Characterization of polypropylene–polyethylene blends by temperature rising elution and crystallization analysis fractionation (original) (raw)
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Polypropylene reactor blends: Composition evaluation by analytical TREF
Polymer Engineering & Science, 1999
The molecular structure of a polypropylene (PP) blend, of the type referred to commercially as "impact polypropylene copolymer" (IPC), was studied and a procedure 1.0 determine its main component composition developed. The constituent species of the whole IPC, PP and ethylene-propylene copolymers (EPC), were separated by step elution analytical Temperature-Rising Elution Fractionation (TREF). The corresponding fraction compositions were calculated as percent areas of the fractogram. Since the EPC elution signal overlaps that of the homopolymer, an independent determination of pure PP fractions has to be performed in order to subtract its effect from the IPC profile. Thermal and molecular analysis of the recovered fractions by Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC), and spectroscopic analysis by FTIR and 13C-NMR supported the necessary assumptions for a good estimation of the composition.
Polymers, 2017
A novel binary homogeneous catalyst system based on (I): rac-Me 2 Si(2-Me-4-PhIn) 2 ZrCl 2 and (II): (2-PhIn) 2 ZrCl 2 catalysts at various molar ratios was utilized for the synthesis of polypropylene (PP) reactor blends with bimodal molecular weight distribution (MWD). The results of gel permeation chromatography analyses revealed that the catalyst (I) was responsible for the production of i-PP with high molecular weight (MW) while the individual use of catalyst (II) led to the production of an elastomeric PP with relatively low MW. However, application of the binary catalyst system led to high MW bimodal MWD products being highly dependent on the catalysts' molar ratios. Increasing the molar ratio of catalyst (II) to catalyst (I) resulted in a notable enhancement of the products' complex viscosity due to the increased MW, a higher level of chains' entanglements and formation of amorphous blocks along the polymer chains. All products exhibited a single relaxation that shifted towards longer times upon changing the catalysts' molar ratios. Scanning electron microscopy results revealed that the fracture surface of the blends, synthesized by the binary catalyst system, became more heterogeneous in comparison with the products obtained by the individual use of the catalyst (I). The observed heterogeneity was found to increase by increasing the amount of catalyst (II). Such morphological change was further corroborated by the dynamic rheological data, indicating a promising correlation between the linear rheological results and the morphological features of the synthesized PP reactor blends.
Structural characterization of reactor blends of polypropylene and ethylene-propylene rubber
Journal of Applied Polymer Science, 2004
Blends of isotactic polypropylene (PP), ethylene-propylene rubber copolymer (EPR), and ethylene-propylene crystalline copolymer (EPC) can be produced through in situ polymerization processes directly in the reactor and blends with different structure and composition can be obtained. In this work we studied the structure of five reactor-made blends of PP, EPR, and EPC produced by a Ziegler-Natta catalyst system. The composition of EPR was related to the ratio between ethylene and propylene used in the copolymerization step. The ethylene content in the EPR was in the range of 50 -70 mol %. The crystallization behav-ior of PP and EPC in the blends was influenced by the presence of the rubber, and some specific interactions between the components could be established. By preparative temperature rising elution fractionation (P-TREF) analysis, the isolation and characterization of crystalline EPC fractions were made.
Properties of polyethylene-polypropylene blends
Journal of Materials Science, 1980
High-density polyethylene (PE)-isotactic polypropylene (PP) blends have been characterized by a number of techniques such as wide-angte X-ray scattering, differential scanning calorimetry, picnometry, swelling in n-hexane and finally stress-strain tensile elongation. All the measurements have been performed on cilindrical shaped specimens, obtained directly by extrusion. The specimens show a complete random orientation of the crystallites of both the components. No co-crystallization phenomenon are observed. The melting point of both PE and PP decreases slightly with increasing concentration of the second component. The fractional crystallinity of PE decreases and that of PP increases with respect to the corresponding homopolymer values with increase in the concentration of the companion polyolefin. Such an effect is related to morphological kinetic effects and to different rates of crystallization of the two components, during the non-isothermal crystallization process following extrusion. Young's modulus, E is proportional to the overall fractional crystallinity. The ultimate properties show a synergistic effect due to the strong interactions between the crystallites and their tie molecules of the twoPE and PP distinct phases. Finally, it is to be remarked that the results obtained in this paper, especially with respect to the ultimate properties, are quite different from those reported by other authors. This can be attributed to the different processing conditions used for obtaining the present blend specimens. Such conditions are certainly very important in determining particular blend morphologies which will determine in turn the properties of the analysed samples.
Polypropylene–polyethylene blend morphology controlled by time–temperature–miscibility
Polymer, 2000
Isotactic polypropylene (PP) has been blended with various types of polyethylene, high density (HDPE), low density (LDPE), linear low density (LLDPE), very low density (VLDPE) and ultra low density (ULDPE). Each blend contained 20% by mass PP. The blends were cooled from the melt to temperatures where PP could crystallise, but not the polyethylene. When the two polymers were immiscible, or immiscible at the crystallisation temperature where liquid-liquid phase separation occurred on cooling, then the two phases crystallised independently. Under these conditions the crystallisation rate (half-time) for PP was very similar to that of pure polypropylene. When the polymers were miscible, crystallisation of PP took place from a solution in the molten polyethylene. Under these conditions the crystallisation rate of PP was greatly decreased since it was in dilute solution. The significant change in rate of crystallisation of PP was a detection of miscibility. After PP had crystallised the blend was cooled to ambient temperature and the polyethylene quickly crystallised in the intervening spaces.
