Phase Size Reduction Research Articles

Microstructure evolution and fatigue crack propagation of AlCoCrFeNi2.1 high entropy alloy after electron beam surface modification

AlCoCrFeNi2.1 eutectic high-entropy alloy has good fatigue properties. However, its application in engineering is hindered by as-cast defects. To solve this problem, vacuum electron-beam surface modification is used to strengthen the surface of as-cast high-entropy alloy. It has been discovered that the remelting zone is still composed of body-centered cubic and face-centered cubic phases and that its phase size is refined. A surface-modified structure consisting of the compact RZ and a heat affect zone is obtained, by applying the same fatigue load to the samples before and after electron-beam, respectively. The fatigue crack growth rate of the electron-beam surface-modified material is slower and its life to fracture is longer. Additionally, the fan-shaped fracture and tear edges are typical fracture characteristics of the specimens before and after modification. The results show that with a significant reduction in phase size, the phase boundary density increases. The enhancement of the high-angle grain boundary content and changes in the stress state are also critical factors for the inhibition of fatigue crack growth rate.

Microstructural Modification Hardness and Surface Roughness of Hypereutectic Al-Si Alloys by a Combination of Bismuth and Phosphorus

This research aimed to investigate the effects of bismuth (Bi) and phosphorus (P) addition on the microstructure and roughness of a B390 hypereutectic Al-Si alloy. Microstructural variation of as-cast alloys showed that P is an effective refiner of primary Si and its distribution, while Bi has the opposite effect. The liquidus temperature increased with greater amounts of P, resulting in a wider solidification range. The solidus temperature increased with Bi content, resulting in a shortened solidification range. The benefit of Bi on eutectic silicon was through changing its morphology from fibrous to lamellar structures. It was observed that both primary Si and eutectic Si were modified when both P and Bi were added to the alloys. For effective refinement, the size of primary Si can be reduced by 50.6% and, the P content should not be less than 0.1 wt% with a Bi content of 0.5–1.0 wt%. Furthermore, an intermetallic phase size reduction also occurs. P addition results in a significant (5.85%) increase in hardness. Adding Bi (up to 1.0 wt%) together with P (up to 0.1 wt%) did not reduce the effect of P on the hardness of the modified alloys. The most effective reduction in roughness achieved during cutting at both low and high speeds was 26.5% and 57.7%, respectively, from modifying the B390 alloy using 0.1 wt%P with 1.0 wt%Bi.

The effect of different compatibilisers on the morphology and rheological properties of PP/PET polymer blends

ABSTRACT In the present study, the compatibilisation of polypropylene/polyethylene terephthalate (PP/PET) blends with different types of compatibilisers including maleic anhydride-grafted polypropylene (PP-g-MA), glycidyl methacrylate-grafted polypropylene (PP-g-GMA) and ethylene propylene diene monomer (EPDM) rubber in different concentrations was examined. Samples were evaluated in terms of morphology, thermal and rheological properties. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) were used. According to the results, all samples had a matrix-droplet morphology. Moreover, with increasing the compatibiliser and its concentration, the droplet sizes in dispersed phase decreased. In other words, compatibilised PP/PET showed a greater dispersed phase size reduction, lower crystallinity percentage and larger storage modulus at low frequencies in comparison with non-compatibilised PP/PET blend. Among different samples, polymer blend compatibilised with PP-g-MA (5 phr) indicated the lowest particle size and significantly improved the compatibilisation of the PP/PET blend.

An investigation on recycled PET/PP and recycled PET/PP‐EP compatibilized blends: Rheological, morphological, and mechanical properties

ABSTRACTThe effectiveness of P(E‐co‐MA‐co‐GMA) as a compatibilizer for recycled PET/PP and recycled PET/PP‐EP (polypropylene (ethylene‐propylene) heterophase copolymer) blends was investigated by means of morphological (scanning electron microscopy), rheological (small amplitude oscillatory shear), mechanical (tensile, flexural and impact tests), and thermal (differential scanning calorimetry) properties. Compatibilizer concentration ranged from 1 to 5 wt % with respect to the whole blend. All blends were obtained in a 90/10 composition using a twin screw extruder. Compatibilization effects for PETr/PP‐EP were more pronounced due to ethylene segments present in both PP‐EP and P(E‐co‐EA‐co‐GMA). PETr/PP‐EP has shown greater dispersed phase size reduction, a more solid‐like complex viscosity behavior and larger storage modulus at low frequencies in relation to PETr/PP blend. For both investigated blends, mechanical properties indicated an improvement in both elongation at break and impact strength with increasing compatibilizer content. PETr/PP‐EP blends showed improved performance for the same level of compatibilizer content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41892.

