Influence of segmental swelling of an asymmetric block copolymer on the morphology of melt-mixed immiscible polymer blends

We investigate the influence of an asymmetric PS-b-PMMA block copolymer (bcp) on the morphology of melt-mixed immiscible binary polymer blends containing poly(styrene-co-acrylonitrile) random copolymer (SAN) and poly(cyclohexylmethacrylate) (PCHMA). By varying the SAN copolymer composition, the balance between the swelling of each block segment located at the interface between the two phases is altered and the effect on blend morphology is studied. As in earlier studies using a symmetric bcp, we find that for a specified shear history, there is a zone of effective emulsification of the blend bounded by regions of internal and external emulsification failure. However, the locations of the boundaries between stable and unstable emulsification differ for an asymmetric versus a symmetric bcp. Thus the morphology depends not only on the segmental swelling ratio but also on the difference in the effective size of each bcp segment. Scaling arguments successfully correlate the limits of stable emulsification for both symmetric and asymmetric bcp.     

Modified interfacial tensions measured in situ in ternary polymer blends demonstrating partial wetting

An in situ Neumann triangle-focused ion beam-atomic force microscopy (NT-FIB-AFM) method has been used to measure modified PS/HDPE interfacial tensions in ternary PS/PP/HDPE blends prepared by melt mixing and demonstrating partial wetting. The ternary blend was modified with SEB, SB and SEBS copolymers. Results related to the position of the PS droplet at the interface show that a symmetrical diblock copolymer is somewhat more efficient in decreasing the interfacial tension compared to an asymmetrical one of similar molecular weight, while the SEBS triblock copolymer appears to have no effect at all. Using the NT-FIB-AFM method, the lowest modified PS/HDPE interfacial tension is 3.0 ± 0.4 mN/m for the symmetric diblock, compared to 4.2 ± 0.6 mN/m (N = 34) for the unmodified interface. This corresponds to an apparent areal density in SEB copolymer equal to 0.16 ± 0.03 molecules/nm², which is near reported saturation values. By varying the concentration of the copolymer, an emulsification curve reporting the value of the PS/HDPE modified interfacial tension as a function of the apparent areal density of the copolymer at the PS/HDPE interface has been obtained. The interfacial tension values obtained by the NT-FIB-AFM approach are significantly higher than the 0.5 ± 0.2 mN/m (N = 3) result obtained by using the classical breaking thread method with the same materials. This discrepancy does not appear to be due to a poor migration of the copolymer to the PS/HDPE interface, but could instead be attributed to the interfacial elasticity of the compatibilized interface, a phenomena that has not been accounted for so far in experimental studies on the morphology of compatibilized multicomponent polymer blends.     

Interface/morphology relationships in polymer blends with thermoplastic starch

In this paper, the interface/morphology relationship in polyethylene/TPS blends prepared by a one-step extrusion process is examined in detail. Emulsification curves tracking the change in phase size with added quantity of PE-g-MA copolymer are used to identify the critical concentration required for saturation of the interface as well as to estimate the areal density of grafted copolymer chains at the interface. The level of glycerol content in the TPS is shown to lead to different emulsification behaviors. Dynamic mechanical analysis clearly shows a partial miscibility between glycerol and starch in the TPS with glycerol-rich and starch-rich peaks being clearly identified. This phase separation is more evident in the case of high glycerol levels in the TPS (>24% glycerol). Furthermore, the glycerol-rich peak decreases in intensity with added PE-g-MA graft copolymer. At high glycerol contents (>24% glycerol) in the TPS, a 20% thermoplastic starch-based binary blend with polyethylene can reach an elongation at break value as high as 200%. When also modified at the appropriate level with a PE-g-MA copolymer, this elongation at break further increases to 600%. However, at lower glycerol contents, the elongation at break is comparatively low at 20-50% even after the addition of PE-g-MA copolymer. We explain these results through a proposed double mechanism of interfacial modification between the HDPE matrix and the TPS dispersed phase. Under dynamic melt-mixing conditions, it is suggested that a small portion of the low molecular weight glycerol-rich phase tends to migrate to the HDPE-TPS interface as predicted by Harkins spreading theory. Once at the interface, this glycerol-rich outer layer is readily deformed by an applied stress and this stress is then transferred to the starch-rich phase due to their mutual partial miscibility. Added PE-g-MA copolymer initially reacts with the glycerol-rich outer layer but if the level of copolymer is high enough, it then reacts with the starch-rich phase via a classic interfacial modification protocol. Also, both the elongation at break and impact properties dramatically increase at a copolymer level associated with interfacial saturation. The above mechanism effectively explains all the emulsification and mechanical property observations.     

