Structural and rheological investigation of interphase in polyethylene/polyamide/nanoclay ternary blends

This study aims at investigating and characterizing the interphase in Polyethylene (PE)/Polyamide (PA) blends with nodular morphology, filled with organically modified Montmorillonite (C30B), using structural and rheological experimental techniques. PE/PA/C30B blends have been prepared by simultaneous mixing at a dispersed phase fraction (PE or PA) of 20% and a clay fraction ranging from 1 to 6%. Structural properties of the interphase have been investigated using XRD combined with TEM micrographs. The presence of numerous interphase defects is evidenced, and the effect of interphase disorder is discussed. Linear viscoelastic properties show the contribution of the interphase in PE matrix ternary blends at all clay fractions, whereas interphase effects are masked by the contribution of dispersed nanoclay particles in PA matrix ternary blends.     

Manipulating the phase morphology in PPS/PA66 blends using clay

By adding a small amount of clay into poly(p‐phenylene sulfide) (PPS)/polyamide 66 blends, the morphology was found to change gradually from sea–island into cocontinuity and lamellar supramolecular structure, as increasing of clay content. Clay was selectively located in the PA66 phase, and the exfoliated clay layers formed an edge‐contacted network. The change of morphology is not caused by the change of volume ratio and viscosity ratio but can be well explained by the dynamic interplay of phase separation between PPS and PA66 through preferential adsorption of PA66 onto the clay layers and through layer–layer repulsion. This provides a means of manipulating the phase morphology for the immiscible polymer blends. The mechanical and tribological properties of PPS/PA66 blends with different phase morphologies (different clay contents) were studied. Both tensile and impact strength of the blends were found obviously increased by the addition of clay. The antiwear property was greatly improved for the blends with cocontinuous phase form. Our work indicates that the phase‐separating behavior of polymer blends contained interacting clay can be exploited to create a rich diversity of new structures and useful nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Dynamic and static properties of SBS triblock copolymer and their blends

By using a dynamic testing method (Rheovibron), it has been established that for a pure triblock copolymer (styrene-butadiene-styrene, SBS), the morphology is composed of a continuous phase, a dispersed phase and an interphase. The predominance of the phase depends upon whether the polymer is cast from a good or poor solvent for each block. For the blends of SBS with PS and PBd, the interphase occupies a greater fraction as indicated by the fact that its corresponding molecular relaxation temperature range is much broader (10°–80°C) than that of pure SBS (60°–80°C). If the blends of SBS with its corresponding homopolymers are heated at 140°C for 45 min, the fraction of the interphase increases significantly and the onset of molecular relaxation is lowered to ?10°C. The viscosities of SBS and their blends are measured by both dynamic and static methods. Complex viscosities calculated from the dynamic method show transitions similar to those of storage moduli. Viscosities at different temperatures from these two methods are superimposed onto master curves.     

Compatibilizing effect of EPM-g-MA in EPDM/poly(trimethylene terephthalate) incompatible blends

The morphology of immiscible and highly incompatible blends of Sorona^® polymer [Poly(trimethylene terephthalate), PTT] and ethylene propylene diene rubber (EPDM) blends has been studied with and without the addition of a compatibilizer precursor EPM-g-MA. These incompatible blends are characterized by a two-phase morphology, narrow interphase, and poor physical and chemical interactions across the phase boundaries. Therefore, a reactive route was employed to compatibilize these blends by the addition of maleic anhydride grafted ethylene propylene rubber (EPM-g-MA). The blends were prepared in an internal mixer. The morphology was examined by scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The morphology of the blends indicated that the EPDM phase was preferentially dispersed as domains in the continuous Sorona^® matrix up to 30% of its concentration. A co-continuous morphology was observed above 30 wt% of EPDM content followed by a phase inversion beyond 60 wt% of EPDM. The influence of EPM-g-MA on the phase morphology of blends was studied quantitatively by SEM. It was found that the addition of EPM-g-MA reduces the domain size of the dispersed phase followed by a leveling off at higher concentrations of the compatibilizer. This is an indication of interfacial saturation. The experimental compatibilization results were compared with theoretical predictions. The conformation of the compatibilizer at the interface was analyzed based on the area occupied by the compatibilizer at the blend interface. Free volume measurements using positron annihilation lifetime spectroscopy (PALS) were done to analyze the interaction of blends. In the case of uncompatibilized blends the free volume values tend to increase by the addition of EPDM phase showing high level of incompatibility. Addition of EPM-g-MA to the blends tends to decrease the free volume showing its compatibilizing effect.     

