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The RTPP/ABS (rubber toughened polypropylene/poly (acrylonitrile-co-butadiene-co-styrene) blends, both noncompatibilized and compatibilized with polypropylene-g-polystyrene, were prepared by melt mixing in a Brabender Plasti-Corder. As the torque ratio of RTPP and ABS was about 2, phase cocontinuity in the blends was achieved at ABS volume fractions around 0.16, which was evidenced by both microscopic analysis and mechanical testing. A new microscopic and image analysis technique was introduced, whose combination provides two semiquantitative parameters: structure roughness and structure cocontinuity. The latter parameter is closely associated with the predictive scheme based on the equivalent box model and percolation theory, which was used in this study. The predicted mechanical properties were confronted with the experimental data for tensile modulus, yield strength, and tensile impact strength. While the modulus of noncompatibilized blends is reasonably fitted by the model, the compatibilizer accounts for a positive deviation attributed to a strong interaction between the compatibilizer and the matrix. The yield strength of noncompatibilized blends indicates poor interfacial adhesion, which is so enhanced by the compatibilizer that no phase debonding occurs before yielding. Tensile impact strength, in contrast to modulus and yield strength, passes through a deep minimum for both types of blends; two tentative explanations of this detrimental behavior were suggested. POLYM. ENG. SCI., 47:582-592, 2007. [c] 2007 Society of Plastics Engineers, INTRODUCTION Preparation of polymer blends is known as a cost-effective way of upgrading various mass-scale polymers. As can be seen in available literature [1-8], polyolefin blends with styrenics still attract [...]

Fluorescence quenching of phenanthrene (Ph) and anthracene (An) fluorophores by maleic anhydride (MAH) and n-octadecenylsuccinic anhydride (ODSA) quenchers in solid polypropylene (PP) films were studied. Results were compared with fluorescence quenching of the same fluorophores by MAH and ODSA quenchers in chloroform solution. Contrary to the results obtained in solution, it was observed that fluorescence emission of Ph fluorophore in PP films was more efficiently quenched by ODSA than by MAH. This was due to the better miscibility of Ph with ODSA than with MAH. When An fluorophore was used instead of Ph, it was observed that its fluorescence intensity in PP films was notably reduced by the addition of MAH. This was mainly due to the Diels--Alder reaction, which consumed a part of the An molecule. However, fluorescence intensity of An strangely increased with the addition of ODSA instead of MAH. Because of short lifetime of An (around 6 ns), ODSA had no quenching effect on An. POLYM. ENG. SCI., 47:192-199, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Fluorescence quenching of polyaromatic molecules by electron deficient molecules was extensively studied in liquid solutions and both dynamic (collisional) and static fluorescence quenching mechanisms were developed [1-3]. The collisional [...]

The effect of the volume fraction of a dispersed phase on improvement in the toughness of injection-molded isotactic polypropylene (i-PP), blended with a styrenic thermoplastic elastomer, has been studied. The volume fraction of the dispersed phase, which indicates compatibility between elastomer and i-PP, depends on the molecular structure of a soft segment and the copolymerization ratio of styrene. The volume fraction of the dispersed phase of the i-PP blended with styrene-ethylene-propylene-styrene tri-block copolymer (SEPS) was higher than that of the i-PP blended with styrene-ethylene-butylene-styrene tri-block copolymer (SEBS). The volume fraction of the dispersed phase increases as the copolymerization ratio of styrene increases. Improvement in the toughness of the blended i-PP clearly depends on relaxation of strain constraint by void formation from the dispersed phase. Its efficiency proved to be dependent on the strength and the volume fraction of the dispersed phase depending on the compatibility between elastomer and i-PP. POLYM. ENG. SCI., 45: 1630-1638, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Frequent studies have been made on the toughness improvement in isotactic polypropylene (i-PP), for example, by melt-mixing the polymer with suitable elastomers [1-3]. The study results suggest that the [...]

Montmorillonite is a promising substitute for aluminum trihydroxide in flame-retardant polypropylene/aluminum trihydroxide (PP/ATH) composites. Study was made of the partial substitution of organoclay for ATH in PP/ATH composites. The total concentration of filler was kept at 30 wt%. The composites were compatibilized with two types of compatibilizer: commercial maleic anhydride functionalized polypropylene (PP-g-MA) and hydroxyl-functionalized polypropylene (PP-co-OH) prepared with metallocene catalyst. The effect of compatibilization on the morphology was studied by the transmission electron microscopy and the scanning electron microscopy. Mechanical properties were characterized by tensile and impact measurements, and flammability properties with a cone calorimeter. Addition of compatibilizer and stearic acid (SA) treatment of the ATH particles contributed to the dispersion of the fillers. Both compatibilizers produced organoclay with exfoliated structure and improved adhesion between the fillers and the matrix. Toughness improved and decomposition and flammability were reduced. POLYM. ENG. SCI., 45:1568-1575, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Flame retardancy is commonly introduced to polymers by adding metal hydroxide filler, such as aluminum trihydroxide (ATH). Typically about 60 wt% of filler is required, however, and this creates [...]

The effects of processing conditions on appearance characteristics of injection-molded mineral-filled polypropylene (compounded with pigments giving differing intensities of a beige color) have been studied; characteristics studied included gloss, color, and texture. A mold cavity embossed with smooth, fine, and coarse surface patterns was used. In-mold rheology and gate-seal analysis were used to select the filling and postfilling processing parameters. Interest was focused on the effects of filling rate, holding pressure, and mold temperature on the appearance characteristics, and a significant influence of these processing conditions on the gloss and color was found. For all the surface patterns examined, a better replication of the mold texture was obtained with a low melt viscosity at a high shear rate (high injection speed or short injection time) and a high mold temperature. This gave a higher gloss in the smooth surface regions and a lower gloss in the textured regions. An increase in the holding pressure had an effect similar to but smaller than increasing the filling rate or mold temperature. The gloss (or surface topography) had a significant effect on the color; an increase in gloss was associated with an increase in the color coordinate b* and a decrease in the lightness L*. POLYM. ENG. SCI., 45:1557-1567, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION A satisfactory visual impression of the end product is one of the basic quality criteria for polymer injection molding. The assessment of surface appearance is increasingly important, including not [...]

