Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Compatibilization by Olefin Block Copolymer (OBC) in Polypropylene/Ethylene-Propylene-Diene Terpolymer (PP/EPDM) Blends

The compatibilization by olefin block copolymer (OBC) in the blends of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) and the phase morphology of the ternary blends were investigated by rheology, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements. It was found that the PP/EPDM blends exhibited enhanced mechanical properties in the presence of OBC. The addition of OBC had a significant influence on the phase separation behavior of the blends. For the PP/EPDM-50/50 heterogeneous blends, the addition of 15 phr OBC enabled the two-phase morphology to change from a droplet-matrix structure to a co-continuous one. In the temperature range of 150 to 200 °C, OBC was shown to have a better compatibility with PP than EPDM. The changes in viscosity ratio of the dispersed phase to matrix phase caused by adding OBC might be the dominant factor in controlling the coalescence of the dispersed phase domains. For the crystallization behavior of PP/EPDM/OBC ternary blends, OBC was found to have an induction effect on the formation of β-crystals of PP that was not proportional to the volume of OBC addition. In addition, DSC results showed that PP could induce the OBC crystallization and improve the crystallization temperature of OBC. The existence of simultaneous crystallization behavior between PP and OBC was also observed. A possible mechanism of phase evolution induced by crystallization was proposed.     

Interfacial activity of styrene-butadiene block copolymers in low-density polyethylene/polystyrene blends

The effect of molecular structure of styrene-butadiene (SB) block copolymers on their interfacial activity in low-density polyethylene/polystyrene (LDPE/PS) (4/1) blends was studied. It was found that addition of some SB copolymers, which are localized in brittle PS particles, leads to a decrease in the blend impact strength in spite of the fact that these SB improve the toughness of both the blend components. Comparison with our previous results showed that the distribution of SB copolymers between the interface and bulk phases and their supermolecular structure in LDPE/PS (4/1) blends strongly differs from those in LDPE/PS (1/4) blends.     

Compositional Dependence of Static Shear Viscosity of Immiscible PP/PS Blends

Phase structures of immiscible polypropylene (PP)/polystyrene (PS) blends with different volume proportions, PP90/PS10, PP80/PS20, PP70/PS30, PP60/PS40, PP50/PS50, PP40/PS60, PP30/PS70, PP20/PS80, PP10/PS90, were observed by means of scanning electronic microscopy (SEM). The zero shear viscosities of the blends were determined according to a modified Carreau model by fitting the curves of static shear rate sweeps of blends tested at 190°C in a Stress Tech Fluids Rheometer. The results showed that the compositional dependence of zero shear viscosity of PP/PS deviated greatly from linear or log‐linear additivity. When PS was dispersed in a PP continuous phase, the blends showed negative deviation, while for blends with PP dispersed in a PS matrix, positive deviation was generated. When different theoretical equations of Nielsen, Utracki, Taylor, Frankel‐Acrivos (FA), Choi‐Schowalter (CS), and Han‐King (HK) were used to fit the experimental data of zero shear viscosities of blends, none of them was suitable for PP/PS blends. These experimental phenomena may result from the complex phase structures of the blends and their response to shear conditions, which are discussed in detail and compared with the experimental analysis.     

Polymer-filler interaction and control of structure in barium sulphate-filled blends of polypropylene

The structure of barium sulphate-filled immiscible blends with a polypropylene (PP) matrix can be controlled with respect to the occlusion of the filler with the aid of maleic anhydride-grafted polypropylene (PP-g-MAH) through the formation of an interlayer around the filler particles. Here we analyze the interlayer and the mechanism of interlayer formation in a blend with a poly(methylmethacrylate) (PMMA) dispersed phase and compare the results with previous studies, which concerned PP blends with polystyrene (PS) and poly(styrene-co-acrylonitrile) (SAN) minority phases. The main analytical tools were scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and Fourier Transform Infrared Spectroscopy (FTIR). The filler is occluded in the PMMA polymer in the PP/PMMA/BaSO₄ (60/20/20 vol.%) blend, but is occluded in the PP phase at the addition of a sufficient amount of PPg-MAH. The reason for the formation of the latter structure is a PP-g-MAH layer surrounding the filler particles, and the most likely mechanism behind this phenomenon is judged to be specific weak interactions between carbonyl groups in the graft copolymer and Ba²⁺ ions at the filler surface.     

