Polypropylene/polyamide 6/polyethylene-octene elastomer blends. Part 2: volume dilatation during plastic deformation under uniaxial tension

Plastic deformation upon stretching was investigated in ternary blends of polypropylene, polyamide 6 and maleic anhydride-grafted polyethylene-octene elastomer (PP/PA6/POE). A novel video-controlled tensile testing method was utilized, which allows recording simultaneously axial strain, axial stress and volume strain while axial strain-rate is regulated at a constant value even after necking has begun. Increasing the alloying content modifies drastically the original stress-strain properties of PP: yield softening is suppressed and strain hardening is increased. As for the volume strain, which is representative of the overall cavitation process, it is found to decrease with increasing alloying content (apart from a small increase for low alloying content). This unexpected result indicates that the finely dispersed cavities nucleated under tension at the POE interphase of PA6 particles and at isolated POE particles favor the profuse development of plastic shear bands in the PP matrix. As such, it can be considered as an experimental evidence of the synergistic effect of cavitation and shear banding in a structural polymer.     

Plastic damage mechanisms of polypropylene/polyamide 6/polyethelene-octene elastomer blends under cyclic tension

A series of three-phase polymer blends, composed of polypropylene (PP) matrix, polyamide-6 (PA6) fillers and polyethylene-octene elastomer grafted with maleic anhydride (POE-g-MA) modifiers, were designed and manufactured. Their mechanical behavior under cyclic loading-unloading was studied by using a video-controlled testing system named as VideoTraction^© system. It was found that with the increasing PA6 and POE content, the strain hardening became more and more prominent, the volume strain decreased, and the energy dissipated increased. A detailed examination of the cryo-fractured surfaces under SEM was undertaken. The microcavity nucleation, growth and coalescence were observed, and represent the main mechanisms of plastic deformation and damage. The high volume strain comes from the abundant formation of microvoids. On the contrary, the formation of microvoids resulted in relatively smaller quantity of energy dissipation. This result coincides well with the toughening mechanisms of polymer blends revealed by other peoples.     

Microstructures and mechanical properties of polypropylene/polyamide 6/polyethelene-octene elastomer blends

A series of polymer blends were designed and manufactured. They are composed of three phases: polypropylene (PP), polyamide-6 (PA6) and polyethylene-octene elastomer (POE) grafted with maleic anhydride. The weight fraction of PA6 was adjusted from 0 to 40% by increments of 10%, and the weight fraction of POE was systematically half that of PA6. The morphology, essentially made of PA6 particles dispersed in the PP matrix, was characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the extruded plates prepared with the blends, the shape of the dispersed PA6 particles showed an elongated ellipsoidal shape, whose aspect ratio increased somehow with alloying content. The POE modifier was observed both as a thin interlayer (less than 100 nm thickness) at the PP/PA6 interface, and as a few isolated particles. The elastic modulus and yield stress in tension are nearly constant for PP and blends. By contrast, the notched Izod impact strength increases very much with alloying content. This remarkable effect is interpreted in terms of POE interphase cavitation, enhanced plastic shear deformation and resistance of PA6 particles to crack propagation.     

Polypropylene/elastomer/poly(styrene-co-acrylonitrile) blends: Manifestation of the critical volume fraction of SAN in dynamic mechanical, tensile and impact properties

The effect of the critical volume fraction v_cr of poly(styrene-co-acrylonitrile) (SAN) on the mechanical properties of its blends with rubber-toughened polypropylene (RTPP) containing about 12% grafted ethylene-propylene copolymer was studied. To encompass a wide spectrum of mechanical properties, blend components were selected which are characterized with rather different viscoelastic, tensile and ultimate properties. The SAN volume fraction in blends covers the interval 0∼0.30; concentration dependencies of measured mechanical properties indicate v_cr = 0.13. Experimental data on storage modulus E_b′, loss modulus E_b″, tensile modulus E_b, yield S_yb and tensile S_ub strength are in plausible accord with their simultaneous prediction based on a predictive scheme which operates with a two-parameter equivalent box model and the data on the phase continuity of components obtained from modified equations of the percolation theory. Strain at break, tensile energy to break and total impact energy of blends show a conspicuous drop in the interval 0∼15 % of SAN where SAN forms a discontinuous component; further growth of the SAN fraction accounts for a reduction of the blend ultimate properties to the values typical of brittle polymers.     

Barrier properties of polypropylene/polyamide blends produced by microlayer coextrusion

The gas barrier properties of injection molded structures prepared from polymer microlayers were investigated. Polypropylene and polyamide-66 were combined as microlayers with tens to thousands of layers. A thin tie layer of compatibilizer coextruded between the layers provided adhesion. Injection molding the microlayered materials at a temperature intermediate between the melting points of the constituents resulted in a high volume fraction of high aspect ratio polyamide-66 microplatelets dispersed in a polypropylene matrix. The resulting material had significantly reduced permeability to oxygen and carbon dioxide compared to the conventional melt blend. Structural models for permeability indicated that enhanced barrier arose primarily from increased tortuosity of the diffusion pathway provided by the oriented, flat platelets of high aspect ratio in the skin region of the complex injected molded structure.     