Temperature-dependent compatibilizing effect of graphene oxide as a compatibilizer for immiscible polymer blends

We demonstrated the compatibilizing effect of graphene oxide (GO) in the immiscible poly(methyl methacrylate)/polystyrene (PMMA/PS, 80/20) blend and showed that such a compatibilizing effect was affected by the processing temperature. For the blends prepared at a relatively low temperature (190 °C), the incorporation of 0.5 wt% of GO results in a dramatic reduction in the domain diameter of dispersed minor phase (PS), indicating that GO is an effective compatibilizer. Increasing the processing temperature decreases the dispersed phase size reduction, illustrating that the compatibilizing effect of GO is adverse to processing temperature. The characterization results including the changes in chemical composition of GO and morphologies evolution of blends at different annealing temperatures reveal that this temperature-dependent compatibilizing effect should be attributed to the in situ thermal reduction of GO during the melt processing, which breaks the hydrophilicity-hydrophobicity balance of GO and renders it more hydrophobic. A comparative experiment shows that chemically reduced GO has almost no compatibilizing effect for PMMA/PS blends, which further confirms the proposed mechanism. In addition, the GO-compatibilized blends exhibit great improvement in the mechanical properties than uncompatibilized blends.

Morphology control of a polythiophene–fullerene bulk heterojunction for enhancement ofthe high-temperature stability of solar cell performance by a new donor–acceptor diblockcopolymer

A well defined diblock copolymer (P3HT-b-C60) based on regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acidmethyl ester (PCBM) was synthesized via two controlled polymerization steps and used asa compatibilizer for the P3HT/PCBM blend, which has widely been used as an active layerin bulk heterojunction polymer solar cells. The addition of a small amount of P3HT-b-C60 results in not only the reduction of phase size of P3HT/PCBM blend but also thesuppression of macrophase separation for long-time thermal annealing owing to thepreferential location of the diblock copolymers at the interface between P3HT and PCBMphases. The morphology change with the annealing time is closely related to the change ofthe power conversion efficiency (PCE) of solar cells: the PCE of P3HT/PCBMgreatly decreases with increasing annealing time while the addition of P3HT-b-C60 significantly reduces the decrease of PCE for long-time thermal annealing.

Reactive compatibilization of nylon copolymer/EPDM blends: experimental aspects and their comparison with theory

AbstractIn situ reactive compatibilization was first time applied to a low melting nylon (nylon 6 and 66 copolymer) and EPDM blend system. The effects of in situ compatibilization and concentration of compatibilizer on the morphology and mechanical properties of nylon/EPDM blends have been investigated. The influence of EPM‐g‐MA on the phase morphology was examined by the scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The compatibilizer concentrations used were 0, 1, 2.5, 5, and 10 wt%. The graft copolymer (nylon‐g‐EPM) formed at the interface showed relatively high emulsifying activity. A maximum phase size reduction was observed when 2.5 wt% of compatibilizer was added to the blend system. This was followed by a leveling‐off at higher loadings indicating interfacial saturation. The conformation of the compatibilizer at the interface was deduced based on the area occupied by the compatibilizer at the blend interface. The experimental compatibilization results were compared with theoretical predictions of Noolandi and Hong. It was concluded that the molecular state of compatibilizer at interface changes with concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties. Measurement of tensile properties shows increased elongation as well as enhanced modulus and strength up on compatibilization. At higher concentrations of compatibilizer, a leveling‐off of the tensile properties was observed. A good correlation has been observed between the mechanical properties and morphological parameters. Copyright © 2007 John Wiley & Sons, Ltd.

Effect of ultrasound on the properties of biodegradable polymer blends of poly(lactic acid) with poly(butylene adipate-co-terephthalate)

This study investigated the effect of ultrasound irradiation on the blend of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). The blends of PLA/PBAT(50/50) (PBAT50) were prepared in a melt mixer with an ultrasonic device attached. Thermal, rheological, and mechanical properties, morphology, and biodegradability of the sonicated blends were analysed. The viscosity of the sonicated blends was increased by the ultrasound irradiation owing to the strong interaction. The morphology of the sonicated blends was significantly dependent on the duration of the ultrasound irradiation. For PBAT50, the phase size reduction was maximized when the blends were ultrasonically irradiated for 30 sec. At longer duration of ultrasound irradiation, the PBAT phase underwent flocculation. Measurement of the tensile properties showed an increased breakage tensile stress and an enhanced Young’s modulus when the blends were properly irradiated. This improvement was ascribed to better adhesion between the PLA matrix and the PBAT domain and to better dispersion of the PBAT phase. However, the tensile properties were maximized after excessive energy irradiation, which was ascribed to an emulsifying effect leading to coalescence of the PBAT phase. Impact strength was increased to reach a peak with the ultrasound irradiation, and was higher than the untreated sample for all sonicated samples due to the difference of failure mechanism between the tensile test and the impact test.