Study of Morphology and Mechanical Properties of In Situ PP/PS Alloy

The in situ polypropylene (PP)/polystyrene (PS) alloy was prepared in the presence of dicumyl peroxide (DCP). Purified styrene (St) and pre‐polymerized styrene (PSt), forming a dispersed PS phase in the PP matrix would react with PP matrix to form PP‐g‐PS graft co‐polymers acting as a compatibilizer in these alloys, leading to the formation of in situ PP/PS alloys with in situ compatibilizer during reactive blending in a mixer. The morphology development of the alloy was examined by scanning electron microscopy (SEM) and was described using the characteristic length L and the average characteristic length L_m. The shape of the dispersed PS phase was regular and the distribution of PS particles was uniform. Tensile properties of the alloy were improved with mixing time and fluctuated in a certain composition range.     

Role of Styrene‐Ethylene/Propylene Block Copolymer in Controlling Morphology Development of PP/PS Blends during Mixing

The role of styrene‐ethylene/propylene (SEP) diblock copolymer in controlling morphology development of polypropylene/polystyrene (PP/PS) blends was studied by means of small angle laser scattering (SALS) and scanning electron microscopy (SEM). According to SALS, a certain amount of SEP was located at the phase boundary, forming a relatively thick transition layer penetrating into the homopolymers. The thickness of the transition layer was quantified in terms of Debye–Bueche light scattering theory. For PP/PS (1/99) and PP/PS (20/80) blends, the incorporation of SEP into PP/PS blends resulted in a decrease in domain size following an emulsification curve as well as a uniform size distribution, and consequently, a fine dispersion of PP domains in the PS matrix. However, for PP/PS (45/55) blends, the addition of SEP results in a nonmonotonous change in domain size. The morphology fluctuation of the fracture surfaces was analyzed using an integral constant Q based on Debye–Bueche light scattering theories. Variation of Q as a function of the concentration of SEP showed that, due to the penetrating transition layer, adhesion between phases was improved, making it possible for applied stress to transfer between phases and leading to a more uniform stress distribution when blends were broken; accordingly, a more complicated morphology fluctuation of the fracture surfaces appeared.     

Fracture Micromechanisms of Polypropylene/Polycarbonate/Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PP/ PC/SEBS) Ternary Blends: The Effects of SEBS Content

Ternary blends of polypropylene/polycarbonate/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PP/PC/SEBS) with varying SEBS contents were produced via melt blending in a co-rotating twin-screw extruder. The phase morphology of the resulting ternary blends and its relationship with bending and impact behaviors were studied. Transmission optical microscopy (TOM) of the crack tip damage zone and scanning electron microscopy (SEM) of impact fractured surfaces were performed to characterize the fracture mechanism. With increasing SEBS content in the PP/PC/SEBS ternary blends, the number of PC/SEBS core-shell particles increased and the size of the core-shell particles enlarged. It was shown that with an SEBS content of 5%, the crack initiation resistance decreased and then was almost unchanged with further increase of SEBS content, while resistance to crack growth increased continuously with increasing of SEBS content. Preliminary analysis of the micromechanical deformation suggested that the high impact toughness observed for samples containing 20 and 30 wt% of SEBS could be attributed to cavitation of the rubbery shell and, consequently, shear yielding of the matrix. This plastic deformation absorbed a tremendous amount of energy. Due to low interfacial adhesion between PC particles and PP matrix in samples containing 5 and 10 wt% of SEBS, debonding occurred too early, so the occurrence of matrix shear yielding was delayed and resulted in premature interfacial failure and, hence, rapid crack propagation.     

CORRELATION AMONG MORPHOLOGY,INTERFACE, AND MECHANICAL PROPERTIES: EXPERIMENTAL STUDY

The effect of the disperse phase and the diffuse interface between phases on the tensile and impact strengths of polypropylene (PP)/poly(ethylene terephthalate) (PET) (75/20 by weight) blends compatibilized with maleic anhydride–grafted PP derivatives and on the tensile modulus of poly(vinyl chloride)/polystyrene (PVC/PS) nanoparticle blends compatibilized with polystyrene/poly(vinyl acetate) (PS/PVAc) block copolymers were investigated experimentally. The weight fraction of the diffuse interface between the PP and PET phases in the PP/PET blends was determined by modulated differential scanning calorimetry (MDSC). A correlation between the diffuse interface content and mechanical properties was found. With increasing diffuse interface weight fraction, the impact and tensile strengths of the PP/PET blends increased. There is a brittle-tough type transition in these PP/PET blends. With increasing diffuse interface content in the PVC/PS nanoparticle blends in which the particle size was fixed at about 100 nm, the tensile modulus also clearly increased.     

