Immiscible Polymer Blends Research Articles

Circumventing Macroscopic Phase Separation in Immiscible Polymer Mixtures by Bottom-up Deposition

Achieving intimate mixing in immiscible polymer blend thin films is of paramount importance for maximizing their performance in numerous applications such as membranes, electronics, and energy devi...

Simultaneously Grafting Poly(lactic acid) (PLLA) and Polyethylene (PE) Chains onto a Reactive SG Copolymer: Formation of Supertough PLLA/PE Blends by Reactive Processing

Reactive compatibilization is a cost-effective and efficient way to fabricate high-performance multicomponent polymeric materials. The reactive compatibilization of low-density polyethylene (LDPE) and poly­(l-lactide) (PLLA) blends has seldom been reported because LDPE is inert to the chemical reaction during melt compounding. In this work, we first grafted carboxylic acid groups onto the PE molecular chains (m-LDPE), followed by a facile binary grafting strategy to compatibilize PLLA/LDPE blends. Poly­(styrene-co-glycidyl methacrylate) (SG) has been used as the main chains for the binary grafting. The carboxylic acid groups of both PLLA and m-LDPE can react with the epoxide groups on SG main chains during the melt blending, leading to the in situ formation of both LDPE and PLLA grafted copolymers. Such binary grafted copolymers act as effective compatibilizers for the highly immiscible PLLA/LDPE (80/20) blends. The compatibilized blends exhibit excellent mechanical performance. The tensile strength of the compatibilized PLLA/LDPE blends increases from 26.4 to 36.7 MPa, and the elongation remarkably enhances from 9 to 367%, as compared with the same blends without compatibilization. At the same time, the Charpy impact strength of the compatibilized blend is 100.1 kJ/m2, which is 6.2 times that of the LDPE/PLLA binary blend. The fabricated PLLA/LDPE blends show potential engineering applications as environment-friendly materials. In addition, the in situ binary grafting strategy paves a new possibility for the reactive compatibilization of immiscible polymer blends with no reactive groups.

Microstructural Contributions of Different Polyolefins to the Deformation Mechanisms of Their Binary Blends.

The mixing of polymers, even structurally similar polyolefins, inevitably leads to blend systems with a phase-separated morphology. Fundamentally understanding the changes in mechanical properties and occurring deformation mechanisms of these immiscible polymer blends, is important with respect to potential mechanical recycling. This work focuses on the behavior of binary blends of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) under tensile deformation and their related changes in crystallinity and morphology. All of these polymers plastically deform by shear yielding. When unmixed, the high crystalline polyolefins HDPE and PP both exhibit a progressive necking phenomenon. LDPE initiates a local neck before material failure, while LLDPE is characterized by a uniform deformation as well as clear strain hardening. LLDPE/LDPE and LLDPE/PP combinations both exhibit a clear-cut matrix switchover. Polymer blends LLDPE/LDPE, LDPE/HDPE, and LDPE/PP show transition forms with features of composing materials. Combining PP in an HDPE matrix causes a radical switch to brittle behavior.

Constructing a Microcapacitor Network of Carbon Nanotubes in Polymer Blends via Crystallization-Induced Phase Separation Toward High Dielectric Constant and Low Loss.

