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 deformation of low‐density polyethylene reinforced with biodegradable polylactide,Part 1: Microstructural analysis and tensile behavior at constant true strain‐rate

Blends of low‐density polyethylene (LDPE) and polylactide (PLA) were prepared by melt coextrusion. The plastic behavior of the LDPE/PLA blends was investigated at room temperature under uniaxial tension by means of a video‐controlled system. The constitutive behavior was analyzed in terms of the variations of true stress vs. true strain at constant true strain rate. With increasing concentrations of PLA, the blend show: (i) higher Young's modulus, (ii) stiffer viscoelastic response, (iii) increase of elastic limit stress, and (iv) earlier fracture. Particular attention was paid to the evolution of the volume strain with the applied strain. While dilatation begins very lately for the neat LDPE, the LDPE/PLA blends show increasing deformation damage as the PLA content is increased. Scanning electron microscopy of deformed specimens shows that cavitation occurs preferentially at the poles of the PLA particles whose adhesion to the LDPE matrix seems very weak despite the partial grafting of polyethylene chains with maleic anhydride. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

The effects of SEBS-g-maleic anhydride reaction on the morphology and properties of polypropylene/PA6/SEBS ternary blends

Ternary blends, based on 70% by weight of polypropylene (PP) with 30% by weight of a dispersed phase, consisting of 15% polyamide-6 (PA6) and 15% of a mixture comprising varying ratios of an unreactive poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) triblock copolymer and a reactive maleic anhydride-grafted SEBS-g-MA, were produced via melt blending in a co-rotating twin-screw extruder. TEM revealed the blend containing only non-reactive SEBS to exhibit individual PA6 and SEBS dispersed phases. However, the progressive replacement of SEBS with reactive SEBS-g-MA increased the degree of interfacial reaction between the SEBS and PA6 phases, thus reducing interfacial tension and providing a driving force for encapsulation of the PA6 by the SEBS. Consequently, the dispersed-phase morphology was observed to transform from two separate phases to acorn-type composite particles, then to individual core-shell particles and finally to agglomerates of the core-shell particles. The resultant blends exhibited significant morphology-induced variations in both thermal and mechanical properties. DSC showed that blends in which the diameter of the PA6 particles was reduced to ≤3 μm by the increasing interfacial reaction exhibited fractionated PA6 crystallisation. In general, mechanical testing showed the blends to exhibit inferior low-strain tensile properties (modulus and yield stress) compared to the matrix PP, but superior ultimate tensile properties (stress and strain at break) and impact strength. These changes are discussed with reference to composite models.     

Deformation of rubber-toughened polycarbonate: Macroscale analysis of the damage zone

Two commercial core-shell rubbers were used as impact modifiers for polycarbonate (PC). Specimens with a single semicircular edge notch were stretched uniaxially in order to study the prefracture damage evolution of blends under a triaxial tensile stress state. The irreversible deformation of modified PC included a cavitation mechanism in addition to the three shear modes of unmodified PC. At the macroscopic level, the cavitation condition could be described by a mean stress concept. The corresponding critical volume strain for cavitation in PC blends was determined to be independent of rubber content but differed for the two impact modifiers. The critical volume strain for cavitation was used as an index of cavitation resistance for the impact modifiers. The effect of rubber content and temperature on Izod impact strength of the PC blends was also reported. From the relationship between the cavitation resistance and the Izod impact strength, it was proposed that impact modifiers with a higher cavitation resistance impart better toughness to blends with PC. © 1994 John Wiley & Sons, Inc.     

Micromechanical modeling of crack-tip rubber particle cavitational process in polymer toughening

A simple micromechanical modeling of the rubber particle cavitational process at the crack tip was conducted using the combination of Irwin's crack tip stress intensity factor analysis, slip-line field theory, and Dewey's closed-form elastic solution. This unique micromechanical modeling provides fruitful insights concerning the possible role(s) the rubber particles play in front of a constrained (plane-strain) crack tip. The cavitation of the rubber particles at the tip of the crack causes the redistribution of the stress and strain fields around the cavitated rubber particles. This, in turn, alters the stress state the surrounding matrix experiences. Consequently, the fracture process is affected by the rubber particle cavitational event. The results of the micromechanical analyses suggest that both the preexisting holes and the occurrence of cavitation in the rubber particles in front of the crack serve (i) to relieve the plane-strain constraint, (ii) to promote shear yielding of the matrix, and (iii) as stress concentrators. The major difference between the preexisting holes and the rubber particle cavitational event lies on the sudden buildup of the octahedral stress component upon the cavitation of rubber particles in the crack tip region. Experimental observations of toughening mechanisms of various rubber-modified polymers support this micromechanical analyses.     

