Fractionation of Polypropylene Impact Copolymers Using Temperature Rising Elution Fractionation (TREF) (original) (raw)
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Impact polypropylene copolymers: fractionation and structural characterization
Polymer, 1993
Impact polypropylene copolymers may be produced in a two-reactor system to yield a blend of homopolymer with an ethylene-propylene rubber (EPR). The polypropylene homopolymer, which is itself brittle and has low impact strength, is markedly toughened by the presence of the EPR. The rubber-like EPR exists as a phase-segregated discrete particle in a continuous matrix of the hard phase. The molecular structure analysis of the resulting complex mixture is a formidable task. The purpose of this paper is to describe a preparative and an analytical temperature-rising elution fractionation (t.r.e.f.) technique as the primary tools to separate and characterize a commercial impact copolymer. These techniques permit the isolation and subsequent characterization of the components of the impact copolymer by ancillary techniques, primarily 13C nuclear magnetic resonance and differential scanning calorimetry. These techniques were applied to the structural analysis of a commercial impact-grade polypropylene with a melt flow rate of 6. It was found that this impact copolymer was composed of about 75wt% of isotactic polypropylene, about 17wt% of a highly non-crystalline EPR and about 8 wt% of semicrystalline ethylene-propylene copolymers. A major component of the semicrystalline ethylene-propylene copolymers was an ethylene-rich copolymer containing between 0 and 8 wt% of propylene comonomer. The separate characterization of the components of the impact copolymer gives insight into the chemical synthesis process used to produce these copolymers. Further, it permits one to gain a better understanding of the location and function of each of the components in the complex mixture.
Degradation of polypropylene impact-copolymer during processing
Polymer Degradation and Stability, 2008
The effect of processing on molecular structure and properties of polypropylene impact-copolymer (ICPP) was investigated. It was confirmed that multiple extrusions induced changes in molecular weight resulting in increased MFI and decreased long-term thermooxidation stability. In terms of mechanical properties only impact strength well reflected the processing history. Tensile and flexural properties remained almost unchanged. The sizes of rubbery domains observed by SEM exhibited only minimum changes. The results of SSA and TREF techniques provided further data helping to elucidate the phenomena in rubbery phase. Based on indirect indications one could conclude that while typical polypropylene degradation resulting in chain backbone cleavage took place in the PP homopolymer phase, the rubbery phase containing EPR and PE homopolymer underwent a certain extent of crosslinking.
Journal of Applied Polymer Science, 2012
Four different grades of commercial, highimpact polypropylene (hiPP) were fractionated by temperature-gradient extraction fractionation, and the chain structure and melting behavior of the fractions were studied by Fourier transform infrared spectroscopy and differential scanning calorimetry. Furthermore, the morphology of the disperse phase in the resins was characterized by scanning electron microscopy of the microtome-cut etched and original samples. The results show that there was a strong relation between the chain structure, content, and distribution of the dispersed phase and the mechanical properties of hiPP. These parameters of the elastomeric phase are really critical in reaching the best rigidity-impact balance in hiPP. V
Mechanical and morphological characterization of polypropylene toughened with olefinic elastomer
Materials Research-ibero-american Journal of Materials, 2000
The effect of incorporating (C2-C8) ethylene-octene elastomer on the mechanical properties and morphology of polypropylene copolymers has been investigated employing two types of PP copolymer, with and without nucleating agent. The results were compared to the ones presented by a commercial PP heterophase (reactor impact modified PP/EPR). The addition of the elastomer increases the toughness of the blends but reduces their stiffness. PP blends in the low elastomer content region (< 20%) show low values of the Izod impact strength and both, elastomer content and impact strength, are directly proportional to the area under the β damping peak or its maximum intensity of the elastomer. The morphology is a continuous pattern of segregate elastomeric particles with average particle size in the range of 0.27 µm to 0.39 µm. The average particle size and particle size distribution plotted in log-normal distribution curves, increases slightly with the increase in the elastomer content. The reactor modified PP heterophase has a broader particle size distribution and an average particle size of 0.56 µm, at the lower limit but inside the range for good impact performance, as observed.
