| 1. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Byproduct-free curing of a highly insulating polyethylene copolymer blend: An alternative to peroxide crosslinking
- 2018
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 6:42, s. 11292-11302
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct-current (HVDC) cables are a critical component of tomorrow's power grids that seamlessly integrate renewable sources of energy. The most advanced power cable technology uses crosslinked polyethylene (XLPE) insulation, which is produced by peroxide crosslinking of low-density polyethylene (LDPE). Peroxide crosslinking gives rise to hazardous byproducts that compromise the initially excellent purity and cleanliness of LDPE, and hence increase the electrical conductivity of the insulation material. Therefore, a byproduct-free curing process, which maintains the processing advantages and high electrical resistivity of LDPE, is in high demand. Here, we demonstrate a viable alternative to peroxide crosslinking that fulfils these requirements. Click chemistry reactions between two polyethylene copolymers allow the design of a curing process that is additive-free and does not result in the release of any byproducts. The thermoplastic copolymer blend offers a broad processing window up to 140 °C, where compounding and shaping can be carried out without curing. At more elevated temperatures, epoxy and acrylic acid functional groups rapidly react without byproduct formation to form an infusible network. Strikingly, the crosslinked copolymer blend exhibits a very low direct-current (DC) electrical conductivity of 2 × 10-16 S cm-1 at a typical cable operating temperature of 70 °C, which is on par with values measured for both ultra-clean LDPE and commercial XLPE. Hence, the use of polyethylene copolymer blends opens up the possibility to replace peroxide crosslinking with click chemistry type reactions, which may considerably expand the versatility of the most common type of plastic used today.
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| 2. |
- Andersson, Mattias, 1985, et al.
(författare)
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Additive-like amounts of HDPE prevent creep of molten LDPE: Phase-behavior and thermo-mechanical properties of a melt-miscible blend
- 2017
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Ingår i: Journal of Polymer Science, Part B: Polymer Physics. - : Wiley. - 1099-0488 .- 0887-6266. ; 55:2, s. 146-156
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Tidskriftsartikel (refereegranskat)abstract
- Low-density polyethylene (LDPE) is the preferred type of polyolefin for many medical and electrical applications because of its superior purity and cleanliness. However, the inferior thermo-mechanical properties as compared to, for example, high-density polyethylene (HDPE), which arise because of the lower melting temperature of LDPE, constitute a significant drawback. Here, we demonstrate that the addition of minute amounts of HDPE to a LDPE resin considerably improves the mechanical integrity above the melting temperature of LDPE. A combination of dynamic mechanical analysis and creep experiments reveals that the addition of as little as 1 to 2 wt% HDPE leads to complete form stability above the melting temperature of LDPE. The investigated LDPE/HDPE blend is found to be miscible in the melt, which facilitates the formation of a solid-state microstructure that features a fine distribution of HDPE-rich lamellae. The absence of creep above the melting temperature of LDPE is rationalized with the presence of tie chains and trapped entanglements that connect the few remaining crystallites.
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| 3. |
- Andersson, Mattias, 1985, et al.
(författare)
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Highly Insulating Polyethylene Blends for High-Voltage Direct-Current Power Cables
- 2017
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Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 6:2, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- The insulation of state-of-the-art extruded high-voltage direct-current (HVDC) power cables is composed of cross-linked low-density polyethylene. Driven by the search for sustainable energy solutions, concepts that improve the ability to withstand high electrical fields and, ultimately, the power transmission efficiency are in high demand. The performance of a HVDC insulation material is limited by its residual electrical conductivity. Here, we demonstrate that the addition of small amounts of high-density polyethylene (HDPE) to a low-density polyethylene (LDPE) resin results in a drastic reduction in DC conductivity. An HDPE content as low as 1 wt % is found to introduce a small population of thicker crystalline lamellae, which are finely distributed throughout the material. The change in nanostructure correlates with a decrease in DC conductivity by approximately 1 order of magnitude to about 10(-15) S m(-1) at high electric fields of 30 and 40 kV mm(-1) and elevated temperature of 70 degrees C. This work opens up an alternative design concept for the insulation of HVDC power cables.
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| 4. |
- Andersson, Mattias, 1985, et al.