Mechanical properties and morphology of PBT/FE blends

The mechanical properties such as tensile properties and Izod impact strength of melt compounded poly (butylene terephthlate)(PBT)/Fluorocarbon terpolymer elastomer (FE) blends at FE concentration from 0 to 0.26 volume fraction were studied. With increase in the FE concentrations the tensile properties decreased while the impact strength increased. Good dispersion and adhesion of FE with major phase PBT was shown by the morphological studies. Crystallinity of PBT and interphase adhesion influenced the tensile properties. Use of simple models relating normalized relative tensile parameters where the data were divided by the crystallinity of PBT in the blends and in the matrix, respectively, supported the interphase adhesion. The concentration and the interparticle distance of the dispersed phase FE influenced the impact toughening.     

Effect of organically modified layered silicates on the morphology of symmetrical blends of polystyrene and poly(methyl methacrylate)

The changes in morphology caused by the addition of organically modified layered silicate on equal volume fraction blends of polystyrene and poly(methyl methacrylate) are investigated. In thin films supported on silicon, without layered silicates, the PMMA forms a layer on the silicon, while the PS tend to minimize contact with both the hydrophilic silicon substrate and the PMMA phase, and tend to form discrete domains on top of the PMMA layer. With the introduction of layered silicates, the characteristic length scale of the structure decreases. On the other hand, in bulk samples, without the layered silicates, the equal volume fraction blend has the PS domains in a PMMA matrix. At 0.6 wt% of added silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous. Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase. The change in morphology is conjectured to be the result of the interfacial location of the layered silicates rather than the change in viscosity ratio between the two phases.     

Improved compatibility between polyamide and polypropylene by the use of maleic anhydride grafted SEBS

Blends containing equal weight fractions of polypropylene (PP) and polyamide (PA-6 and PA-6.6) and up to 25% of a compatibilizing thermoplastic elastomer, either polystyrene-block-poly(ethylene-stat-butylene)-block-polystyrene (SEBS) or SEBS modified by maleic anhydride (SEBS-MA), were prepared by melt mixing. In all these blends, PP formed the continuous matrix phase. Even at high concentrations, unmodified SEBS was found to be a poor compatibilizer, affecting mainly the properties of the matrix. The graft copolymer formed, by reaction between SEBS-MA and polyamide during melt mixing, strongly influenced the blend morphology, by forming an interphase, separating the PA phase domains from the matrix. The crystallization behaviour of PP indicated that full coverage required between 3% and 5% SEBS-MA at the intense mixing conditions used. Above this level, the total surface area of the polyamide domains seemed to increase in direct proportion to the concentration of SEBS-MA. The thickness of the interphase layer was estimated to be about 15 nm. At high concentrations of SEBS-MA, the PA domains agglomerated and formed extended structures held together by the interphase polymer. This was reflected by the stress–strain and rheological behaviour of the blends. In blends with PA domains of small volume, crystallization of PA was delayed. The rate of water absorption was very low in blends containing SEBS-MA, much lower than in corresponding blends containing SEBS.     

Blending PP with PA6 industrial wastes: Effect of the composition and the compatibilization

Blending polypropylene to recycled PA6 industrial wastes at different compositions, with and without compatibilizer PPgMA was produced in a corotating twin screw extruder where, polypropylene acts as the polymer matrix and polyamide as the dispersed phase. Several techniques were used to investigate the morphology, thermal, viscoelastic and tensile properties of these blend. Binary PP/PA6 blends showed the presence of PA6 particles dispersed in the PP continuous phase and exhibited a coarse morphology. Increasing PA6 contents in the blend increased their crystallinity and their size and improved the tensile properties at weak deformation. In addition to compatibilizer PPgMA, the morphology shows lower diameters and a decrease in size of the dispersed PA6 particles. The interfacial adhesion was also improved, as a result of the creation of an interphase that was formed by the interaction between the formed PPgPA6 copolymer in situ and both phases. This interphase induced an improvement in tensile properties. The PPgPA6 copolymer generated by the interphase was identified with DMA analysis thanks to an additional transition in loss modulus curves. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheology,morphology, and crystallization behavior of melt‐mixed blends of polyamide6 and acrylonitrile‐butadiene‐styrene: Influence of reactive compatibilizer premixed with multiwall carbon nanotubes