This research explores the interlayer effect, dynamic mechanical properties, hysteresis behavior, and dynamic antivibration properties of PEL (polypropylene oxide-polyethylene oxide copolymer with LiCI[O.sub.4] 20 wt%) for modified PU (mPU) blends with clay and organoclay of varying amounts. The results show that the d-spacing between the layers of clay and organoclay ranges between 1.78-1.88 nm in the presence of PEL. The dynamic mechanical analysis indicates that the presence of clay and organoclay increases the vibration isolators of the nanocomposites under 20°C. It is found that organically modified clay significantly improves the antivibration performance of the blends based on the compressive vibration hysteresis effect. From the results of the dynamic antivibration test, the dynamic ratio of the blends decreases with the addition of clay or organoclay. In addition, clay is better than organoclay in enhancing the vibration isolation of the mPU blends. POLYM. ENG. SCI., 45:539-548, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION Polymers exhibit uniquely high damping behavior in their glass transition zone due to conversion of mechanical vibration into heat energy through friction between molecular chains and heat dissipation [1]. [...]

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (~0.15-mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in-plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being [ν.sub.xy] = -1.12 ± 0.06 and [E.sub.x] = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are [ν.sub.yx] = -0.77 ± 0.01 and [E.sub.y] = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517-528, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION Auxetic materials [1, 2] are those which when stretched expand rather than contract in width. In other words, they display negative Poisson's ratio behavior. A variety of products have [...]

It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE-particles of two different sizes in various concentrations were melt-blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR-SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X-ray diffraction (WAXD) pole-figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate ([G.sub.1]) and the E-modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458-468, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION Polytetrafluoroethylene (PTFE) possesses a unique combination of properties such as low bulk shear strength, low surface tension, low coefficient of friction, low yield stress, and high toughness [1]. Due [...]

This paper reports the fatigue behavior of an injection molded 40wt% talc-filled polypropylene. The effects of specimen orientation relative to the flow direction, weld line, hole stress concentration and test frequency on the fatigue performance of this material have been considered. The fatigue strength in the flow direction was higher than that normal to the flow direction. However the orientation effect decreased at lower fatigue stress level. The presence of weld line reduced the fatigue strength. On the other hand, the fatigue strength showed very little sensitivity to the presence of hole stress concentration. The failure mode in fatigue was influenced by the test frequency. When the test frequency was less than or equal to 2 Hz, the failure mode of the talc-filled polypropylene was due to fatigue and the fatigue life increased with frequency. However, when the test frequency was greater than or equal to 5 Hz, the failure of the talc-filled polypropylene was due to thermal softening and the fatigue life did not appear to be influenced much by the frequency. POLYM. ENG. SCI., 45:510-516, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION During the past several years, both unfilled and filled thermoplastic polymers have found increasing number of applications in structures that are subjected to cyclic or fatigue loading. Many of [...]

The effects of processing parameters on the thermoforming of polymeric foam sheets are highly nonlinear and fully coupled. The complex interconnection of these dominant processing parameters makes the process design a difficult task. In this study, the optimal processing parameters of polypropylene foam thermoforming are obtained by the use of an artificial neural network. Data from tests carried out on a lab-scale thermoforming machine were used to train an artificial neural network, which serves as an inverse model of the process. The inverse model has the desired product dimensions as inputs and the corresponding processing parameters as outputs. The structure, together with the training methods, of the artificial neural network is also investigated. The feasibility of the proposed method is demonstrated by experimental manufacturing of cups with optimal geometry derived from the finite element method. Except the dimension deviation at one location, which amounts to 17.14%, deviations of the other locations are all below 3.5%. POLYM. ENG. SCI., 45:375-384, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Using thermoforming in the processing of foamed plastics has the benefits of low cost, good formability, uncomplicated molds, and the capability to build large or thin structures [1, 2]. [...]

In the present work, the influence of well-defined simple shear flow histories on the isothermal crystallization of an isotactic polypropylene (i-PP) has been investigated. At first, the research of the flow conditions in terms of temperature, shear rate ([dot.γ]) and shear strain (γ) has been performed by means of the rheological technique. The continuous shearing analysis enabled us to build the flow curve at 144°C showing a Newtonian region as well as a shear-thinning zone. Indeed, for [dot.γ] above a critical value, the molecular orientation occurring during flow provides a kinetic promotion of the crystallization process. In the rheological step-shear flow analysis, an increase of the flow sensitivity parameter, [k.sub.S]/[k.sub.Q], with increasing the shear rate at a constant strain (γ = 150) is observed. The structure of the crystallized samples has been investigated by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS) methods. In agreement with the DSC, the WAXS results show that crystals with a certain bimodal distribution are generated in the samples crystallized under step-shear flow conditions. A small orientation of the (110) plane of the i-PP α-phase crystals is also detected. POLYM. ENG. SCI., 45:153-162, 2005. © 2005 Society of Plastics Engineers, INTRODUCTION The isothermal crystallization of semi crystalline polymers may strongly be influenced when external physical fields are applied. Indeed, the flow-induced crystallization (FIC) phenomenon can increase the overall crystallization kinetics [...]

