Co-continuous and encapsulated three phase morphologies in uncompatibilized and reactively compatibilized polyamide 6/polypropylene/polystyrene ternary blends using two reactive precursors

Phase morphology development in ternary uncompatibilized and reactively compatibilized blends based on polyamide 6 (PA6), polypropylene (PP) and polystyrene (PS) has been investigated. Reactive compatibilization of the blends has been performed using two reactive precursors; maleic anhydride grafted polypropylene (PP-g-MA) and styrene maleic anhydride copolymer (SMA) for PA6/PP and PA6/PS pairs, respectively. For comparison purposes, uncompatibilized and reactively compatibilized PA6/PP and PA6/PS binary blends, were first investigated. All the blends were melt-blended using a co-rotating twin-screw extruder. The phase morphology investigated using scanning electron microscope (SEM) and selective solvent extraction tests revealed that PA6/PP/PS blends having a weight percent composition of 70/15/15 is constituted from polyamide 6 matrix in which are dispersed composite droplets of PP core encapsulated by PS phase. Whereas, a co-continuous three-phase morphology was formed in the blends having a composition of 40/30/30. This morphology has been significantly affected by the reactive compatibilization. In the compatibilized PA6/(PP/PP–MA)/(PS/SMA) blends, PA6 phase was no more continuous but gets finely dispersed in the PS continuous phase. The DSC measurements confirmed the dispersed character of the PA6 phase. Indeed, in the compatibilized PA6/(PP/PP–MA)/(PS/SMA) blends where the PA6 particle size was smaller than 1 μm, the bulk crystallization temperature of PA6 (188 °C) was completely suppressed and a new crystallization peak emerges at a lower temperature of 93 °C as a result of homogeneous nucleation of PA6.     

Phase morphology development and stabilization in polycyclohexylmethacrylate/polypropylene blends: uncompatibilized and reactively compatibilized blends using two reactive precursors

The phase morphology developed in immiscible polypropylene (PP)/polycyclohexylmethacrylate (PCHMA) blends has been studied using an in situ reactively generated polystyrene-graft-polypropylene compatibilizer from maleic anhydride grafted polypropylene (MA-g-PP) and amine end-capped polystyrene (PS-NH2) reactive precursors during melt-blending. The imidation reaction responsible for the formation of the compatibilizer is similar to the reaction occurring in polyamide/MA-PP (MA-EPR or MA-EPDM) blends which are industrially important. In the present blend PP/PCHMA/(PP-MA-PS-NH2), no undesired reaction occurs between the maleic anhydride groups and the backbone of the PCHMA chain, as is usually the case with polyamide homopolymer. This type of reaction, although considered non significant, has consequences on the phase morphology development as it affects the viscosity of the polyamide matrix when chain scission takes place. PP/PCHMA blends covering the whole range of compositions were prepared. The composition window at which the blends exhibit a droplet-in-matrix phase morphology and that where the two phases are co-continuous were determined using a selective phase extraction in combination with scanning electron microscopy. The generation in situ of the PP-g-PS compatibilizer substantially changed the state of the phase morphology developed. In the blends having a droplet-in-matrix type of morphology, the particle sizes were significantly reduced (by a factor of more than 10). Two types of MA-g-PP reactive copolymers differing in maleic anhydride content (1 and 8 wt%) have been separately employed with the same grade of PS-NH2. Emphasis was put on a detailed investigation of the behaviour and structural stability of the blends exhibiting a co-continuous phase morphology when the compatibilizer is generated. Significant differences were found in relation to the maleic anhydride content of the MA-PP reactive compatibilizer precursor.     

