Incompatible Polymer Blends Research Articles

Modeling linear and nonlinear rheology of industrial incompatible polymer blends

The ability to accurately predict the rheological behavior of the blends of two incompatible polymers is critical to the polymer industry. The constitutive modeling of incompatible polymer blends requires understanding the structure and dynamics of the blends across different length scales. The polydispersity of chain length at the molecular level and nonuniformity of flow field due to dispersed domains at the mesoscopic level present significant challenges to this industrially relevant problem. This work proposes a modeling framework for linear and nonlinear rheology of industrial incompatible polymer blends with sea-island morphology. For the individual components, we adopt the Rolie-Double-Poly model and generate the relaxation spectrum from an optimized molecular weight distribution. We derive a new mixing rule without empirical parameters from the flow field analysis inside and outside the droplets. The phase interface, modeled by an ellipsoidal model, contributes to the apparent rheology only at low shear rates. Our modeling approach is verified by the shear and extensional rheology of eight polymer blends with a broad range of viscosity ratios (0.01–100). We also show that the model has the ability to predict the nonlinear rheological behaviors of incompatible polymer blends with known molecular weight distributions and phase morphology.

Upcycling Polyolefin Blends into High-Performance Materials by Exploiting Azidotriazine Chemistry Using Reactive Extrusion.

The revalorization of incompatible polymer blends is a key obstacle in realizing a circular economy in the plastics industry. Polyolefin waste is particularly challenging because it is difficult to sort into its constituent components. Untreated blends of polyethylene and polypropylene typically exhibit poor mechanical properties that are suitable only for low-value applications. Herein, we disclose a simple azidotriazine-based grafting agent that enables polyolefin blends to be directly upcycled into high-performance materials by using reactive extrusion at industrially relevant processing temperatures. Based on a series of model experiments, the azidotriazine thermally decomposes to form a triplet nitrene species, which subsequently undergoes a complex mixture of grafting, oligomerization, and cross-linking reactions; strikingly, the oligomerization and cross-linking reactions proceed through the formation of nitrogen-nitrogen bonds. When applied to polyolefin blends during reactive extrusion, this combination of reactions leads to the generation of amorphous, phase-separated nanostructures that tend to exist at polymer-polymer interfaces. These nanostructures act as multivalent cross-linkers that reinforce the resulting material, leading to dramatically improved ductility compared with the untreated blends, along with high dimensional stability at high temperatures and excellent mechanical recyclability. We propose that this unique behavior is derived from the thermomechanically activated reversibility of the nitrogen-nitrogen bonds that make up the cross-linking structures. Finally, the scope of this chemistry is demonstrated by applying it to ternary polyolefin blends as well as postconsumer polyolefin feedstocks.

Compatibilization Efficiency of Graft Copolymers in Incompatible Polymer Blends: Dissipative Particle Dynamics Simulations Combined with Machine Learning

Compatibilization Efficiency of Graft Copolymers in Incompatible Polymer Blends: Dissipative Particle Dynamics Simulations Combined with Machine Learning

Thermally and organomodified montmorillonite as effective regulators of the structure formation process in polypropylene/polystyrene blends

The influence of the concentration of thermally and organomodified montmorillonite on the processes of structure formation in a blend of polypropylene/polystyrene (PP/PS) was studied. It is established that in nanofilled compositions, as well as in the original, is formed a microfibrillar structure, the dimensional characteristics of which depend on the content of the additive and the method of its modification. The investigated clays by content (0.2–2.0) wt. % by weight of polypropylene have a compatibilizing effect in the blend of PP/PS, which reduces the average diameter of microfibers by 1.6 times and increases the homogeneity of their distribution by diameter: statistical indicators decrease (standard deviation, variance, coefficient of variation). The modifying effect of thermally modified clay is higher—the improvement of the dimensional characteristics of PP microfibers is achieved at its minimum content in the blend (0.2 wt. %). The formation of anisotropic PP structures in the PS matrix and the relaxation of the accumulated stresses at the exit of the molding hole is the main factor that causes high values of the coefficient of swelling of the extrudates (4.0–7.7). The change in the microstructure of the extrudates of nanofilled systems during spinning depends on the composition of the blend and the method of modification of montmorillonite. The average diameters of microfibers decrease from 2.2 μm (in the original blend) to (1.3–2.0) μm (in three-component) depending on the content of additives. The ability to regulate the microstructure of incompatible polymer blends by introducing additives of thermally and organomodified montmorillonite will contribute to the creation of nanocomposites with controlled morphology, as well as new fine-fiber materials with improved filtering characteristics.

