On significant retention of impact strength in clay-reinforced high-density polyethylene (HDPE) nanocomposites

The mechanical response of clay-reinforced polyethylene nanocomposite is investigated and the behavior compared with the un-reinforced polyethylene under identical conditions of processing. The micromechanism of plastic deformation during impact loading of neat polyethylene and clay-reinforced polyethylene nanocomposite are studied with scanning electron microscopy (SEM). The impact strength of composites is linked to structural studies by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) and SEM observations. The addition of clay to polyethylene retains adequately high-impact strength in the investigated temperature range of −40 to +70 °C. The micromechanism of deformation is altered from a combination of craze and drawing of fibrils in neat polyethylene to microvoid coalescence-fibrillated process in the nanocomposite. The aspects related to micromechanism of deformation are discussed.     

Phenolic rigid organic filler/isotactic polypropylene composites. III. Impact resistance property

A novel phenolic rigid organic filler (KT) was used to modify isotactic polypropylene (iPP). The influence of KT particles on the impact resistance property of PP/KT specimens (with similar interparticles distance, 1.8 μm) was studied by notched izod impact tests. It was found that the brittle-ductile transition (BDT) of the PP/KT microcomposites took place at the filler content of about 4%, and the impact strength attains the maximum at 5% (with filler particles size of 1.5 μm), which is about 2.5 times that of unfilled iPP specimens. The impact fracture morphology was investigated by scanning electron microscopy (SEM). For the PP/KT specimens and the highdensity polyethylene/KT (HDPE/KT) specimens in ductile fracture mode, many microfibers could be found on the whole impact fracture surface. It was the filler particles that induced the plastic deformation of interparticles ligament and hence improved the capability of iPP matrix on absorbing impact energy dramatically. The determinants on the BDT were further discussed on the basis of stress concentration and debonding resistance. It can be concluded that aside from the interparticle distance, the filler particles size also plays an important role in semicrystalline polymer toughening. Keywords rigid organic filler, polypropylene, impact     

Effect of various organic fibers on the stiffness,strength and impact resistance of polypropylene; a comparison

Composites were prepared from a polypropylene homopolymer and four types of organic fibers, wood, flax, poly(ethylene terephthalate) (PET) and poly(vinyl alcohol) (PVA). Mechanical properties were studied by tensile and impact testing, and structure by scanning electron microscopy. Local deformation processes were followed by acoustic emission testing. Composite strength changes in a wide range and depends on coupling. The deformability of the composites also varies considerably, more plastic deformation occurring in composites prepared with the PET and PVA fibers. Compared to traditional stiff fibers, fracture resistance can be improved significantly with PET and PVA fibers; impact strength as large as 30 kJ m^–2 can be achieved with PVA. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

Relationship of fracture behavior and morphology in polyolefin blends

High-density polyethylene (HDPE) and isotactic polypropylene (PP) were mixed either with a stabilizer or with a stabilizer and a compatibilizer in different mixing ratios. The structure and properties of these blends were analyzed by methods such as torsion pendulum measurements, mechanical short time experiments, electron microscopy, and fracture mechanical toughness tests. The results display a strongly increased impact strength in the HDPE/PP blend with compatibilizer within a specific mixing region. The deformation behavior and the mechanism leading to the increased impact strength of the blends were investigated in tensile tests by acoustic emission analysis and scanning electron microscopy: Increased fibrilation and strong strain was registered in the blend with compatibilizer. The impact strength was modeled, using experimentally measured properties such as energy release rate, matrix and inclusion volumes, the impact strength of each component. The inclusion volume that causes plastic deformation was chosen as an additional parameter. The calculated results are in good agreement with the experimental ones.     

Nanocomposites of polypropylene impact copolymer and organoclays: role of compatibilizers

Nanocomposites of polypropylene impact copolymer and organoclays were prepared using different compatibilizers (polypropylene‐graft‐(maleic anhydride) (PPMA), polyethylene‐graft‐(maleic anhydride) (PEMA) and their mixture) and varying percentages of clay (3 and 6%) in an attempt to obtain balanced mechanical properties. The nanocomposites were prepared by melt compounding and test specimens were prepared by injection molding. Mechanical properties such as tensile, flexural and Izod impact strength are reported. The clay dispersion was investigated using wide‐angle X‐ray diffraction while the phase morphology was characterized using scanning electron microscopy. It is shown that the mechanical properties of the system with mixed PPMA and PEMA compatibilizers showed the best balance of mechanical properties among the nanocomposites explored. Copyright © 2006 Society of Chemical Industry     