Fractographic study of vinylidene polyfluoride copolymers by scanning electronic microscopy

This work enabled the observation of the emulsifying effect of a synthesized copolymer. The surface quality of the prepared alloys fracture was analyzed using the SEM. The examination of the stereotypes obtained on various alloys allowed the visualization of the two involved phases system. We observed on the initial mixture a continuous more or less extended PVDF phase, in which polystyrene PS nodules were inserted, forming a heterogeneous system. In addition, with certain films we noticed that, as the emulsifying rate of the mixture increases, the size of the PS nodules formed decreases significantly. Thus, it appears that in these mixtures the emulsifier agent seems to play a major role in the phase size reduction and subsequently in the increase of the dispersion state. On the other hand, it appears that more the concentration of the emulsifying agent increases, more the size of the phases decreases. All these observations confirm the emulsifying effect of our copolymer.

Rheological Behaviour of PP/PET and Modified PP/PET Blends. II. Dynamic Viscoelastic Properties

The increasing amount of post-consumer waste leads to a search for effective recycling methods. Compatibilisation of immiscible blends of polypropylene (PP) and polyethylene terephthalate (PET) represents one such novel approach that allows recycling of significant scrap materials without any need for separation steps. The intention of this paper is to investigate the dynamic viscoelastic properties of unmodified and modified PP/PET blends. To study the effect of the matrix, three polypropylenes differing in flow properties were chosen. The compatibilisation was carried out by both one- or two-step reactive in situ techniques. In the former case, the addition of 1 wt.% of maleic anhydride, and in the latter, polypropylene supplied already modified by the producer were employed. The measurements were performed by using a rotational cone and plate rheometer at temperatures of 265 °C and 245 °C. Since PET is not melted at the lower temperature, completely different behaviour is observed in the two cases. The rheological functions generally decrease with PET content at 265 °C (conventional blend behaviour), while they increase at 245 °C, in a manner reminiscent particle-filled systems (including the yield behaviour). The positive effect of compatibilisation can be deduced not only from the results of the morphological study (dispersed phase size reduction, strengthened interfacial adhesion), but also through increased values of the viscous and elastic characteristics, which suggests enhanced interactions between the blend components. Comparing steady shear and dynamic viscoelastic properties, the extent of deformation applied during both types of measurements leading to different material responses should be considered.

Morphology Effects from Advances in Polymer Blend Processing

Abstract Innovations in the processing of polymers and polymer mixtures can have unintended consequences for microstructure. Microscopic investigations have been motivated in some cases by acquisition of new processing machinery which is larger, such as the supercompounding extruders. Strategies to expand the capacity of existing machines also necessitate detailed property and morphology comparisons between old and new batches of commercially important blends. Other types of innovations use a temporary processing aid. Dispersed phase size reduction in melt blends on addition of supercritical carbon dioxide has been reported for PMMA/PS blends. TEM images showed smaller, more uniform domains attributed to reduction in melt viscosity. Blends are also under investigation now in flash spun plexifilament fibers to extend the range of end-use properties, but the need for a common solvent limits the possible pairs of polymers. A two-step R.UO4 vapor staining procedure, in which the bulk and sectioned material are exposed, has been used to examine non-equilibrium morphologies frozen in from flash spinning.

The relative role of coalescence and interfacial tension in controlling dispersed phase size reduction during the compatibilization of polyethylene terephthalate/polypropylene blends

The breaking thread and the sessile drop methods have been used to evaluate the interfacial tension between a polypropylene (PP) and a polyethylene-terephthalate (PET). An excellent correlation was found between the two. The breaking thread technique was then used to evaluate the interfacial tension of these blends at various levels of a styrene-ethylene butylene-styrene grafted with maleic anhydride (SEBS-g-MA) compatibilizer. In order to evaluate the relative roles of coalescence and interfacial tension in controlling dispersed phase size reduction during compatibilization, the morphology of PP/PET 1/99 and 10/90 blends compatibilized by a SEBS-g-MA were studied and compared. The samples were prepared in a Brabender mixer. For the 10/90 blend, the addition of the compatibilizer leads to a typical emulsification curve, and a decrease in dispersed phase size of 3.4 times is observed. For the 1/99 blend, a 1.7 times reduction in particle size is observed. In the latter case, this decrease can only be attributed to the decrease of the interfacial tension. It is evident from these results that the drop in particle size for the 10/90 PP/PET blend after compatibilization is almost equally due to diminished coalescence and interfacial tension reduction. These results were corroborated with the interfacial tension data in the presence of the copolymer. A direct relationship between the drop in dispersed phase size for the 1/99 PP/PET blend and the interfacial tension reduction was found for this predominantly shear mixing device. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2271–2280, 1997

The relative role of coalescence and interfacial tension in controlling dispersed phase size reduction during the compatibilization of polyethylene terephthalate/polypropylene blends