Formation of the Percolation Network by Carbon Black Particles in Blends of Incompatible Polymers under the Conditions of Shear Strain of the Melt

Formation of the Percolation Network by Carbon Black Particles in Blends of Incompatible Polymers under the Conditions of Shear Strain of the Melt

Molecular Dynamics Simulations of Crystal Nucleation near Interfaces in Incompatible Polymer Blends.

We apply molecular dynamics (MD) simulations to investigate crystal nucleation in incompatible polymer blends under deep supercooling conditions. Simulations of isothermal nucleation are performed for phase-separated blends with different degrees of incompatibility. In weakly segregated blends, slow and incompatible chains in crystallizable polymer domains can significantly hinder the crystal nucleation and growth. When a crystallizable polymer is blended with a more mobile species in interfacial regions, enhanced molecular mobility leads to the fast growth of crystalline order. However, the incubation time remains the same as that in pure samples. By inducing anisotropic alignment near the interfaces of strongly segregated blends, phase separation also promotes crystalline order to grow near interfaces between different polymer domains.

Influence of coordination complexes of transition metals on EMI-shielding properties and permeability of polymer blend/carbon nanotube/nickel composites

In this work the influence of transition metal coordination compounds was analyzed on the EMI-shielding characteristics and permeability for a paramagnetic probe of polymer composites based on cross-linked polyurethane or incompatible polymer blend (simultaneous semi-IPN based on cross-linked polyurethane and linear poly(methylmethacrylate) filled in situ with conductive and/or magnetic filler. Cross-linked polyurethane/carbon nanotube composites, polymer blend/carbon nanotube composites and polymer blend/carbon nanotube/nickel composites contained of 1.5 wt% and 3 wt% of fillers were modified with Fe(3+)acetylacetonate or Cr(3+)acetylacetonate coordination compounds of different complexing ability. It was shown that opposite effect of Fe (3+) and Cr(3+) complexes on the phase separation in the polymer blend allows regulate the level of the multiple reflection of the electromagnetic wave at the interfacial boundaries as well as protective characteristics and permeability of the investigated systems. The shielding efficiency of chromium-modified composite in the frequency range of (25.8–37.5) GHz is up to 25 dB in the segregated polymer. It has been shown that the effect of conductive nanofillers on polymer loosening is opposite to that of magnetic fillers and is sensitive to the presence in the system of coordination complexing agent.

In Situ Microfibril Structure in Incompatible Isotactic Polypropylene/Polylactic Acid Blends Controlled By Viscosity Ratio

In situ microfibril structure can significantly improve the mechanical properties of incompatible blends. In this work, the in situ microfibrils were constructed in isotactic polypropylene/polylactic acid (iPP/PLA) blends by direct injection molding process, and the effect of viscosity ratio on the morphology was systematically analyzed. The results of scanning electron microscope and rheology show that the viscosity ratio plays a decisive role in the formation of in situ microfibrils. When the viscosity ratio of PLA/iPP is near 1, deformation and microfibrillation of PLA particles can be conducted due to the larger and more uniform distributed PLA domains as well as stronger viscous drag forces. However, irregular cylinders are observed when the viscosity ratio is far lower than 1. The poor deformation ability of PLA particles should be attributed to the much smaller size and weaker viscous drag forces. The well‐defined PLA microfibrils are conducive to avoid damage at the interface, and play a significant role in the enhancement of tensile strength and modulus. This work can simplify the traditional preparation process, construct in situ microfibrils directly by using conventional melt processing techniques and provide a new ideal for the high performance of incompatible polymer blends. POLYM. ENG. SCI., 60:832–840, 2020. © 2020 Society of Plastics Engineers

Heat transfer coefficient in internal mixers for different polymers and processing conditions

Tests with five different neat polymers, two different blends and one composite were conducted on a Haake Rheomix 3000 and Rheomix 600 internal laboratory mixers with two different types of rotors. The heat transfer coefficient per unit area was determined from the temperature and torque values recorded by each equipment. In all cases, dispersion of the experimental data was significant. Results showed that the heat transfer coefficient in internal mixers is higher than in common single screw extruders and similar to the values found for corrotational twin screw extruders. Data indicates that heat transfer coefficient in internal mixers is independent of the internal mixer capacity, the type of rotor used, the processing temperature and the type of neat polymer processed. In contrast, it is dependent on the nominal speed of the rotors and the polymer for incompatible polymer blends and for polymer matrix composites.

