Morphology Of Dispersed Phase Research Articles

Evaluation of olefinic block copolymer blends with amorphous polyolefins—effect of different unsaturated and saturated hydrocarbon tackifier resins on blend miscibility

ABSTRACTBlends of ethylene–octene based olefinic block copolymer (OBC) with two amorphous polyolefin (APO) polymers [atactic propylene homopolymer (PP) and ethylene–propylene copolymer (PE–PP)] were evaluated at three different ratios. Dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) evaluations were performed to determine the blend miscibility characteristics. Viscoelastic properties of both OBC blends with PP polymer, and OBC blends with PE–PP copolymer showed incompatibility. Analysis revealed that both blends formed two phase morphologies. The effect of three unsaturated aliphatic hydrocarbon resins with varying aromatic content and two saturated hydrocarbon resins with different chemistries were evaluated as compatibilizing agent for OBC/PP and OBC/PE–PP blends. A 1 : 1 polymer blend ratio of OBC/PP and OBC/PE–PP was selected to better understand the influence of resin addition at three different levels 20, 30, and 40 wt %. The fully aliphatic unsaturated resin seems to improve the miscibility of the OBC/PP blends at higher resin addition levels, but reduced the miscibility as the aromatic content of the resin increases. However, OBC/PE–PP blends showed improved miscibility with increasing aromatic content. A ternary phase morphology was particularly observed for both OBC/PP and OBC/PE–PP blends with highly aromatic (14%) unsaturated hydrocarbon resin, in which OBC formed the continuous phase, and PP, PE–PP, and unsaturated hydrocarbon resins formed the dispersed phase. Interestingly, we did not observe much difference in miscibility characteristics between the two saturated resin chemistries in both blend systems (OBC/PP and OBC/PE–PP). The Harkins spreading coefficient concept was used to better understand the ternary blend dispersed phase morphology. Spreading coefficients indicate that the free hydrocarbon resins (both unsaturated and saturated) were encapsulated by the amorphous PP or amorphous PE–PP polymer in the dispersed phase for the respective blend compositions. Overall OBC–PP and OBC/PE–PP blends showed better miscibility characteristics with both saturated aliphatic hydrocarbon resins, irrespective of the difference in resin chemistries. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2624–2644, 2013

Investigation on the Influence of Different Compatibilizers on Polycarbonate and High Density Polyethylene Blends: Mechanical Properties, Thermal Properties, Morphology, and Chemical Resistance

This investigation focused on a systematic approach of selecting the best possible polycarbonate/high density polyethylene (PC/HDPE) blend ratio and a suitable compatibilizer to improve the notch sensitivity, craze, and cracking tendency of PC. Among five different compatibilizers, polyethylene glycol (PEG) was found to be more effective based on mechanical performance and changes in phase morphology. The phase morphology of dispersed HDPE phase changed from elongated domain to fine spherical domain, and the tensile modulus and heat distortion temperature of PC/HDPE blend increased with increase in PEG content. DSC analysis showed an inward shift in the glass transition temperature (Tg), indicating enhanced compatibility between the PC and HDPE phases. Furthermore, PEG compatibilized PC/HDPE (80/20) blend was found to have very good notch performance and chemical resistance compared to PC. Hence, this blend can be used to design products with intricate shapes with less notch sensitivity and high chemical resistance with the superior mechanical performance of PC.

Droplet breakup and coalescence in a twin-screw extrusion processing of starch based matrix

Formation of oil droplets during twin screw extrusion processing of maize starch was investigated by analyzing the droplet breakup and coalescence mechanisms separately. For this purpose, the flow was characterized by computational fluid dynamics (CFD) using material data derived from online rheological measurements. The simulated results on local flow conditions were coupled to experimental data on the dispersed phase morphology, which was analyzed by confocal laser scanning microscopy (CLSM). This was used to elucidate the influence of process characteristics relevant for droplet breakup and coalescence. The results showed that increasing screw speed does not necessarily result in smaller droplet sizes. This could be related to the contradictory effects: increasing screw speed improves droplet breakup but also increases the rate of coalescence. Smaller droplet sizes were obtained at higher blend viscosities, which could be achieved either by increasing the feed rate or by using screw configuration that applies less mechanical stress. The results suggest that an increase in blend viscosity reduced the rate of coalescence. Moreover, increasing oil content led to an increased rate of coalescence, and therefore to remarkably bigger droplets. Selection of process parameters (e.g. screw configuration, feed rate, screw speed) based on the findings of this study allowed enhancing the dispersive mixing efficiency of triglyceride droplets during extrusion processing of maize starch.