The breaking thread and the sessile drop methods have been used to evaluate the interfacial tension between a polypropylene ( PP ) and a polyethylene-terephthalate (PET). An excellent correlation was found between the two. The breaking thread technique was then used to evaluate the interfacial tension of these blends at various levels of a styrene-ethylene butylene-styrene grafted with maleic anhydride (SEBS-g-MA) compatibilizer. In order to evaluate the relative roles of coalescence and interfacial tension in controlling dispersed phase size reduction during compatibilization, the morphology of PP/PET 1/99 and 10/90 blends compatibilized by a SEBS-g-MA were studied and compared. The samples were prepared in a Brabender mixer. For the 10/90 blend, the addition of the compatibilizer leads to a typical emulsification curve, and a decrease in dispersed phase size of 3.4 times is observed. For the 1/99 blend, a 1.7 times reduction in particle size is observed. In the latter case, this decrease can only be attributed to the decrease of the interfacial tension. It is evident from these results that the drop in particle size for the 10/90 PP/PET blend after compatibilization is almost equally due to diminished coalescence and interfacial tension reduction. These results were corroborated with the interfacial tension data in the presence of the copolymer. A direct relationship between the drop in dispersed phase size for the 1/99 PP/PET blend and the interfacial tension reduction was found for this predominantly shear mixing device.

Interaction characterization of PA1010/PP blends using PP‐g‐AA as compatibilizer

AbstractThe morphology of polyamide 1010/polypropylene blends was found to significantly depend upon the concentration of the compatibilizer[polypropylene‐grafted‐acrylic acid (PP‐g‐AA)]. A significant reduction in phase size was observed because of the interaction that existed between the PP‐g‐AA and polyamide. These interactions have been confirmed by several methods. The tensile mechanical properties and impact behavior of the prepared blends were investigated and correlated with scanning electron microscope (SEM) analysis of the fracture surfaces. It was found that PP‐g‐AA as the compatibilizer has a profound effect upon the properties of the blends. This behavior is attributed to a series of chemical and physico‐chemical interactions taking place between the two components.

Compatibilizing effect of a poly(ester imide) on the properties of the blends of poly(ether imide) and a thermotropic liquid crystalline polymer: 2. Morphology and mechanical properties of the in situ composite system

Blends of a thermotropic liquid crystalline polymer (TLCP), [poly(ester amide), PEA, Vectra B950 from Hoechst Celanese] and poly(ether imide) (PEI, Ultem 1000 from G.E.) with the compatibilizer [poly(ester imide), PEsI] were extruded in a twin-screw extruder. The extruded strands were evaluated in terms of morphology and mechanical properties. The morphology of the compatibilized in situ composites was found to be significantly dependent on the concentration of the compatibilizer in the blend. For a TLCP phase content of 25 phr, a maximum reduction in phase size was observed when 1.5 phr by weight of compatibilizer was added to the blend. At high concentrations of the compatibilizer, flocculation of the TLCP phase was observed. Measurement of the tensile properties shows increased elongation as well as enhanced modulus and strength when properly compatibilized. This improvement is ascribed to better adhesion between the TLCP fibrils and the PEI matrix and better dispersion of the TLCP fibrils. Synthesized PEsI significantly improved the adhesion between the matrix phase (PEI) and fibril phase (PEA). However, maxima in tensile modulus, tensile strength and elongation were observed when excess compatibilizer was added. An emulsifying effect of the compatibilizer to coalesce the fibrils is believed to be the cause of the maxima in the tensile properties. Impact strength was seriously increased with the compatibilizer. A maximum in impact strength was also observed, but all compatibilized samples exhibited a higher impact strength than the non-compatibilized one. The reason is believed to be the failure mode difference between the tensile properties and the impact strength.

Processing‐morphology relationships of compatibilized polyolefin/polyamide blends. Part I: The effect of an lonomer compatibilizer on blend morphology

AbstractThe morphology of compatibilized polyolef in/polyamide blends was found to be significantly dependent on the concentration of an ionomer compatibilizer (polyethylene‐methacrylic acid‐isobutyl acrylate terpolymer) in the blend. For a dispersed phase content of 10% by weight, a maximum reduction in phase size was observed when only 0.5% by weight of ionomer was added to the blend, A more significant reduction of the dispersed phase size was observed when the minor phase was nylon, due to interactions which exist between the ionomer and the polyamide. These interactions have been confirmed by Fourier transform infrared spectroscopy. At high concentrations of the ionomer, flocculation of the nylon dispersed phase was observed. In comparison to one‐step mixing, blends prepared by two‐step or batch mixing were characterized by a smaller dispersed phase when nylon was the matrix, and a larger particle size when nylon was the minor phase. The results observed are explained in terms of a speculative model of the interactions occurring across the nylon‐polvolefin interface.