Self-Stratification of Ternary Systems Including a Flame Retardant Liquid Additive

Particular coating compositions based on incompatible polymer blends can produce coatings having complex layered structures after film formation. The most traditional approaches to their structural modification are the introduction of additives (extenders, inorganic pigments, surface active agents, etc.). As minor additives, some are capable of substantially accelerating the phase separation process with a moderate or negligible influence on the composition equilibrium of solutions. In contrast, in order to be effective, some have to be introduced in significant amounts, thereby substantially changing the resulting distribution of components through the film. Up to now, most of the liquid additives that have been tested destabilized the solutions while impacting the layering process. In this work, two phosphorus based liquid fillers have been introduced (at 2.5 and 5 wt.%) in a partially incompatible polymer blend based on a silicone resin and a curable epoxy resin to fire retard a polycarbonate matrix. Self-stratification was evidenced by microscopic and chemical analyses, flammability by Limiting Oxygen Index (LOI) and UL-94 tests, fire performances by Mass Loss Calorimetry and thermal stability by using a tubular furnace and ThermoGravimetric Analysis. The ternary compositions including 5 wt.% of additives exhibit the best stratification and excellent adhesion onto polycarbonate. Improvements of the fire resistant properties were observed (+7% for the LOI compared to the virgin matrix) when a 200 µm wet thick coating was applied, due to reduced flame propagation and dripping.

In-situ grafting of carboxylic acid terminated poly(methyl methacrylate) onto ethylene-glycidyl methacrylate copolymers:One-pot strategy to compatibilize immiscible poly(vinylidene fluoride)/ low density polyethylene blends

Reactive compatibilization is an effective strategy to improve compatibility of incompatible polymer blends. However, the strategy is usually limited to the polymer blends that one of the components contains reactive groups. In this work, we have succeeded in the reactive compatibilization of the immiscible poly(vinylidene fluoride)/low density polyethylene (PVDF/LDPE) blends of which both components do not contain the reactive groups. We simultaneously incorporated the carboxylic acid terminated poly(methyl methacrylate) (PMMA) oligomer (PMMA−COOH) and ethylene-glycidyl methacrylate copolymer (EGMA) into the PVDF/LDPE blend. The ring-opening reactions of the carboxylic acid groups of PMMA oligomer and epoxide groups on the EGMA main chains happen during the melt blending and the in-situ formed EGMA-g-PMMA graft copolymers enhance the compatibility of PVDF/LDPE blends significantly. The reactive compatibilized PVDF/LDPE blends have the elongation at break and fracture strength of 507% and 40.2 MPa, respectively, as compared with the 11% and 25.6 MPa of the uncompatibilization blends. Moreover, the architecture effects of the in-situ formed EGMA-g-PMMA by varying PMMA-COOH oligomer loadings, PMMA-COOH molecular weight and the processing time on the compatibilization efficiency have been investigated. It was found that compatibilizing efficiency increases with increasing the grafted density, the length of the side chain and the degree of reaction. This one-pot strategy with the in-situ formed graft compatibilizers in incompatible blends paves new possibility for unreactive blends by reactive compatibilization.

Catalyst driven preferential growth of in-situ generated nanosilica particles in the phases of incompatible polymer blend and its effect on physico-mechanical properties

Selectively localizing nanofillers in a particular phase of polymer blend to achieve required properties are hardly possible. Herein, an approach to solve the above mentioned problem is reported by exploring the effect of catalyst in preferentially growing in-situ generated nanosilica particles in the phases of incompatible natural rubber (NR): carboxylated nitrile rubber (XNBR) (50:50) blend. In-situ generated nanosilica particles prepared using tetraethylorthosilane (TEOS) as silica precursor and n-butylamine (nBA) as catalyst preferentially grow in the dispersed non polar NR phase (due to the hydrophobic nature of the silica particles) and ultimately leads to significant enhancement in the blend properties. On the other hand, in-situ generated nanosilica particles prepared using TEOS as silica precursor and hydrochloric acid (HCl) as catalyst preferentially grow in the continuous polar XNBR phase (due to the hydrophilic nature of the silica particles) and ultimately does not increase the blend properties to a greater extent.

