Polyethylene structural heterogeneity by thermal and rheological techniques

Westphal, Stanley P.; Ling, T.K.; Woo, Lecon

doi:10.1016/0040-6031(95)02614-2

Cited by 8 publications

(4 citation statements)

References 3 publications

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“…Polymer meVLD‐18, produced with a CGC catalyst, displayed the highest intensity value of the curves, as shown in Figure 3. We suggest that this spectral narrowing of the tan δ peak of the metallocene copolymers compared to the ZN copolymers was an indication that the local environment near the branch point, which gave rise to the amorphous phase, was becoming more homogeneous 17, 18. For more branched copolymers (VLDPEs), the location and the size of the β relaxation peak displayed the differences in SCBDs between metallocene and ZN copolymers 17.…”

Section: Resultsmentioning

confidence: 86%

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Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Starck¹,

Malmberg²,

Löfgren³

2001

J of Applied Polymer Sci

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ABSTRACT:The relationship between the molecular structure and the thermal and rheological behaviors of metallocene-and Ziegler-Natta (ZN)-catalyzed ethylene copolymers and high-density polyethylenes was studied. Of special interest in this work were the differences and similarities of the metallocene-catalyzed (homogeneous) polymers with conventional coordination-catalyzed (heterogeneous) polyethylenes and low-density polyethylenes. The short-chain branching distribution was analyzed with stepwise crystallization by differential scanning calorimetry and by dynamic mechanical analysis. The metallocene copolymers exhibited much more effective comonomer incorporation in the chain than the ZN copolymers; they also exhibited narrower lamellar thickness distributions. Homogeneous, vanadium-catalyzed ZN copolymers displayed a very similar comonomer incorporation to metallocene copolymers at the same density level. The small amplitude rheological measurements revealed the expected trend of increasing viscosity with weight-average molecular weight and shear-thinning tendency with polydispersity for the heterogeneous linear low-density polyethylene and very-low-density polyethylene resins. The high activation energy values (34 -53 kJ/mol) and elevated elasticity found for some of our experimental metallocene polymers suggest the presence of long-chain branching in these polymers. This was also supported by the comparison of the relationship between low shear rate viscosity and molecular weight.

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Section: Resultsmentioning

confidence: 86%

“…Normally, three relaxations are observed, identified as α, β, and γ in order of decreasing temperature. The β‐transitions occurring between about −40 and 20°C17–20 have yielded the best information for studies of branch distribution and branch‐type influence.…”

Section: Introductionmentioning

confidence: 99%

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Starck¹,

Malmberg²,

Löfgren³

2001

J of Applied Polymer Sci

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“…[11][12][13] High and low molecular weights of high-density polyethylene (HDPE) made by metallocene catalyst are found to be miscible themselves by rheological measurements although they are different in molecular weight. 14,15 Blends of HDPE and LLDPE show liquid-liquid phase separation at about 125 and 170°C according to morphological study.…”

Section: Introductionmentioning

confidence: 99%

Blends of ethylene 1-octene copolymer synthesized by Ziegler-Natta and metallocene catalysts. I. Thermal and mechanical properties

Rana¹,

Cho²,

Woo³

et al. 1999

J. Appl. Polym. Sci.

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ABSTRACT:The thermal, viscoelastic, and mechanical behaviors of three binary blends of ethylene 1-octene copolymer (EOC) regarding the melt index and density, one component made by Ziegler-Natta (FA and RF in abbreviation of the commercial name) and the other by metallocene catalysts (FM, EN and PL in abbreviation of the commercial name), have been investigated to understand molecular mechanism of the blends. Thermal studies reveal that the two constituents in the three blends exclude one another during crystallization, implying a phase separation. Viscoelastic properties show a single ␤ or ␥ transition in all the compositions, suggesting a miscibility in the amorphous region. The tensile modulus, yield stress, maximum strength at break, and elongation at break follow the rule of mixtures if the comonomer content does not differ too much. Otherwise, the modulus and yield stress are negatively deviated, whereas elongation at break is positively deviated from the weight-average value. The tensile properties of film at yield and break in the machine direction is increased with an addition of FM in the FA ϩ FM blend. Although all three blends form separate crystals in the crystalline state, a correlation exists between the mechanical properties and the density of EOCs.

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“…The b-transition in PE, observed between þ 10 and 2408C, is attributed to the amorphous phase. Furthermore some recent papers (26)(27)(28)(29) have demonstrated, that the intensity of the b-transition is strongly related to the branch level and to the degree of crystallinity, since for linear ethylene-a-olefin copolymers, the b peak decreases with increasing comonomer content. Especially for polymers cooled slowly down from the melt, the disordered interlamellar thickness may strongly affect the b-transition (24).…”

Section: Starck and Lö Fgren 580mentioning

confidence: 99%

Thermal studies on ethylene–vinylcyclohexane copolymers prepared with bis-indenyl type metallocene catalyst systems

Starck¹,

Löfgren²

2002

Journal of Macromolecular Science, Part B

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Ethylene -vinylcyclohexane copolymers (EVCH) were synthesized with unsubstituted and substituted bis-indenyl type metallocene catalysts and their thermal and dynamic mechanical behavior was studied and compared to a series of metallocene catalyzed ethylene-1-hexene (EH) and ethylene-1hexadecene (EHD) copolymers. Increasing comonomer incorporation in the chain decreased the melting point, the level of crystallinity, and the density of all copolymers, but the bulky size of the vinylcyclohexane (VCH) group made this decrease very insignificant for the EVCH copolymers. The influence of the VCH group was also noticed in the loss tangent curves by dynamic mechanical analysis as a very insignificant shift of the b-transition to lower temperatures at increasing comonomer content, a behavior quite opposite to the behavior of the EH and EHD copolymers. The storage modulus curves explained that the stiffness properties of the EVCH copolymers are as good or better than those of the EH and EHD copolymers at the same comonomer level. The intensities of the maximum in the loss tangent curves indicate that EVCH copolymers may have good impact properties. Fractionation studies by differential scanning calorimetry (DSC) using a self-nucleation/annealing (SSA) procedure confirmed a broadening of the lamellar thickness distribution as the amount of comonomer increased. Self-nucleation/annealing curves of 579

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Polyethylene structural heterogeneity by thermal and rheological techniques

Cited by 8 publications

References 3 publications

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Blends of ethylene 1-octene copolymer synthesized by Ziegler-Natta and metallocene catalysts. I. Thermal and mechanical properties

Thermal studies on ethylene–vinylcyclohexane copolymers prepared with bis-indenyl type metallocene catalyst systems

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