Synthesis, characterization, and properties of a novel acrylic terpolymer with pendant perfluoropolyether segments

A novel acrylic terpolymer with pendant perfluoropolyether (PFPE) segments has been synthesized and fully characterized. By hexamethylene diisocyanate functional groups PFPE monofunctional macromonomers have been grafted on a poly(butyl methacrylate-co-hydroxyethyl acrylate-co-ethyl acrylate) random terpolymer. Such grafted copolymer behaves like an interface-active material, since the perfluoropolyether segments in solvent cast films rearrange themselves at the air-polymer interface by surface segregation. In addition, blends of the above graft copolymer with acrylic base polymers (either the terpolymer itself or a commercial copolymer) have been examined in terms of surface segregation and fluorine enrichment of the external layers.The critical surface tension, γ_c, of solid films made of the neat graft copolymer as well as of the polymer blend has been evaluated by contact angle measurements and Zisman plots. Even a small addition (5 wt%) of the fluorinated copolymer to the acrylic component has been found very effective in lowering the surface tension. The outermost surface composition has been investigated by XPS technique, confirming the strong fluorine enrichment. Furthermore, SEM and EDX analyses have been performed on cross-sectioned films, showing that in the above polymer blends macrophase surface segregation has originated a thick layer made of fluorinated copolymer close to the air-polymer interface.     

Mechanical properties of polystyrene/low density polyethylene blends

Some mechanical properties of blends of polystyrene and low density polyethylene have been derived from stress-strain and impact measurements. The strength and impact properties are improved by adding a graft copolymer of polystyrene and low density polyethylene to the blends. It is assumed that the copolymer acts as an adhesive at the interface of the homopolymers thus decreasing the stress concentrations around the dispersed polymer particles at yield. The impact strength and modulus of polystyrene-graft copolymer blends could be made comparable to those of commercial rubber-modified impact polystyrenes by adjusting the fraction of copolymer in the blend.     

Effects of processing conditions and copolymer molecular weight on the mechanical properties and morphology of compatibilized polymer blends

The mechanical properties and morphology of melt mixed polystyrene (PS)/polyethylene (PE) blends that were modified by the addition of up to 16% of a semicrystalline PS-b-hPB (hydrogenated polybutadiene) diblock copolymer with varying molecular weight are reported. As a result of the blocks of the copolymer penetrating the corresponding homopolymers, these diblock copolymers are capable of reinforcing the PS/PE interface significantly. This increase in interfacial strength between the immiscible blend components does not necessarily result in an improvement in the mechanical properties of the blends as measured by Izod or tensile tests. This may be because the effect of the copolymers on the rheological properties of the blends during processing outweighs their emulsifying/reinforcing effects. If found to be universally true for polymer blends, these results suggest that the relationship between the effects of copolymers on interfacial strength, their emulsifying effects, and the mechanical properties of copolymer modified blends are not as simple as suggested by many statements found in the literature.     

Compatibilization of styrene–butadiene–styrene block copolymer in polypropylene/polystyrene blends by analysis of phase morphology

Effect of compatibilization of styrene–butadiene–styrene (SBS) block copolymer in polypropylene/polystyrene (PP/PS) blends was studied by means of small angle X‐ray scattering (SAXS) and scanning electron microscope (SEM). According to SAXS, a certain amount of SBS was located at the interface in all the analyzed samples, forming the relatively thicker interface layer penetrating into homopolymers, and the thickness of the interface layer was quantified in terms of Porod light scattering theory. The incorporation of SBS into PP/PS blends resulted in a decrease in domain size following an emulsification curve as well as an uniform size distribution, and consequently, a fine dispersion of PP domains in the PS matrix. This effect was more pronounced when the concentration of SBS was higher. A critical concentration of SBS of 15% above which the interface layer approaches to saturation and domain size attains a steady‐state was observed. Further, the morphology fluctuation of unetched fracture surface of umcompatibilized and compatibilized blends was analyzed using an integral constant Q based on Debye‐Bueche light scattering theories. Variation of Q as a function of the concentration of SBS showed that, due to the penetrating interface layer, adhesion between phases was improved, making it possible for applied stress to transfer between phases and leading to more uniform stress distribution when blends were broken; accordingly, a more complicated morphology fluctuation of fracture surface appeared. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:365–370, 2007     

Flow induced deformation of dual-phase continuity in polymer blends and alloys. Part I

A hypothesis for formation of bi-continuous phase structures in immiscible polymer blends is proposed. It is based on the observation that a critical volume fraction φ_cr for the dual continuity of phases may be calculated considering the geometry of the dispersed phase. The knowledge of the form of discrete domains at the volume fractions φ < φ_cr and the probability that two close neighbor domains will form a strongly fused connection are sufficient to calculate φ_cr. Furthermore, it can be predicted that φ_cr should increase with stabilization of the interface. A comparative study showed that an addition of block copolymer may narrow the volume fraction range where bi-continuous phase structures are formed. Both annealing in the molten state and shearing history influence the measured φ_cr for the formation of bi-continuous phase structure in amorphous immiscible polymer blends.     