Tailoring the distribution of nanoparticles and further constructing effective microcapacitors in polymer blends are important issues for developing high-performance polymer dielectric nanocomposites. The common method to control the selective localization of nanoparticles in an immiscible polymer blend is relatively difficult and it easily results in the accumulation of nanoparticles in one component, which usually leads to a dramatic increase of the dielectric loss in the nanocomposites. In this work, a novel strategy based on step-by-step crystallization has been proposed to tailor the refined distribution and dispersion of carbon nanotubes (CNTs) in a melt-miscible blend poly(butylene succinate)/poly(vinylidene fluoride) (PBS/PVDF) through the crystallization-induced phase separation and the engineered interfacial affinity between CNTs and polymer components to acquire high dielectric constant and low dielectric loss. The results reveal that PBS is excluded along the growth front of PVDF spherulites and locates in the margin areas of PVDF spherulites during the step-by-step crystallization process. Moreover, because of the higher interfacial interaction between CNTs and PBS, CNTs are located in the PBS-rich domain, resulting in a high concentration of CNTs in the interspherulites of PVDF. Thus, the dielectric constants of the nanocomposites are greatly improved by nearly 5-24 times compared with the nanocomposites achieved by quick cooling and, simultaneously, the dielectric loss of the nanocomposites is still maintained at a low level. This work shows that the step-by-step crystallization method can be used to fabricate the nanocomposites with a synergistic increase in the dielectric performance due to the formation of a refined microcapacitor assembly. To the best of our knowledge, this is the first report to show that the dielectric constant of the nanocomposites can be greatly enhanced just through the crystallization-optimized distribution and dispersion of CNTs in immiscible polymer blends, and it possibly gives a new technical route for the fabrication of advanced dielectric composites.

Guar gum (GG) / Methylcellulose (MC) Blends and their Composites with Maghemite Nanoparticles

Miscibility of polymers decides the applicability of the resulting blends and immiscible polymer blends can be made compatible with suitable compatibilizer. Miscibility of blends of guar gum (GG) and methyl cellulose (MC) in common solvent water were studied by refractive index, density, ultrasonic velocity, and dilute solution viscometry methods at 30°C and 40°C. Based on these measurements, it is found that the polymer blend of GG/MC is immiscible. The effect of compatibilization with 0.02 wt% maghemite nanoparticle was studied in aqueous solution and found that 10/90 GG/MC blend is miscible in the presence of maghemite. Solution cast technique was used to prepare thin films of GG/MC blend – maghemite composite and characterized by scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) method.

Dispersion and Localization Behavior of Modified MWCNTs in Immiscible Polymer Blends of Polystyrene and Polybutadiene and in Corresponding Nanostructured Block Copolymers

The influence of carbon nanotube (CNT) modification on the dispersion and localization behavior of the CNTs in immiscible blends of polystyrene (PS) and polybutadiene (PB), and in the nanostructured morphology of a star-shaped styrene-butadiene based block copolymer (BCP), was studied to form a basis for the development of functional materials with defined electrical property profiles. Unmodified multi-walled CNTs (MWCNTs) were dispersed in PS, PB and PS/PB blends by solution mixing. Additionally, MWCNTs were functionalized with n-octadecylamine and monoamino-terminated polystyrene to increase the compatibility between the homopolymers and the nanofiller. The MWCNT dispersion and the blend morphology formation were studied using transmission light microscopy and scanning electron microscopy. The MWCNT dispersion could be significantly improved by the modification of the MWCNTs. All MWCNT types were found to preferably localize in the PS phase of the PS/PB blend. However, only blends containing unmodified MWCNTs were electrically conductive. Similar effects were found in BCP/MWCNT composites. The BCP was already electrically conductive with a filler content of 0.1 wt % of unmodified MWCNTs. The stress–strain behavior of the BCP was slightly influenced by MWCNT addition and CNT modification. The dispersability of MWCNTs was significantly improved by CNT functionalization, which indicates a strong polymer-filler interaction.

Compatibilization of immiscible blends of polypropylene and isosorbide containing copolyester with silica nanoparticles

AbstractIn the present study, compatibilization of immiscible blends of polymers was investigated based on the Pickering emulsion concept with various mixing procedures. Silica nanoparticles were incorporated into poly (1,4‐cyclohexanedimethylene isosorbide terephthalate) (PEICT)/isotactic polypropylene (iPP) blends. Localization of nanoparticles was effectively modified by varying mixing procedures. Relocation of hydrophilic silica occurred in a secondary mixing procedure with the PEICT, which has relatively high affinity when primarily mixed with iPP. The final location of the silica nanoparticles was confirmed by SEM images. SEM and an optical microscope were used to follow morphological change. By simply changing the mixing procedure, the hydrophilic silica nanoparticles were able to perform the role of a morphology modifier successfully without modifying the surface characteristics. The mechanical properties and crystallization behavior were also compared depending on the surface characteristics of the silica nanoparticles and their final localization.