Crystallization behaviors, spherulite growth and structure, and the crystallization kinetics of polypropylene (PP)/ethylene-[alpha]-olefin copolymer (mPE)/high-density polyethylene (HDPE) ternary blends and of mPE/HDPE binary blends have been studied using polarizing optical micrography (POM) and differential scanning calorimetry (DSC). In mPE/HDPE blends, large pendant groups of mPE disturbed spherulite growth of HDPE, leading to a different crystallite morphology and isothermal kinetics. Non-isothermal properties, morphology, and isothermal crystallization kinetics of PP in ternary blends were significantly influenced by the composition and crystallization behavior of the mPE/HDPE binary blends as well as the crystallization condition. Polym. Eng. Sci. 44:1858-1865, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Isotactic polypropylene (PP) has been used for various applications because of its low cost and ease of processing. However, because of its poor impact strength especially at low temperature, [...]

It was reported that a nanocrystal ZnO had a thermal stabilizing effect for branched low-density polyethylene (BLDPE). In this study, the thermal stabilizing effect of the nanocrystal ZnO was studied in more detail in comparison to a conventional, micron-size ZnO using several polymers and a common antioxidant. The experimental results in this investigation suggest that the nanocrystal ZnO particles have different surface properties from micron-size particles because of their extremely small size, and the particular surface properties are responsible for the thermal stabilizing effect. Polym. Eng. Sci. 44:1702-1706, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Hong et al. (1) reported a new finding that a nanocrystal ZnO retarded gelation of branched low-density polyethylene (BLDPE). It has been reported that nanocrystals of inorganic materials exhibit [...]

Dynamic mechanical thermal analysis (DMTA) and oscillatory flow measurements are carried out to investigate the rheological properties of 70/30 blends of a bitumen with metallocene catalyzed atactic polypropylenes. DMTA results indicate that saturated liquid resins of the bitumen act as a plasticizer on polypropylene. The glass transition temperature of polypropylene decreases, and the pure bitumen broad relaxation disappears, which signifies that a polypropylene-saturated resin mixture constitutes the continuous phase. Such results are not obtained when a conventional atactic polypropylene is used in the blend. Oscillatory flow measurements show a viscosity reduction of the blends with respect to pure polypropylene, beyond what could be expected from a simple additive rule, reflecting the plasticization of polypropylene. One of the blends displays a viscoplastic behavior at low frequency, which is attributed to the presence of small crystals, formed on cooling from the mixing temperature. Some viscoelastic properties related to the use of these materials as roofing membranes are analyzed. Polym. Eng. Sci. 44: 1792-1799, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Metallocene-type catalytic systems are well known as catalysts of single centers, in contrast to conventional Ziegler-Natta multiple-center catalysts. The performance of these catalysts to polymerize industrial polyethylenes and polypropylenes [...]

Composites of polypropylene (PP) and non-treated sisal fiber (SF) were prepared in a non-conventional two-step process that offers significant advantages. Maleic anhydride-grafted polypropylene (MA-g-PP) was used as a coupling agent, to improve adhesion between the polar sisal fiber and the non-polar polypropylene continuous matrix. At a first step, SF/MA-g-PP pellets with large aspect ratio and very high fiber content are prepared by extrusion impregnation and coating of a continuous SF yarn, followed by cooling and cutting. The composite pellets are thus dry blended with regular PP pellets in the injection machine hopper, and injected to obtain composite tensile specimens with a minimum quantity of expensive MA-g-PP, minimum fiber breakage and thermal degradation, and excellent mechanical properties. The SF/MA-g-PP pellets have a fiber content of 70% (w/w). The composite tensile specimens have final fiber contents ranging from about 3.5% to 24.5% (w/w). The PP tensile strength rises by about 44%. The tensile modulus increases by 126%, and the heat distortion temperature (HDT) is raised by about 35 K. FT-IR spectroscopy and SEM micrographic observation show that the MA-g-PP is covalently bonded to SF through esterification. Besides the improvement in mechanical and thermal properties, costs are reduced because of the lower content of very expensive MA-g-PP, and the use of a single-screw extruder at high production rates. Polym. Eng. Sci. 44:1766-1772, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Cellulosic natural fibers are being incorporated into polymeric matrices to reduce cost and to improve mechanical properties, this trend being driven mainly by government regulations that promote the use [...]

The crystallization behavior of two polypropylene (PP) resins as used for biaxially oriented polypropylene (BOPP) and general injection mold applications, respectively, has been intensively investigated and compared by means of polarized light optical micrography (POM), differential scanning calorimetry (DSC), conventional transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). It is found that both molecular weight distribution and isotacticity of polypropylene strongly affect its crystallization characteristics, e.g., the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size and perfection of crystals in the final product, and so on. The results indicate and appropriate molecular structure is vital in producing high-quality BOPP film. Polym. Eng. Sci. 44: 1749-1754, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Biaxially oriented polypropylene (BOPP) film, one major type of biaxially oriented film, has been developed since the 1960s through the mass production of polypropylene. This film is today widely [...]

In a number of applications, a brittle polymeric surface layer is deliberately molded onto a tough substrate for decorative or protective purposes. This can increase the susceptibility of the tough polymer to premature failure. Similar problems arise when a surface layer becomes embrittled by environmental effects. Choosing a surface material that has good mechanical properties without having this effect can be difficult. In this work the fracture resistances of two polyethylenes and an ethylene/propylene copolymer, and of symmetrical two-component multilayers of these polymers, were determined as a function of temperature, using instrumented impact tests. The law of mixtures accounts adequately for the fracture resistance of multilayer structures where there is no mechanical interaction between skin and core. However, it gave misleading results for a structure in which high skin modulus at low temperatures appeared to influence the fracture resistance of the core through a constraint effect. Polym. Eng. Sci. 44:1627-1635, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION In an increasing number of components, two thermoplastics are co-processed to form a multilayer structure. Two component polymers may be co-injected successively into a single cavity, or into a [...]