Macromolecular Symposia, 2017
The role of rubber particle size, À distribution, and the constitutive behaviour of the isotactic Polypropylene matrix has been studied by combining the Lazerri-Dompas energy criterion for cavitation and the Van der Sanden, Meier, Tervoort ligament model, adapted for impact conditions. It is concluded that optimising the morphology offers great potential to achieve ultimate properties with far less rubber and hence achieve a superior Stiffness-Toughness-Processing balance.
The present work was done to improve the impact property of isotactic polypropylene (PP), especially at low temperatures, by incorporating ethylene propylene diene monomers (EPDM). This was done by ensuring compatibility between the two polymers with phase modifiers polyethylene grafted with maleic an-hydride (PEg -MA) and initiator dicumyl peroxide (DCP). In addition, attempts were also made to understand the fundamentals of impact toughening as well as fracture toughness, and to correlate the results with that of morphological evidences obtained from scanning electron microscopy (SEM) and X-ray dif-fraction (XRD) methods. Varying the ratios of all blend composition , mechanical properties were studied. It was observed that as the rubber fraction increased, the impact property as well as fracture toughness increased. All these tests also showed promising results when PEg -MA was added, leading to more improvement in all the mechanical properties including increase in crystallite size. It had shown plasticization effect on the compositions , which could be further confirmed by differential scanning calorimetry (DSC) compared to the uncompatibilized ones. But when DCP was added, it behaved like an initiator which directly reacted with the PP matrix, decreasing the molecular weight of the blend with decreasing size of the crystallites.
Macromolecular Symposia, 2013
SummaryHeterophasic poly(propylene) copolymers obtained by sequential polymerization are multi‐component products formed by a crystalline matrix of poly(propylene) and an ethylene‐propylene rubber phase. Some crystalline polyethylene and poly(ethylene‐co‐propylene) are formed in the rubber synthesis step by copolymerization of ethylene and propylene. These multi‐component systems present a complicated microstructure and heterophasic morphology. In this study, two heterophasic copolymers with the same total amount of rubber but different composition and molecular weight, were thoroughly analyzed. The morphology was evaluated by SEM and AFM techniques. The complexity of the system required some attention in the fractionation methodology to perform an accurate interpretation of results and different methodologies of fractionation, especially for obtaining PE fractions as free of PP as possible, were performed in order to better characterize the crystalline polyethylene fractions in the...
Journal of Applied Polymer Science, 2006
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
Journal of Applied Polymer Science, 2012
In this work, composition effects on interfacial tension and morphology of binary polyolefin blends were studied using rheology and electron microscopy. The amount of dispersed phase (5-30 wt %) and its type [ethylene-octene copolymer, linear lowdensity polyethylene (LLDPE), and high-density polyethylene] was varied, and the influence of different matrix materials was also studied by using a polypropylene homopolymer and a ethylene-propylene (EP) random copolymer. The particle size distribution of the blends was determined using micrographs from transmission electron microscopy (TEM). A clear matrix effect on the flow behavior could be found from the viscosity curves of the blends. Analyzing the viscosity of the blends applying the logarithmic mixing rule indicated a partial miscibility of the EP random copolymer with low amounts of the LLDPE in the melt. Micrographs from TEM also showed a clear difference in morphology if the base polymer is changed, with PE lamellae growing out of the inclusions or being present directly embedded in the matrix. To verify these findings, the interfacial tension was determined. The applicability of Palierne's emulsion model was found to be limited for such complex systems, whereas Gramespacher-Meissner analysis led to interfacial tensions comparable with those already reported in the literature. The improved compatibility when changing the matrix polymer from the homopolymer to the random copolymer allows the development of multiphase materials with finer phase structure, which will also result in improved mechanical and optical performance. V