Quantitative characterization of dispersed particle size,size distribution,and matrix ligament thickness in polypropylene blended with metallocene ethylene–octene copolymers

The average rubber particle size, size distribution, and matrix ligament thickness between particles in polypropylene blends containing metallocene catalyzed ethylene–octene copolymers have been quantitatively analyzed, as functions of blend composition and phase viscosity ratio. Comparison has been made between experimental data and those predicted from a number of theoretical models. All blends showed two‐phase morphology, with interestingly a bimodal distribution of the rubber particle size. The ranges and averages of rubber particle size were mainly determined by blend composition and viscosity ratio between the phases, irrespective of comonomer content along the rubber chains. The logarithmic relationship between the matrix ligament thickness and rubber concentration was observed. The values of ligament thickness obtained from the experiments and theoretical models were not in agreement. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2140–2149, 2001     

Polypropylene-elastomer (TPO) nanocomposites: 2. Room temperature Izod impact strength and tensile properties

Room temperature Izod impact strength was determined for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites, containing organoclays based on montmorillonite (MMT), at fixed elastomer content of 30 wt% and 0-7 wt% MMT. A ratio of maleated polypropylene, PP-g-MA to organoclay of unity was used as a compatibilizer in the nanocomposites. The organoclay serves to reduce the size of the EOR dispersed phase particles and facilitates toughening. The Izod impact strength is also influenced by the molecular weight of PP, elastomer octene content, elastomer MFI in addition to MMT content. Nanocomposites based on a low molecular weight polypropylene (L-PP) containing a higher octene content elastomer showed higher impact strength at lower MMT contents compared to those based on a low octene content elastomer. The effect of elastomer octene content on impact strength of high molecular weight polypropylene (H-PP) nanocomposites is not so significant. Elastomers having a melt flow index (MFI) in the range of 0.5-1.0 showed significant improvement in the impact strength of L-PP based nanocomposites. Most H-PP/EOR blends gave ‘super-tough’ materials without MMT and maintain this toughness in the presence of MMT. The critical elastomer particle size below which the toughness is observed is reduced by decreasing the octene content of the elastomer. For the similar elastomer particle sizes in nanocomposites, the impact strength varies as H-PP > M-PP > L-PP. The tensile modulus and yield strength improved with increasing MMT content; however, elongation at break was reduced. The extruder-made TPO showed a good-balance of properties in the presence of MMT compared to reactor-made TPO having similar modulus and elastomer content.     

A generalized criterion for rubber toughening: The critical matrix ligament thickness

The thickness of matrix ligament is shown to be the single parameter determining whether a polymer/rubber blend will be tough or brittle. The matrix ligament is defined as the region of the matrix between two neighboring rubber particles. Specifically, the ligament thickness is the surface-to-surface interparticle distance. When the average ligament thickness is smaller than a critical value, a blend will be tough; when greater, it will be brittle. In other words, a sharp brittle–tough transition occurs at the critical ligament thickness. This critical parameter is independent of rubber volume fraction and particle size, and is characteristic of the matrix for a given mode, temperature and rate of deformation. What is important is the matrix ligament, not rubber particles. The single matrix parameter explains the effects of phase morphology, rubber volume fraction, particle size, particle-size polydispersity, and particle flocculation on toughness.     

Study on the microstructures and mechanical behaviour of compatibilized polypropylene/polyamide‐6 blends

A series of blends of polypropylene (PP)–polyamide‐6 (PA6) with either reactive polyethylene–octene elastomer (POE) grafted with maleic anhydride (POE‐g‐MA) or with maleated PP (PP‐g‐MA) as compatibilizers were prepared. The microstructures and mechanical properties of the blends were investigated by means of tensile and impact testing and by scanning electron microscopy and transmission electron microscopy. The results indicated that the miscibility of PP–PA6 blends was improved with the addition of POE‐g‐MA and PP‐g‐MA. For the PP/PA6/POE‐g‐MA system, an elastic interfacial POE layer was formed around PA6 particles and the dispersed POE phases were also observed in the PP matrix. Its Izod impact strength was four times that of pure PP matrix, whilst the tensile strength and Young's modulus were almost unchanged. The greatest tensile strength was obtained for PP/PA6/PP‐g‐MA blend, but its Izod impact strength was reduced in comparison with the pure PP matrix. © 2002 Society of Chemical Industry     

