Influence of structural and morphological factors on the mechanical properties of the polyethylenes

Popli, R.; Mandelkern, L.

doi:10.1002/polb.1987.090250301

Cited by 347 publications

(263 citation statements)

References 108 publications

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“…melt-spinning or fibres prepared from semi-dilute polymer solutions) and the process variables, as extensively described in the literature [27,29,[30][31][32][33][34][35]. During cold-drawing the lamellar structures are transformed into fibrillar structures by rotation/translation of (parts of) lamellae and/or by local melting of the lamellae due to local high stress concentrations.…”

Section: Resultsmentioning

confidence: 99%

Gel-spun polyethylene fibres

et al. 1988

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In addition to spinning temperature, spinline stretching and spinning speed, the properties of gel-spun polyethylene fibres hot-drawn to the maximum draw ratio also depend on the polymer concentration, molecular weight and molecular weight distribution. Reducing the polymer concentration reduces the number of entanglements, and fibres with better properties are obtained. However, a minimum number of entanglements is necessary to ensure sufficient coherence of the entanglement network and avoid premature breakage of the spinline. Therefore, an optimal concentration exists which is shown to shift to a lower value for polyethylene with a smaller molecular weight distribution. Fibres with a tensile strength exceeding 6 GPa and a modulus of about 160GPa can be prepared as long as spinline stretching is avoided. A smaller molecular weight distribution enhances the deteriorating effect of spinline stretching. The difference in morphologies for as-spun fibres prepared from different gel compositions and under different spinning conditions also strongly affects the cold-drawing behaviour of the extracted as-spun fibres.

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Section: Resultsmentioning

confidence: 99%

Gel-spun polyethylene fibres

et al. 1988

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“…The observed differences were attributed to level of crystallinity. 20 The effect of cooling rate was only observed indirectly in ref 19 since they used tensile experiments, where brittle failure was observed for the lower molecular weight, slowly cooled samples. In macroscopic tensile behavior localization and failure phenomena cannot be overcome as in the compressive measurements of this study.…”

Section: Strain Hardening Petmentioning

confidence: 99%

Intrinsic Deformation Behavior of Semicrystalline Polymers

et al. 2004

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The influence of crystallinity and lamellar thickness on the intrinsic deformation behavior of a number of semicrystalline polymers is studied: a poly(ethylene terephthalate) and two different molecular weight grades of polyethylene and polypropylene. The crystallinity and lamellar thickness are altered by varying the rate of crystallization from the melt and by cold crystallization (annealing) at elevated temperatures above T g but below the melting point. Crystallinity and lamellar thickness are determined by wide-angle X-ray diffraction and small-angle X-ray scattering measurements. Uniaxial compression tests are performed to obtain the large strain intrinsic deformation behavior, e.g., yield stress, strain softening, and strain hardening modulus. The yield stress is found to be proportional to lamellar thickness, whereas the strain hardening modulus is shown not to depend on crystallinity or lamellar thickness. Over the strain range experimentally covered, the strain hardening modulus appears to be well described by a simple neo-Hookean relation and appears to be related to the chain entanglement density. An affirmation for this relation arises from the observation that slowly melt crystallized samples exhibit a lower strain hardening, resulting from a lower chain entanglement density, which is expected to be caused by reeling in of the molecular chains in such a slow crystallization process. The similarity in the results observed on all polymers tested supports the conclusion that the crystalline phase does not contribute to strain hardening, which is primary controlled by the chain entanglement density.

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“…A similar decrease of τ was observed in simulations of n-alkanes 43 and experimentally it has been found that ultimate tensile strength of certain polymeric systems, such as amorphous polyethylene, decreases with increasing molecular weight. 63 Such a decrease in τ is non-trivial, since one expects longer chains to exhibit more chain "entanglement". Such a view neglects the importance of packing, however, which is crucially important in the low temperature glass regime.…”

Section: Calculation Of τmentioning

confidence: 99%

The effect of nanoparticle shape on polymer‐nanocomposite rheology and tensile strength

Knauert

Douglas

Starr

2007

J Polym Sci B Polym Phys

213

158

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Nanoparticles can influence the properties of polymer materials by a variety of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet nanocomposites in mind, we investigate how particle shape influences the melt shear viscosity η and the tensile strength τ , which we determine via molecular dynamics simulations. Our simulations of compact (icosahedral), tube or rod-like, and sheet-like model nanoparticles, all at a volume fraction φ ≈ 0.05, indicate an order of magnitude increase in the viscosity η relative to the pure melt. This finding evidently can not be explained by continuum hydrodynamics and we provide evidence that the η increase in our model nanocomposites has its origin in chain bridging between the nanoparticles. We find that this increase is the largest for the rod-like nanoparticles and least for the sheet-like nanoparticles. Curiously, the enhancements of η and τ exhibit opposite trends with increasing chain length N and with particle shape anisotropy. Evidently, the concept of bridging chains alone cannot account for the increase in τ and we suggest that the deformability or flexibility of the sheet nanoparticles contributes to nanocomposite strength and toughness by reducing the relative value of the Poisson ratio of the composite. The molecular dynamics simulations in the present work focus on the reference case where the modification of the melt structure associated with glass-formation and entanglement interactions should not be an issue. Since many applications require good particle dispersion, we also focus on the case where the polymer-particle interactions favor nanoparticle dispersion. Our simulations point to a substantial contribution of nanoparticle shape to both mechanical and processing properties of polymer nanocomposites.

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Influence of structural and morphological factors on the mechanical properties of the polyethylenes

Cited by 347 publications

References 108 publications

Gel-spun polyethylene fibres

Gel-spun polyethylene fibres

Intrinsic Deformation Behavior of Semicrystalline Polymers

The effect of nanoparticle shape on polymer‐nanocomposite rheology and tensile strength

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