(författare)
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Influence of Molecular Weight on the Creep Resistance of Almost Molten Polyethylene Blends
- 2018
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Ingår i: Macromolecular Chemistry and Physics. - : Wiley. - 1022-1352 .- 1521-3935. ; 219:3
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Tidskriftsartikel (refereegranskat)abstract
- The most common route to improve the creep resistance of low density polyethylene (LDPE) is crosslinking, which however results in volatile decomposition products that must be removed. Blends of LDPE and an additive-like amount of a linear polyethylene are found to offer improved creep resistance. Above the melting temperature of LDPE, T m ≈ 111 °C, a load-bearing network of higher-melting crystallites—connected through tie chains and trapped entanglements—provides additional form stability. The molecular weight of the linear polyethylene is found to be critical for the ability to arrest creep, which is correlated with the probability of tie chain formation as well as cocrystallization of the two polyethylenes. A number of high-density polyethylenes (HDPE) and one ultrahigh molecular weight polyethylene (UHMW-PE) are explored. For blends of LDPE and 2 wt% of the linear polyethylene, an HDPE with a weight-average molecular weight M w of 16 kg mol −1 is found to be sufficient to arrest creep at 115 °C. Further improvement in terms of creep resistance is obtained in case of UHMW-PE with creep fracture occurring only at a stress of 12 kPa at 115 °C. (Figure presented.).
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| 5. |
- 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. ; , 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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| 6. |
- Carmeli, Enrico, et al.
(författare)
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Crystallization kinetics of melt-mixed 3D hierarchical graphene/polypropylene nanocomposites at processing-relevant cooling rates
- 2022
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368. ; 247
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the solidification behaviour of isotactic polypropylene (iPP) composites with reduced graphene oxide nanoplatelets is key to open the possibility to widespread use of these high performing nanocomposites. The crystallization behaviour of these systems, with filler content in the range of 0.2–3.5 wt% has been investigated by differential scanning calorimetry (up to 100 °C/min) and ex-situ structural and morphological characterization of samples prepared at processing-relevant cooling conditions (up to 2000 °C/s). Compared to the self-nucleated neat iPP, the nucleation efficiency was estimated to vary from 44 to 93% when increasing the filler content. Such a high nucleating efficiency has not been reported yet for a nanocomposite with iPP matrix. This result is due to the very good dispersion of the filler in these melt-mixed graphene-based polypropylene systems. The nucleation ability of the graphene filler does not reach a saturation in the concentration range studied. The gap between laboratory and industrial cooling rate scale is here reduced thanks to the information achieved from the fast-cooling experiments. By varying the filler amount in the investigated range, a significant shift of the cooling rate window in which the transition from α-to mesophase dominated crystallization takes place was detected. Notably, with 3.5 wt% graphene platelets, α-phase crystals are predominantly present in the material even after quenching at 1000 °C/s, similar to highly nucleated commercial iPP grades.
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| 7. |
- Erdtman, Edvin, et al.
(författare)
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A molecular-level computational study of the diffusion and solubility of water and oxygen in carbonaceous polyethylene nanocomposites
- 2016
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Ingår i: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 54:5, s. 589-602
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo and molecular dynamics simulations were performed to investigate the effect on the solubility, diffusion, and permeability of water and oxygen when adding graphene or single-walled carbon nanotubes (SWCNTs) to polyethylene (PE). When compared with pure PE, addition of graphene lowered the solubility of water, whereas at lower temperatures, the oxygen solubility increased because of the oxygen–graphene interaction. Addition of SWCNTs lowered the solubility of both water and oxygen when compared with pure PE. A detailed analysis showed that an ordered structure of PE is induced near the additive surface, which leads to a decrease in the diffusion coefficient of both penetrants in this region. The addition of graphene does not change the permeation coefficient of oxygen (in the direction parallel to the filler) and, in fact, may even increase this coefficient when compared with pure PE. In contrast, the water permeability is decreased when graphene is added to PE. The addition of SWCNTs decreases the permeability of both penetrants. Graphene can consequently be added to selectively increase the solubility and permeation of oxygen over water, at least at lower temperatures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 589–602
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| 8. |
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| 9. |
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| 10. |
- 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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