Polypropylene-elastomer (TPO) nanocomposites: 3. Ductile-brittle transition temperature

Izod impact strength was determined as a function of temperature for polypropylene (PP)/ethylene-co-octene elastomer (EOR) blends and nanocomposites to determine the effect of PP molecular weight, elastomer MFI, EOR octene content and MMT content on the ductile-brittle (D-B) transition temperature. The D-B transition temperature decreases with increased molecular weight of the PP (H = high, M = medium and L = low) and the addition of MMT. The D-B transition temperature also decreases as the elastomer particle size is decreased, and at a fixed elastomer particle sizes, the D-B transition varies as H-PP< M-PP< L-PP. The H-PP based materials show a smaller decrease in the D-B transition temperature compared to L-PP based materials in the presence of MMT. Elastomers having a melt flow index (MFI) in the range of 0.5–1.0 showed a significant decrease in the D-B transition temperature for both L-PP and H-PP nanocomposites. The D-B transition temperature also decreases with increasing octene content of the elastomer.     

Influence of rubber particle size on mechanical properties of polypropylene–SEBS blends

Isotactic polypropylene blends with 0–20 vol % thermoplastic elastomers were prepared to study the influence of elastomer particle size on mechanical properties. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) was used as thermoplastic elastomer. SEBS particle size, determined by means of transmission electron and atomic force microscopy, was varied by using polypropylene and SEBS of different molecular weight. With increasing polypropylene molecular weight and, consequently, melt viscosity and decreasing SEBS molecular weight, SEBS particle size decreases. Impact strength of pure polypropylene is almost independent of molecular weight, whereas impact strength of polypropylene blends increases strongly with increasing polypropylene molecular weight. The observed sharp brittle–tough transition is caused by micromechanical processes, mostly shear yielding, especially occurring below a critical interparticle distance. The interparticle distance is decreasing with decreasing SEBS particle size and increasing volume fraction. If the polypropylene matrix ligament between the SEBS particles is thinner than 0.27 μm, the blends become ductile. Stiffness and yield stress of polypropylene and polypropylene blends increase with increasing polypropylene molecular weight in the same extent, and are consequently only dependent on matrix properties and not on SEBS particle size. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1891–1901, 1998     

Rubber‐toughened polypropylene nanocomposite: Effect of polyethylene octene copolymer on mechanical properties and phase morphology

Rubber‐toughened polypropylene (PP)/org‐Montmorillonite (org‐MMT) nanocomposite with polyethylene octene (POE) copolymer were compounded in a twin‐screw extruder at 230°C and injection‐molded. The POE used had 25 wt % 1‐octene content and the weight fraction of POE in the blend was varied in the range of 0–20 wt %. X‐ray diffraction analysis (XRD) revealed that an intercalation org‐MMT silicate layer structure was formed in rubber‐toughened polypropylene nanocomposites (RTPPNC). Izod impact measurements indicated that the addition of POE led to a significant improvement in the impact strength of the RTPPNC, from 6.2 kJ/m² in untoughened PP nanocomposites to 17.8 kJ/m² in RTPPNC containing 20 wt % POE. This shows that the POE elastomer was very effective in converting brittle PP nanocomposites into tough nanocomposites. However, the Young's modulus, tensile strength, flexural modulus, and flexural strength of the blends decreased with respect to the PP nanocomposites, as the weight fraction of POE was increased to 20 wt %. Scanning electron microscopy (SEM) was used for the investigation of the phase morphology and rubber particles size. SEM study revealed a two‐phase morphology where POE, as droplets was dispersed finely and uniformly in the PP matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3441–3450, 2006     

Toughening of polyvinylchloride by methyl methacrylate–butadiene–styrene core–shell rubber particles: Influence of rubber particle size

An analysis was made on the effects of rubber particle size on the mechanical properties and deformation mechanisms of transparent polyvinyl chloride (PVC) blends containing core–shell methyl methacrylate–butadiene–styrene (MBS) impact modifiers. The critical interparticle distance was found not to be the criterion for the brittle‐ductile transition in the blends. In tensile tests, the blends with larger (100–280 nm) rubber particles exhibited intense stress‐whitening, while one blend with small (83 nm) rubber particles showed only slight stress‐whitening. These differences were due to an increase in resistance to cavitation with decreasing rubber particle size. Transmission electron microscopy studies on blends with a bimodal distribution of particle sizes showed that in the whitened zone of Izod specimens the larger rubber particles cavitated and expanded on yielding, while the smaller particles remained intact. However, Izod test results showed that small MBS rubber particles can toughen the PVC matrix very effectively, especially at low temperatures and at low rubber concentrations. The deformation mechanisms responsible for these effects were discussed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

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.     