Macromolecular Reaction Engineering, 2015
Novel results on using mixtures of two external electron donors ''phenyltriethoxysilane (donor A)'' and ''cyclohexylmethyldimethoxysilane (donor C)'' in the synthesis of polypropylene/poly (ethylene-co-propylene) in-reactor blends were presented. Thermal gradient elution fractionation (TGEF) was carried out to separate crystallizable copolymer fractions from the blends. FTIR, DSC, DMTA, and SEM were used to analyze the microstructure of the blends and separated fractions. Although using donor A as pure decreased the catalyst activity and molecular weight, using ''donor A'' in combination with donor C had a synergistic effect on the molecular weight of polypropylene homopolymers and the blends. The glass transition temperature (T g) of the blend rubbery phase was the lowest in the case of the blend based on pure donor A because of formation of higher sequences of polyethylene and the T g increased with increasing donor C concentration. PP-PE copolymer concentration and impact strength were found to be higher in the case of the blend based on donor ratio of A/C: 75/25 than other blends.
Journal of Applied Polymer Science, 2001
Liquid-liquid (L-L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene-propylene rubber (EPR) blends obtained by melt extrusion were investigated by time-resolved light scattering (TRLS) and optical microscopy. L-L phase separation via spinodal decomposition (SD) was confirmed by TRLS data. After L-L phase separation at 250°C for various durations, blend samples were subjected to a temperature drop to 130°C for isothermal crystallization, and the effects of L-L phase separation on crystallization were investigated. Memory of the L-L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L-L phase-separated time at 250°C. Slow crystallization for the long L-L phase-separated time could be ascribed to decreasing chain mobility of PP with a decrease in the EPR component in the PP-rich region. The propylene-rich EPR exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing.
European Polymer Journal, 2003
Polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in situ blends of different composition were synthesized by spherical Ziegler-Natta catalyst, and were fractionated into three portions: the random copolymer (EPR), the block copolymer, and the iPP matrix. The EPR fraction was characterized by 13 C NMR, and the block copolymer fraction was characterized by crystalline segregation and differential scanning calorimetry analysis. The blends showed bi-phase structure with EPR existing in the dispersed phase. Increasing EPR in the blends resulted in increase of the number and diameter of the EPR particles, but there is an upper limit for the particle number. There were only highly irregular spherulites or tiny crystallites in the isothermal crystallized blends. The morphology of the impact fracture surfaces of the blends clearly showed that they were fractured in ductile fashion. There was strong dependence of impact strength of the blends on their morphology, and the sequence distributions of the EPR and segmented copolymer fractions also markedly influenced the mechanical properties.
Polymer-Plastics Technology and Engineering, 2017
A homogenous binary metallocene catalytic system comprising of isospecific rac-Me 2 Si(2-Me-4-Ph In) 2 ZrCl 2 (I) producing high molecular weight isotactic polypropylene and oscillating (2-Ph In) 2 ZrCl 2 (II) precursor producing low isotactic elastomer polypropylene at three varying molar ratios of two types of catalysts was used to synthesize polypropylene reactor blends. Dynamic mechanical thermal analysis and rheological properties along with molecular weight of synthesized polypropylene reactor blends were studied and correlations among these properties were established. It was found that molar ratio of catalysts is a significant factor in determination of molecular weight and its distribution. The produced polymers with unimodal molecular weight distribution showed intermediate modulus during dynamic mechanical thermal experiment, while the ones with bimodal molecular weight distribution exhibited a kind of phase separation at low temperature. Depending on strength of the developed structures, determined by the presence of interfacial connectors, the modulus could be adjusted. Origins of other types of relaxations and their differences for each type of the developed products were discussed in detail. From rheological results and particularly the relaxation curves, the characteristics of the chain structure of the synthesized reactor blends could be resolved. It was revealed that one of the synthesized polymers had long chain branches unlike the rest of the samples having linear chain structure.
Polymer, 2001
A polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in-situ blend synthesized by spherical Ziegler±Natta catalyst was fractionated by temperature-gradient extraction fractionation. The fractions were characterized using FTIR, 13 C NMR, DSC and WAXD. The in-situ blend was found to contain mainly three portions: an ethylene±propylene random copolymer, a series of segmented copolymer with PE and PP segments of different length, and propylene homopolymer. The impact strength of in-situ blends of different structural heterogeneity was measured, and the results show that increasing the amount of segmented copolymer has a positive effect on the impact strength. The segmented copolymer portion alone is found to increase the impact strength at room temperature greatly, while the low temperature impact strength can be markedly enhanced only when random copolymer coexists with the segmented copolymer. q