Composition Of Ethylene-propylene Copolymers Research Articles

Rapid characterization of high-impact ethylene–propylene copolymer composition by crystallization extraction separation: comparability to standard separation methods

High-impact copolymers of propylene and ethylene are complex materials with several components and at least two different phases, a crystalline polypropylene (PP) matrix and a predominantly amorphous ethylene–propylene copolymer (EPC) normally present as disperse particles. Next to overall composition analysis and morphology studies, fractionation into crystalline and amorphous components followed by further analysis of those components is the most important characterization technique for this technically very relevant class of copolymers. This process, involving separation into xylene cold-soluble (XCS) and insoluble fractions and follow-up determination of intrinsic viscosities (IV) as well as ethylene (C2) content is, however, tedious and time-consuming. A far more rapid approach is presented here through the separation of the amorphous and crystalline fractions of PP in 1,2,4-trichlorobenzene (TCB) using the crystallization extraction technique and the Crystex QC instrument. As the standard methods and Crystex technique are using different solvents (xylene and decalin versus TCB), correlations need to be established in order to be able to compare the results. Based on nine structurally very different polymers, respective correlation curves were developed and predictions for 95% confidence intervals were calculated statistically. In addition, these correlation curves were validated by testing over 100 different PP samples covering a broad range of all tested characteristics. The results show agreement and comparability between the traditional test methods techniques and the Crystex technique inside statistically calculated prediction intervals at 95% over a broad range of all tested characteristics (XCS, C2 and IV).

Microstructural characterization of semicrystalline copolymers by Raman spectroscopy

We employ Raman spectroscopy to characterize several microstructural aspects of a family of ethylene-propylene copolymers (EPC). Focus is made on the simultaneous analysis of crystallinity and chemical composition. A curve fitting procedure is used to isolate Raman bands ascribed to polypropylene chains in the crystal lattice from contributions of the amorphous phase. Crystal contents of EPC calculated on this basis are in the range 10–34 wt%, in good agreement with independent wide angle x-ray diffraction and differential scanning calorimetry measurements. Besides, Raman spectroscopy captures in some of the samples a mixed crystalline structure with both, polyethylene and polypropylene crystals, indicating a distinctive molecular architecture. The chemical composition of EPC is obtained from Raman spectra in the melt state to decouple peaks characteristics of the crystal lattice from fundamental vibrational modes of the polymer chain. EPC present ethylene contents in the range 5–26 mol%, in good agreement with parallel results from 13C nuclear magnetic resonance analysis. Remarkably, a rather complete characterization of EPC can be achieved on the base of a single experimental technique.

Phase interactions and structure evolution of heterophasic ethylene–propylene copolymers as a function of system composition

AbstractHeterophasic copolymers comprised of polypropylene (PP) matrix and ethylene–propylene copolymer (EPC) dispersed phase were investigated with respect to the dispersed phase composition, i.e., ethylene/propylene ratio. The rheological properties, morphology, as well as thermal and mechanical relaxation behavior were studied to describe the structure evolution and phase interactions between the components of the PP copolymers. Decrease of the ethylene content of the EPC leads to a higher matrix‐dispersed phase compatibility, as evaluated by the shift of the glass transition temperatures of EPC and PP towards each other. At ethylene content of EPC of 17 wt %, the glass transition temperatures of the both phases merged into a joint relaxation. The effect of the EPC composition on the internal structure of the dispersed domains and on the morphology development of the heterophasic copolymers was demonstrated. Decreasing ethylene content was found to induce a refinement of the dispersed phase with several orders of magnitude down to 0.18 μm for propylene‐rich EPC. Optical microscopy observations showed that the dispersed propylene‐rich phase is preferably rejected at the interlamellar regions of the spherulites and/or at the interspherulitic regions, while the ethylene‐rich domains are engulfed within the PP spherulites. Both of these processes impose an additional energetic barrier and influence the spherulite growth rate of the heterophasic materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2825–2837, 2006

Determination of the composition of ethylene-propylene copolymers by pyrolytic gas chromatography

Methods were developed for determining the composition of ethylene-propylene copolymers from data of pyrolytic capillary reaction gas chromatography with a relative standard deviation s r = 0·002−0·02 and a limit of detection of comonometer content of 0·3−1·0%.