Evaluation of process parameters using Taguchi methodology for blends of low density polyethylene (LDPE) and polydimethyl siloxane (PDMS) rubber

Processing parameters such as temperature, rotor speed and time of melt blending have been optimised using design of experiments as per the Taguchi methodology at a blend ratio of low density polyethylene (LDPE)/polydimethyl siloxane (PDMS) of 50∶50. Mechanical properties such as tensile strength, impact strength, hardness and phase morphology of the blends have been evaluated at different temperatures, rotor speeds and times for assessing the optimisation of the processing parameters. The formation of a finer dispersed phase morphology in case of the LD 508 and LD 509 blend mix is an indication of good dispersion and narrow size distribution of the PDMS rubber in the LDPE matrix. It has been found that the LD 509 mix gives a better dispersion of silicone rubber as the dispersed phase in the continuous LDPE matrix. Analysis of variance on the performance characteristic has been analysed using signal to noise ratios and mean response data.

Thermal and rheological behavior of reactive blends from metallocene olefin elastomers and polypropylene

Reactive blends of metallocene polyolefin elastomers (POE)/polypropylene (PP) with 60/40 composition were prepared with an organic peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, and a bis-azide derivative, diphenyloxid-4,4'-bis(sulfonylazide) (BSA). Ethylene-1-butene (EB) and ethylene-1-octene (EO) copolymers and elastomeric polypropylene (ePP) were used as the elastomeric phase. The effect of elastomeric phase on the thermal, rheological, morphological and mechanical properties of the thermoplastic vulcanizates (TPVs) or dynamic vulcanizates were studied. All TPVs depicted pseudoplastic behavior and blends cured with azide curative showed higher viscosities. The TPVs showed both dispersed and continuous phase morphology that depends on the elastomeric phase type revealing a limited degree of compatibility between PP and the elastomers EO or EB. On the other hand, the TPV PP/ePP showed a uniform morphology suggesting an improved compatibility. Substantial changes observed in physical properties were explained on the basis of blends' morphology and dynamic vulcanization. The results confirm that the mechanical properties are more influenced by the elastomeric phase than by the curative agent. This study revealed a broad new range of opportunities for POE-based TPVs.

The morphology and dynamic viscoelasticity for PPS/low-melting temperature glass hybrids prepared by melt blending

Abstract Polyphenylene sulfides (PPS) and low-melting temperature glasses (LMTG) were used to prepare a PPS/LMTG organic–inorganic hybrid material by melt blending. The etched surfaces of the hybrids were observed by scanning electron microscope (SEM) and the images showed different dispersed phase morphologies compared to traditional filled composites, which maybe induced by shear. Advanced rheometric expanded system (ARES) was used to investigate the rheological behaviors of the hybrids and the results showed that the strain γ dependence of dynamic storage modulus G′ for the hybrids with high contents of LMTG did not appear Payne effect.

Shapes of dispersed phase in confined PIB/PDMS blends with different compositions during shear flow

The morphology of immiscible fluid mixtures under confined environment usually displays different scenarios compared with those presented in bulk systems. In this work, the influence of confinement and component ratio on the droplet morphology of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends in confined steady shear flow was investigated. While increasing the degree of confinement, the morphology of dispersed phase experienced a transition from the bulk behavior toward the confined behavior. Increasing the concentration of PIB phases in confined blends resulted in more coarsened structure under low shear rate and generated pearl necklace or string-like structures under a higher shear rate. The maximum aspect ratio of PIB droplets increased while increasing PIB concentration. The width and the aspect ratio of PIB droplets obtained experimentally were compared to the predictions of a single droplet MM model for bulk flow and an M model considering confinement. The experimental droplet width agreed well with the predictions of these two models only in the small droplet zone, large deviations appeared for the degree of confinement up to 0.36 and higher, whereas constant droplet width was found. The M model decreased the deviation between the experimental aspect ratio and the prediction of MM model in the high Ca zone. Good agreement between the prediction of M model and experiment results was found when the orientation angles of the droplets were corrected by using the M model.

Phase morphology and melt rheological behavior of uncrosslinked and dynamically crosslinked polyolefin blends: role of macromolecular structure

Thermoplastic vulcanizates (TPVs) based on polypropylene (PP) with ethylene–octene copolymer (EOC) and ethylene propylene diene rubber (EPDM) have been prepared by co-agent-assisted peroxide crosslinking system. The study was pursued to explore the influence of two dissimilar polyolefin polymers having different molecular architecture on the state and mode of dispersion of the blend components and their influence on melt rheological properties. The effects of dynamic crosslinking of the PP/EOC and PP/EPDM have been compared with special reference to the concentration of crosslinking agent and ratio of blend components. Morphological analyses show that, irrespective of blend ratio, dynamic vulcanization exhibits a dispersed phase morphology with crosslinked EOC or EPDM particles in the continuous PP matrix. It was found that viscosity ratio plays a crucial role in determining the state and mode of dispersion of blend components in the uncrosslinked system. The lower viscosity and torque values of uncrosslinked and dynamically crosslinked blends of PP/EOC in the melt state indicates that they exhibit better processing characteristics when compared to corresponding PP/EPDM blends.