Toughening of polypropylene with calcium carbonate particles

Polypropylene-CaCO₃ composites were prepared on a twin screw extruder with a particle content of 0-32 vol%. The influence of particle size (0.07-1.9 μm) and surface treatment of the particles (with and without stearic acid) on the toughening properties were studied. The matrix molecular weight of the polypropylene was also varied (MFI 0.3-24 dg/min). The experiments included tensile tests, notched Izod impact tests, differential scanning calorimetry (DSC), scanning electron microscopy and rheology experiments. The modulus of the composites increased, while the yield stress was lowered with filler content. This lowering of yield stress was connected to the debonding of the particles from the polypropylene matrix. From DSC experiments it was shown that the particle content had no influence on the melting temperature or crystallinity of the PP phase, also particle size showed no effect on the thermal properties. The impact resistance showed large improvement with particle content. The brittle-to-ductile transition was lowered from 90 to 40 °C with the addition of CaCO₃ particles. Notched Izod fracture energy was increased from 2 up to 40-50 kJ/m². The stearic acid coating on the particle surface showed a large positive effect on the impact strength. This was mainly due to the improved dispersion of the CaCO₃ particles. Aggregates of particles clearly had a detrimental effect on the impact behaviour of the composites. The smaller particle sizes (<0.7 μm) showed coarse morphologies and this lowered the toughening efficiency. The molecular weight of the polypropylene matrix had a profound effect on the toughening properties. A higher molecular mass shifted the brittle-to-ductile transition towards lower temperatures. At the higher filler loads (>20 vol%), however, still problems seem to occur with dispersion, lowering the toughening efficiency. Of all particle types used in this study the stearic acid treated particles of 0.7 μm were found to give the best combination of properties. From the study of the micro-toughening mechanism it was shown that at low strain the particles remain attached to the matrix polymer. At higher strain the particles debond and this leads to a change in stress state at the particle size level. This prevents crazing of the matrix polymer and allows extensive plastic deformation, resulting in large quantities of fracture energy.     

Fracture behaviour of polypropylene films at different temperatures: fractography and deformation mechanisms studied by SEM

The fracture surfaces and the deformation micro-mechanisms of one polypropylene homopolymer and three ethylene-propylene block copolymers (EPBC) have been studied by scanning electron microscopy. The results are compared to the essential work of fracture parameters obtained in a previous study with deeply double-edge-notched-tension samples of films fractured between −40 and 70 °C. The homopolymer shows shear-yielding at T≥−20 °C, but at lower T, crazing prevails. The EPBC display shear-yielding for T>0 °C, while a combination of cavitation and shear-yielding occurs at lower T, which is responsible for stress-whitening. The variations of the specific essential fracture work and specific plastic work with T and with ethylene content have been successfully explained in terms of the prevalent deformation mechanisms.     

Modified polypropylene wood flour composites. II. Fracture,deformation, and mechanical properties

The effect of grafting level of maleic anhydride (MA) in the maleated polypropylene (PPMA) on the fracture, deformation mechanisms, and mechanical properties of polypropylene (PP) wood flour composites was studied. Tensile strength, elongation at break, and impact strength are noticeably improved with addition of interfacial modifiers as maximum values of the examined mechanical properties were detected when concentration of MA in the compatibilizer was 1 wt %. To explore the microstructure and deformation mechanisms, scanning electron microscopy was employed. It was found that low concentrations of MA up to 1 wt % led to the creation of a thin and irregular polymer layer assisted formation of fibrillated plastic deformation zone around the wood particles, while the bulk PP matrix experienced voiding and brittle fracture. Higher concentrations of MA fetch to stronger interaction between PP and wood flour, the reason for brittle fracture and reduced ductility of the matrix. The impact fracture behavior of the composites during Instrumented impact tests is also discussed with respect to the interfacial bond strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1286–1292, 2004     

Mass transfer resistance in the production of high impact polypropylene

Mass transfer resistance in the production of high impact polypropylene (hiPP) produced by a two-stage slurry/gas polymerization was investigated by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. It is found that the formation of ethylene-propylene copolymer (EPR) phases in polypropylene (iPP) particle produced in the first stage slurry polymerization exhibits a developing process from exterior to interior. During the early stage of ethylene-propylene copolymerization, with lower content of copolymerized ethylene (7.4 mol%), the EPR phases occur only in the external layer of the particle, while at the later stage of the copolymerization with higher content of copolymerized ethylene (26.7 mol%), the elastomer phases distribute uniformly in the whole particle. This phenomenon is due to an effect of mass transfer resistance. The origin of mass transfer resistance is loosely agglomerate inclusions of low tacticity polypropylene within the semi-filled micropores inside the iPP particle. It is the inclusions inside the micropores that resist the diffusion of ethylene/propylene comonomers into the particle.     