Dynamic mechanical properties and morphology of polypropylene block copolymers and polypropylene/elastomer blends

The relation between the dynamic mechanical properties and the morphology of polypropylene (PP) block copolymers and polypropylene/elastomer blends was studied by dynamic mechanical analysis (DMA), light- and electron microscopy. The latter techniques contributed to an improvement in assignments of relaxation transitions in the DMA spectra. It was established that PP block copolymers had multiphase structure since the ethylene/propylene rubber phase (EPR) formed in the copolymerization contained polyethylene (PE) domains. An identical morphology was found in the case of PP/polyolefin thermoplastic rubber (TPO) blends. Impact modification of PP by styrene/butadiene block copolymers led to a multiphase structure, too, due to the polystyrene (PS) domains aggregated in the soft rubbery polybutadiene phase. In the semicrystalline polyolefinic and in the amorphous styrene/butadienebased thermoplastic rubbers, PE crystallites and PS do mains acted as nodes of the physical network structure, respectively. PP/EPDM/TPO ternary blends developed for replacing high-density PE showed very high dispersion of the modifiers as compared to that of PP block copolymers. This fine dispersion of the impact modifier is a basic regulating factor of impact energy dissipation in the form of shear yielding and crazing.     

Effect of blend ratio on bulk properties and matrix-fibril morphology of polypropylene/nylon 6 polyblend fibers

Ternary blends of polypropylene (PP), nylon 6 (N6) and polypropylene grafted with maleic anhydride (PP/N6/PP-g-MAH) as compatibilizer with up to 50 wt% of N6 were investigated. PP-g-MAH content was varied from 2.5 to 10%. Blends of the two polymers PP/N6 (80/20) without the compatibilizer were also prepared using an internal batch mixer and studied. The ternary blends showed different rheological properties at low and high shear rates. The difference depended on the amount of N6 dispersed phase. Co-continuous morphology was observed for the blend containing 50% N6. This blend also exhibited higher viscosity at low shear rate and lower viscosity at high shear rates than the value calculated by the simple rule of mixture. At higher shear rates, viscosity was lower than that given by the rule of mixture for all blend ratios. An increase in viscosity was observed in the 80/20 PP/N6 blend after the concentration of the interfacial agent (PP-g-MAH) was increased. Polyblends containing up to 30% N6 could be successfully melt spun into fibers. DSC results showed that dispersed and matrix phases in the fiber maintained crystallinity comparable to or better than the corresponding values found in the neat fibers. The dispersed phase was found to contain fibrils. By using SEM and LSCM analyses we were able to show that the N6 droplets coalesced during melt spinning which led to the development of fibrillar morphology.     

Morphology and mechanical properties of polypropylene/polystyrene blends compatibilized with styrene–butadiene block copolymers

The effect of molecular structure of styrene–butadiene block (SB) copolymers on the morphology, tensile properties, impact strength, and microhardness of polypropylene/polystyrene (PP/PS) (80/20) blends was studied. The addition of SB copolymers substantially reduces the size of dispersed PS particles formed at mixing. The distribution of SB copolymers between the interface and bulk phases is controlled by the length of styrene blocks in SB, but a decrease in the size of PS particles at mixing correlates with total molecular weight of SB copolymers. For a substantial part of compatibilized blends, PS particles aggregate rapidly during compression molding and form honeycomb‐like particles split by SB partitions, which persist at further annealing. Aggregation of PS particles continues slowly at further annealing. Blends containing PS particles with well‐developed honeycomb structure show lower yield stress, higher plasticity, and lower tensile impact strength than the blends having PS particles with simple or undeveloped honeycomb structure. Microhardness of PP/PS blends is additive and of PP/PS/SB blends is lower than the additive due to the effect of SB copolymers on crystalline structure of PP matrix. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effect of composition and comonomer type on the rheology, morphology and properties of ethylene-α-olefin copolymer/polypropylene blends

The rheology, morphology, thermal and mechanical properties of blends containing low molecular weight polypropylene (PP) and metallocene-based ethylene-α-olefin copolymers (ECs) have been investigated. Evaluation of the thermo-rheological properties of the blends showed that they are immiscible, both in the solid and melt state, over the whole range of compositions. Rheological properties were correlated to blend morphology, by using the Palierne emulsion model. The resulting low values of interfacial tension confirmed excellent compatibility between the phases.Addition of ECs in PP resulted in significant ductility improvement. The transition from plastic to elastomeric properties coincided with phase inversion. The butene-based EC was found to be the most beneficial in terms of impact properties.Fine morphologies, with sub-micron sizes of the dispersed phase, were obtained upon post-extrusion shearing of the blends.     