Fabrication of Super Tough Polycarbonate/Styrene-Etylene-Butylene-Styrene Grafted Maleic Anhydride (SEBS-g-MA) Blends: Morphological,Short Term Static Mechanical and Fracture Performance Interpretation

Impact behaviours, tensile properties and fracture performance of polycarbonate (PC)/styrene ethylene-butylene-styrene-grafted-maleic anhydride (SEBS-g-MA) copolymer blends at SEBS-g-MA volume fraction Φ_d = 0–0.39 are evaluated. In presence of rubber a significant augmentation in notched Izod impact strength was observed while tensile modulus and strength decreased. Morphological studies reveal good interaction between the PC and the rubber particles showing homogeneous dispersion of SEBS-g-MA in the polycarbonate matrix. Interparticle distance of the dispersed phase evaluated from the morphology studies by scanning electron microscopy (SEM) and the impact strength dependence on the concentration of the blending rubber were analysed. The essential work of fracture approach is applied to study fracture properties of the blends. With increasing SEBS-g-MA concentration nonessential or plastic work increased which explained the enhancement of impact strength of blends.     

Effect of the composition of structured rubber particles on the toughness of poly(methylmethacrylate)

Composite natural rubber (NR) and monodisperse poly(n-butylacrylate) (PBuA) based latex particles were tested as possible impact modifiers for a poly(methylmethacrylate) (PMMA) matrix. A continuous extrusion process was used for the incorporation of wet latexes directly into a twin-screw extruder. All latexes had been coated by a PMMA shell. Furthermore, polystyrene (PS) subinclusions were introduced into the NR core. The impact resistance of the prepared PMMA blends can be most effectively improved by NR particles containing a large weight fraction of compatibilising PMMA in the shell. The degree of crosslinking of the shell polymer has to be restricted. PBuA based latex particles of 180 nm in size are ineffective to toughen the PMMA matrix. The degree of grafting of the NR phase in core–shell particles containing PS subinclusions is not crucial. Scanning electron microscopy was used to analyse the failure processes in composite rubber particle toughened PMMA blends at fast (impact conditions) and slow (tensile testing) deformation speeds.     

Phase morphology and toughening mechanism of polyamide 6/EPDM-g-MA blends obtained via dynamic packing injection molding

One of the most important findings in polymer-toughening is known as the critical matrix ligament thickness (τ_c) theory, which is directly related to both rubber concentration and average size of particles. All these studies assume that rubber particles are spherical and randomly distributed in the matrix. Rubber particles may be stretched and oriented along the shear flow direction in real processing. In this paper the effect of stretched and oriented rubber particles on the impact strength of PA6/EPDM-g-MA blends have been studied via dynamic packing injection molding (DPIM). The impact strength of specimens obtained by DPIM was found substantially increase at all the blends investigated, compared with the one obtained via conventional injection molding. Particularly, more than 30 kJ m⁻² increase of the impact strength was observed for specimens with a higher rubber content (more than 15 wt%). SEM results showed a remarkably decrease of rubber particle size and more uniform dispersion of the dynamic molded specimens. This can be attributed to the shear induced reaction at the interface between polyamide 6 and EPDM-g-MA during the packing stage. The rubber particles were found stretched along the melt shear flow direction when it is content above 15 wt%. A master curve can be also constructed by plotting the impact strength versus the inter-particle distance, indicating that Wu's criterion still works for blends with stretched and oriented rubber particles when the crack propagation direction is perpendicular to the orientation direction of rubber particles. The observed higher impact strength in dynamic specimens could be due to, in part, the enhanced flexural stiffness, which will absorb more energy during impact process when the fracture of IZOD bars is incomplete, but more importantly due to the existence of the stretched and oriented rubber particles, which are more efficient in slowing the velocity of crack propagation and thus cause higher impact resistance when the fracture propagation direction is perpendicular to the rubber oriented direction.     