Dynamic mechanical, thermal, physico-mechanical and morphological properties of LLDPE/EMA blends

The effect of blend composition on the morphology, dynamic mechanical properties, thermal and physico-mechanical properties of linear low density polyethylene (LLDPE)/ ethylene-co-methyl acrylate (EMA) blends were studied. The blend showed both dispersed and continuous phase morphology that depends on the blend composition. A co-continuous structure is formed for blends containing 50 wt% of EMA. Dynamic mechanical studies showed that flexibility of the blend enhanced with the expansion of the amorphous region as EMA content increased. However, two separate melting temperature peak observed in differential scanning calorimetry (DSC) analysis indicate that the blends are immiscible in crystalline region of the two polymers. X-ray diffraction (XRD) studies showed that crystallinity of blends decreases with increase in EMA content and negative deviation of tensile strength from the mixing rule indicates the poor interfacial adhesion between the two components. FTIR spectroscopy established the lack of chemical interaction between LLDPE and EMA, which support the SEM, DSC, DMA and XRD observations. Parallel-Voids model has been applied to characterize phase morphology of these blends.

Morphology Evolution in PC/PE Blends with and without Compatibilization During Twin-Screw Extrusion

The morphology evolution in polycarbonate/polyethylene (PC/PE) blends with and without compatibilization in a twin-screw extruder was studied using a scanning electron microscope (SEM). The effects of screw speed and compatibilizer on the morphology of PC/PE blend during the extrusion were discussed in detail. It was found that the shape and size of the dispersed phase in the uncompatibilized PC/PE blend are both influenced by the screw speed. The evolution of dispersed phase morphology can be affected by increasing screw speed, and the dispersed particle size decreases with the increasing of the screw speed. As a compatibilizer, the addition of the (ethylene-methyl acrylate-glycidyl methacrylate) copolymer (E-MA-GMA) could accelerate the breakup of the PC dispersed phase and decrease the dispersed particle size. The dispersed droplet size in the PC/PE blend with compatibilization was hard to change at different positions along the screw axis with a higher screw speed. Along with the addition of the compatibilizer, the dispersed particle size was slightly influenced by the screw speed.

CRYSTALLIZATION AND PHASE MORPHOLOGY OF IMPACT POLYPROPYLENE COPOLYMERS

Crystal morphology,internal structure of dispersed phase and phase morphology for two impact polypropylene copolymers with the same ethylene content,rubber content,relative molecular weight and relative molecular weight distribution,but obviously different toughness were investigated by polarized optical microscope,differential scanning calorimetry,wide angle X-ray diffraction,dynamic mechanical analysis and atomic force microscope.It was found that the crystallization morphology and behavior of both samples were similar,but the compatibility between the dispersed phase and the matrix in IPC-A was better than that in IPC-B.Moreover,phase composition of the matrix and the dispersed phase of the different IPC were analyzed.It was found that the dispese phase displayed a complex concealment structure.Models of phase structure were proposed to describe the phase structure of both IPC heterophase systems and the action of Eb-P in the IPC.It is suggested that phase morphology plays a more important role as a compatibilizer in enhancing impact strength of IPC.

Deformation of dispersed PA66 phase in drawn PA66/SAN blend

Polyamide 66/styrene acrylonitrile (PA66/SAN) drawn strands were prepared by stretching the corresponding extrudates at 130 °C. During stretching, the PA66 droplets in the extrudate are deformed as a result of the stretching-induced stress. In drawn strands, the morphology of the deformed PA66 is greatly affected by the morphology of the PA66 dispersed phase in the extrudate as well as by the interfacial adhesion between the PA66 and SAN matrix. Upon stretching, the cylindrical PA66 threads in the uncompatibilized extrudate [styrene acrylonitrile maleic anhydride (SANMA) as compatibilizer] deform into PA66 fibrils with large aspect ratio, while the small spherical PA66 droplets are only slightly deformed. Interfacial adhesion between the PA66 and SAN is improved in the compatibilized PA66/SAN extrudate. Consequently, despite the small diameter, PA66 droplets in the compatibilized blend are greatly deformed during stretching.