Enhancement of interfacial adhesion in immiscible polymer blend by using a graft copolymer synthesized from propargyl-terminated poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) is a biomass-derived polymer synthesized by the fermentation inside the bacteria, which has excellent flexibility and mechanical toughness. However, the industrial applications of PHBH have been limited because of its poor modulus of elasticity and tensile strength. For improving the mechanical characteristics of PHBH to eventually broaden its industrial applications, it was blended with poly(methyl methacrylate) (PMMA), a rigid polymer. Moreover, blending PHBH was also expected to increase the toughness of PMMA. Nevertheless, PHBH/PMMA blends lack interfacial adhesion due to low miscibility, thus restricting potential applications. This work focusses on enhancing the compatibility of PHBH/PMMA blend by developing a compatibilizer. The synthesis of PMMA-g-PHBH, a graft copolymer, was carried out using methyl methacrylate and vinyl-terminated PHBH derived from propargyl-terminated PHBH. The findings obtained from scanning electron microscopy and thermal analysis showed improvement in the miscibility of PHBH and PMMA upon the inclusion of PMMA-g-PHBH in the blend structure. The mechanical properties of the blends can also be tuned by controlling the weight fraction of PHBH/PMMA/PMMA-g-PHBH. This study proves that PMMA-g-PHBH acts as an effective compatibilizer for PHBH/PMMA blends.

Vorticity-Aligned Droplet Bands in Sheared Immiscible Polymer Blends Induced by Solid Particles

The spatiotemporal organization of complex fluids under flow can be strongly affected by incorporating solid particles. Here, we report that a monolayer of interfacially active microspheres preferentially wetted by the matrix phase can bridge droplets into vorticity-aligned bands in immiscible polymer blends at intermediate particle concentrations and low shear rates. Strong particle bridging ability and the formation of rigid anisotropic droplet bands with a negligible inertia effect in the Newtonian matrix are suggested to be responsible for the vorticity orientation of droplet bands during slow shear flow, which could be understood based on Jeffery orbit theory in the framework of fluid mechanics and strong confinement effect acted by shear walls and adjacent bands. However, increasing the aspect ratio of particles could restrain the formation of anisotropic bands because of reduced particle coverage and promoted droplet coalescence induced by sharp particle corners, increased and uneven distribution of particle aggregates in the matrix phase, and weakened particle bridging ability.

Morphology evolution of poly(lactic acid) during in situ reaction with poly(butylenesuccinate) and ethylene‐methyl acrylate‐glycidyl methacrylate: The formation of a novel 3D star‐like structure

AbstractMorphology control of polymer alloys is an attractive topic for investigators due to its ability to improve the performance of products for years. However, it is hard to control the morphology of immiscible polymer blends during melt processing. Herein, we studied the morphology evolution of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) with the inclusion of ethylene‐methyl acrylate‐glycidyl methacrylate (EGMA). Scanning electron microscopy of both cryo‐fractured and etched cryo‐fractured samples indicates that the in situ reaction among PLA, PBS, and EGMA can induce the morphology change and result in a novel 3D star‐like structure. Rheology behaviors of the samples under different angular frequencies were used to validate the formation of 3D networks in the samples. Tensile stiffness reinforcements at both room temperature and high temperature were provided through dynamic mechanical analysis. In addition, a 10‐fold improvement in impact strength is also monitored by the unnotched impact test to indicate the superior toughening effect. Furthermore, the crystalline behavior and thermal properties of the blends were also studied. It is believed that our work not only gives a deeper understanding of the reaction‐induced morphology evolution of the PLA/PBS/EGMA blends but also reveals an avenue toward morphology control by melt processing.