Effects of reactive reinforced interface on the morphology and tensile properties of amorphous polyamide–SAN blends

The effects of reactive reinforced interface on the morphology and tensile properties of amorphous polyamide (a-PA) and styrene-acrylonitrile (SAN) copolymer blend have been investigated using styrene maleic anhydride (SMA) copolymer as a reactive compatibilizer. The anhydride groups of SMA copolymer can react with the amine groups of polyamide and form in situ graft copolymers at the a-PA–SAN interfaces during the blend preparation. The interfacial adhesion strength of the reactive reinforced interface was evaluated quantitatively using an asymmetric double cantilever beam fracture test as a function of SMA copolymer content using a model adhesive joint. The interfacial adhesion strength was found to increase with the content of SMA copolymer and then level off. The morphological observations of a-PA–SAN (80/20 w/w) blends showed that the finer dispersion of the SAN domains with rather narrow distribution was obtained by the addition of SMA copolymer into the blends. The trend of morphology change was not in accord with that of the interfacial adhesion strength with respect to the content of SMA copolymer. However, the results of tensile properties showed very similar behavior to the case of the interfacial adhesion strength with respect to SMA content; that is, there was an optimum level of the reactive compatibilizer beyond which the interfacial adhesion strength and tensile strength did not change significantly. These results clearly reveal that tensile properties of polymer blend are highly dependent on the interfacial adhesion strength. Furthermore, it is suggested that the asymmetric double cantilever beam fracture test using a model interface is a useful method to quantify the adhesion strength between the phases in real polymer blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1925–1933, 1998     

Tracer‐compatibilizer: Synthesis and applications in polymer blending processes

This article reports on a route to synthesizing fluorescent labeled graft copolymers, on the one hand; and on a concept of tracer‐compatibilizer for facile build‐up of emulsification curves of polymer blends, on the other hand. For these purposes, blends composed of polystyrene (PS) and polyamide 6 (PA6) are chosen. The synthesis of the corresponding tracer‐compatibilizer consists of three steps: (1) copolymerization of styrene with 3‐isopropenyl‐α,α'‐dimethybenzyl isocyanate (TMI); (2) conversion of a fraction of the isocyanate moieties of the resulting copolymer into anthracene ones upon reacting with 9‐(methylamino‐methyl)anthracene (MAMA); and (3) polymerization of ε‐caprolactam (CL) from the remaining isocyanate moieties. The resulting fluorescent labeled graft copolymer, denoted as PS‐g‐PA6‐Ant, is used to build up emulsification curves of PS/PA6 blends in a twin screw extruder (TSE), showing great usefulness of the concept of tracer‐compatibilizer. POLYM. ENG. SCI. 2012. © 2011 Society of Plastics Engineers     

Effect of block copolymers of various molecular architecture on the phase morphology and tensile properties of LDPE rich (LDPE/PS) blends

The emulsification efficiency of three different block copolymers consisting of hydrogenated polybutadiene (HPB) and polystyrene (PS), i.e. a pure diblock , a tapered diblock and a triblock copolymer has been compared in low density polyethylene/polystyrene (LDPE/PS) blends rich in polyethylene. The comparison relies upon the ability of these potential interfacial agents to stabilize fine phase dispersion and to promote good interfacial adhesion. Based on the phase morphology, the ultimate tensile properties and the dynamic viscosity of the modified blends, the tapered diblock copolymer is clearly the most efficient emulsifier. For instance a plateau is observed in the property-copolymer content dependence when 2 wt% tapered diblock are used compared to ca. 5 wt% in case of the pure diblock. In contrast, no plateau is observed when the triblock copolymer is used. This is assumed to result from a less quantitative localization of these two copolymers i.e. the pue diblock or the triblock at the LDPE/PS interface.     