Investigation of the oscillating flow phenomenon in high density polyethylene

The nature and causes of the oscillating flow phenomenon in high density polyethylene are examined in this report. Empirical equations are developed describing the onset (both stress, SSOF, and rate, SROF) of oscillating flow in terms of molecular structure. The SSOF is not constant, but is found to vary slightly with the molecular weight distribution. The SROF is shown to be predictable in terms of molecular weight distribution. The physics of the oscillations is critically examined, and the simple model of Okubo and Hori describing these oscillations has been successfully tested. The model involves alternating compression of the polymer in the capillary rheometer barrel and decompression after a material breakdown in the die, in which flow from the capillary exceeds that expected from the rheometer output for an incompressible material. The point for initiation for oscillating flow is positively identified to be in the die, not, as some have suggested, in the die entrance region. Examination of the critical shear stress for random ethylene–propylene rubbers suggests that the reason why linear polyethylene appears unique is that the critical stress may be unattainable in other polymers and that the magnitude of the effect tends toward being vanishingly small. A critical shear strain criterion seems to describe the variations in critical stress with ethylene–propylene copolymer composition, but the critical strain criterion appears to be an oversimplification in general.

The effect of catalytic system on the composition of ethylene-propylene copolymers

Copolymers with a relatively narrow composition distribution (less than 5% deviation from the average) can be produced in the ethylene copolymerization with propylene over catalytic complexes based on diethyl-, sesquiethyl- and di-isobutyl-aluminium chlorides with VOCl 3 or VCl 4, prepared in the presence of the monomers. Copolymers with an irregular composition will be obtained when the alkyl aluminium chlorides are replaced by tri-isobutyl aluminium under the same conditions. The method of preparation of the catalytic complex (with or without the monomers present) i.e from 1 2 ( C 2 H 5) Al 2Cl 3&.zsbnd;VOCl 3 , does not affect the distribution range of composition in the copolymers, while other systems, such as (C 2H 5) 2) AlClVOCl 3, or iso-(C 4H 9) 2AlCl 3VOCl 3, will give a much greater composition irregularity when the complex is prepared without the monomers.

Ternary copolymerization of ethylene, propylene and hex-1-ene

The ternary copolymerization of ethylene, propylene and hex-1-ene on the catalyst system vanadium triacetylacetonate-di-isobutylaluminium chloride has been investigated. The addition of hex-1-ene to the composition of the ethylene-propylene copolymer leads to a lower yield and to a change in the composition of the ternary copolymer. Some kinetics features of the process have been investigated. When hex-1-ene is added to the liquid phase, the rate of the process and the MWD of the resulting copolymer are bimodal in character. The addition of from 3 to 12 mole % hex-1-ene units to the ethylene-propylene elastomer composition enhances some properties of the elastomer. It was shown in [1–6] that the addition of small amounts of but-1-ene to the composition of ethylenepropylene copolymers markedly improves their mechanical properties. In the present instance hex-1-ene is used as the third comonomer, and some features of the ternary copolymerization of ethylene, propylene and hex-1-ene have been investigated.

Relation between Glass Transition Temperature and Composition of Ethylene Propylene Copolymers

Abstract Vulcanizate properties and processability of ethylene propylene copolymers (EPR) are known to be sensitive to variations in polymer microstructure. A basic understanding of the practical performance of EPR requires a knowledge of this microstructure and means for evaluating it. This study was concerned with determining the utility of a previously proposed method for quantitative analysis of microstructure in EPR. The influence of crystallinity effects on the glass transition temperature (Tg) of this polymer was also examined. A major objective of this work was to determine whether, as suggested by literature data, a minimum can exist in the relation between Tg and composition of EPR. If so, it would seriously impair the proposed method for quantitative microstructure analysis. Data relating Tg and composition were obtained by differential thermal analysis (DTA) and infrared analysis (IR) of EPR fractions obtained by gradient elution fractionation. An apparent minimum was observed in the curve defined by this data. Analysis of this minimum suggests that it is due to nonrandom microstructure. In the samples examined, it was evident in the 25 to 40 mole per cent propylene range. Low temperature annealing studies indicate that the minimum is not from crystallinity although there is some indication that small amounts of crystallinity can be induced in these systems by annealing. Analysis of the main Tg interval in a variety of EPR samples showed that three types can be distinguished. These appear to correspond to random, stereoblock, and random-block polymers. Further, a main Tg near −58° C. was observed over the 20 to 74 mole per cent propylene range in some nonrandom systems. Because of this, it is concluded that the proposed system for quantitative microstructure analysis in EPR is generally inapplicable to nonrandom systems. However, the data indicate that useful information about EPR microstructure can be obtained by the techniques described.

Determination of Ethylene-Propylene Copolymer Composition by Infrared Analysis

Determination of Ethylene-Propylene Copolymer Composition by Infrared Analysis

Determination of Ethylene-Propylene Copolymer Composition by Infrared Analysis

Determination of Ethylene-Propylene Copolymer Composition by Infrared Analysis