Deformation and fracture of polystyrene/polypropylene blends: A simulation study

The mechanical behavior of binary polymer blends polystyrene/polypropylene were studied by a continuous mesoscopic simulation method. The dynamic density functional theory approach embodied in MesoDyn method was adopted to obtain the meso-structures of polymer blends. The output of MesoDyn serves as the input of a micromechanical lattice spring model (LSM), which consists of a three-dimensional network of springs. Mechanical properties, such as young’s modulus and stress distribution can be obtained through applying strain in LSM. Subsequently, a stress-related probabilistic method was applied in LSM to study the fracturing process of materials. The fracture positions were shown in detail which have close relationship with the meso-structures. Due to the significance of interface which has a notable influence on the global mechanical properties of immiscible blends, we proposed a new method to define the stiffness in the interfacial area to study the global stiffness (young’s modulus) of materials. The results show a good agreement with the existing experiments. Besides, we varied the minimum fracture stress (related to toughness) of the interface to investigate the strength of polymer blends. A graphic representation was shown in this work, it indicates that the system with continuous interface perpendicular to the applied strain are more likely to exhibit catastrophic failure. The methods developed in this work provide important tools to predict the mechanical properties of real polymer blends.     

Adding EPDM Rubber Makes Poly(propylene) Brittle

To better understand the mechanism of polymer‐toughing with rubber and the critical matrix ligament thickness theory developed by Wu, the rubber particle shape was controlled as elongated and oriented instead of spherical in PP/EPDM blends via dynamic packing injection molding. For the first time, the brittle‐ductile‐brittle transition was observed with increasing rubber content. This result clearly indicates that Wu's theory applies only for cubic or spherical particles but not for elongated and oriented particles. The higher stress concentration will be expected at the tip, which causes blends to fail in brittle mode. More work is needed to verify this expectation.     

高分子合金的力学性能与分散粒子径的关系

本文讨论了高分子合金中的平均分散粒子径d、粒子间距离与力学性能间的关系,当d小于临界平均分散粒子径d_c(dd_c时,冲击强度明显下降;在d=d_c附近,高分子合金的冲击强度发生急剧变化;分散相粒子间距离τ及其临界值τ_c对冲击强度的影响与平均分散粒子径的作用相似。同时,本文分析了影响分散形态的因素。     

Cavitation in hard/soft/hard three-layer core-shell structural rubber particles

The microvoiding mechanisms and mechanical properties of blends of poly(viny1chloride)(PVC) with hard/soft/hard three-layer core-shell structural particles polystyrene/polybutadiene/polymethylmethacrylate (PSBM) are investigated. The core-shell particles ranging from 110 to 182 nm to 254 nm. Toughened blends with higher tensile strength are obtained, which is related to the presence of hard polystyrene glassy domains in the core acting as stiffening agents. Cavitation occurs in all size rubber, relieves the triaxial tension and thereby promotes shear yielding of the PVC matrix. The three layer structure of the particles provides multi- interface, which act as trigger of cavitation. Furthermore, cavitiation in the blend containing small particles (110 nm) is observed due to its higher tensile stress, under which the cavitation process can be completed.     

Fracture toughening behavior and mechanical properties of polyphenylene oxide/high-impact polystyrene blends

Blends of a poly(phenylene oxide) (PPO) with high-impact polystyrene (HIPS) were injection molded. The static mechanical properties and fracture toughness of the blends were determined by means of the uniaxial tension, Brinell hardness and three-point-bending measurements. From the static mechanical test results, it was shown that the yield strength, Young's modulus and hardness values of the PPO/HIPS blends were considerably higher than those of their PPO and HIPS component polymers. Dynamic mechanical measurements indicated that the PPO/HIPS blends appear to be miscible as shown by the existence of a single glass transition temperature. Furthermore, the J integral method based on ASTM E813-89 procedure was used to characterize the fracture toughness of PPO/HIPS blends. The J integral analysis indicated that the PPO specimen exhibited the lowest fracture toughness (J_c). The PPO containing 50 wt% HIPS blend had the highest J_c. SEM observations revealed that the crack growth zone of the pure PPO is relatively smooth. However, cavitation of the elastomeric particles and shear band formation were observed in the deformed zones ahead of the crack tip of the PPO with 50 wt% HIPS blend. The cavitation and shear band formation would dissipate bulk strain energy and their formation was responsible for the highest J_c value observed in this blend.     