The crystal structures of different grades of cast polypropylene (CPP) extrudates were characterized by Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). The effects of the crystallization temperature, draw ratio, and cooling rate on crystal structure are discussed in detail. The results demonstrate that stretching cannot induce the formation of the γ crystal, but the crystallization temperature and the cooling rate do affect the formation of the γ crystal. The slower the cooling rate, the more easily the γ crystal develops. It was found that at the optimum crystallization temperature ([T.sub.c]) of about 110°C, the γ crystal developed distinctly, and a slower cooling rate made the formation of γ crystal easier. Also, the crystal structures of different resins at the same conditions were discriminative, suggesting that the formation of the γ crystal was due to interruptions of comonomer units in the isotactic propylene sequences, which prevented the PP chain segment from entering the crystal lattice of the α crystal in some degree. If the length of the comonomer sequences was shorter and the distribution of the comonomer units more symmetrical, the formation of the γ crystal would be more distinct. Polym. Eng. Sci. 44:1656-1661, 2004. © 2004 Society of Plastics Engineers., INTRODUCTION In many packaging applications, there is an increasing use of polypropylene, easily extrudable in film form, commonly known as cast polypropylene (CPP). In film casting, the melt is forced [...]

The creep behavior of composites prepared from woodflour and polypropylene has been analyzed. The woodflour content was varied from 0% to 60%. The compatibility between filler and matrix was varied by adding a non-commercial polypropylene-maleic anhydride copolymer (PPMAN) to the mixture. Short-term and long-term creep tests of woodflour/polypropylene composites at different temperatures were carried out. The effects of filler content, addition of compatibilizing agent and temperature were discussed. The creep deformation was generally reduced with woodflour addition, except at very high filler concentrations because of filler-wetting and dispersion problems. Low temperatures and addition of PPMAN also reduced the creep deformation. The creep compliance was modeled using the Burgers model and a power law equation. The parameters were found from the best fitting of experimental data using an optimization method. The Burgers model was found to provide a good description of the linear viscoelastic behavior. The mathematical description obtained from the short-term creep was utilized to predict the dynamic mechanical behavior of the composites with very good agreement between experimental and calculated values. Attempts to use the time-temperature-superposition principle to predict long-term creep from high temperature results were not successful because of the aging of the samples during creep at low temperatures. However, there was a good superposition of the short-term and long-term data at temperatures close to 70[degrees]C-80[degrees]C. The reason for this behavior is a relaxation of the PP matrix that takes place in that temperature range and erases any previous aging of the material. Polym. Eng. Sci. 44:1594-1603, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION The use of natural fibers as reinforcement of polymeric matrices has attained great academic and commercial interest in the past decade owing to the low cost, large availability and [...]

The effects of ultrasonic irradiation on the mechanical properties, morphology, and crystal structure of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends were examined. Results show that appropriate irradiation intensity can noticeably increase the toughness of the PP/EPDM blends without reducing rigidity. Scanning electron microscopic (SEM) observation shows that with ultrasonic irradiation, the morphology of a well-dispersed EPDM phase is formed in the PP/EPDM blend. The glass transition temperatures of PP and EPDM phase approach each other as a result of ultrasonic irradiation. Differential Scanning Calorimetric (DSC) analysis indicates that the crystallinities of the PP and EPDM phases increase with ultrasonic irradiation, and [beta] crystals of PP form in the PP/EPDM blend with ultrasonic irradiation, which is proven by wide angle X-ray diffraction (WAXD) analysis. Polym. Eng. Sci. 44:1509-1513. 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Isotactic polypropylene (iPP) is used in a wide range of applications because of its attractive properties of relative high stiffness, heat distortion temperature, and its low price. However, the [...]

Polypropylene homopolymer melts containing up to 50 percent by weight of talc filler (24 vol%) were tested on a Gottfert Rheotens melt strength testing unit. Melt strength and drawability parameters were measured from these tests to evaluate changes in the extensional behavior of the melt induced by filler addition. It was found that the melt strength of the polypropylene was decreased for talc additions of less than 40 wt% (17.5 vol%) under all test conditions. Addition of 50 wt% talc improved the melt strength under all testing conditions. Drawability, defined as the stretch ratio at strand break, decreased with increased filler loading. The melt strength of all materials was found to decrease with increased temperature within the range 180°C to 210°C. The melt strength of all melts showed dependence on the test extrusion rate, and this dependence was well described by an exponential relationship. Highest dependencies were seen for the unfilled and 50 wt% talc-filled polymer. While it was found that addition of 50 wt% talc provided improvement in melt strength, high melt strength alone was a poor indicator of the melt process-ability, as drawability was also regarded as an important consideration., 1. INTRODUCTION Polypropylene is a widely used commodity thermoplastic polymer, which as a result of its favorable properties is increasingly finding uses in new products for a variety of applications. [...]

The mechanical properties and crystal morphological structures of dynamically photocrosslinked polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends have been studied by mechanical tests, wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Dynamically photocrosslinking of PP/EPDM blends can improve the mechanical properties considerably, especially the notched Izod impact strength at low temperature. Data obtained from mechanical tests show that the notched Izod impact strength of a dynamically photocrosslinked sample with 30% EPDM at -20°C is about six times that of an uncrosslinked sample with the same EPDM component. The results from the WAXD, SEM, and DSC measurements reveal the enhanced mechanism of impact strength for the dynamically photocrosslinked PP/EPDM blends as follows: (i) the β-type crystal structure of PP is formed and the interplanar distance of α-type crystal increases slightly with an increase in the EPDM component; (ii) the droplet size of the EPDM phase in the photocrosslinked PP/EPDM blends is obviously reduced and the droplet number is increased with an increase in the EPDM component during the dynamical photocrosslinking process; (iii) the graft copolymer of PP-g-EPDM is formed at the interface between PP and EPDM components. All the above changes from the crystal morphological structures are favorable for increasing the compatibility and enhancing the toughness of PP/EPDM blends at low temperatures., INTRODUCTION Polypropylene (PP) as a thermoplastic is widely used in many fields, such as building materials, furniture, automobiles, the toy industry, and so on. However, its main disadvantage is its [...]

