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- Andersson, Mattias, 1985, et al.
(författare)
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Invariant Dielectric Strength upon Addition of Low Amounts of HDPE to LDPE
- 2016
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; 2016-December, s. 711-714
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Konferensbidrag (refereegranskat)abstract
- Blending of polyethylenes permits to combine the superior mechanical properties of high-density material with the higher purity that is associated with low-density resins. Mixing different polyethylene architectures offers a lot of advantages, but for electrical applications it is important that there is no detrimental effect on the resulting dielectric strength. Here, the nanostructure of crosslinked blends that comprise low-and high-density polyethylene (LDPE and HDPE) is explored. Despite the presence of higher-melting lamellae the formation of electrical trees under alternating current (AC) conditions is found to be invariant for the investigated HDPE content of 1 to 10 wt%. This observation suggests that the use of polyethylene blends is feasible for AC electrical applications.
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| 2. |
- Gaska, Karolina, 1986, et al.
(författare)
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Mechanical Behavior of Melt‐Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites
- 2020
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of novel low percolation melt-mixed 3D hierarchical graphene/polypropylene nanocomposites are analyzed in this study. The analysis spans a broad range of techniques and time scales, from impact to tensile, dynamic mechanical behavior, and creep. The applicability of the time–temperature superposition principle and its limitations in the construction of the master curve for the isotactic polypropylene (iPP)-based graphene nanocomposites has been verified and presented. The Williams–Landel–Ferry method has been used to evaluate the dynamics and also Cole–Cole curves were presented to verify the thermorheological character of the nanocomposites. Short term (quasi-static) tensile tests, creep, and impact strength measurements were used to evaluate the load transfer efficiency. A significant increase of Young’s modulus with increasing filler content indicates reasonably good dispersion and adhesion between the iPP and the filler. The Young’s modulus results were compared with predicted modulus values using Halpin–Tsai model. An increase in brittleness resulting in lower impact strength values has also been recorded.
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| 6. |
- Kádár, Roland, 1982, et al.
(författare)
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Nonlinear “oddities” at the percolation of 3D hierarchical graphene polymer nanocomposites
- 2020
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 59:5, s. 333-347
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear rheology of a novel 3D hierarchical graphene polymer nanocomposites was investigated in this study. Based on an isotactic polypropylene, the nanocomposites were prepared using simple melt mixing, which is an industrially relevant and scalable technique. The novel nanocomposites stand out as having an electrical percolation threshold (≈0.94 wt%) comparable to solution mixing graphene-based polymer nanocomposites. Their nonlinear flow behavior was investigated in oscillatory shear via Fourier-transform (FT) rheology and Chebyshev polynomial decomposition. It was shown that in addition to an increase in the magnitude of nonlinearities with filler concentration, the electrical percolation threshold corresponds to a unique nonlinear rheological signature. Thus, in dynamic strain sweep tests, the nonlinearities are dependent on the applied angular frequency, potentially detecting the emergence of a weakly connected network that is being disrupted by the flow. This is valid for both the third relative higher harmonic from Fourier-transform rheology, I3/1, as well as the third relative viscous, v3/1, Chebyshev coefficient. The angular frequency dependency comprised non-quadratic scaling in I3/1 with the applied strain amplitude and a sign change in v3/1. The development of the nonlinear signatures was monitored up to concentrations in the conductor region to reveal the influence of a more robust percolated network.
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| 7. |
- Mitchell, Geoffrey R., et al.
(författare)
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New Tools for Understanding Complex Polymer Behaviour
- 2017
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Ingår i: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 12, s. 280-290
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Tidskriftsartikel (refereegranskat)abstract
- The process of manufacturing with polymers usually involves shaping in the melt followed by a transition to the solid to preserve that shape and provide the required mechanical properties. The development of an understanding of those transitions is critical to the optimisation of materials and manufacturing technology. For synthetic polymers there are three key length scales in any phase transition such as crystallisation: the first involves the thin (?10 nm) lamellar crystals, the second is the crystal planes in the unit cell (?1 nm) and the third the regular local chain conformation (?0.1 nm). We are using the extended Q range available with NIMROD at the ISIS Facility in the UK to obtain neutron scattering data which follows the transformation pathways of these three length scales simultaneously. We are using computational modelling procedures to analyse these data to develop a firm understanding of the multiscale processes involved in crystallisation. This paper describes the methodology and some of the experimental challenges using data drawn from this study. This work is part of the FCT funded programme UC4EP.
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