Effect of organoclay on the morphology, phase stability and mechanical properties of polypropylene/polystyrene blends

The effect of organically modified clay on the morphology, phase stability and mechanical properties of polypropylene (PP) and polystyrene (PS) blends was studied using three molecular weight grades of PP. Maleated polypropylene was used, at a PP-g-MA/organoclay ratio of 1, to preferentially promote dispersion of the organoclay in the PP matrix. The MMT content was fixed at 3 wt% based on the PP/PP-g-MA/MMT phase and the PS content was varied from 0-100 wt% in the blend. All blends were processed using a twin screw extruder. The organoclay resides in the PP phase and at the PP/PS interface. The dispersed PS particle size is significantly reduced by the presence of MMT, with maximum decrease observed for the low viscosity PP compared to its blend without MMT. The blends with MMT did not show any change in onset of co-continuity, though MMT shifts the phase inversion composition toward lower PS contents. The phase stability of the blend was significantly improved by the presence of MMT; for blends annealed at 210 °C for 2 h the dispersed phase particle size increased by as much as 10x without MMT with little change was noted with MMT present in the blend. The tensile modulus of blends improved with the addition of MMT at low PS contents. Blends based on the highest molecular weight grade PP showed increase in the tensile yield stress up to 40 wt% PS in the absence of MMT. The tensile strength at break for blend increased slightly with MMT while elongation at break and impact strength decreased in the presence of MMT. Surface energy analysis model was used to predict the orientation and equilibrium position of the clay platelet at the interface based on the surface energies.     

Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends

This paper reports the effect of nanosilica (SiO₂) on the morphology of co-continuous immiscible polypropylene (PP)/polyolefin elastomer (POE) blends. The unfilled blends display phase inversion and a co-continuous structure at a ratio of 50/50 PP/POE by weight. Upon addition of SiO₂ in the presence of maleated PP compatibilizer a finer structure, consisting of elongated POE particles dispersed within the PP phase is obtained. This transformation is associated to the presence of finely dispersed SiO₂ particles that are localized exclusively within the PP matrix. The impact properties, flexural and Young's moduli of the blends increase significantly, pointing to a synergistic effect arising from the presence of the reinforced PP phase, containing high amounts of the finely dispersed elastomeric phase.     

Morphology evolution during cooling of quiescent immiscible polymer blends: matrix crystallization effect on the dispersed phase coalescence

The influence of the matrix crystallization on the coalescence of the dispersed phase particles, in quiescent immiscible polymer blends, is a topic that is scientifically addressed scarcely. The coarsening of the phase structure that is induced by the matrix crystallizing domains was studied using the well-established system comprising a polypropylene and an ethylene–propylene rubber (PP/EPR blends). This subject is of great importance as the effectiveness in the toughening of PP is directly determined by the EPR particle size. Cooling experiments were commenced for resolving the correlation among the imposed cooling conditions, the formed matrix crystalline morphology, and the coalescence of the dispersed phase particles. A confirmation of the profound effect of the PP crystallization on the coalescence of EPR particles was undoubtedly obtained. The contribution of the crystallization to the coalescence of the dispersed phase particles is largest at a finite rate of cooling. A thorough discussion regarding the observed effects, encompassing a potential rejection or an engulfing of the dispersed phase particles by the growing crystallites, was undertaken.     