Rubber‐toughened PLA blends with low thermal expansion

In this study, poly (lactic acid) (PLA) blended with various rubber components, i.e., poly (ethylene‐glycidyl methacrylate) (EGMA), maleic anhydride grafted poly(styrene‐ethylene/butylene‐styrene) triblock elastomer (m‐SEBS), and poly(ethylene‐co‐octene) (EOR), was investigated. It was observed that EGMA is highly compatible due to its reaction with PLA. m‐SEBS is less compatible with PLA and EOR is incompatible with PLA. Electron microscopy (SEM and TEM) revealed that a fine co‐continuous microlayer structure is formed in the injection‐molded PLA/EGMA blends. This leads to polymer blends with high toughness and very low linear thermal expansion both in the flow direction and in the transverse direction. The microlayer thickness of rubber in PLA blends was found to play key roles in reducing the linear thermal expansion and achieving high toughness of the blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Impact modification of polypropylene

This paper compares the modification mechanism provided by ethylene‐octene (EO) copolymer to that of ethylene‐propylene‐diene terpolymer (EPDM) rubber. Within the limits of this study, the highest impact strength was achieved at 30–40% rubber content, regardless of the rubber type. An increase in rubber melt viscosity resulted in overall greater impact strength. At the optimum concentration, the high‐viscosity (MFI = 1 to 5) EO rubber provided modification mainly via a crazing mechanism, while the EPDM rubber functioned by energy dissipation through the three‐dimensional network structure formed with the polypropylene matrix. This paper also discusses the effects of the processing conditions on the physical properties of PP/EPR copolymer. An increase in processing temperature and screw speed resulted in a reduced number of discrete rubber particles and nearly no or very slight increase in impact strength, but a very significant reduction in tensile strength and tensile modulus.     

Polypropylene-elastomer (TPO) nanocomposites: 1. Morphology

PP/PP-g-MA/MMT/elastomer nanocomposites were prepared in a twin-screw extruder at fixed 30 wt% elastomer and 0-7 wt% MMT content. The ratio of maleated polypropylene, PP-g-MA and organoclay was maintained at 1. Elastomer particle size and shape in the presence of MMT were evaluated for three different molecular weight grades of polypropylene (PP) and five different ethylene-co-octene elastomers (EOR) with different melt flow index (MFI) and octene contents. The MMT particles are located exclusively in the PP phase in the PP/PP-g-MA/MMT/EOR nanocomposites as seen from TEM images. Injection molded nanocomposite samples show significant decreases in elastomer particle size and increases in elastomer aspect ratio and particle density compared to as-extruded or pelletized samples. The elastomer particle size decreased significantly with increased MMT content and the molecular weight of PP. Low molecular weight PP based nanocomposite showed a greater reduction in elastomer particle size compared to medium and high molecular weight PP based nanocomposites. Elastomers having MFI in the range of 0.5-1.0 gave minimum elastomer particle sizes in the PP/PP-g-MA/MMT/EOR nanocomposite. The elastomer particles were deformed during injection molding leading to an increase in their aspect ratio. The nanocomposites containing high octene content elastomer gave smaller elastomer particle size and higher elastomer aspect ratios compared to nanocomposites containing low octene content elastomer.     

Effect of matrix SAN in ABS/PMMA blends

The effect of the molecular weight and acrylonitrile (AN) content of the styrene–acrylonitrile copolymer (SAN) on the morphology, mechanical properties, and rheological properties of acrylonitrile–butadiene–styrene terpolymer/poly(methyl methacrylate) (ABS)/PMMA (60/40 by weight) blends were studied. When the AN content of matrix SAN (32%) was close to that of graft SAN (30%) AN, rubber particles existed separately. However, with matrix SAN having 35% AN, rubber particles showed tendency to agglomerate each other. With increasing molecular weight of matrix SAN, impact strength, ultimate elongation, and abrasion resistance of the blend generally increased. Yield strength increased with molecular weight at a constant AN content of matrix SAN, and it decreased with the decrease of AN content in spite of the increasing molecular weight of SAN. Melt properties, rather than the morphological and mechanical properties, were more sensitive to the AN content, rather than the molecular weight of matrix SAN. © 1994 John Wiley & Sons, Inc.     