We report the solid-state die-drawing of polypropylene and blends of polypropylene with a polyethylene elastomer to produce highly oriented products with enhanced mechanical properties. The blends showed an improvement in [...]

Melt blending of polypropylene (PP) with a low molecular weight (MW) crosslinkable unsaturated polyester (UP) was studied in a batch mixer and a twin-screw extruder in the presence of peroxide [...]

New types of compatibilizers based on functionalized polypropylene (PP) were synthesized by radical melt grafting either with monomethyl itaconate or dimethyl itaconate. The effect of these new modified PP compounds [...]

Blends of polypropylene/ethylene vinyl acetate (PP/EVA) have been investigated for linear and transient characteristics. The emulsion model developed by Palierne in 1990 is used to characterize the linear viscoelastic properties of the blends. PP/EVA blends with the viscosity ratio of 0.26 and different compositions, such as 90/10, 80/20 and 70/30 wt% PP/EVA have been studied. It was found that the Palierne Model predicts well the linear behavior of all the compositions studied. At low frequencies, some deviation in dynamic moduli was found in case of the 70/30 composition. Structural changes are studied during transient shear flow (step-up) experiments. A nonlinear rheological model for blends, developed by Peters, Hansen and Meijer (PHM model), is used to describe these transient rheological data. Overshoots and undershoots observed in the experimental data are compared to numerical results obtained with PHM model and explained on the basis of the deformation of the dispersed phase. A modification of the mo del is proposed in order to get a better description of the behavior of the viscoelastic blend. Predictions of the morphological evolution of the blends under stepwise increase in shear rate experiments were calculated from the modified model and are found to describe the break-up phenomenon under moderately high shear flow., INTRODUCTION The relationship between rheology and morphology of emulsions and polymer blends is of importance, theoretically and experimentally, in order to understand the evolution of the two-phase morphology during mixing, [...]

The elaboration of a TPV based on copolymer of ethylene and vinyl acetate (EVA) and polypropylene (PP) as thermoplastic phase was investigated in a batch mixer. The crosslinking reaction is carried out through a transesterification reaction between ester groups of EVA and alcoxysilane groups of the crosslinker agent tetrapropoxyorthosilicate (TPOS). The main advantage of this crosslinking reaction is that it can be well controlled and suitable for different processing conditions. The aim of the present study is to get a better understanding of the dispersion mechanism and of the phase inversion of the EVA major phase during its dynamic vulcanization into the PP minor phase. It was proved that the initial viscosity ratio, λ = [η.sub.PP]/[η.sub.EVA], between EVA and PP plays an important part in the morphology development of the reactive blend. The viscosity ratio must be close to the critical ratio expressed by Utracki's model of phase inversion mechanism. Furthermore, the influence of different processing parameters on the variation of the morphology and on the mechanical properties of the ultimate TPV was investigated. The main conclusion of this study is that the characteristic time of crosslinking must be of the same order than the time of mixing. Indeed, better mechanical properties are obtained when a progressive phase inversion occurred and when it is controlled by rheological aspects and transient morphology equilibrium of the two phases and not by the mechanical fragmentation of the crosslinked EVA. For example, in our experimental conditions (concerning the amounts of catalyst and crosslinker reagents), high shear rates can be avoided (γ < 80 [s.sup.-1]) as the self-heating of the blend under shear considerably increases (ΔT ≅ 50°C for γ = 225 [s.sup.-1]), leading to faster kinetics and consequently to a phase inversion controlled by the fragmentation of the crosslinked EVA phase., INTRODUCTION Among different kinds of thermoplastic elastomers (TPE), the thermoplastic vulcanizates (TPV) prepared by dynamic vulcanization have reached an important place in the polymer industry. The process of dynamic vulcanization [...]

The synthesis of polypropylenes via polymerization of propylene using 2-arylindene metallocenes is described. This article presents kinetic and mechanistic models of the synthetic approaches, catalysis, and stereoselectivity. Application of the process in the polyolefin manufacture is also discussed.

A unified formulation is presented for modeling the injection molding of isotactic polypropylene (i-PP). The crystallization kinetics are based upon the differential Nakamura equation in which the characteristic time is dependent upon temperature, pressure and flow-induced shear stress, without any explicit need for an induction time. A Cross/WLF model is used to represent the shear viscosity in which [[eta].sub.0] is dependent upon temperature, pressure and crystallinity. Use is made of a recent correlation for the PVT behavior of i-PP with an explicit dependence upon crystallinity. A finite-difference implementation of the modeling is applied to two independent molding experiments available from the literature, with notable results concerning the late-time cavity pressure traces and time-dependent gapwise shrinkage prior to ejection.

Morphological characteristics and mechanical properties of PP-EP/EVA blends were studied and compared to those of PP/EVA previously reported. For the PPEP/EVA blends, interfacial interactions in amorphous zones, which were associated with shifts in [T.sub.g], were well defined compared to those of PP/EVA blends, a]though the nature of crystalline zones was similar for both systems. At EVA concentrations up to 20%, the elongation at break and impact strength slightly increased in both systems. However, PP-EP/EVA displayed higher values of these properties compared with PP/EVA. At high EVA concentrations (above 20%), the indicated properties were enhanced in both polymeric systems, and the same proportional behavior was maintained. The decrease in tensile strength of PP-EP/EVA was not as marked as in PP/EVA with the addition of EVA, and it remained below PP/EVA at high EVA concentrations. The improvement in properties of PP-EP/EVA was attributed to favorable interactions between the ethylene groups contained in both copolymers. These interactions rendered a high degree of compatibility between the PP-EP and EVA components., INTRODUCTION Poly(propylene) (PP) and poly(ethylene vinylacetate) (EVA) are two important commercial polymers. The former is a semicrystalline thermoplastic, whereas the latter is considered an elastomer. In the last few years, [...]