Polypropylene/cycloolefin copolymer blends: effects of fibrous phase structure on tensile mechanical properties

Tensile mechanical properties of polypropylene (PP)/cycloolefin copolymer (COC) blends were studied using an Instron tensile tester. As COC was expected to impart enhanced mechanical properties to the blends, their modulus, yield strength, tensile strength and tensile energy to break were measured as functions of blend composition. With regard to the reported sensitivity of the COC structure to thermal history, the influence of annealing at two different temperatures was also tested. The attention was primarily concentrated on blends with the volume fraction of COC in the interval 0<v₂<0.40, where COC formed (short) fibres almost uniaxially oriented in the direction of injection moulding. In the interval 0.40<v₂<0.75, the blends consisted of partially co-continuous components. Two different models were applied in the analysis of mechanical properties, namely (i) the rule of mixtures for fibre composites and (ii) the equivalent box model for isotropic blends (employing the data on the phase continuity of components obtained from modified equations of the percolation theory). Experimental data on the studied mechanical properties were better fitted by the models for fibre composites. Annealing of the samples (75 °C for 45 days; 120 °C for 3 h) did not markedly affect the tensile modulus, yield stress, and stress at break of the blends. On the other hand, the strain at break was markedly reduced by the annealing up to v₂=0.2; COC and the blend with 75% of COC ruptured in a brittle manner without yielding.     

Oxygen permeation through films of compatibilized polypropylene/polyamide 6 blends

Polypropylene/polyamide 6 blends were prepared by melt mixing, without or with the addition of a suitable commercial product, a polypropylene grafted with 1% maleic anhydride, used as an interfacial modifier. The oxygen permeation through their films was studied as a function of temperature and the effect of the presence of the compatibilizer on the barrier properties of the material was examined. In addition, the diffusion coefficients were measured. The relationships between transport parameters and blend morphology were investigated by microscopic observations, together with chemical etchings, and a simple model was applied for interpreting the experimental permeation data. Differential scanning calorimetry was used in the determination of the degree of crystallinity of the blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1941–1949, 1999     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.     

Micromechanical processes and failure phenomena in reactively compatibilized blends of polyamide 6 and styrenic polymers. I. Polyamide 6/acrylonitrile– butadiene–styrene copolymer blends

In this work, in situ investigations of the micromechanical properties of reactively compatibilized blends of polyamide 6 (PA6) and an acrylonitrile–butadiene–styrene copolymer (ABS) were performed with transmission electron microscopy. Three PA6/ABS blends were prepared with a disperse morphology (inclusions of PA6 or ABS) and with a cocontinuous structure. The objective of this work was to study the deformation of the inclusions and the interface between the PA6 phase and the ABS phase. Our transmission electron microscopy investigations revealed that the morphology of the blends was strongly influenced by the asymmetric nature of the interface between PA6 and ABS. In the blends with a PA6 matrix, the interface between PA6 and the ABS inclusions was deformed in tensile deformation under uniaxial loading. A strong influence of the PA6 water content on the (micro)mechanical behavior was observed. Although the “dry” blends behaved in a brittle fashion, the “wet” blends behaved in a ductile fashion with the formation of deformation bands in the matrix (PA6 or ABS), which were initiated by stress concentration at the particles (ABS or PA6, respectively). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis of phase morphology and dynamics of immiscible PP/PA1010 blends and its partial-miscible blends during melt mixing from SEM patterns

The formation and evolution of the phase morphology of polypropylene (PP) with Nylon1010 (PA1010) blends before and after adding the compatibilizer, polypropylene grafted maleic anhydride (PP-g-MAH), during melt mixing are investigated by the pattern analysis of scanning electron microscope (SEM). The average particle diameter DP_AV, characteristic length Λ and the average characteristic length Λm are calculated to discuss the melt mixing process. It is proved, by the figure-estimation theory, that the distribution of Λ is log-normal distribution. Furthermore, the phase morphology during melt mixing is discussed in depth by the parameters of the log-normal distribution. The results demonstrate that the structure of the dispersed phase during melt mixing evolves with dynamical self-similarity through the competition of break-up and coalescence of dispersed phase. A fractal dimension, based on the probability density of the character length, is calculated in this study. The results show that the fractal dimension is an effective parameter to characterize the melt mixing process of polymer blends.     