Quantification of the distribution of carbon black in natural rubber/polybutadiene blends by differential scanning calorimetry

AbstractThe distribution of carbon black (CB) in uncured blends of natural rubber (NR) and polybutadiene (PB) can be quantified using DSC. The crystallization temperature of PB containing CB, measured during cooling from the melt, increases with the CB loading. This phenomenon was used to calculate the CB content in PB and conversely in NR in NR/PB/CB mixtures. Two different blends containing N550 CB were studied. A deeper analysis was performed over the entire composition range of NR/PB blends filled with N234 CB. Two different trends were highlighted depending on composition. Below 50 wt% of NR in the elastomer phase, the crystallization temperature of PB is higher than that of pure PB indicating that a part of the CB is dispersed in PB. Above 50 wt% of NR, the crystallization temperature of PB is lower than that of pure PB, indicating that the whole CB is in the NR phase and that fractionated crystallization of PB simultaneously occurs. Both phenomena are consistent as the dispersed phase morphology is favored by a large increase of the matrix viscosity by the filler. For both CBs, the results indicate that CB has larger affinity for NR than for PB. This tendency was confirmed by transmission electron microscopy. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Influence of chain extension on the compatibilization and properties of recycled poly(ethylene terephthalate)/linear low density polyethylene blends

Polymeric methylene diphenyl diisocyanate (PMDI) was added as chain extender to a blend of recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) with compatibilizer of maleic anhydride- grafted poly(styrene–ethylene/butadiene–styrene) (SEBS- g-MA). Hydroxyl end groups of PET can react with both isocyanate groups of PMDI and maleic anhydride groups of SEBS- g-MA, which are competing reactions during reactive extrusion. The compatibility and properties of the blends with various contents of PMDI were systemically evaluated and investigated. WAXD results and SEM observations indicated that chain extension inhibits the reaction between PET and SEBS- g-MA. As the PMDI content increased, the morphology of dispersed phase changed from droplet dispersion to rodlike shape and then to an irregular structure. The DSC results showed that the crystallinity of PET decreased in the presence of PMDI, and the glass transition temperature ( T g) of PET increased with addition of 0–0.7 w% PMDI. The impact strength of the blend with 1.1 w% PMDI increased by 120% with respect to the blend without PMDI, accompanied by only an 8% tensile strength decrease. It was demonstrated that the chain extension of PET with PMDI in R-PET/LLDPE/SEBS- g-MA blends not only decreased the compatibilization effect of SEBS- g-MA but also hindered the crystallization of PET.

Dynamic mechanical properties and morphological structure of PS/EPDM blends prepared by in situ‐polymerization of styrene

AbstractPS/EPDM blends prepared by in situ‐polymerization of styrene in the presence of EPDM are immiscible and show two phases. Furthermore, the dynamic mechanical behavior of injected specimens is quite different from that of noninjected blends. This is attributed to the differences in morphology before and after injection molding. The morphology of the noninjected blends consists of PS spherical domains covered by a thin layer of EPDM, whereas the injected blends show elastomeric dispersed phase morphology in a rigid matrix. SEM analysis was important to elucidate the changes in the dynamic mechanical behavior of PS/EPDM blends, but TEM analysis is more precise for morphological characterization and yielded the real average diameter of EPDM particles. Comparing the average diameters for the PS/EPDM blends obtained from SEM and TEM analyses, the diameters obtained from the SEM analysis are wider than those of TEM which is due to the solvent extraction effect on the blend morphology. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Dispersed phase morphology and fractionated crystallization of high-density polyethylene in PET/HDPE blends

The fractionated crystallization of high density polyethylene dispersed in a poly(ethylene terephthalate) matrix at composition of 15 wt-% was studied. The effect of the molecular weight of polyethylene with and without compatibilization was particularly addressed regarding its influence on the morphology of the blends. For non-compatibilized blends, the dramatic influence of the molecular weight of the polyethylene on the viscosity ratio and therefore on the dispersion is reflected on the relative intensities of the twin crystallization peaks of polyethylene that are developed upon cooling. These peaks reflect two sets of particles that are nucleated by more or less active heterogeneities. The influence of the addition of an ethylene-glycidyl methacrylate copolymer on the morphology and on the crystallization of the blends was also investigated. For a high molecular weight polyethylene, the compatibilizer shows less efficiency as far as dispersion is concerned.