Morphological Aspects of In-Situ Compatiblized Binary Polymer Blends With Variable Viscosity Ratios of Components

The in-situ compatiblized binary polymer blend polypropylene(PP)/polystyrene(PS)/ anhydrous aluminum chloride(AlCl₃) was selected as a model system of a reactive polymer blend to investigate the effect of viscosity ratio of components at a constant shear rate on the phase morphological behavior in in-situ compatibilized systems. The results showed that the well-known interfacial compatibilization effect was related to variations of viscosity ratios of components in the reactive PP/PS blends with different contents of AlCl₃ catalyst. The phase morphology evolution of the in-situ compatiblized reactive blend was determined by both the interfacial compatibilization and the variation of the viscosity ratio of components under the fixed mixing conditions, which showed characteristics obviously different from and much more complex than those in binary polymer blends generally compatiblized by added compatiblizers. The results implied that the variation of the viscosity ratio of components should be checked carefully and taken into account if necessary, when the phase morphology of binary polymer blends is investigated, especially in complex in-situ compatiblized reactive polymer blends.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 1. Rheology,Morphology, Melting,and Mechanical Properties

Poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends were prepared by melt blending. The rheology, morphology, melting, and mechanical properties of PTT/PP blends were investigated with and without the addition of polypropylene‐graft‐maleic anhydride (PP‐g‐MAH). The melt viscosity results showed that the fluid behavior of PTT/PP blends exhibited great disparity to that of PTT but similar to that of PP; the dispersed flexible PP phase in the blends served as a “ball bearing effect” under shear stress, which made the fluid resistance markedly reduced; by contrast, the relatively rigid PTT dispersed phase made only a small contribution to the viscosity. With 5 wt.% PP‐g‐MAH addition during melt processing, both the shear viscosity and the non‐Newtonian index of 70/30 PTT/PP blend were increased over that of the corresponding uncompatibilized one, whereas the shear viscosity of the 30/70 PTT/PP melt decreased slightly indicating that a considerable amount of PP‐g‐MAH did not act as compatibilizer but probably served as plasticizer.

With the increasing of the other component, the melting temperature of the PTT phase showed a slight decrease while the melting temperature of the PP phase showed a slight increase. 5 wt.% PP‐g‐MAH addition had little influence on the melting temperatures of the two components. When PP≤20 wt.%, the cold crystallization temperature of the PTT phase (T_cc (PTT‐phase)) showed little change with the composition; however, it shifted to higher temperature when PP≥30 wt.%. The variations of the T_cc (PTT‐phase), with and without PP‐g‐MAH, suggested that, when PTT was a minor component, the excess PP‐g‐MAH which did not act as compatibilizer might serve as a plasticizer that made the PTT's cold crystallization process to be easier. The SEM results indicated that, for the uncompatibilized blends, the interfaces from particles pulling‐out are clear and smooth, while, for compatibilized blends, the reactive products are at the interfaces. The mechanical properties suggested that PP‐g‐MAH did not result in significant improvement of the toughness of the blend, but the tensile strength increased markedly.     

Large Strain Tensile Deformation and Failure in Oriented Isotactic Polypropylene/Clay Nanocomposite: Role of Voiding and Molecular Orientation

Plane strain compression of isotactic polypropylene iPP)/clay nanocomposite in a channel die at 140 and 160°C, respectively, has been adopted to prepare oriented samples with well-controlled structure for comparative studies. Molecular orientation in the amorphous phase, independent of clay loadings, decreases with increasing preparation temperature, whereas crystallographic orientation is nearly the same for all oriented samples. Severer voiding and void coalescence during stretching, mostly induced by the crystals and inter-chain sliding in the amorphous phase, respectively, is suggested to be responsible for higher volume dilatation and lower failure strain in the oriented samples prepared at higher temperature (e.g., 160°C). Fracture toughness is well correlated with the molecular orientation and crystal-dependent voiding in the oriented samples with respect to preparation temperatures. Furthermore, debonding of clay in the iPP matrix, especially in the oriented samples prepared at 140°C, is another contributor to the enhanced toughness.     