Microstructure‐properties correlations in dynamically vulcanized nanocomposite thermoplastic elastomers based on PP/EPDM

Thermoplastic vulcanized (TPV) nanocomposites were prepared in a laboratory mixer using EPDM, polypropylene of different viscosities, maleic anhydride modified polypropylene, an organo‐clay, and a sulfur‐based curing system. Based on the obtained results from X‐ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter, and mechanical properties, the microstructure of the prepared nanocomposites was found to be sensitive to the viscosity difference between the two phases and the clay content. X‐ray diffraction and TEM images of the TPV nanocomposites showed that clay was nearly exfoliated and randomly distributed into the polypropylene phase. The SEM photomicrographs of the dynamically vulcanized thermoplastic elastomer samples showed that the rubber particles were dispersed through the polypropylene in form of aggregates and their size increased with the introduction of clay. The nanoscale dimensions of the dispersed clay resulted in a significant improvement of the tensile modulus of the TPV nanocomposite samples, from 20 to 90% depending on clay content and the viscosity ratio of PP/EPDM. In the PP nanocomposites, the clay layers act as nucleating agents, resulting in higher crystallization temperature and reduced degree of crystallinity. Moreover, the oxygen permeability in the TPV nanocomposites was found to be lower than in unfilled but otherwise similar materials. POLYM. ENG. SCI., 47:207–217, 2007. © 2007 Society of Plastics Engineers.     

Modification of polymers using multilayered “smart pellet” additives: Part II

A magnesium-based inorganic whisker was compounded with polypropylene and with polysulfone (FP/PP and FPSF/PP^*, respectively) and then multilayered into alternating structures with unfilled polypropylene (PP). These multilayered materials were cut into FP/PP and FPSF/PP^* “smart pellets”, which were then added to polypropylene matrix polymer as masterbatches to deliver potential reinforcement to injection molded parts. The morphologies of both the smart pellets and the composites produced with them were studied by scanning electron microscopy (SEM). The inorganic whiskers were found to be aligned in the machine direction in the smart pellets. Mechanical properties of the composites were investigated by performing tensile, flexural, and impact strength tests. Inorganic whiskers combined with PSF offered higher flexural modulus in comparison to those via conventional blending; no significant improvement was observed in tensile modulus or impact strength of these composites.     

Influence of PP‐g‐MA on morphology,mechanical properties and deformation mechanism of copolypropylene/clay nanocomposite

Copolypropylene/organoclay nanocomposites are prepared by melt intercalation method in this research. Two different routes for addition of compatibilizer are examined, i.e. addition in the twin‐screw extruder along with the polymer and the clay powder simultaneously and premixing the compatibilizer with the reinforcement in a batch mixer before addition to the polypropylene (PP) matrix. Morphology, tensile and impact properties and deformation mechanisms of the samples made via two procedures are studied and compared with those of the noncompatibilized system. To study the structure of nanocomposites, x‐ray diffraction and transmission electron microscopy techniques are utilized. The deformation mechanisms of different samples are examined via reflected and transmitted optical microscopy. The results reveal that introduction of compatibilizer and also the procedure in which the compatibilizer is added to the compound, affect structure and mechanical properties of nanocomposite. The elastic modulus of PP‐clay nanocomposite has increased 11.5% with incorporation of compatibilizer. Also, introduction of organoclay without compatibilizer facilitates crazing at the notch tip of PP in 3PB testing. Incorporation of compatibilizer, however, makes difficulties in initiation and growth of crazes at the notch tip. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler‐Natta catalyst

In this article, preparation of polypropylene/clay nanocomposites (PPCNC) via in situ polymerization is investigated. MgCl₂/montmorillonite bisupported Ziegler‐Natta catalyst was used to prepare PPCNC samples. Montmorillonite (MMT) was used as an inert support and reinforcement agent. The nanostructure of the composites was characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Obtained results showed that silica layers of the MMT in these PPCNC were intercalated, partially exfoliated, and uniformly dispersed in the polypropylene matrix. Thermogravimetric analysis showed good thermal stability for the prepared PPCNC. Differential scanning calorimetric was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the PPCNC samples. Results of permeability analysis showed significant increase in barrier properties of PPCNC films. Effective parameters on molecular weight and flow ability of produced samples such as Al/Ti molar ratio and H₂ concentration were also investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polyamide-12 layered silicate nanocomposites by melt blending