Micromechanical processes and failure phenomena in reactively compatibilized blends of polyamide 6 and styrenic polymers. II. Polyamide 6/styrene‐acrylonitrile copolymer blends

This work reports on morphological, mechanical, and micromechanical properties of polyamide 6 (PA 6), a styrene‐acrylonitrile copolymer (SAN), and their blends, which were reactively compatibilized using a styrene‐acrylonitrile maleic anhydride (SANMA) terpolymer. Transmission electron microscopy (TEM) investigations revealed the phase morphology of the blends, which is characterized by inclusions of the minor component in the matrix of the major phase. The blend with 50% PA 6 and 50% SAN depicted a cocontinuous morphology. Using a microtensile device for TEM, the samples were deformed under uniaxial loading in the “dry” state (characterized by a zero water content in the PA 6 phase) and in a “wet” state (with water in the PA 6 phase). Whereas the dry blends behaved brittle, the wet blends showed a larger ductility with the formation of deformation bands in the matrix (PA 6 or SAN), which were initiated by stress concentration at the SAN and PA 6 particles, respectively. In the interface of blends with a PA 6 matrix and SAN inclusions, two phenomena were observed: partial cavitation and debonding on the one hand and partial fibrillation on the other hand. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of β-irradiation on mechanical properties of metallocene elastomers/PA6 blends

Binary blends of metallocene polymers with polyamide-6 as dispersed phase and ternary blends with a metallocene-grafted rubber as compatibilizer were prepared and treated by electron beam radiation. Thermal stability and mechanical properties were studied, showing that thermosetting rubbers and thermoplastic elastomers with excellent mechanical properties and thermal stability may be obtained by β-irradiation. The irradiated ternary blends displayed high break elongation values, similar to other thermoplastic rubbers based on EPDM or EPR materials. On the other hand, the Shore D hardness, tensile strength, high-temperature behavior, compression set and reprocessing ability were found to be clearly dependent on the metallocene polymer used as bulk phase and the irradiation dose employed.     

Morphology of PEO/PDMS blends during shear: Coexistence of two droplet/matrix structures and additive effects

The morphologies of blends of polyethyleneoxide (PEO 37) and poly(dimethylsiloxane)s (PDSM), with viscosity ratios, λ, of approximately one (PDMS 230) or 2.8 (PDMS 314, being the component of higher viscosity) and interfacial tensions on the order of 10 mN/m, were investigated at 70 °C as a function of shear rate (up to 10 s⁻¹) and of time. For the system PEO 37/PDMS 230 we have also studied the influence of the compatibilizer dimethyl-ethyleneoxide-copolymer (PDMS-co-PEO), which is only reasonably soluble in PEO. To investigate the morphologies we have used an optical shear cell in combination with a light microscope. The most important observation consists in the formation of two coexisting droplet/matrix structures for volume fractions of PDMS ranging from 0.4 to 0.6 for both λ values; the presence of the copolymer extends this region to 0.7. In the case of λ≈1 the average droplet radii are within experimental error independent of composition and morphology; for λ=2.8 they depend on the matrix phase in which they are contained and do again not vary with composition. The reduction in drop size caused by the copolymer is markedly larger if PEO forms the matrix. The present morphological observations suggest that the two coexisting droplet/matrix phases develop out of a single droplet/matrix structure via coalescence processes.     

Phase behavior and physical properties of injection‐molded polyamide 6/phenoxy blends

Polyamide 6 (PA 6)/poly(hydroxyether of bisphenol A) (phenoxy) blends were obtained by direct injection molding over the whole composition range. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM) showed the almost full immiscibility of the blends and the lack of effect of phenoxy on the crystalline phase of PA 6. The rodlike and fine‐dispersed phase of the tensile specimens was strongly deformed during tensile testing, giving characteristic fibrilar structures. The Young's modulus and yield stress showed small deviations from additivity that appeared related mainly to the blending‐induced free‐volume change. Despite immiscibility, the ductility behavior was also additive, probably due to the fibrilar morphology. However, the thicker impact specimens gave rise to less oriented larger dispersed phases and to full plane strain conditions that, in opposition to ductility, yielded impact strength values well below linearity. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1113–1124, 1999     

Filler/matrix-debonding and micro-mechanisms of deformation in particulate filled polypropylene composites under tension

Volume strain measurements of particulate filled polypropylene (PP) composites containing different glass beads and talc as filler were carried out in tension as a function of temperature and strain rate to determine the micro-mechanisms of deformation. While local cavitation mechanisms (micro-voiding, crazing, and micro-cracking) and subsequent debonding of the particles dominated as failure mechanisms at high strain rates and at room temperature, a more significant contribution of local shear yielding was observed with a reduced contribution of cavitational mechanisms at low strain rates or at 80 °C. This change in the dominating micro-mechanisms of deformation resulted in smaller volume strains during the tensile loading of the composites than for the respective neat matrix. Moreover, a novel approach is introduced for the detection of debonding using volume strain measurements, which takes into account the dilatational and deviatoric behavior of the neat matrix polymer and the composite. The results are supported by acoustic emission measurements carried out simultaneously on the same specimens.     