乙丙嵌段共聚物相对分子质量及链结构对PP/EPR共混体系结构与性能的影响

设计合成了一系列不同相对分子质量和乙烯平均序列长度的乙丙嵌段共聚物（EP）,并将其作为聚丙烯（PP）/二元乙丙橡胶（EPR）共混体系的增容剂,考察了EP用量、相对分子质量及乙烯平均序列长度对共混体系性能及分散相形态演变的影响。结果表明,EP增容PP/EPR体系时存在最佳添加量,少量EP的加入可有效提高PP/EPR共混体系的抗冲击性能,并对分散相尺寸及形态起到良好的调控作用;同时,EP的相对分子质量越大对共混体系的冲击性能提高越明显,EP的组成与EPR越接近,对共混体系的增容效果越明显。     

The morphology of hyperbranched polymer compatibilized polypropylene/polyamide 6 blends

The influence of hyperbranched polymer grafted polypropylene (PP‐HBP) on the morphology of polypropylene (PP)/polyamide 6 (PA6) blends has been investigated. The final morphology was strongly influenced by the PP‐HBP compatibilizer concentration. At low concentrations, PP‐HBP acts as an emulsifying agent, reducing the size of the dispersed phase and preventing coalescence. This is due to the high reactivity and diffusitivity of PP‐HBP rapidly forming a high density of copolymers at the interface. Compared to the use of maleic anhydride grafted PP (PP‐MAH) at identical concentrations, PP‐HBP yielded a smaller dispersed phase particle size. Therefore, PP‐HBP allows the use of less compatibilizer to obtain identical morphologies. At higher compatibilizer concentrations, it has been shown that the PP‐HBP efficiently stabilizes the interface and inhibits both coalescence and breakup of the PA6 droplets. The high concentration of reactive sites and the ability of PP‐HBP to react with both chain‐ends of PA6 suggest that interfacial stabilization occurs because of the formation of a partly crosslinked interface. The interfacial stabilization effects generated by PP‐HBP should allow one to control the morphology of polymer blends in order to create specific functional morphologies.     

Morphology and thermal properties in the binary blends of poly(propylene-co-ethylene) copolymer and isotactic polypropylene with polyethylene

The morphology and thermal properties of isothermal crystallized binary blends of poly(propylene-co-ethylene) copolymer (PP-co-PE) and isotactic polypropylene (iPP) with low molecular weight polyethylene (PE) were studied with differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). In PP-co-PE/PE binary blends, however, the connected PE acted as a phase separating agent to promote phase separation for PP-co-PE/PE binary blends during crystallization. Therefore, the thermal properties of PP-co-PE/PE presented double melting peaks of PE and a single melting temperature of PP during melting trace; on the other hand, at cooling trace, the connected PE promoted crystallization rate because of enhanced segmental mobility of PP-co-PE during crystallization. At isothermal crystallization temperature between the melting points of iPP and PE, the binary blend was a crystalline/amorphous system resulting in persistent remarkable molten PE separated domains in the broken iPP spherulite. And then, when temperature was quenched to room temperature, the melted PE separated domains were crystallized that presented a crystalline/crystalline system and formed the intra-spherulite segregation morphology: these PE separated domains/droplet crystals contained mixed diluent PE with connected PE components. On the other hand, in the iPP/PE binary blends, the thermal properties showed only single melting peaks for both PE and iPP. Moreover, the glass transition temperature of iPP shifted to lower temperature with increasing PE content, implying that the diluent PE molecules were miscible with iPP to form two interfibrillar segregation morphologies: iPP-rich and PE-rich spherulites. In this work, therefore, we considered that the connected PE in PP-co-PE functioned as an effective phase separating agent for PP and diluent PE may be due to the miscibility between connected PE and diluent PE larger than that between PP and dispersed PE.     

Phase morphology development of polypropylene/ethylene-octene copolymer blends: effects of blend composition and processing conditions

Summary Blends of polypropylene (PP)/ethylene-octene copolymer (EOC) was studied. The influences of blend composition and processing conditions on phase morphology development of the blends were investigated by scanning electron microscopy (SEM) in detail. The minor composition formed the dispersed phase and the major composition formed the continuous phase, and the blends formed interpenetrating co-continuous morphology just at the intermediate concentration. The effect of concentration on phase coarsening was explained by the increase of dispersed phase coalescence with dispersed phase concentration’s increase. Phase coarsening and phase fine dispersing were studied. The effect of mixing time on phase morphology development of the blends was investigated, the PP/EOC (80/20) blends has already formed a well-established droplet/matrix morphology after 1.5 min of mixing, and the similar blends phase morphology persisted until 11 min of mixing. The most prominent phenomenon is that the dispersed phase domain deformed from spherical droplet to elliptical droplet, even fibrillar or sheet morphology as the rotor speed increased. The increase of shear rate and elasticity ratio was applied to interpret this phenomenon.     