Blends of polyamide6 (PA6) and acrylonitrile butadiene styrene (ABS) were prepared in presence or absence of up to 5 wt % of a reactive compatibilizer [styrene maleic anhydride copolymer (SMA) modified with 5 wt % multiwall carbon nanotubes (MWNT)] by melt‐mixing using conical twin screw microcompounder where the ABS content was varied from 20 to 50 wt %. The melt viscosity of the blends was significantly enhanced in presence of SMA modified by multiwall carbon nanotubes due to the reactive compatibilization, which leads to stabilized interphase in the blends. Furthermore, the presence of MWNT in the compatibilizer phase led to additional increase in viscosity and storage modulus. Morphological studies revealed the presence of either droplet‐dispersed or cocontinuous type depending on the blend compositions. Further, reactive compatibilization led to a significant change in the morphology, namely a structure refining, which was enhanced by MWNT presence as observed from SEM micrographs. DSC crystallization studies indicated a delayed crystallization response of PA6 in presence of ABS presumably due to high melt viscosity of ABS. The crystallization temperature and the degree of crystallinity were strongly dependent on the type of morphology and content of reactive compatibilizer, whereas the presence of MWNT had an additional influence. SAXS studies revealed the formation of thinner and less perfect crystallites of PA6 phase in the blends, which showed cocontinuous morphology. A unique observation of multiple scattering maxima at higher q region has been found in the blends of cocontinuous morphology, which was observed to be successively broadened in presence of the compatibilizer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Studies on the characteristics of microphase separation and stabilization of interphase for blended systems of high performance polymers

In this report, we review and discuss the results of our recent studies on the characteristics of microphase separation behavior and interphase stabilization for high performance polymer blends. The blends investigated include crystalline/crystalline polymers, crystalline/amorphous polymers, liquid crystalline polymer/thermoplastics, and amorphous/amorphous thermoplastics or thermosetting systems. Most of the blends are either immiscible or partially miscible, and are thermodynamically unstable or meta-stable systems. The macro-properties of these blends are controlled by many factors such as the miscibility, phase morphology and structure, crystallinity, kinetics of crystallization or phase separation processing, and interfacial adhesion of the components. Among these, the microphase and interfacial structures are the most significant factors influencing the ultimate properties of the blends. In order to obtain relatively stable blends, formation of semi-IPN in either the bulk or interphase, and/or the occurrence of crosslinking, transesterification and physical entanglement in the interfacial region will be profitable to the stabilization of the blending systems.The project supported by FORD and NSFC No. 09415312     

Co-continuous morphology development in partially miscible PMMA/PC blends

Poly(methyl methacrylate) (PMMA)/polycarbonate (PC) partially miscible blends were produced via melt blending in an internal mixer over the entire range of composition at two different viscosity ratios. The morphology of this low interfacial tension system was investigated by scanning electron microscopy, solvent extraction/gravimetry and surface area measurement (BET) after selective extraction. The partial miscibility of these blends was evaluated by T_g measurements from dynamic mechanical thermal analysis. The co-continuous morphology development curve obtained from gravimetry is commonly reported in the literature as the %continuity vs. the vol% fraction of the dispersed phase for fully phase separated systems. Such systems possess pure phases of A and B. Partially miscible blends on the other hand demonstrate immiscibility between an A-rich phase and a B-rich phase. Quantitative estimation of the partial composition of the minor components in each respective rich phase was calculated using the Fox equation. Using this data, an approach to correcting the gravimetry results to take into account the partial miscibility of the PMMA/PC system is proposed. The co-continuous morphology development curve is then presented as the %continuity vs. the vol% fraction of the PMMA-rich phase. This corrected curve demonstrates the features of a highly interacting polymer blend: a low percolation threshold and a broad co-continuity region. The BET technique shows that the pore size of the extracted co-continuous blends is dependent on composition, the pore diameter increases with total PMMA content. Use of a low molecular weight PC shifts the co-continuous morphology development curve to higher volume fraction values of PMMA-rich phase. It is suggested that this is the result of a lower dispersed phase thread stability due to the lower matrix viscosity.     