Monotonic compressive loading and bending tests are conducted for solid polypropylene (PP) under constant or time-varying strain-rates and temperatures of 10, 25, 40°C. The observed compressive stress-strain responses under constant conditions have revealed that the inelastic deformation behavior is remarkably dependent on loading rates and temperatures of normal use. The examination of such inelastic behavior has indicated that the strain-rate effects correspond with the temperature effects based on the concept of time-temperature equivalence. The viscoplastic constitutive theory based on overstress (VBO) has successfully reproduced the experimental responses with stress-jumping phenomena using the equivalent time. Four-point bending tests are performed under monotonic loading and holding for PP beams at three different temperatures. The observed deformation behavior has shown that the Bernoulli-Euler hypothesis is valid. The VBO model and beam bending theory has generated the basic equations for PP beams, showing an analogy with the uniaxial one. In the numerical analysis, the equations are transformed into nonlinear ordinary differential equations with use of Gaussian quadrature for the spatial integrals. The comparison of numerical and experimental results has suggested some modifications for actually loaded moment taking the effect of deflection and friction into consideration. Finally, the numerical calculation has simulated the experimental time-histories of curvatures fairly well., INTRODUCTION The growing use of solid polymers is remarkable in modern society. Especially, the employment of engineering plastics as primary members is expanding to achieve lightweight structures. Therefore, reliable deformation [...]

Polypropylenes (PP) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) and strands were prepared by extrusion and stretching. The strands were subsequently pelletized and then injection molded at temperatures below the melting point of LCP. The mechanical properties and the morphology of the strands and injection-molded specimens were investigated as a function of draw ratio, LOP concentration, and PP molecular weight. The results for strands show that an increase in the draw ratio, LCP concentration and matrix molecular weight in general enhance the modulus and tensile strength. However, the tensile properties of injection-molded specimens are found to be reduced compared with those of the original strands, in particular at high LOP concentration. The morphology of LCP changes from spherical or ellipsoidal droplets to elongated fibrils in the strands as the draw ratio increases, but this aligned LOP fibrillar morphology was not transferred to the injection-molded specime ns because of the disorientation of fibrils during injection molding. Compatibilization of PP/LCP blends was also studied by using various polymers. Maleic anhydride and acrylic acid modified PPs improved the tensile properties modestly, but maleic anhydride modified EPDM reduced the tensile properties., INTRODUCTION Self-reinforced composites involving LCPs have many advantages over conventional glass fiber reinforced composites, such as lower energy consumption in melt blending, less machine abrasion, etc. Such thermoplastic/LOP composites have [...]

Microporous flat films with potential as membranes were produced via melt processing and post-extrusion drawing from immiscible polypropylene/polystyrene blends containing a compatibilizing copolymer. The blends were first compounded in a co-rotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially drawn (100%-500%) with respect to the original dimensions to induce porosity and then post-treated at elevated temperatures to stabilize the resultant structure, which consisted of uniform microcracks in the order of a few nanometers in width. The effects of blend composition and extrusion process parameters on surface and cross- sectional porosity and solvent permeability of the prepared films are presented and related to specific microstructural features of the films before and after drawing. Finite element modeling of the stretching operation in the solid state yielded a successful Interpretation of the blend response to uniaxial tension that resulted in microcrack formation. Comparison of some of the novel microporous structures of this work with commercial membranes prepared by solvent-based phase inversion processes suggests comparable pore size and porosity ranges, with narrower pore size distribution., INTRODUCTION Microporous polymeric membranes are conventionally produced by phase inversion processes that use solvents to dissolve, usually, amorphous polymers. Semicrystalline homopolymers having much higher solvent resistance, e.g. polypropylene (PP), polyethylene, [...]

Polypropylene powder and sisal fibers were oxygen plasma treated, and the mechanical properties of their composites were tested. Two main effects were investigated: the incorporation of oxygen polar groups in the polypropylene surface and the surface degradation and chain scission of both polypropylene and sisal fibers. Prior to these treatments, three reactor configurations were tested to investigate the best condition for both effects to occur in PP films. Results showed that polypropylene-cellulose adhesion forces are about an order of magnitude higher for PP film treatments at 13.56 MHz than at 40 kHz owing to much higher chain scission at lower frequencies, although it probably also occurs at high frequency and high power. Polypropylene powder treated with oxygen plasmas in optimum conditions for polar group incorporation did not result in improvement in any composite mechanical property, probably owing to the polymer melting. Sisal fibers and PP powder treated in conditions of surface degradation did no t improve flexural or tensile properties but resulted in higher impact resistance, comparable to the improvement obtained with the addition of compatibilizer., INTRODUCTION The growing need for environmentally friendlier materials has stimulated research in composite materials of thermoplastics reinforced with lignocellulosic fibers. Besides improvement in mechanical properties, the partial replacement of oil-based [...]

Pure isotactic polypropylene (iPP) and 90/10 wt iPP/ultra high molecular weight polyethylene (UHMWPE) blends, prepared by a novel vibration internal mixer reformed from a conventional internal mixer via parallel superposition of an oscillatory shear on a steady shear, were investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction. After plasticating pure iPP in the vibration field, the number of [betta] form crystals of IPP was increased. The β form exhibited a single DSC melting peak different from that of the bulk form crystals of IPP. After mixing of UHMWPE with iPP, the melting point of the UHMWPE component shifted to a lower temperature. For blends mixed at the higher-frequency and/or largeramplitude vibrations, the melting point of the UHMWPE component was further gently lowered while the bulk melting point of the iPP component was slightiy increased. The crystallization peaks of the two components overlapped into one single peak, and the total crystallinity became hi gher, together with a larger amount of the β IPP. These results showed that the two components influenced each other in blending. Hence, the resultant morphology affected the subsequent ciystallization and melting behaviors. Additionally, vibration in mixing possibly affected the conformation of some polypropylene chains to favor the subsequent packing in the β form., Chixing Zhou (*) INTRODUCTION Blends of isotactic polypropylene (iPP) with low and high density polyethylene (LDPE and HDPE) have been widely investigated to improve the low-temperature toughness of iPP (1, [...]