Reactive Comb Polymer Compatibilized Immiscible PVDF/PLLA Blends: Effects of the Main Chain Structure of Compatibilizer.

The compatibilizer with double comb structure has a superior compatibilizing effect for immiscible polymer blends due to the symmetrical structure on both sides of main chains. Extensive study related to the architectural effects of compatibilizer on the compatibilization has mainly focused on the side chains. We investigated the influence of the compatibilizer-main-chain structure on the compatibilizing effect for immiscible poly(vinylidene fluoride)/poly(L-lactic acid) (PVDF/PLLA) blends. Two reactive-comb compatibilizers with polystyrene (PS) and polymethylmethacrylate (PMMA) as main chains and PMMA as the side chains have been synthesized. PS is immiscible with both PLLA and PVDF, while PMMA is miscible with PVDF. It was found that both compatibilizers can improve the compatibility between the PLLA and PVDF, with different compatibilization effects. In the PVDF/PLLA (50/50) blends, 1 wt.% poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC–SG) tuned the morphology from the droplet-in-matrix structure to the co-continuous structure, while the blends with poly(methyl methacrylate-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC–MMG) kept the sea-island structure with even 3 wt.% loading. Moreover, RC–SG induces a wider co-continuous interval range than RC–MMG. The co-continuous structure obtained by RC–SG was also more stable than that by RC–MMG. It was further found that RC–SG-compatibilized PVDF/PLLA blends exhibit higher mechanical properties than the RC–MMG-compatibilized blends.

A model for the prediction of the morphology of immiscible blends of polymers

This paper presents a micro-rheological model to predict the morphology of immiscible polymer blends, established during melt processing, on the whole composition range. This model based on elementary mechanisms of dispersion described in the literature, uses two different descriptions of the topology in the case of dispersed and co-continuous phases. By using a small number of material and process parameters (shear rate, viscosity of the phases and interfacial tension) and by analysing the stability of the droplets or threads of one phase in the matrix, it enables to calculate diagrams of continuity, sizes of phases and interfacial areas. The model was tested in comparison with experimental results on selected polyolefin blends, regarding the type of morphology, the interfacial area and the excess of elasticity at low frequency in oscillatory shear.

Modeling and Simulation of the Process for the Generation of Gradient Porous Structures From Immiscible Polymer Blends

Abstract There has been growing interest in integrating gradient porous structures into synthetic materials like polymers. One particular method for making gradient porous polymers is nonisothermal annealing of co-continuous phase structures of immiscible polymer blends under well-defined thermal boundary conditions. In this paper, we report a method to simulate this nonisothermal phase coarsening process for the generation of gradient-phase structures by the combined implementation of phase-field transport and momentum transport. Specifically, a phase-field equation is solved first to obtain a phase structure with phase size comparable with that of the blend to be annealed. This phase structure is then used as an initial geometry in a two-phase moving-interface flow simulation to gauge into the phase structure coarsening process. Several case studies were performed, and the results show that the controllable generation of gradient-phase structures can be enabled by well-designed geometry and thermal boundary conditions. Using 2D simulations, different types of gradient-phase structures experimentally observed were predicted. With increasing power in computation, the capability of 3D simulation may be unveiled for a more accurate prediction of the nonisothermal phase coarsening process and may ultimately evolve into a useful tool for the design and processing of gradient porous polymers.

Nanoparticles influence miscibility in LCST polymer blends: from fundamental perspective to current applications.