Compatibilization of multicomponent composites through a transitioning phase: Interfacial tensions considerations

A novel interfacial compatibilization technique for incompatible polymer blends or composites is proposed, in which a transitioning layer was introduced between the matrix and the dispersed phase of the otherwise incompatible components. The transitioning phase should have good interactions with both the components, resulting in lower interfacial energy between the phases. Theoretically, it is hypothesized that if the sum of the interfacial tension between the transitioning phase and both the components of the composite is smaller than the interfacial tension between the two components, the encapsulation of the dispersed phase by the transitioning phase is spontaneous, which will lead to better interphase interfacial interactions. Since this compatibilizing technique relies purely on judicial selection of a polymer with suitable surface energy as the transitioning layer, no tedious chemical synthetic processes are required. To illustrate the proposed technique, incompatible Poly(lactic acid)/Thermoplastic Starch (PLA/TPS) blend is compatibilized with Poly(butylene succinate) (PBS) as the transitioning layer in this paper. With PBS encapsulating the dispersed TPS phase, PLA/PBS/TPS 60/10/30 wt% demonstrate a better mechanical synergy, with significant improvement in strength, ductility and toughness as compared to PLA/TPS 70/30 wt%. This technique can also be applied to design other multicomponent blends or composites.

Self-stratifying coatings: A review

Abstract Self-stratifying coatings are promising coating systems based on incompatible polymer blends which can produce polymer/polymer laminate. A complex multi-layer or gradient coating structure is formed from one single coat, providing an undercoat and finishing coating. The preferential distribution of concentration through the film thickness greatly eliminates the interfacial adhesion failure without compromising the advantages of a multi-layer system, and thus favors an industrial eco-efficient process. Powder, waterborne and solventborne coating systems are able to stratify: the most well-known and effective systems are described in this review. Finally, this concept constitutes a great possible versatile process for a broad range of applications and could thus favor the development of new products, taking into account the reduction of solvent and labor cost

Effect of the degree of crosslinking on the interfacial layer structure of poly(vinyl chloride) dispersed with crosslinked poly(n-butyl methacrylate) particles

The interfacial layer structure of a model incompatible polymer blend system was analyzed using 1H pulse nuclear magnetic resonance (pulse NMR) spectroscopy. Non-crosslinked and crosslinked poly(n-butyl methacrylate) particles with a mean size of ca. 0.9 μm were prepared by seeded emulsion polymerization, and the degree of crosslinking was varied. The particles were powdered using a freeze-dry method and dispersed in poly(vinyl chloride) by melt blending. Dynamic mechanical analysis indicated that the non-crosslinked particles were completely compatible. In contrast, mutual diffusion of the polymer chains in the crosslinked particles was restricted within the particle/matrix interfacial layer. As a result, an incompatible phase structure in which the crosslinked particles were dispersed in the continuous phase was formed. Pulse NMR analysis indicated that the interfacial layer thickness was in the range of 17–98 nm. The thickness decreased with an increase in the degree of crosslinking in the particles. The interfacial layer thickness in the particles was approximately 10 times larger than that for the incompatible polymer pair. Tensile test results indicated that the elongation at break was dependent on the thickness of the interfacial layer. The yield stress was developed for the particles with high hardness that was independent of the interfacial thickness.