An experimental and theoretical investigation of the phase behavior of blends of aliphatic polyesters, possessing different methylene content and chlorinated polypropylenes (PP-Cl), containing 26, 32 and 65 wt% chlorine, respectively, has been performed. A window of miscibility was found only for the PC-C165; however, this was sufficient to apply a binary interaction model of phase behavior in polymers and allow for an estimation of the segmental interaction parameters that define the overall polymer pair interaction. Complete immiscibility was found in all blends of polyesters containing PP-C126 and PP-C132; a result consistent with model calculations. A number of simplifications have been made concerning the structures of polymers and assumptions have been made to apply the theoretical model. The segmental interaction parameters obtained have been extended to estimate the thermodynamic interaction in blends of polyolefins and chlorinated polyolefins and then used to calculate the relevant interfacial thickn esses. These results have been compared with information presented in the literature., INTRODUCTION The practical utility of quantifying interactions between polymers is illustrated by a recent analysis of the interfacial properties of thermoplastic polyolefins (TPOs) and their chlorinated derivatives (1). A large [...]

Polypropylene-based compounds are increasingly attractive because of low cost, processability, and good balance of properties. In recent years, metallocene ethylene-octene copolymers have started displacing EPR and EPDM as an impact modifier for PP. This study examines the effect of compounding conditions and composition on the properties of talc/ethylene-octene copolymer/PP compounds. The mechanical properties of the compounds were not significantly affected by the mixing conditions on a laboratory twin screw extruder. The use of 30 wt% of talc provided a twofold increase in tensile modulus compared with pure PP. Impact resistance of filled and unfilled compounds was found to increase rapidly once the copolymer concentration reached around 20 wt% based on the polymer phase. Modulus and tensile strength decreased linearly with copolymer concentration. Four different commercial maleic anhydride-grafted PPs were tested as interfacial modifiers. In the best cases, a slight tensile strength increase was observed when using between 2 and 10 wt% of modified PP., INTRODUCTION AND BACKGROUND Polypropylene, PP, offers a combination of inexpensive price, easy processability, and a wide spectrum of properties. Therefore PP is used to produce a variety of products such [...]

Modified and nonmodified blends of linear low-density polyethylene (PE) and polypropylene (PP) form separated phases of crystalline PP and PE. They form spherulitic crystals in the core, but highly oriented nonspherulitic phases at the skin of injection molded test bars. The dimension of the spherulites decreases with increasing PE content within the blends. Crystallization behavior of both crystalline phases is influenced by the other phase. The crystallization temperature of PP is increased in the presence of the compatibilizer. Transmission electron micrographs of blends modified by poly(styrene-block-ethylene/butylene) (SEBS) and stained by Os[O.sub.4] showed co-continuous lamellar structure of the blends with a polypropylene phase containing the majority of the modifier. Smaller portions of the modifier can be found on the surface of the two olefinic phases as dispersed spheres, with an average diameter of 50-90 nm. The lamellar structure is independent of the spherulitic structure, and interpenetrates the spherulites. The conclusion of this study is that this block copolymer, while improving the physical properties of the blends, is not a true compatibilizer of the system according to the conventional terminology of physical chemistry., INTRODUCTION Compatibilization is one of the key elements in the preparation of polymer blends with technical importance. According to Teyssie et al. (1-3), a compatibilizer is a material that reduces [...]

The influence of sodium oleate additives on processing and morphology of polypropylene - co-polyamide (PP/CPA) mixture melts has been investigated. It is shown that sodium oleate is located in the interphase of the components and acts at small additives (up to 3 wt%) as an interfacial tension agent, improving miscibility of polymers, and increasing the kinetic stability of mixtures and the degree of PP dispersion in the co-polyamide matrix. The plasticizing effect on mixture melt was observed at 7 wt% sodium oleate as a reduction of mixture viscosity. The ultrathin PP fibers (microfibers) strictly oriented in the direction of extrusion are the main type of structure produced during extrusion of a PP/CPA mixture. Addition of sodium oleate changed the PP fiber-formation in the CPA matrix: the total number of fibers increased, their diameter and diameter distribution decreased., INTRODUCTION Previous investigations have studied modification of polymers by forming of polymer mixtures (1, 2). It is known that extrusion of polymer mixture melts opens a new way to ultrathin [...]

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP-g-GMA) was studied. Two PP-g-GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20-fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub-micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10-20 [µmeter] wide. The low-GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated., INTRODUCTION Polypropylene/polyamide (PP/PA) blends are good examples of the blending and alloying techniques as a method of producing commercially successful materials. Polyethylene terephthalate (PET) and polyamides bear, to some extent, [...]

INTRODUCTION Composites represent an important class of engineering materials. The incorporation of mineral fillers into thermoplastics has been widely practiced in industry to extend them and to enhance certain properties. [...]

Extruded thermoplastic sheet is widely used in the production of thin-gauge tubs and containers for the food and beverage industry using the thermoforming process. The production of high quality thermoformed parts is critically dependent on the standard of extruded sheet feedstock used. The extrusion process itself imparts a thermal history to the sheet, and this in turn partly dictates its subsequent thermoformability. This paper assesses the influence of various extrusion parameters on the mechanical and morphological properties of polypropylene sheet, with a view to defining the optimum extrusion conditions for polypropylene. The extrusion parameters under consideration are chill-roll temperature, line speed, sheet thickness and melt temperature., 1. INTRODUCTION Recent advances in materials and process machinery have increased the popularity of the thermoforming process for the conversion of extruded thermoplastic sheet into thin-gauge tubs and containers for [...]