Effect of Polydispersity on the Phase Behavior of Polystyrene (PS)/Poly (Vinyl Methyl Ether) (PVME)

The thermodynamics and kinetics of phase separation in partially miscible blends of poly (vinyl methyl ether) (PVME) and two kinds of polystyrene (PS) with the same weight average molecular weight but different polydispersity were studied. The miscibility of PS/PVME with the monodisperse PS was better than that of PS/PVME with the polydisperse PS. Different morphology was observed for the two kinds of PS/PVME (10/90) blends during the nonisothermal phase separation process. The blend with monodisperse PS presented a co-continuous structure while the blend with polydisperse PS presented a viscoelastic phase separated network structure at a quench depth of 29°C. With increase of the heating rate, the increase of cloud point of PS/PVME (30/70) with polydisperse PS was smaller than that of PS/PVME (30/70) with monodisperse PS. During the isothermal phase separation of the critical composition (20/80) of PS/PVME with a quench depth of 30°C, it was found that the phase morphology of the two kinds of blends was nearly the same at the early stage of phase separation. However, as the dispersed phase, an approximately spherical droplet structure was observed in the blend with monodisperse PS at the late stage of phase separation, which did not appear in the blend with polydisperse PS.     

Effect of Clay Addition on the Properties of Carbon Nanotubes-Filled Immiscible Polyethylene/Polypropylene Blends

The effects of organically modified clay (OMC) incorporation on the microstructure and the electrical and mechanical properties of polypropylene (PP)/polyethylene (PE) blends filled with carbon nanotubes (CNT) were investigated. All blends were prepared by melt mixing in a batch mixer. The microstructures were characterized by scanning electron microscopy. In the OMC:CNT filled blends, the CNT were found to selectively localize within the PE phase, while the clay particles were observed in the PP phase. The electrical resistivity of OMC:CNT filled blends did not show any significant change as a result of the clay addition since it was localized in the CNT-free phase. On the other hand, the addition of clay degraded the blends' mechanical properties due to the poor adhesion between the OMC and the PP matrix.     

Morphology-property relationships in polycarbonate-based blends. I. Modulus

The tensile, dynamic mechanical and morphological properties of PC/HDPE, PC/LDPE and PC/PS blends have been investigated with the intent of clarifying the major factors governing the modulus of these essentially incompatible blends. Scanning electron microscopy shows that all of the PC/HDPE, PC/LDPE and PC/PS blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase; when the dispersed phase concentration is less than 15%, the domains are mostly of spherical shape, while above 20% agglomeration takes place to form rodlike structures. Dynamic mechanical data shows there is essentially no adhesion at the PC-HDPE and PC-LDPE boundaries, while there is appreciable adhesion at the PC-PS interface. The existence of an intermixed zone was postulated to explain this interfacial adhesion. Morphological and thermal analysis results also indicate that both the HDPE and LDPE inclusions are loosely sitting in the holes in the PC matrix while the PS inclusions are compactly embedded in the PC matrix. These differences in boundary nature give marked effects on the tensile properties including the modulus. For the modulus, PC/HDPE and PC/LDPE blend systems can be regarded to be mechanically equivalent to a PC matrix alone with holes in it when the dispersed phase concentration is lower than 15%, while in the case of PC/PS blends the PS inclusions contribute substantially to the sample's overall modulus.     

Influence of High-Density Polyethylene and Nano-Calcium Carbonate of Various Content Ratios on the Crystallization of Polypropylene

The influence of high-density polyethylene (HDPE) and nano-CaCO₃ of various content ratios on the crystallization of polypropylene (PP) was investigated by differential scanning calorimetry, dynamic rheology, wide angle X-ray diffraction (WAXD), and Izod impact strength measurements. The results showed that HDPE and PP were phase separated in their blends and the additive CaCO₃ filler mainly dispersed in the PP phase, acting as a nucleation agent to promote the crystallization of PP. For the samples HDPE/ nano-CaCO₃ 30/0 and 25/5, the β crystals content was much higher than the other samples. The reason is that the viscosity difference between HDPE and PP led to a velocity difference, which could induce shear stress at the interfaces of HDPE and PP during injection molding. The intensive shear stress at their phase interfaces is advantageous for orientation of the chains, inducing the formation of β crystals. However, with the increment of CaCO₃ content, there were dual effects of CaCO₃ on the crystallization of PP: at low CaCO₃ content, it would hamper the orientation of PP chains, thus leading to a decrease of β crystals; at high CaCO₃ content, it would induce β crystals by itself.     

