model was used to predict mechanical coupling effects in such binary multiphased systems by accounting for the actual morphology of samples. Thus, it was shown that the magnitude of mechanical coupling effects between phases in polymer blends, as in composite materials, depends not only on mechanical properties and relative content of each phase but also on the geometric arrangement of the polymeric phases. Furthermore, based on both theory and experiment, a well‐suited probe of blend morphology was also proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 530–541, 2000     

The phase inversion and morphology of nylon 1010/polypropylene blends

Noncompatibilized and compatibilized blends of nylon 1010/PP blends having five different viscosity ratios were prepared by melt extrusion. Glycidyl methacrylate-grafted-polypro-pylene (PP-g-GMA) was used as the compatibilizer to enbance the adhesion between the two polymers and to stabilize the blend morphology. The effect of the viscosity ratio on the morphology of nylon 1010/polypropylene blends was investigated, with primary attention to the phase-inversion behavior and the average particle size of the dispersed phase. The relationship between the mechanical properties and the phase-inversion composition was investigated as well. Investigation of the morphology of the blends by microscopy indicated that the smaller the viscosity ratio (ηpp/ηpa) the smaller was the polypropylene concentration at which the phase inversion took place and polypropylene became the continuous phase. The compatibilizer induced a sharp reduction of particle size, but did not have a major effect on the phase-inversion point. An improvement in the mechanical properties was found when nylon 1010 provided the matrix phase. © 1996 John Wiley & Sons, Inc.     

Morphology development during blending of immiscible polymers in screw extruders

The present work reports evolution of morphology from initial (presence of striation) to final (droplet formation) stages in a single‐screw extruder. Morphology development during the blending process controls the final size of the dispersed phase, which in turn significantly affects the properties of the blends. The experiments were carried out using a 70/30 wt% polypropylene/ethylene vinyl acetate (PP/EVA) blend; samples were collected along the length of the screw, by screw pullout experiment, to analyze the size and size distribution of the dispersed phase present both as striated layers and subsequently as droplets. Average size of the dispersed phase and standard deviation were taken into account to monitor the morphology evolution along the length of the screw. Pre‐breakup morphology development was studied by analyzing the sample collected from the feed zone of the extruder in terms of upper and lower layers along the cross section of screw channel. Examination of micrographs revealed the existence of pattern of ordered striations along the length of the melting zone containing striations from average size of 1000 μm down to 50 μm decreasing rapidly along the length of the screw. The breakup process was captured at the start of compression zone where step‐up in the shear as well as elongational flow was applied due to decrease in the channel depth along the compression zone. The observed droplet size formed by the breakup of filaments is found to be in accordance with theory. The final droplet size is found to be governed by the emulsification process occurring as a result of stretching, breakup and coalescence in the metering section of the screw and is in the order of 2 μm.     

PP接枝聚合物对PP/PS共混物相形态的影响

通过原子转移自由基反应合成了聚丙烯(PP)接枝聚苯乙烯(PS) (PP-g-PS),研究了PP-g-PS对PP/PS共混物相形态的影响.采用扫描电子显微镜、偏光显微镜观察了共混物的断面形貌和等温结晶形态.结果表明: 加入PP-g-PS对PP/PS共混物起到了良好的增容作用,表现在两相界面模糊,分散相尺寸减小.当PP-g-PS中x(PS)为5.10% 左右时即可起到增容改善相界面的作用.相容性的提高改善了PP/PS共混物的发泡性能.     

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.     

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.     

Compatibilization and morphology development of immiscible ternary polymer blends

We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphology development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St) as prepared by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. Scanning electron microscopy (SEM) results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addition of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technologically attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphology development, the morphology of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphology changed from a three-phase co-continuous morphology (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).     

Mixing and morphological transformations in the compounding process for polymer blends: The phase inversion mechanism

This study reports on the progression of processes occurring in polymer blends during mixing. For the polymer pellet blends studied, an abrupt phase inversion was observed simultaneous with attainment of maximum torque in the batch mixer. A four-step phase inversion mechanism is described as predominant where dissipative mix-melting of the polymer system occurred in the mixing process.     

Study on morphology development for in situ fiber–reinforced composites by blending polyolefin and polycaprolactone

The morphology developments and interfacial properties of extruded polyethylene/polycaprolactone and polypropylene/polycaprolactone blends were investigated. The interfacial thicknesses of both polymer blends were thin and this was investigated by interfacial tension measurement in the melt state. The aspect of boundary area was observed by AFM, and a clear line could be observed at the interface area as a result of thin interfacial thickness. The in situ fiber formation of the dispersed phase was remarkably generated under elongational flow (between die exit and solidification) rather than under shear flow (in the cylinder and die). Drawing ratio was varied at three levels to study its effect on elongation of the dispersed phases. The dispersions dramatically changed from spherical to spheroidal and filament shapes depending on the drawing ratio. Reduced capillary number (Ca*) was used to characterize droplet deformation. The deformation mode under shear flow was classified as nondeformation mode due to the fact that the Ca* was almost 0. On the other hand, the deformation mode under elongational flow was classified into filament shape mode (Ca* > 4). This classification was in agreement with the SEM images. The tensile properties were increased at the border line where the Ca* was 4.0. The melt interfacial tensions of polyolefin/polycaprolactone were relatively large, and a clear line could be observed at the interface area as a result of little affinity of polymer interface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 500–508, 2005     

The effect of phase inversion during semibatch aromatic nitrations

The effect of phase inversion during semibatch aromatic nitrations is experimentally characterized and analysed. The influence of various parameters, i.e. interfacial area, effective heat-transfer coefficient and overall mass-transfer coefficient, is studied. The implications for optimizing nitrations are discussed from performance and safety points of view. The accumulation of unreacted nitric acid can be dangerous if accompanied by a phase inversion, owing to the fact that the rate may increase suddenly.