聚苯乙烯水基微粒体系形成过程相反转的研究

分别用阴、阳离子型高分子表面活性剂及低分子非离子 /阴离子型高分子表面活性剂复配 ,实现了聚苯乙烯的微粒化水基化。用乳化过程中体系电导率和粘度的变化表征了乳化相反转过程 ,实验结果表明 :N 甲基 4 乙烯基吡啶 苯乙烯共聚物季铵盐比聚苯乙烯磺酸钠作表面活性剂对PS实现微乳化的相反转点时体系的含水量低。用TX 10和聚苯乙烯磺酸钠复配可提高油水界面的界面膜强度、乳化作用增强。     

Compatibilization of polymer blends with high‐molecular‐weight peroxides

A novel approach for the compatibilization of heterogeneous polymer blends with interface‐active high‐molecular‐weight peroxides is presented. This three‐step approach includes the synthesis of an anchor peroxide copolymer, the preparation of an interface‐active, peroxide‐containing graft copolymer (precompatibilizer) on its basis, and the localization of the precompatibilizer at the interfaces of the polymer blends during reactive blending with the in situ formation of compatibilizer macromolecules. We found that the precompatibilizer incorporating polypropylene fragments compatibilized blends of polypropylene with polystyrene, polyethylene, and unsaturated polyester resin. This verified a certain universality of the approach proposed for the compatibilization of polymer blends. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 232–242, 2005     

Strategies to measure and optimize the migration of the interfacial modifier to the interface in immiscible polymer blends

A family of emulsification curves has been systematically prepared in order to determine the extent of interfacial modifier migration to the high density polyethylene (HDPE)/polystyrene (PS) interface. Through an examination of the evolution of the equilibrium dispersed phase size after interfacial saturation, as well as a comparison of the apparent interfacial area occupied per modifier molecule (A_app) at the different dispersed phase concentrations, it is possible to detect the onset of micelle formation and to estimate the extent of interfacial coverage. This approach has been applied to HDPE/PS blends, using a variety of triblock and diblock copolymer interfacial modifiers for that system. It is shown quantitatively that it is the affinity of the block copolymer for the matrix material that dominates migration efficacy to the interface. Asymmetrical block copolymers (30PS/70EB) show a strong tendency to form micelles when HDPE is the matrix. This effect is virtually eliminated when PS is the matrix material or when symmetrical block copolymers (50PS/50EB) are used. In these latter cases all the interfacial modifier finds its way to the interface.     

Hydroresin dispersions: tailoring morphology of latex particles and films

Hydroresin dispersions are a new class of emulsifier free polyacrylate secondary dispersions. They are prepared by the emulsification of self-emulsifying polymer blends in water. The blends typically consist of two polymers, one is a salt group containing copolymer, the other is a hydrophobic polymer without salt groups. The particle diameters can be controlled by the amount of salt group containing polymer and the concentration of salt groups in this polymer. One advantage over conventional secondary dispersions is the fact that they are not only water dilutable but free of organic solvents. Another advantage is the extremely low content of hydrophilic salt groups in the resulting polymer mixture, which leads to very hydrophobic films. The application properties of these aqueous systems are more similar to those of organic polymer solutions than to conventional emulsion polymers. Applications of these surfactant free binders are in areas such as solvent face road marking paints and corrosion protection coatings without active pigments. The technique for the preparation of hydroresin dispersions is also useful for the creation of latex particles with core-shell structures. Two examples are given, which differ in the glass transition temperature of both the cores and the shells. From these dispersions, films with defined morphology can be prepared. A blending of the polymers with hydrophobic low molecular weight compounds, before the emulsification step, is also possible. It can be used for the incorporation of additional functions into the latex particles. As an example, the loading of latexes with a hydrophobic fluorescent dye is given.     

The effect of interface characteristics on the static and dynamic mechanical properties of three‐component polymer alloys

The effect of interfacial characteristics on the structure‐property relationships of ternary polymer alloys and blends comprising polypropylene (PP), ethylene‐vinyl alcohol copolymer (EVOH) and glass beads (GB) or fibers (GF) was investigated. The systems studied were based on a binary PP/EVOH immiscible blend, representing a blend of a semi‐crystalline apolar polymer with a semi‐crystalline highly polar copolymer. The ternary systems studied consisted of filler particles encapsulated by EVOH, with some of the minor EVOH component separately dispersed within the PP matrix. Modification of the interfacial properties was done using silane coupling agents for the EVOH/glass interface and compatibilization using a maleic anhydride grafted PP (MA‐g‐PP) for the PP/EVOH interface. Both glass fillers increased the dynamic modulus and decreased the damping of the neat polymers and of their binary blends, especially in the rubbery region. GF has a more profound effect on both the modulus and the damping. Glass surface treatments and compatibilization have only a marginal effect on the dynamic mechanical behavior of the ternary blends. Yet, compatibilization shifted the polymers' T_gS to higher temperatures. Both glass fillers increased the elastic modulus of the binary blends, where GF performed better than GB as a reinforcing agent. GF slightly increased the strength of the binary blends while, GB reduced it. Both fillers reduced the ductility of the binary blends. The blends' mechanical properties were related to the morphology and their components' crystallinity. The compatibilizer increases both stiffness and strength and reduces deformability.     