Mechanical properties and deformation behaviors of acrylonitrile‐butadiene‐styrene under Izod impact test and uniaxial tension at various strain rates

Two polybutadiene‐graft‐acrylonitrile‐styrene copolymer (PBD‐g‐SAN) impact modifiers with different rubber particle size were synthesized by seeded emulsion polymerization. Acrylonitrile‐butadiene‐styrene (ABS) blends with a constant rubber concentration of 15 wt% were prepared by blending those impact modifiers and SAN resin. The major focus was the mechanical properties and deformation mechanisms of ABS blends under Izod impact test and uniaxial tension at various strain rates from 2.564 × 10^?4 S^?1 upto 1.282 × 10^?1 S^?1. By the combination of transmission electron microscope and scanning electron microscope, it was concluded that crazes and cavitation coexisted in ABS blends. The deformation mechanisms of ABS blend containing large rubber particles was rubber particles cavitation and shear yielding in the matrix including crazes, and they do not change with the strain rate. Different from ABS blend with large rubber particles, deformation mechanism of ABS with small rubber particles under tensile condition was only involved in shear yielding in the matrix and no crazes were formed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

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     

Phase separation of poly (methyl methacrylate) / poly (styrene-co-acrylonitrile) blends in the presence of silica nanoparticles

The effects of silica nanoparticles on the phase separation of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blends are studied by the rheological method. The binodal temperatures of near-critical compositions were obtained by the gel-like behavior during spinodal decomposition, which is a character of polymer blends with co-continuous morphology. The shifted Cole–Cole plot method was introduced to determine the binodal temperatures of off-critical compositions based on the appearance of shoulder-like transition in the terminal regime of blends with droplet morphology. Such method is found also applicable in nanoparticle filled polymer blends. Moreover, a new method to determine the spinodal temperature from Fredrickson-Larson mean field theory was suggested, where the concentration fluctuation's contribution to the storage modulus is used instead of the whole dynamic moduli. This method was also successfully extended to nanoparticle filled polymer blend. The influences of the concentration and the average diameter of silica particles on the phase separation temperature were studied. It was found that the small amount of the silica nanoparticles in PMMA/SAN blends will significantly change the phase diagram, which is related to the selective location of silica in PMMA. The comparisons with thermodynamic theory of particle-filled polymer blends are also discussed.     

Hybrid Model of Viscosity of Polymer Blends

A hybrid model of the viscous properties of polymeric matrix blends with isolated (MPBs) and continuous phases (CPBs) was proposed. The hybrid model combines the analytical Hill's model of the average stresses and strains for viscous composites and semi‐empirical model of porous materials. A distinctive feature of the model is to calculate the concentration ratios of the average strain rate through the effective volume of the average strain rate. Effective volumes are determined by solving the boundary problem of viscous deformation of the representative volume of two‐phase MPBs or CPBs considering a possible porous state of a material. The comparison of the calculation results with the experimental data was made. The new model more accurately describes the viscosity of the two‐phase polymer blends than the known phenomenological models. The area of application of the hybrid model is limited to melts of polymer blends, the viscosity of which is inside the Hashin‐Shtrikman's bounds. POLYM. ENG. SCI., 59:E212–E218, 2019. © 2018 Society of Plastics Engineers     

Influence of sample thickness on fracture behaviour of a polyketone and a polyketone-rubber blend