Structured polymer blends: 2. Processing of polypropylene/EDPM blends: controlled rheology and morphology fixation via electron beam irradiation

Electron beam irradiation has been used to improve the processability of polypropylene/ethylene-propylenediene monomer (PP/EPDM) blends (controlled rheology) in combination with fixation of morphology by inducing crosslinks in the dispersed EPDM phase. An optimum morphology for impact toughening has been obtained via extrusion-blending high molecular weight PP with EPDM. Upon irradiation before subsequent processing (injection moulding) this morphology is fixated, whereas the viscosity of the blend decreases as a result of chain scission of the PP matrix. Impact strength and elongation at break of these irradiated blends are better than those of blends of low molecular weight PP with EPDM, which possess comparable overall viscosity.     

Morphology, microstructure and compatibility of impact polypropylene copolymer

The morphology of impact polypropylene copolymer (IPC) was studied through scanning electron microscope (SEM) and transmission electron microscope (TEM) observation, and a modified dispersed phase model of IPC with core-shell structure was proposed. Through fractionation of IPC, the glass transitions of the ethylene-propylene random copolymer (EPR) fraction, ethylene-propylene block copolymer (EbP) fraction and propylene homopolymer (iPP) fraction were detected, respectively. Moreover, the glass transitions and crystallization behaviors of EbP/iPP and EPR/EbP fraction blends were systemically investigated and several reasonable chain structures of EbP component were confirmed. The results reveal that the EbP component presents three glass transition peaks, and the glass transition temperature of ethylene-propylene random copolymer in IPC sample is remarkably lower than that of pure EPR fraction due to the existence of special structure of EbP component in IPC. In addition, co-crystallization occurring between the polypropylene chains in EbP fraction and in iPP fraction was found for solution-mixed EbP/iPP blends, and it is believed that there exists a dilute effect of EPR on the crystallization of EbP fraction for the solution-mixed EPR/EbP blends. Accordingly, it can be inferred that EbP fraction has good compatibility with both EPR and iPP fraction, and indeed it confirms that the compatibilization effect of EbP fraction in IPC was good.     

Partial replacement of EPR by GTR in highly flowable PP/EPR blends: Effects on morphology and mechanical properties

This research analyzes the effect of ground tire rubber (GTR) and a novel metallocene‐based ethylene–propylene copolymer (EPR), with high propylene content, on the morphology and mechanical behavior of ternary polymer blends based on a highly flowable polypropylene homopolymer (PP). The PP/EPR blends morphology, with very small domains of EPR dispersed in the PP matrix, indicates a good compatibility among these materials, which leads to a significant improvement on elongation at break and impact strength. The incorporation of EPR on the rubber phase of thermoplastic elastomeric blends (TPE) based on GTR and PP (TPE^GTR) has a positive effect on their mechanical performance, attributed to the toughness enhancement of the PP matrix and to the establishment of shell‐core morphology between the rubber phases. The mechanical properties of the ternary blends reveal that TPE^GTR blends allow the upcycling of this GTR material by injection molding technologies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42011.     

Anisotropy and instability of the co-continuous phase morphology in uncompatibilized and reactively compatibilized polypropylene/polystyrene blends