Polymer blending is an effective method that can be used to fabricate new versatile materials with enhanced properties. The blending of two polymers can result in either a miscible or an immiscible polymer blend system. This present review provides an in-depth summary of the miscibility of LCST polymer blend systems, an area that has garnered much attention in the past few years. The initial discourse of the present review mainly focuses on process-induced changes in the miscibility of polymer blend systems, and how the preparation of polymer blends affects their final properties. This review further highlights how nanoparticles induce miscibility and describes the various methods that can be implemented to avoid nanoparticle aggregation. The concepts and different state-of-the-art experimental methods which can be used to determine miscibility in polymer blends are also highlighted. Lastly, the importance of studying miscible polymer blends is extensively explored by looking at their importance in barrier materials, EMI shielding, corrosion protection, light-emitting diodes, gas separation, and lithium battery applications. The primary goal of this review is to cover the journey from the fundamental aspects of miscible polymer blends to their applications.

Compatibilization of immiscible polymer blends (R-PET/PP) by adding PP-g-MA as compatibilizer: analysis of phase morphology and mechanical properties

In the current study, the compatibilization of polypropylene/recycled polyethylene terephthalate (PP/r-PET) blends with different percentages of maleic anhydride (PP-g-MA) was examined. Exploited resource for r-PET was used as water bottles. Specimens of PP/r-PET blends in different percentages, i.e., 90/10, 70/30, and 50/50 were prepared in a corotating twin-screw extruder to evaluate the mechanical properties. Results indicated that PP-g-MA improved compatibilization of the PP/r-PET blends (modulus of elasticity and yield stress were enhanced to about 1450 MPa and 30 MPa) and also enhanced the morphological and mechanical properties. By adding about 2% of the compatibilizer into specimens containing 10% of r-PET, the highest enhancement in mechanical properties was achieved. Besides, both yield strength and the impact of energy were improved 8.3% and 24.6% by increasing the amount of 50% and 10% r-PET in the system. Also, results showed that specimens have higher yield stress and modulus of elasticity after 10 days compared to those specimens without aging due to the presence of stronger interaction after a period of time.

Effects of processing conditions on hybrid filler selective localization, rheological, and thermal properties of poly(ε‐caprolactone)/poly(lactic acid) blends

ABSTRACTIn this study, the effects of processing conditions through different mixing sequences were used to analyze the factors, which could influence the hybrid filler selective localization in an immiscible polymer blend and how localization can influence the rheological and thermal properties. Different selective localizations were observed depending on the mixing sequence used when the hybrid filler was added. Notably, nanoparticles can interact with each other, which favor a synergy between them and alters, besides the localization, the dispersion state, or can interact with one polymer phase, and also alter the nanoparticles' selective localization. An improvement in rheological properties was observed in the hybrid nanocomposite in which there was interaction between the nanoparticles, favoring the hexagonal boron nitride exfoliation. On the other hand, for the storage modulus and degree of crystallinity, the sharpest increase occurred in the hybrid nanocomposite in which the nanoparticles could interact preferably with one polymer phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48711.

Carbon nanotube localization at interface in cocontinuous blends of polyethylene and polycarbonate

ABSTRACTA new technique to show good electroconductivity was proposed using carbon nanotube (CNT) localization in cocontinuous immiscible polymer blends comprising ultrahigh‐molecular‐weight polyethylene (UHMWPE) and polycarbonate (PC). When UHMWPE was added to PC/CNT in the molten state in an internal mixer, CNTs started moving to the UHMWPE phase. However, CNTs require a long time to diffuse into the UHMWPE phase owing to a low diffusion constant. Consequently, they remain at the interface between PC and UHMWPE. When the blends have cocontinuous structure, the localized CNTs at the phase boundary act as a conductive path, leading to a good electroconductivity. Although a similar morphology is obtained by adjusting the balance of interfacial tensions among polymers and CNT, it is difficult to find a system showing appropriate interfacial tensions. As the present method is applicable to various polymer blends, it will be an important technique to prepare a conductive nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48676.

Selection of Immiscible Polymer Blends Filled with Carbon Nanotubes for Heating Applications.