PET/PEN blends of industrial interest as barrier materials. Part I. Many-scale molecular modeling of PET/PEN blends

Mesoscale molecular simulations, based on parameters obtained through atomistic molecular dynamics and Monte Carlo calculations, have been used for modeling and predicting the behavior of PET/PEN blends. Different simulations have been performed in order to study and compare pure homopolymer blends with blends characterized by the presence of PET/PEN block copolymers acting as compatibilizer. A many-scale molecular modeling strategy was devised to evaluate PET/PEN blend characteristics, simulate phase segregation in pure PET/PEN blends, and demonstrate the improvement of miscibility due to the presence of the transesterification reaction products. The behavior of distribution densities and order parameters of the compatibilized blends demonstrates that mixing properties improve significantly, in agreement with experimental evidences. Barrier properties such as oxygen diffusivity and permeability have also been evaluated by finite element simulations. Accordingly, many-scale modeling seems to be a successful way to estimate PET/PEN blend properties and behavior upon different concentrations and processing conditions.     

Using organoclay to promote morphology refinement and co-continuity in high-density polyethylene/polyamide 6 blends - Effect of filler content and polymer matrix composition

We investigate the gradual changes of the microstructure of two blends of high-density polyethylene (HDPE) and polyamide 6 (PA6) at opposite composition filled with increasing amounts of an organomodified clay. The filler locates preferentially inside the polyamide phase, bringing about radical alterations in the micron-scale arrangement of the polymer phases. When the host polyamide represents the major constituent, a sudden reduction of the average sizes of the polyethylene droplets was observed upon addition of even low amounts of organoclay. A morphology refinement was also noticed at low filler contents when the particles distributes inside the minor phase. In this case, however, keep increasing the organoclay content eventually results in a high degree of PA6 phase continuity. Rheological analyses reveal that the filler loading at which the polyamide assembles in a continuous network corresponds to the critical threshold for its rheological transition from a liquid- to a gel-like behaviour, which is indicative of the structuring of the filler inside the host PA6. On the basis of this finding, a schematic mechanism is proposed in which the role of the filler in driving the space arrangement of the polymer phases is discussed. Finally, we show that the synergism between the reinforcing action of the filler and its ability to affect the blend microstructure can be exploited in order to enhance relevant technological properties of the materials, such as their high temperature structural integrity.     

Influence of properties and morphology of elastomeric phase on the behavior of ternary reactive blends of polyamide 6/rigid polymer/elastomer

A ternary blend of the PA6 matrix with a finely dispersed rigid polymer and elastomer is a system with well‐balanced mechanical properties. Its micromechanical behavior, especially that of the elastomer phase, apparently differs from corresponding binary mixtures. This study shows the influence of the elastomer type, modulus, and reactivity on the behavior of ternary blends in comparison with analogous binary PA6/elastomer combinations. The presence of rigid reactive poly(styrene‐co‐maleic anhydride) (SMA) enhanced the properties of all the systems studied. For nonreactive elastomers, the dominant effect was refinement of their size due to enhanced viscosity, whereas for functionalized low‐modulus elastomers, the very good balance of properties was due to synergistic influences of both finely dispersed phases. Of interest is the enhanced toughness of ternary blends also for more rigid elastomers having a low toughening efficiency in binary blends. An appropriate addition of rigid SMA together with an elastomer enhances the energy absorption of the matrix, probably without cavitation of very small elastomer particles. Of importance also is the simultaneous strain‐hardening effect of deformed rigid particles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3647–3651, 2003     

Optimization of polyethylene/binder/polyamide extrusion blow‐molded films. III. Slippability improvement with fatty acid amides

The slippability of packaging films has to be controlled to facilitate confectionary operations and guarantee an easy opening for filling. In the case of single‐layer polyethylene (PE) films, the addition of slip agents made of fatty acid amides such as erucamide or oleamide usually allows the tailoring of the coefficient of friction (COF) in the film to match industrial targets, which depend on the final application. The coupling of Fourier transform infrared spectroscopy and atomic force microscopy analysis showed that this method has a limited efficiency and may even be detrimental in the case of multilayer PE + ethylene vinyl acetate (EVA)/maleic anhydride grafted polyethylene (PEgMAH) + EVA/polyamide films. The reason is that the migration of the slip additives toward the outermost surface of the PE layer, which leads to a reduction in the COF, are strongly affected by both the existence of the adjacent layers and the presence of EVA in the PE and PEgMAH layers. Nevertheless, a proper knowledge of the effect of this perturbation allows one to reach a slippability level that is required for some confectionary operations and/or for an easy opening for filling without the degradation of the heat sealability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010