Polyamide-12/tetrasilisic fluoromica (PA12-ME100) and polyamide-12/quaternary tallow ammonium chloride modified fluoromica nanocomposites (PA12-MAE) were prepared by melt compounding. The nanocomposite morphology and clay dispersion were investigated using wide angle X-ray diffraction (XRD), scanning electron microscopy (SEM), SEM-energy dispersive X-ray analysis (SEM-EDX), transmission electron miscroscopy (TEM), high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). A predominantly intercalated morphology was observed for PA12-ME100, and a very high degree of exfoliation for PA12-MAE. HRTEM showed that the polymer crystallites lie perpendicular to the clay surface. The tensile and flexural properties of the PA12-MAE nanocomposite were significantly enhanced compared to neat polyamide-12, even with the addition of only 4 wt% nanoclay. Furthermore, the elongation at break (%) increased from 180% for polyamide-12 up to >500% for the PA12-MAE nanocomposite. In situ measurement of the heat generated in the test specimens during uniaxial tensile deformation using infra-red thermal imaging showed that the temperature of the dumbbell samples increased from room temperature (23 °C) to as high as 70 °C regardless of the strain rate used. This is considerably above the glass transition temperature (T_g) of PA12-MAE (30 °C), as measured by dynamic mechanical thermal analysis (DMTA). The mechanism of deformation is partially explained in terms of microvoid formation. The shear viscosity of the PA12-MAE nanocomposite determined by dual capillary rheometry was lower than both neat polyamide-12 and PA12-ME100. The reduction in shear viscosity of the nanocomposites was shown, from gel permeation chromatography (GPC) studies, not to originate from polymer degradation during melt blending. The coefficient of thermal expansion, decomposition temperature, and melting and crystallisation temperatures and relative crystalline content of the nanocomposite materials were measured by thermo-mechanical analysis (TMA), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) respectively—properties which can be related to polymer nanoclay interactions.     

Pyrolysis-gasification of plastics, mixed plastics and real-world plastic waste with and without Ni-Mg-Al catalyst

Polypropylene, polystyrene, high density polyethylene and their mixtures and real-world plastic waste were investigated for the production of hydrogen in a two-stage pyrolysis-gasification reactor. The experiments were carried out at gasification temperatures of 800 or 850 °C with or without a Ni-Mg-Al catalyst. The influence of plastic type on the product distribution and hydrogen production in relation to process conditions were investigated. The reacted Ni-Mg-Al catalysts were analyzed by temperature-programmed oxidation and scanning electron microscopy. The results showed that lower gas yield (11.2 wt.% related to the mass of plastic) was obtained for the non-catalytic non-steam pyrolysis-gasification of polystyrene at the gasification temperature of 800 °C, compared with the polypropylene (59.6 wt.%) and high density polyethylene (53.5 wt.%) and waste plastic (45.5 wt.%). In addition, the largest oil product was observed for the non-catalytic pyrolysis-gasification of polystyrene. The presence of the Ni-Mg-Al catalyst greatly improved the steam pyrolysis-gasification of plastics for hydrogen production. The steam catalytic pyrolysis-gasification of polystyrene presented the lowest hydrogen production of 0.155 and 0.196 (g H₂/g polystyrene) at the gasification temperatures of 800 and 850 °C, respectively. More coke was deposited on the catalyst for the pyrolysis-gasification of polypropylene and waste plastic compared with steam catalytic pyrolysis-gasification of polystyrene and high density polyethylene. Filamentous carbons were observed for the used Ni-Mg-Al catalysts from the pyrolysis-gasification of polypropylene, high density polyethylene, waste plastic and mixed plastics. However, the formation of filamentous carbons on the coked catalyst from the pyrolysis-gasification of polystyrene was low.     

The effect of microstructure on the toughness of polypropylene random copolymer

ABSTRACT

This article mainly explores the mechanism and deformation of polypropylene random copolymer at different temperatures and the role of microstructure in the toughening process. Firstly, the conventional differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electron microscopy were employed to study different structures of crystalline and amorphous regions. Furthermore, the dynamic thermomechanical analysis was used to study the changes in the molecular mobility in samples. Secondly, the toughness and fracture morphology of the material was analyzed by notched Izod impact test and scanning electron microscopy. Thirdly, samples were stretched and combined 2D-WAXD to analyses the changes in its crystal regions. The thickness and distribution of the lamellae, as well as stress transmitters, work synergistically during polypropylene random copolymer deformation. The yield is due to the spherulite deformation and a small part of lamellae rotation and reorientation when the temperature is 25 C. When near the glass transition temperature, a large number of lamellae are crushed and oriented to form a large number of microfibers at the yield point.