The shear viscosity of carbon black filled polypropylene with a range of different carbon blacks was investigated. This was accomplished using (a) a constant shear stress creep instrument, (b) a cone-plate rotational rheometer, (c) a capillary extrusion rheometer. It was found that stresses exist for these compounds below which there are only finite deformations and no steady flow. Much attention was given to measurements of creep at low stresses, especially in the neighborhood of yield values. The magnitudes of yield stresses obtained from such creep measurements are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stress data from rotational instruments. The shear viscosity behavior near the yield value differs significantly depending upon the carbon black used. A high shear viscosity was observed ([approximately][10.sup.9] to [10.sup.10] Pa [center dot] s) plateau in some compounds., INTRODUCTION Carbon black has long been the major reinforcing filler used in polymers, its most important application being with elastomers for tires. It also plays a useful role with thermoplastics [...]

Isotactic polypropylene (iPP) was nucleated specifically for structural and mechanical studies, especially of impact resistance. Nucleation was accomplished by two red pigments: a linear trans-quinacridone dye (as Β-phase nucleator) and a dimethyl quinacridone resulting in the formation of a pure [Alpha]-phase structure. This procedure allowed the comparison of both the crystal structure and the morphology of the polymer. For the Β-nucleated iPP, by means of the WAXS measurements in the transmission mode, a maximum of the k-value (fraction of Β-phase) was found for a concentration of 5 x [10.sup.-5] wt% of the trans-quinacridone. By means of polarized light microscopy (PLM), the mold temperature and pigment concentration dependent spherulites distribution on the cross section of the samples was observed. DSC permitted confirmation of the WAXS measurements, giving a characteristic double melting peak for the Β polypropylene. By isothermal WAXS measurements the temperature of 135 ° C as the upper limit of the Β phase was detected. For both nucleating agents (linear trans-quinacridone and dimethyl quinacridone) the dependence of the mechanical properties (modulus of elasticity and brittleness by impact resistance) on the pigment concentration was observed. For the Β-phase iPP the highest ductility by impact testing corresponds to the highest values of the k parameter. The explanation is based on the SEM observations, which permitted the detection of spherulites with cross-hatched lamellae (for the [Alpha]-spherulites) and with simple radial growth lamellae for the Β-spherulites., INTRODUCTION By the selective heterogeneous nucleation of the monoclinic a and hexagonal Β crystalline forms of isotactic polypropylene (iPP), and by the action of physical effects like pressure or shear [...]

Scanning force microscopy (SFM) was used to study the lamellar morphology of [Alpha] and Β spherulites in bulk intruded isotactic polypropylene (iPP) samples deformed under shear stress. The iPP specimens were sheared at a constant shear rate at room temperature. Just beyond yielding, at a shear strain level of 0.5, the lamellar structure of the [Alpha]-spherulites resembles that for unsheared iPP; few cracks are observed along the interfaces between neighboring [Alpha]-spherulites: this behavior is attributed to a 'cross-hatched' lamellar texture of the [Alpha]-spherulites. In Β-spherulites, at the same shear strain, SFM observations reveal the presence of nanocracks perpendicular to the principal tensile strain axis, going through stacks of crystalline lamellae. Profuse local lamellar kinkings occur along the principal compressive strain axis and few nanocracks parallel to the molecular axis are seen in individual lamellae that lie along the shear direction. Neither particular preferred lamellar orientation nor localization of deformation within shear bands has been detected., INTRODUCTION The plastic deformation of semicrystalline polymers is of great importance to many technological processes such as uniaxial drawing of films, biaxial stretching and solid state forming (1). Because of [...]

The macroscopic stress-strain behavior of monoclinic polypropylene samples was investigated at 70 ° C under uniaxial tension and simple shear by means of a special videometric testing system that gives access to the constitutive equation of plastic behavior at constant strain rate up to large deformation. At several levels of plastic strain, the microstructural evolution of the material was characterized by means of X-ray scattering, densitometry and viscoelastic analysis. It appears that the strain hardening is high in tension, whereas it is nearly zero in shear. This behavior is associated with the development of a fiber texture in tension, which differs drastically from the planar crystalline texture developed in shear. Furthermore, it is shown that structural damage takes place as the plastic deformation proceeds in tension, while only little damage is recorded in shear. A viscoplastic model has been developed that specifically takes into account the various slip systems activated in the polypropylene crystallites and the elastic interactions of the lamellae through a self-consistent scheme. Simulations based on this model reproduce correctly the contrasting strain-hardening in tension and in shear and the different crystalline textures induced for these two loading paths., 1. INTRODUCTION Since efficient polymerization techniques were developed to control the branching and tacticity of polyolefins, numerous researchers have focused attention on their mechanical properties at large strains, particularly on [...]

The purpose of this study was to accumulate material data for use in a simulation of morphology and crystallization in quenched slabs of isotactic polypropylenes (i-PP's). The molecular weight effect on the crystallization kinetics of various i-PP's were studied using isothermal and nonisothermal experiments. An experimental setup was constructed to measure the spherulite growth rate of i-PP's using isothermal and nonisothermal melt crystallization experiments. The molecular weight effect on spherulite growth rate of i-PP's was determined. Molecular weight effect on nuclei concentrations as a function of temperature was determined from growth and crystallization rate constants. The morphology and crystallization in quenched slabs of i-PP's were determined from experiments and compared to computer simulations. The molecular weight effect on the degree of crystallinity and morphology was determined for i-PP during quenching., INTRODUCTION A great deal of work (1-3) has been done on quiescent crystallization of i-PP's including effects of nucleating agent, molecular weight, isotacticity, catalyst system, and filler. Numerous isothermal and [...]