Synergetic toughness and morphology of poly(propylene)/nylon 11/maleated ethylene‐propylene diene copolymer blends

AbstractPolypropylene (PP)/nylon 11/maleated ethylene‐propylene‐diene rubber (EPDM‐g‐MAH) ternary polymer blends were prepared via melt blending in a corotating twin‐screw extruder. The effect of nylon 11 and EPDM‐g‐MAH on the phase morphology and mechanical properties was investigated. Scanning electron microscopy observation revealed that there was apparent phase separation for PP/EPDM‐g‐MAH binary blends at the level of 10 wt % maleated elastomer. For the PP/nylon 11/EPDM‐g‐MAH ternary blends, the dispersed phase morphology of the maleated elastomer was hardly affected by the addition of nylon 11, whereas the reduced dispersed phase domains of nylon 11 were observed with the increasing maleated elastomer loading. Furthermore, a core‐shell structure, in which nylon 11 as a rigid core was surrounded by a soft EPDM‐g‐MAH shell, was formed in the case of 10 wt % nylon 11 and higher EPDM‐g‐MAH concentration. In general, the results of mechanical property measurement showed that the ternary blends exhibited inferior tensile strength in comparison with the PP matrix, but superior toughness. Especially low‐temperature impact strength was obtained. The toughening mechanism was discussed with reference to the phase morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Influence of compatibilizer precursor structure on the phase distribution of low density poly(ethylene) in a poly(ethylene terephthalate) matrix

AbstractIn attempt to enhance the compatibility of PET/LDPE blends by using a proper functionalized polymer as third component, diethyl maleate (DEM)‐functionalized ultralow density poly(ethylene) (ULDPE‐g‐DEM) and styrene‐b‐(ethylene‐co‐1‐butene)‐b‐styrene triblock copolymer (SEBS‐g‐DEM) were prepared by radical functionalization in the melt. Immiscible PET/LDPE blends having compositions of 70/30 and 80/20 by weight were then extruded in the presence of 1–10% by weight of ULDPE‐g‐DEM and SEBS‐g‐DEM as compatibilizer precursors and ZnO (0.3% by weight) as transesterification catalyst. In both cases, evidences about the occurring of compatibilization between the two immiscible phases, thanks to the studied reactive processes, were obtained. Moreover, the phase distribution and particle size of blends were deeply investigated. Completely different kinds of phase morphology were achieved, as ULDPE‐g‐DEM stabilized a dispersed phase morphology, whereas SEBS‐g‐DEM favored the development of a cocontinuous phase morphology. The observed differences are tentatively explained onthe basis of reactivity and physical features of polymers. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.

Preparation and characterization of vinylidene chloride‐co‐vinyl chloride copolymer/fluorinated synthetic mica nanocomposites I thermal and mechanical properties studies

AbstractPoly(vinylidene chloride‐co‐vinylchloride)/organically modified fluorinated synthetic mica (MEE) (VDC‐VC/MEE) nanocomposites were prepared by melt blending of VDC‐VC copolymer with MEE, in the presence of dioctyl phthalate (DOP) which acted as a plasticizer and a cointercalating agent. The nanostructure, thermal, and dynamic mechanical properties of the VDC‐VC/MEE nanocomposites were studied by wide angle X‐ray diffractometer (WAXD), scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), and dynamic mechanical analyzer (DMA). It was found that partially intercalated and partially exfoliated structures coexisted in VDC‐VC/MEE nanocomposities. Below 8 wt % MEE content, the intercalation effect of nanocomposites decreased with increasing the MEE content. Under a nitrogen atmosphere, VDC‐VC/MEE nanocomposites exhibited a single step thermal degradation behavior. The nanostructure of VDC‐VC/MEE can effectively prevent volatile gases from being released, and thus enhances its thermal stability. The thermal stability of VDC‐VC/MEE nanocomposites is strongly related to the morphology of nanocomposites and the degraded composites structure. DMA revealed a significant improvement in the storage modulus within the testing temperature range. The increase in storage modulus depends on the MEE content, which is attributed to the dispersed phase morphology. The glass transition temperature of VDC‐VC/MEE nanocomposites is affected by the chain mobility in the nanocomposites rather than the aggregative morphology. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1214–1225, 2008

Fractionated Crystallization of High-Density Polyethylene as an Evidence of Dispersed Phase Morphology in PET/HDPE Blends

The fractionated crystallization of HDPE as a dispersed phase in immiscible polymer blends with PET at composition of 15 wt-% was investigated. The dramatic influence of the molecular weight of the HDPE on its melt viscosity and therefore on the dispersion is reflected on the relative intensities of the twin peaks that are observed during the crystallization of the PE phase. The minimum volume of a nucleated domain was found to be in agreement with the typical size of PE spherulites. The effect of the addition of a compatibilizer of the E-GMA type was also studied.