The in-situ formed rubber phase in polypropylene random copolymer plays a significant role in the toughening process. When the temperature is 25 C the yield is due to the spherulite deformation and a small part of lamellae rotation and reorientation. While a large number of lamellae are crushed and oriented to form a large number of microfibers at the yield point when the temperature is 0 C.     

Structural and thermal stabilization of isotactic polypropylene/organo-montmorillonite/poly(ethylene-co-octene) nanocomposites by an elastomer component

Rheological and thermal properties of isotactic polypropylene (iPP)/organo-montmorillonite (OMMT)/poly(ethylene-co-octene) (PEOc) ternary nanocomposites and iPP/OMMT binary nanocomposites were studied by X-ray diffraction (XRD), rheometry, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) in this paper. The clay layers were mainly intercalated and partially exfoliated and well dispersed in these nanocomposites with the help of maleic anhydride modified polypropylene (PPgMA). Clay layers were mainly localized close to/inside the PEOc-rich phase from the direct observation of morphological study. A compact and stable network structure was formed in ternary composites when clay content was 2 phr (parts per hundred parts of iPP/PPgMA) or higher, which resulted in the lower stress relaxation rate and a pseudo-solid like behavior in low frequency region. Compared with iPP/OMMT composites, iPP/OMMT/PEOc composites had a much stronger ability to resist thermal decomposition. In another word, combining with the filler network, PEOc greatly improved the structural and thermal stabilities of iPP/OMMT nanocomposites.     

Adhesion of CPO onto high modulus TPO: Lap-shear tests in conjunction with microscopy studies of the fracture surface structure

A lap-shear test was employed to investigate the failure mechanism of a chlorinated polyolefin (CPO) coating on a high-modulus thermoplastic olefin (TPO) substrate fabricated as a blend of a highly crystalline Ziegler-Natta isotactic polypropylene (iPP) and a crystalline metallocene poly(ethylene-butene) (9 wt% butene, EB9) impact modifier. The CPO was a chlorinated polypropylene containing 20 wt% Cl. The results showed that the fracture strength increased with increasing EB9 content in TPO blends. They also showed that the presence of xylene vapor during the bake step improved the adhesion between CPO and iPP itself (by 40%), but had a much smaller effect for the TPOs. Optical and transmission electronic microscopy images revealed a well-defined skin layer approximately 230 μm thick at the mold surface of the injection molded substrates. For the 25 wt% EB9 blend (TPO₂₅), this skin layer consists of thin fibers of EB trapped in a transcrystalline iPP matrix, with crystalline lamellae propagating from the matrix across the EB9 domains. Laser scanning confocal fluorescence microscopy (LCFM) and scanning electron microscopy images of iPP/CPO/iPP samples indicate that failure occurred close to the interface between the CPO and the iPP substrate, and, during fracture, the CPO layer maintained its original thickness. For the TPO/CPO/TPO sandwich samples, the fracture surfaces themselves were much rougher than that between CPO and iPP. Substantial deformation of the CPO layer was seen in the fractured samples, and failure was due primarily to cohesive fracture of the CPO in the region adjacent to the TPO substrate. From the perspective of newly introduced environmental regulations restricting aromatic hydrocarbons in automotive coatings, the most important result was the strong adhesion between CPO and TPO₂₅, with little difference between the samples exposed to xylene vapor and those not exposed to xylene.     

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.     

Preparation and characterization of nanoclay‐filled polyurethane/polypropylene blends

Ester‐based thermoplastic polyurethane (TPU) nanocomposites were prepared by melt blending at 190°C, using 3 wt% Cloisite 10A (organically modified montmorillonite clay) as the nanoscale reinforcement [TPU(C10A)]. The nanocomposites were subsequently melt‐blended with polypropylene (PP) using maleic anhydride–grafted polypropylene (MA‐g‐PP) as a compatibilizer [in the ratio of 70/30‐TPU/PP, 70/25/5‐TPU/PP/MA‐g‐PP, 70/25/5‐TPU (C10A)/PP/MA‐g‐PP]. Besides giving substantial increase in modulus, tensile strength, and other properties, organoclay reinforcement functions as a surface modifier for TPU hard segment resulting in improved dispersion. The morphology and other characteristics of the nanocomposite blends were investigated in terms of X‐ray diffraction, fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile properties, scanning electron microscopy, and atomic force microscopy. The results indicate that the ester‐TPU(C10A)/PP/MA‐g‐PP exhibited better dispersion than other blend systems; abrasion resistance and water absorption resistance were also better for this system. POLYM. ENG. SCI., 50:1878–1886, 2010. © 2010 Society of Plastics Engineers