Nonfouling biomaterials based on polyethylene oxide‐containing amphiphilic triblock copolymers as surface modifying additives: Synthesis and characterization of copolymers and surface properties of copolymer–polyurethane blends

The objective of this work is to develop nonfouling biomaterials by blending polyethylene oxide (PEO)‐containing block copolymers with a polyurethane (PU) matrix; it is expected that the PEO component will migrate to the tissue‐material interface. Three amphiphilic triblock copolymers, PEO‐PU‐PEO, in which the PEO MW was 550 (copolymer 1), 2000 (copolymer 2), and 5000 (copolymer 3), respectively, were synthesized. XPS data showed that the polymer/vacuum interfaces of copolymers 2 and 3 were enriched in the PU block, whereas that of copolymer 1 was enriched in the PEO block. In contact with water, the PEO blocks for all three copolymers migrated to the surface as indicated by water contact angles. Blends of the copolymers with a segmented polyurethane were investigated. Surface enrichment of the copolymers occurred and increased over time up to a limit; the degree of enrichment was dependent on PEO block size and copolymer content. At copolymer content <10%, enrichment decreased with increasing PEO block size. For the copolymer 2 and copolymer 3 blends, enrichment increased with increasing copolymer content; at 20% copolymer the surfaces consisted essentially of pure copolymer. For the copolymer 1 blends, the surface was completely covered by copolymer at content ≥ 1%. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of triblock copolymer interfacial modifiers on fracture behavior of polystyrene/ethylene-propylene rubber blends

In a previous study, two triblock copolymers of styrene/ethylene-butylene/styrene (SEBS), of different molecular weights, were used to compatibilize a blend of 80 vol% polystyrene (PS) and 20% ethylene-propylene rubber (EPR). The emulsification curve, which relates the average minor phase particle diameter to the concentration of interfacial agent added, was used to quantify the effect of the interfacial agents on the blend morphology. Links between morphology, interface, and properties were established by combining the emulsification curve with a fracture mechanics approach. The aim of this work is to foster the understanding of the effects of these two triblock copolymers on the fracture behavior of the blend over various loading rates and temperatures. The focus is on the brittle-ductile transition in fracture behavior, which is a critical condition for the application of these materials. It has been found that adding an interfacial agent lowers the temperature at brittle-ductile transition. However, this effect is much more pronounced for the copolymer with a lower molecular weight. The time-temperature dependence of fracture performance of the blend is also affected by the interface and morphology. When loading rate increases, the shift of the temperature at brittle-ductile transition is less significant for the blend with an interfacial agent having a lower molecular weight. The effect of loading rate and temperature on the brittle-ductile transition in fracture performance of the blends is controlled by an energy activation process. Adding the interfacial agents results in a plasticizing effect of the polystyrene matrix and a reduction in the energy barrier controlling the fracture process. With the addition of interfacial agent, the yield stress slightly increases at low concentration, attains a maximum value, and then decreases. The increase in yield stress confirms the coupling role of the copolymer and is in agreement with the observed emulsification curves. The reduction of yield stress and increase in ultimate strain with the copolymer concentration demonstrate the plasticizing effect of the interfacial agent. The result of stress relaxation tests also confirms the above effects of the interfacial agent.     

Addition compatibilization of PP/PS blends by tailor‐made copolymers

The thermoplastic polymer blends of commercial interest generally need a phase compatibilization to reduce the interfacial tension, to stabilize the morphology, and to increment the interfacial adhesion. This work deals with the compatibilization of PP/PS blends by addition of a tailor‐made copolymer, which is prepared from the pure homopolymers by a Friedel‐Crafts reaction. This addition compatibilization process comes out as an economic alternative applicable to the recycling of mixed plastics from urban and industrial wastes. The influence of compatibilizer concentration and blending time on the emulsifying effect, morphology, and mechanical properties of the resulting blends are analyzed. The compatibilization process effectiveness is assessed through the improvement in phase adhesion, emulsification and ductility of the compatibilized with respect to the physical blends. An increase of three times in ductility is achieved using very low compatibilizer concentrations (0.5–0.7 wt%). No appreciable detriment in yield strength or modulus is observed in these compatibilized blends. POLYM. ENG. SCI. 46:329–336, 2006. © 2006 Society of Plastics Engineers