The influence of sample thickness on the fracture behaviour of an aliphatic polyketone and a blend of this polymer and 10 wt% core-shell rubber was studied. The sample thickness was varied from 0.1 to 8 mm. The skin morphology was studied by SEM. The fracture behaviour was studied on single edge notch specimen at a high strain rate (30 s⁻¹) in the temperature range of −40 to 120 °C. The fracture stress, fracture strain and fracture energies were determined. The temperature development in the notch area was followed with an Infra Red camera. The cavitation of the rubber particles was studied on tensile bars with a laser setup.With decreasing specimen thickness the fracture energies increased strongly and the brittle-ductile transition shifted to lower temperatures this both for the aliphatic polyketone and the polyketone-rubber blend. The deformation in these materials in accompanied with a strong temperature increase in the deformation zone. The addition of rubber particles decreases the sensitivity towards the thickness. However, in very thin samples the cavitation of the rubber particles is more difficult and the rubber toughening effect decreases. The strong thickness effects on the fracture toughness indicate for both the homo polymer and the blend indicate that data from a standard test with 4 mm thick samples are not representative for thin walled applications.     

Rheological behavior of noncompatibilized and compatibilized PP/PET blends with SEBS‐g‐MA

The rheological behaviors of noncompatibilized and compatibilized polypropylene/polyethylene terephthalate blends (80/20) in relation with their morphology were studied at two constant levels using maleic anhydride‐modified styrene‐ethylene‐butylene‐styrene polymer. By scanning electron microscopy of cryofractured surfaces, the morphology of the blends was examined after etching. The frequency sweep and step strain experiments were carried out for the blends. The frequency sweep results indicated that increasing the compatibilizer causes behavioral changes of the rheological properties, which could be related to the aggregation of the dispersed particles with rubbery shell. Also, the frequency sweep and step strain experiments in linear region, after cessation of simple steady shear flow with various preshear rates (higher shear stress values than G′_p), were done on compatibilized blend. The results showed that the morphology characteristics, defined by the aggregation of the dispersed particles based on rheological experimental data, were destroyed and replaced by an alignment in the flow direction for present imposed shear rates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties and volume dilatation of HDPE/CaCO3 blends with and without impact modifier

Different blends of high‐density polyethylene (HDPE) with calcium carbonate (CaCO₃) were mechanically tested under uniaxial tension with or without poly(ethylene‐co‐octene) elastomer grafted with maleic anhydride (POEg), as an impact modifier. In some materials, the surface of the CaCO₃ was treated with an amino acid and in others the mineral particles were left untreated. The stress–strain behavior were determined at constant true strain rate by using the VidéoTraction^© system. Also, the volume changes upon stretching was assessed by means of the video extensometer and correlated with X‐ray densitometry measurements. The dependence of modulus, yield stress, and cavitation is shown to depend on the relative percentage of the three constituents. In particular, the cavitation rate increases markedly with the CaCO₃ content and decreases with the POEg content. By contrast, the surface pretreatment of the CaCO₃ particles appear to be of much lesser importance. POLYM. ENG. SCI., 46:1512–1522, 2006. © 2006 Society of Plastics Engineers     

Nanomechanical characterization of single micron‐sized polymer particles

The mechanical characterization of single micron‐sized polymer particles is very important for understanding the anisotropic conductive adhesives interconnection. In this article, a nanoindentation‐based flat punch method was employed to investigate the mechanical properties of single polymer particles. A diamond flat tip, instead of a commonly used sharp tip for indentation, was specially designed to deform single polymer particles. The maximum applied load is 10 mN and the linear loading/unloading rate is 2 mN/s. Two types of amorphous polymer particles were examined. The polymer particles display significantly different stress–strain behaviors. The material responses at different strain levels were analyzed and compared. A particle size effect, the smaller the diameter, the harder the particle, on the compression stress–strain behavior, was observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Particle Interaction Effects on Interfacial Stress in Extension of Rubber-Toughened Polypropylene

Polypropylene (PP) toughened with rubber particles is extensively used in polymer industry. Strength or toughness of polymer blends and polymer composites depends, to a great extent, upon their interfacial stress state. A finite element analysis of interfacial stress and its distribution during extension of PP/rubber blends was made by means ANSYS software, to investigate the effects of interaction between neighboring rubber particles on the interfacial stress and its distribution during extension of toughening PP. The simulation results showed that there was obvious stress concentration between rubber particles, especially around the equator zone of the rubber particles. Large shear stress presented at about 45 degrees between the surface and the equator of the rubber particles, and it was symmetry. The pressed and pulled effect subjected by the pole zone of the rubber particles was maximal. Furthermore, the variation extent of the interfacial stress between the particle and the matrix increased with an increase of the particle number.     

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.