The present work describes the anisotropy and instability observed upon the formation of co-continuous phase morphologies in model polystyrene/polypropylene melt-extruded blends. Uncompatibilized and reactively compatibilized blends using amino-terminated polystyrene, PS-NH₂, and maleic anhydride grafted polypropylene, PP-MAh, reactive precursors were investigated. Differences in phase morphology are discussed based on the viscoelastic properties of the components used, the blend composition and, the type and content of the compatibilizer precursor employed. As expected, for the same polystyrene grade at a concentration in the blend below 20 wt%, a polypropylene matrix having a higher viscosity enables the formation of a more co-continuous phase morphology than a less viscous one, as quantified by solvent extraction. The co-continuous phase morphology developed was found to exhibit a highly elongated structure upon melt flow through the die of the extruder. Isotropic co-continuity, observed inside the barrel of extruder, was transformed into anisotropic phase co-continuity in the form of interconnected infinite strands of the minor phase highly oriented in the extrusion direction.When the blends were thermally annealed, a 50/50 PS/PP co-continuous blend exhibits a substantial phase coarsening from micro- to millimeter scale without alteration of the phase co-continuity. The reactive compatibilization of the polypropylene and the polystyrene phases using 5 wt% PP-graft-PS, reactively in situ generated was able to significantly retard the phase evolution process.     

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene (hiPP) were studied by solvent extraction fractionation, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nuclear magnetic resonance (¹³C‐NMR), and selected reblending of different fractions of hiPP. The results indicate that hiPP contains, in addition to polypropylene (PP) and amorphous ethylene‐propylene random copolymer (EPR) as well as a small amount of polyethylene (PE), a series of crystallizable ethylene‐propylene copolymers. The crystallizable ethylene‐propylene copolymers can be further divided into ethylene‐propylene segmented copolymer (PE‐s‐PP) with a short sequence length of PE and PP segments, and ethylene‐propylene block copolymer (PE‐b‐PP) with a long sequence length of PE and PP blocks. PE‐s‐PP and PE‐b‐PP participate differently in the formation of multilayered core‐shell structure of the dispersed phase in hiPP. PE‐s‐PP (like PE) constructs inner core, PE‐b‐PP forms outer shell, while intermediate layer is resulted from EPR. The main reason of the different functions of the crystallizable ethylene‐propylene copolymers is due to their different compatibility with the PP matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phase continuity detection and phase inversion phenomena in immiscible polypropylene/polystyrene blends with different viscosity ratios

Blends of polypropylene (PP) and polystyrene (PS) were prepared in a twin-screw extruder and studied in a wide range of compositions. Phase continuity was first determined using selective solvent extraction. Subsequently, dynamic stress rheometry and dynamic mechanical analysis were used to detect the co-continuity and phase inversion compositions in the melt and the solid states. It appears that the phase inversion occurs in a domain rather than at a single point. The evaluation of the storage modulus of PP/PS blends in the melt at a constant low frequency gives information about the co-continuity, as far as the onset of co-continuity and phase inversion composition of the PS phase are concerned. The evaluation of the storage modulus and mechanical loss factor at a constant high temperature, or the glass transition temperature intensity allowed to precisely detect the phase inversion composition. The fractionated or bulk crystallization behavior of the crystallizable PP phase in the PP/PS blends can also be used to identify the matrix/dispersed phase or co-continuous phase morphology. Several semi-empirical models using the dynamic viscoelastic properties of blend components have been applied to detect the phase inversion composition. An extensive data set presented, can also be used to guide future modeling.     

Influences of component ratio of minor phases and charge sequence on the morphology and mechanical properties of PP/PS/PA6 ternary blends

In this study, influences of both component ratio of minor phases and charge sequence on the morphology and mechanical performance in typical ternary blends, polypropylene (PP)/polystyrene (PS)/polyamide-6 (PA6), have been studied. Reactive compatibilization of the blends has been carried out using multi-monomer melt grafted PP with anhydride groups and styrene segments. For uncompatibilized blends, scanning electron microscope (SEM) and selective solvent extraction showed that the blends presented a core–shell morphology with PS as shell and PA6 as core in the PP matrix, in spite of the component ratio and charge sequence. The shell thickened and droplet size decreased with increasing the PS/PA6 component ratio. While for compatibilized blends, the addition of compatibilizers resulted in a significant reduction of the dispersed droplet size and the phase structure of the dispersed phases was greatly dependent on the charge sequence. When the blending of PA6, g-PP, and PP are preceded, the encapsulation structure reversed into the structure of PS phase encapsulated by PA6 phase, which led to better tensile and flexural strength of the blends.