In many application fields, such as medicine or sports, heating textiles use electrically conductive multifilaments. This multifilament can be developed from conductive polymer composites (CPC), which are blends of an insulating polymer filled with electrically conductive particles. However, this multifilament must have filler content above the percolation threshold, which leads to an increase of the viscosity and problems during the melt spinning process. Immiscible blends between two polymers (one being a CPC) can be used to allow the reduction of the global filler content if each polymer is co-continuous with a selective localization of the fillers in only one polymer. In this study, three immiscible blends were developed between polypropylene, polyethylene terephthalate, or polyamide 6 and a filled polycaprolactone with carbon nanotubes. The morphology of each blend at different ratios was studied using models of co-continuity and prediction of fillers localization according to viscosity, interfacial energy, elastic modulus, and loss factor of each polymer. This theoretical approach was compared to experimental values to find out differences between methods. The electrical properties (electrical conductivity and Joule effect) were also studied. The co-continuity, the selective localization in the polycaprolactone, and the Joule effect were only exhibited by the polypropylene/filled polycaprolactone 50/50 wt.%.

Reactive splicing compatibilization of immiscible polymer blends: Compatibilizer synthesis in the melt state and compatibilizer architecture effects

Reactive compatibilization is an effective method to improve the compatibility of immiscible polymer blends. The in-situ-formed graft/block copolymers should be thermodynamically located at the interface to bridge the neighboring phases. Unfortunately, they are often pulled out of the interface because of the asymmetric molecular structures. Here, we propose a new strategy to compatibilize immiscible polymer blends called reactive splicing compatibilization. Poly (styrene-co-glycidyl methacrylate) (SG) with high glycidyl methacrylate (GMA) content is used as the reactive backbone chain. Both poly (l-lactic acid) (PLLA) and poly (butylene adipate-co-terephthalate) (PBAT) molecular chains can be easily grafted onto the SG main backbone by the reaction of the terminal carboxylic acid groups with the epoxide groups in the melt. Direct melt blending SG with PLLA and/or PBAT leads to reactive compatibilizers with various molecular architectures, which are used for subsequent compatibilization of PLLA/PBAT blends. It was found that the compatibilizer architecture significantly affects the compatibilization efficiency. The best compatibilization occurs with a reactive compatibilizer of SG-g-PBAT with the SG to PBAT weight ratio of 1:2. The compatibilized PLLA/PBAT (50/50 w/w) blend has precise co-continuous phase morphology with very few micelles. The blend exhibits extremely high Charpy notched impact strength of 90.2 kJ/m2 and tensile strength of 33.3 MPa. The principle of the facile splicing compatibilization strategy is highly applicable to many other immiscible blends with both components containing reactive groups.

Effects of Three Different Injection-Molding Methods on the Mechanical Properties and Electrical Conductivity of Carbon Nanotube/Polyethylene/Polyamide 6 Nanocomposite.

Morphological evolution under shear, during different injection processes, is an important issue in the phase morphology control, electrical conductivity, and physical properties of immiscible polymer blends. In the current work, conductive nanocomposites were produced through three different injection-molding methods, namely, conventional injection molding, multi-flow vibration injection molding (MFVIM), and pressure vibration injection molding (PVIM). Carbon nanotubes in the polyamide (PA) phase and the morphology of the PA phase were controlled by various injection methods. For MFVIM, multi-flows provided consistently stable shear forces, and mechanical properties were considerably improved after the application of high shear stress. Shear forces improved electrical property along the flow direction by forming an oriented conductive path. However, shear does not always promote the formation of conductive paths. Oscillatory shear stress from a vibration system of PVIM can tear a conductive path, thereby reducing electrical conductivity by six orders of magnitude. Although unstable high shear forces can greatly improve mechanical properties compared with the conventional injection molding (CIM) sample, oscillatory shear stress increases the dispersion of the PA phase. These interesting results provide insights into the production of nanocomposites with high mechanical properties and suitable electrical conductivity by efficient injection molding.