Effect of network formation on the electrical, mechanical, and processability behaviors through the preferential distribution of carbon black in the incompatible polymer blend composite

Four different methods of preferential addition of fixed amount of HAF carbon black have been done in two phases of an immiscible blend of NBR–EPDM (50/50 wt%). However, it is found that redistribution of carbon black occurs in blend phases during mixing even after preferential addition. This is revealed from the measurement of both dynamic mechanical, and mechanical properties. Carbon black redistribution in different phases of blends also affects the electrical properties, especially the frequency dependent AC‐conductivity to a great extent. The surface tension and viscosity of two components of the blend namely NBR and EPDM play an important role in the distribution of carbon black in respective phases. Carbon black distribution also affects hysteresis behavior of the blend and can be correlated with the variation in AC conductivity. The processability behavior of black filled compound is also affected by the preferential addition of carbon black in the elastomer blend. POLYM. COMPOS., 39:2620–2633, 2018. © 2016 Society of Plastics Engineers

Poly(N-vinylimidazole)-l-poly(propylene glycol) amphiphilic conetworks and gels: molecularly forced blends of incompatible polymers with single glass transition temperatures of unusual dependence on the composition

New molecularly forced blends of incompatible poly(N-vinylimidazole) and poly(propylene glycol) polymers with single glass transition temperatures.

Compatibilization of polyethylene/polyamide 6 blend nanocomposite films

Polymer blends of incompatible components need to undergo compatibilization, in order to give rise to a blend with good physical properties. At the same way, polymer/clay nanocomposites show this problem because of different chemical nature of the polymer matrix and of the clay. Compatibilization is therefore more necessary if an incompatible polymer blend is filled with an organomodified clay in order to give a final material with good properties. In this work, a polyethylene/polyamide 6 blend filled with an organomodified clay has been compatibilized with a maleic anhydride grafted SEBS (styrene‐ethylene‐butylene‐styrene) copolymer and a glicidylmethacrylate‐ethylene copolymer. The results show that compatibilization improves the mechanical properties in terms of elongation at break, as well as the rheological properties under nonisothermal elongational flow; furthermore, an unexpected effect has been found, since going from the isotropic to the anisotropic material, a fragile‐ductile transition occurs, with a significant increase of the elongation values, while a small reduction of the elastic modulus was found, because of the lower crystallinity in comparison to isotropic samples. POLYM. COMPOS., 36:992–998, 2015. © 2015 Society of Plastics Engineers

Modifying polyester surfaces with incompatible polymer additives

Surface modification of amorphous PET in incompatible blends is demonstrated using fluorocarbon end-functional polystyrenes. Contact angles with water and decane were consistent with high levels of surface fluorocarbon, even for spin-cast films with no further processing required. Hydrophobicity and lipophobicity were further increased by annealing above the glass transition temperature. High resolution depth profiling using complementary ion beam analysis and specular neutron reflectometry has enabled accurate characterisation of the composition profile of the additive including the minimum in additive concentration found just below the surface enriched layer. This analysis quantified the very low compatibility between the modifying polymer and the amorphous PET and was consistent with the highly segregated nature of the adsorbing species and its sharp interface with the subphase. For these incompatible polymer blends, surfaces enriched with the surface active polymer could coexist at equilibrium with extremely low (∼0.4%) bulk loadings of the additive. This suggests that for thicker films at even lower additive concentrations than the minimum 1% that we studied, it may be possible to achieve efficient surface modification. However, at this concentration, the efficiency of surface modification is limited by the processing conditions. Finally we note that in higher loadings of surface active additive there is clear evidence for lateral phase separation into patterned domains of differing composition. The enhancement in surface properties is due to local reorganisation rather than bulk redistribution of the components within the film, as the composition versus depth distributions of the polymer blend components was observed to be relatively unaffected by annealing.

End-Coupling Reactions in Incompatible Polymer Blends: From Droplets to Complex Micelles through Interfacial Instability

Simulations by dissipative particle dynamics revealed a possibility to produce micelles of diverse morphologies via irreversible end-coupling reaction in polymer melts containing a particulate phase. It is demonstrated that the reaction at the surface of a polymer A droplet immersed in a melt of polymer B leads to the droplet instability and subsequent micelle formation. Depending on the length ratio of reacting chains and its own size, the droplet is either emulsified into a set of small micelles or converted into a single micelle, which can have rather complex internal structure. A morphology diagram containing structures that are typical for polymer solutions, in particular vesicles, bowls, worms, star-like and crew-cut micelles with multiple internal domains, is first presented for polymer melts. Investigation of the reaction kinetics reveals subsequent linear, saturation, and exponential autoacceleration regimes. By simulations and using simple scaling arguments, it is explained how the barrier properties of a diblock copolymer layer formed at the A/B interface depend on the copolymer composition and droplet curvature. It is found that the scenario of the instability development is much different for flat and spherical A/B interfaces.