Effect of interfacial stress on the crystalline structure of the matrix and the mechanical properties of high‐density polyethylene/CaCO3 blends

A series of high‐density polyethylene (HDPE)/CaCO₃ blends were prepared with different kinds of coupling agents, with CaCO₃ particles of different sizes, and with matrixes of different molecular weights during the melt‐mixing of HDPE and CaCO₃ particles. The mechanical properties of these blends and their dependence on the interfacial adhesion and matrix crystalline structure were studied. The results showed that the Charpy notched impact strength of these blends could be significantly improved with an increase in the interfacial adhesion or matrix molecular weight or a decrease in the CaCO₃ particle size. When a CaCO₃ surface was treated with a compounded coupling agent, the impact strength of the HDPE/CaCO₃(60/40) blend was 62.0 kJ/m², 2.3 times higher than that of unimproved HDPE; its Young's modulus was 2070 MPa, 1.07 times higher than that of unimproved HDPE. The heat distortion temperature of this blend was also obviously improved. The improvement of the mechanical properties and the occurrence of the brittle–tough transition of these blends were the results of a crystallization effect induced by the interfacial stress. When the interfacial adhesion was higher and the CaCO₃ content was greater than 30%, the interfacial stress produced from matrix shrinkage in the blend molding process could strain‐induce crystallization of the matrix, leading to an increase in the matrix crystallinity and the formation of an extended‐chain (or microfibrillar) crystal network. The increase in the critical ligament thickness with an increasing matrix molecular weight was attributed to the strain‐induced areas becoming wider, the extended‐chain crystal layers becoming thicker, and the interparticle distance that formed the extended‐chain crystal network structure becoming larger with a higher matrix molecular weight. The formation of the extended‐chain crystal network and the increase in the matrix crystallinity were also the main reasons that Young's modulus and the heat distortion temperature of this blend were improved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2120–2129, 2003     

Mechanical properties and morphology of PA6/EVA blends

The mechanical properties of blends of polyamide6 (PA6) and ethylene vinyl acetate (EVA) at a blending composition of 0–50 wt % EVA were studied. The notched Izod impact strength of PA6 increased with the incorporation of EVA, the increase being more than 100% compared to PA6 at 10% EVA. The tensile strength and the tensile modulus of the blends decreased steadily as the weight percent of EVA increased. Analysis of the tensile data using predictive theories indicated the extent of the interaction of the dispersed phase and the matrix up to 20 wt % EVA. SEM studies of the cryogenically fractured surfaces indicated increase in the dispersed phase domain size with EVA concentrations. On the other hand, impact fractured surfaces of PA6/EVA blends indicated debonding of EVA particles, leaving hemispherical bumps, indicating inadequate interfacial adhesion between PA6 and EVA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1593–1606, 2002     

Preparation of PBT/POE-g-GMA/PP ternary blends with good rigidity–toughness balance by core–shell particles

Compared with poly(butylene terephthalate)/glycidyl methacrylate grafted poly(ethylene–octene) (PBT/POE-g-GMA) binary blends, supertough PBT-based ternary blends with little rigidity loss were successfully obtained by adding rigid polypropylene (PP) into PBT/POE-g-GMA blends to construct core–shell particles during melt blending. The effects of PP content and type on the phase morphology and mechanical properties of the blends were systematically investigated. Theoretical predictions and scanning electron microscopy observation showed that a core–shell structure was formed in PBT matrix with PP as the core and POE-g-GMA as the shell. The mechanical property tests showed that POE-g-GMA and PP had significant synergistic toughening effect. When PP with high melt flow index (H-PP) was used, PBT/POE-g-GMA/H-PP (70/15/15) blends possessed the highest Izod notched impact strength, which was 1.9-fold compared with PBT/POE-g-GMA (70/30) binary blends, while the tensile performance loss was little. The essential work of fracture tests was performed to evaluate the fracture resistance of different samples. The results demonstrated that PBT/POE-g-GMA/PP ternary blends possessed much better resistance to crack propagation than PBT/POE-g-GMA binary blends. The decrease of interparticle distance and the fibrillation of core–shell particles activated intense matrix shear yielding, which was the reason for the high crack resistance of ternary blends. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48872.