Solid-state NMR characterization of unsaturated polyester thermoset blends containing PEO-PPO-PEO block copolymers

First, the NMR method proposed in our previous work was improved to provide more accurate measurement of interphase thickness in multiphase polymers. Then the improved method, in combination with other techniques, was applied to elucidate the phase behavior, miscibility, heterogeneous dynamics and microdomain structure in thermoset blends of unsaturated polyester resin (UPR) and amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The experimental results were compared with those of epoxy resin (ER)/PEO-PPO-PEO blends to systematically elucidate the influence of binary polymer-polymer interaction on the phase behavior, domain size and especially the interphase thickness in thermoset blends of UPR and ER, respectively, with the same PEO-PPO-PEO triblock copolymer. It was found that UPR/PEO-PPO-PEO exhibits strong phase separation with considerably small interphase, and only a small fraction of PEO is mixed with UPR. Whereas ER/PEO-PPO-PEO exhibits weak phase separation with thick interphase, and a large amount of PEO is intimately mixed with ER. It was suggested that the thermodynamic interaction between the block copolymer and cross-linked thermoset resin is one of the key factors in controlling the phase behavior, domain size and interphase thickness in these blends. These NMR results are qualitatively in good agreement with the previous theoretical prediction of interphase properties between two immiscible polymers. Our NMR works on different thermoset blend systems with weak and strong microphase separations clearly demonstrate that the improved NMR method is a general and useful method for measuring the interphase thickness and elucidating the phase behavior and subtle microdomain structure in multiphase polymers with detectable heterogeneous dynamics.     

The effect of mixing time on the morphology of immiscible polymer blends

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for two immiscible binary polyblend systems, polyamide/polyethersulfone (PA/PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by selective dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases, shown by the results of PA/PES blends with a viscosity ratio of 0.03. The lower viscous phase (PA) forms particles, fibrils, and layers successively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase (PES) appears mainly in the form of particles and directly becomes a continuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is determined mainly by the volume fraction of each phase. Particles are the final morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixing time the same, and any one of these two components is in the form of particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The composition range of co-phase continuity is decided not only by the viscosity ratio but also by the mixing time. With increasing mixing time, this range becomes narrower and finally occurs at volume fraction of 50/50, no longer affected by the viscosity ratio. © 1996 John Wiley & Sons, Inc.     

Compatible polycarbonate/polyamide 6,6 blends with fibrillar morphology

Blends of bisphenol A polycarbonate (PC) and polyamide 6,6 (PA6,6) were prepared directly during the plasticization step of an injection molding process in an attempt to attain both (i) the reinforcement of the blends through fibrillar morphology, and (ii) an adequate compatibilization despite the short processing procedure used. Differential scanning calorimetry and dynamic‐mechanical analysis indicated that the blends were made up of a PC‐rich phase where some PA6,6 was present and, ruling out a possible degradation, of an almost pure PA6,6‐phase. The cryogenically fractured surfaces observed by scanning electron microscopy showed both rather fine particles and larger particles with occluded subparticles. This complex morphology indicates low interphase tension and, therefore, compatibilization, which can be attributed to the presence of PA6,6 in the two phases of the blends. The values of Young's modulus, determined by means of tensile tests, were always synergistic and, in the case of the 25/75 blend, the modulus was even higher than those of any of the two pure components. It appears this could be due to both the highly fibrillar morphology of the dispersed phase, and the significant decrease observed in specific volume. The blends remained ductile throughout the full composition range, which also indicates compatibilization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

辐射对PP／BR共混体系界面粘接的影响

研究了在多官能团单体异氰尿酸三烯丙酯存在下，辐射对ＰＰ／ＢＲ共混体系的影响，并用ＳＥＭ，ＤＳＣ和动态力学等技术对其进行了表征。结果显示，辐射引发ＴＡＩＣ参与的界面反应改变了ＰＰ／ＢＲ的形态结构，增强了两相的界面粘接，改善了相容性，提高了力学性能。     

Toughening of unsaturated polyester with rubber particles. Part I: Morphological study

The morphology of rubber-modified unsaturated polyester is described. In order to modify the particle-matrix interface, different rubbers were used; BFGoodrich Hycar liquid rubbers and high molecular weight rubbers. Blends of different compositions were prepared. The microstructure of the materials was investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The volume fraction and the particle size of the rubbers' second phase was determined by applying quantitative metallography. The volume fraction of the precipitated phase was higher than the amount of added rubber. Such blends show phase inversion above 35 wt% of rubber.     