Structure and Properties of Ultradrawn Polylactide/Thermoplastic Polyurethane Elastomer Blends

Highly oriented self-reinforced 80/20 blends of polylactide (PLA)/thermoplastic polyurethane elastomer (TPU) were successfully fabricated through solid hot stretching technology. Different from the isotropic sample, stress rose rapidly in a low strain region, and exhibited strain hardening for the drawn samples of the PLA/TPU blend. Superior mechanical properties of the blend, with the notched Charpy impact strength 150 KJ/m², and tensile strength 197 MPa, were achieved. With increasing hot stretch ratio, the storage modulus increased, the glass transition temperatures of the PLA-rich phase and TPU-rich phase in the blends moved to higher temperatures, and the melting temperature and crystallinity of the blend increased, indicating the stress-induced crystallization of the blend during drawing. The longitudinal fracture surfaces of the blends at different stretch ratios exhibited orderly arranged fibrillar bundle structure, which contributed to the significantly higher strength and toughness of the blend.     

Polypropylene/Poly (Trimethylene Terephthalate)–Blend Fibers

Polypropylene (PP)/polyester (PES)–blend fibers were prepared by extruder melt spinning. The polymer blend consisted of PP and a “master batch” (MB) based on polytrimethylene terephthalate (PTT) or polyethylene terephthalate (PET), binary PTT/PET or PP/PTT blends, and also on a ternary PP/(PTT/PET) blend. The phase structure of PP/PES–blend fibers was examined. PES microfibers showed separation from the PP matrix in blend fibers. The impact of MB composition and rheological characteristics on phase structure parameters indicate a significant contribution of the PTT in the binary MB on the length of dispersed PES microfibers in the PP matrix. However, the blends of PP and ternary MB (PP/PTT/PET) have a lower diameter and length of the PES microfibers. The presence of PTT/PET (PES) enhances the structural and mechanical properties of the blend PP/PES fibers. In addition, PTT increases the tensile strength of the PP/PES–blend fibers if a binary MB is used, while the fiber nonuniformity is reduced in the presence of a ternary MB.     

The Effects of Different Processing Methods on the Morphology and Properties of PP/EPDM/Nano-CaCO3 Ternary Blend

The effects of different processing methods (direct extrusion, two-step extrusion or lateral injection extrusion) on the morphology of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/calcium carbonate nanoparticles (nano-CaCO₃) ternary blend were investigated, including the morphology of the EPDM phase and the distribution of nano-CaCO₃ particles, by means of scanning electron microscopy (SEM). The results showed that the processing methods had a significant influence on the morphology of the EPDM phase and the distribution of nano-CaCO₃ particles. In the lateral injection extruded blends, it was amazingly observed that the EPDM particles encapsulated the PP phase tightly, and the dimension of EPDM particles was remarkably decreased. It was also found that the content of nano-CaCO₃ particles in the matrix of the lateral injection extruded blends was less than that of the two-step extruded blend, and that of the direct extruded blend was most. The properties of the ternary blend, including dynamic mechanical properties, rheological properties, and crystallization, were characterized in order to confirm the variety of morphologies caused by the different processing methods. The differences in the crystallization temperature, elastic modulus, and glass transition temperature of the blends prepared by different methods well agreed with the variation of their morphology.     

CORRELATION BETWEEN MORPHOLOGY AND MECHANICAL PROPERTIES OF DIFFERENT STYRENE/BUTADIENE TRIBLOCK COPOLYMERS: A SCANNING FORCE MICROSCOPY STUDY*

The morphology of different styrene/butadiene (SB) block copolymers with triblock architectures was investigated using tapping mode scanning force microscopy (SFM). Comparative analysis of the morphology of the samples at the polymer/substrate interface of solution-cast films and in bulk was performed. It was found that, besides the total phase volume ratio, the interfacial structure between the incompatible chains determines the phase morphology and mechanical properties of the investigated block copolymers. The asymmetric SBS triblock copolymer (φ_ps( 74 vol%) forms, as expected, a cylindrical morphology with hexagonally packed polybutadiene (PB) cylinders in the polystyrene (PS) matrix. Depending on the interfacial structure, block configuration, and the hard/soft phase ratio, other triblock copolymers (φ_ps( 74 vol% and 65 vol%) show lamellae and randomly distributed PS cylinders in a random styrene/butadiene copolymer S/B matrix, respectively.