Coarsening in molten quiescent polymer blends: The role of the initial morphology

Coarsening of the phase dimensions in polymer blends under quiescent conditions is studied in blends of different morphologies; the dependence of the rate and extent of coarsening on the initial morphology is demonstrated. In blends with a droplet/matrix structure, coarsening via coalescence is found only above the percolation threshold for spherical particles (16 vol%). The rate of coalescence in the droplet/matrix structure is shown to obey the theory of Fortelny and Zivny for coalescence of droplets in quiescent media, and no constant level of the phase dimensions is reached. Below a volume fraction of 0.16 limited coarsening is found only for fibrillar and co-continuous morphologies. This coarsening is in fact the result of a restructuring because retraction and breakup occur, leading to a droplet/matrix morphology in which the droplet diameter is approximately twice the diameter of the original fiber. Breakup and retraction are completed in a short time relative to coalescence. At higher volume fractions in co-continuous structures (>30 vol%), these structures do not break up, and coarsening is found to take place by retraction only. No constant level of the phase dimensions is reached in the latter case.     

Positron annihilation studies of nanoholes and microphase formation control of a PMMA+MMA+TEGDMA system

Positron annihilation lifetime spectroscopy (PALS) was applied for the study of a set of PMMA (polimethyl-methacrylate)+MMA (methyl-methacrylate)+TEGDMA (triethyleneglycol-dimethacrylate) blends prepared by two synthesis routes (standard and phase separation methods). The aim was to investigate the correlation between free volume and miscibility of the compounds. PALS measurements were performed in order to determine contents and sizes of free volume on the ‘standard’ and ‘phase-separation’ polymers; important differences in the behavior of the free volume composition curves were found, which are explained in terms of the formation of microregions in the phase separation material. When considering simple binary interchain interaction, the mean free volume hole fraction in a blend was computed in terms of an interaction parameter (β) that might be correlated to the Flory-Huggins interaction parameter (χ). This suggests that local free volume properties of polymer in blends are very important for local packing and segmental arrangements. We have re-encountered the task of defining miscibility depending upon the scale of observation: we observed distinct phases in the micrometer scale while still nothing can be discerned in the nanometer scale. We conclude that it is possible to produce a PMMA+TEGDMA blend with the presence of a low fraction of MMA/TEGDMA copolymer situated at the interphase between the PMMA and TEGDMA regions allowing a higher degree of compatibility of the components.     

Modification of tensile and impact properties of poly(butylene terephthlate) by incorporation of styrene‐ethylene‐butylene‐styrene and maleic anhydride‐grafted‐SEBS (SEBS‐g‐MA) terpolymer

Tensile behavior and impact strength of poly(butylene terephthlate) (PBT)/styrene‐ethylene‐butylene‐styrene (SEBS) copolymer blends were studied at SEBS volume fraction 0–0.38. Tensile modulus and strength decreased, whereas breaking elongation increased with SEBS content. Predictive models are used to evaluate the tensile properties. Strength properties were dependent on the crystallinity of PBT and phase adhesion. The normalized notched Izod impact strength increased with the SEBS content; at Φ_d = 0.38, the impact strength enhanced to five times that of PBT. Scanning electron microscopy was used to examine phase morphology. Concentration and interparticle distance of the dispersed phase influenced impact toughening. In the presence of maleic anhydride‐grafted SEBS (SEBS‐g‐MAH), the tensile modulus and strength decreased significantly, while normalized relative notched Izod impact strength enhanced to 7.5 times because of enhanced interphase adhesion. POLYM. ENG. SCI., 53:2242–2253, 2013. © 2013 Society of Plastics Engineers     

Composite droplets with core/shell morphologies prepared from HDPE/PS/PMMA ternary blends by twin‐screw extrusion

Ternary blends of PS and PMMA in a PE matrix were prepared by twin‐screw extrusion to investigate the core/shell encapsulation phenomenon in the composite droplet. The PS was found to encapsulate the PMMA to form composite droplets within the PE matrix as expected from the spreading coefficient theory. The effects of dispersed phase concentration, viscosity ratio, feeding sequence and twin‐screw operating conditions were investigated. The blend morphology was observed by scanning electron microscopy after selective extraction of either PS or PMMA, and average core and composite droplet diameters were determined by image analysis. Although it is known that the structure of composite droplet blends can be substantially altered through control of the volume fraction of the components in the dispersed phase, this study demonstrates that blends with a 1:1 composite droplet volume fraction are relatively stable to large variations in the minor phase viscosities and processing conditions. Twin‐screw extrusion thus provides a highly robust technique for the melt processing of blends possessing composite droplet morphologies. Polym. Eng. Sci. 44:749–759, 2004. © 2004 Society of Plastics Engineers.