| 1. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Click chemistry-type crosslinking of a low-conductivity polyethylene copolymer ternary blend for power cable insulation
- 2020
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Ingår i: Polymer International. - : Wiley. - 1097-0126 .- 0959-8103. ; 69:4, s. 404-412
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct-current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high-voltage power cable insulation - low-density polyethylene (LDPE) - is usually crosslinked with peroxides, a process that releases unwanted by-products. Hence, by-product-free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry-type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co-monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co-monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 degrees C. Instead, at 200 degrees C rapid curing is possible, leading to thermosets with a low direct-current electrical conductivity of about 10(-16) S cm(-1) at an electric field of 20 kV mm(-1) and 70 degrees C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide-cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. (c) 2019 Society of Chemical Industry
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| 2. |
- Leone, G., et al.
(författare)
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Polyolefin thermoplastic elastomers from 1-octene chain-walking polymerization
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 100, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- This work reports the polymerization of 1-octene to yield semicrystalline, branched poly(ethylene) like materials with high molecular weight and narrow molecular weight distribution. The polymerization of 1-octene was catalyzed by an alpha-diimine Ni(II) complex [(ArN)C(CH3)-(CH3) C(NAr)]NiBr2 [Ar = 2,6-(iPr)(2)C6H3], in combination with different aluminum alkyls, i.e., Et2AlCl, MAO and MMAO. The effect of the aluminum alkyl, monomer concentration, polymerization temperature and Al/Ni ratio on the activity, selectivity of monomer insertion, polymers microstructure, and structure/properties is investigated. The results indicate the possibility to tune the polymer microstructure, which in turn strongly affects the structure, thermal and mechanical polymer properties. Mechanical testing carried out by uniaxial stretching until failure and step-cycle tensile experiments served to establish these materials as a new class of polyolefin thermoplastic elastomers with different performances depending on the microstructure and crystallinity.
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| 3. |
- Mauri, Massimiliano, 1987
(författare)
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ALTERNATIVE POLYETHYLENE CROSSLINKING CONCEPTS FOR POWER CABLE INSULATION
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We currently witness an accelerating shift from fossil energy sources to renewables driven by the urgent need to reduce carbon emissions. Wind, solar and hydro power is most abundant in places far away from the end user, which necessitates the efficient transport of electricity over long distances. Alternative grid designs are needed that complement high-voltage alternating current (HVAC) with high-voltage direct current (HVDC) cables. The most advanced power cable technology uses crosslinked polyethylene (XLPE) insulation, which is produced by peroxide crosslinking of low-density polyethylene (LDPE). However, peroxide crosslinking gives rise to by-products that compromise the cleanliness of LDPE and raise the electrical conductivity of the insulation material. Therefore, a by-product free curing process, which maintains the processing advantages and high electrical resistivity of LDPE, would considerably ease cable manufacturing and is therefore in high demand. This thesis introduces alternative concepts for the crosslinking of polyethylene that fulfil these requirements. In particular, the suitability of click-chemistry epoxy ring opening reactions for curing of an ethylene-glycidyl methacrylate copolymer has been explored. Three main concepts for by-products free cable insulation have been studied: (i) crosslinking of LDPE copolymers with low molecular-weight multifunctional curing agents, (ii) Lewis acid assisted crosslinking of LDPE copolymer formulations, and (iii) reactive blending of LDPE copolymers. After extensive characterization of the thermo-mechanical properties of the materials, as well as preliminary conductivity studies, it can be anticipated that the concepts introduced in this thesis are a viable, by-product free and sustainable alternative to peroxide-based crosslinking of polyethylenes.
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| 4. |
- 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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| 5. |
- Mauri, Massimiliano, 1987
(författare)
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Copolymerization of ethylene with a-olefins and cyclic olefins catalyzed by a Ti(IV) diisopropoxy complex bearing a tridentate [O¯,S,O¯]-type bis(phenolato) ligand
- 2014
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Ingår i: Polymer Chemistry. - 1759-9954 .- 1759-9962. ; :5, s. 3412-3423
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Tidskriftsartikel (refereegranskat)abstract
- Ethylene (E) was copolymerized with some α-olefins [1-pentene (PEN), 1-hexene (HEX), and 4-methyl-1-pentene (4M1P)] and cyclic olefins [cyclopentene (CPE), norbornene (NB), and dicyclopentadiene (DCPD)] using the Ti(IV) thiobis(phenolate) complex [2,2′-S(4-Me,6-tBuC6H2O)2]Ti(OiPr)2 in combination with methylaluminoxane (MAO). The catalyst exhibited excellent activities (up to 106 g molTi−1 h−1). Crystalline E/α-olefin copolymers with a strong tendency for comonomer alternation were obtained with good comonomer incorporation (about 15 mol% for [Y]/[E] = 8; Y = comonomer) decreasing in the order HEX > PEN > 4M1P. Random copolymers with NB and DCPD were obtained with efficient comonomer incorporation (from 10 to 40 mol%) even for the Y/E molar ratio = 1 to 2, while the catalyst gave poor CPE incorporation. In order to collect information on the comonomer distribution in the copolymers, boiling solvent extraction was carried out and all the fractions were characterized by DSC, XRD, SEC, and NMR.
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| 6. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Crosslinking of an ethylene-glycidyl methacrylate copolymer with amine click chemistry
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 111, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- Commonly used crosslinking methods for polyethylenes result in the release of harmful by-products. Here, we demonstrate that an epoxy-bearing polyethylene copolymer, which contains 8 wt% glycidyl methacrylate, can be efficiently crosslinked without by-product formation. Click chemistry based on multifunctional amine curing agents, which carry at least two functional groups separated by a flexible spacer, was used to prepare thermosets. Compounding of the crosslinker and copolymer through extrusion at 120 °C could be carried out without onset of the curing reactions. Careful adjustment of the curing time and temperature, ranging from 20 to 120 min and 160–200 °C, resulted in a high network density of at least 2.8 crosslinks per 1000 carbons at a curing agent stoichiometry of as little as 0.5 wt%.
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| 7. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Orange is the new white: Rapid curing of an ethylene-glycidyl methacrylate copolymer with a Ti-bisphenolate type catalyst
- 2018
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 9:13, s. 1710-1718
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Tidskriftsartikel (refereegranskat)abstract
- Polyethylene must be crosslinked if the polymer is to be used at elevated temperatures. However, established crosslinking methods result in the release of volatile by-products that can compromise the cleanliness and purity required for many electrical and medical applications. Currently available alternative curing processes, free from by-product formation, are too slow to be of practical relevance. Here, we demonstrate that an epoxy-bearing polyethylene copolymer, which contains one glycidyl methacrylate comonomer per 64 ethylene monomers, can be rapidly crosslinked with a click-chemistry curing process. We show that a titanium-based Lewis acid together with a bisphenol crosslinking agent allows the formation of thermosets. Compounding of the Lewis acid catalyst, crosslinking agent and copolymer through extrusion at 140 °C can be carried out without onset of the curing reaction. Then, at more elevated temperatures of 180 °C and above rapid crosslinking occurs. The competitive curing rate of the here explored formulation is due to in situ generation of a new titanium-phenoxide catalyst, which efficiently promotes crosslinking of the epoxy-bearing polyethylene copolymer. Adjustment of the curing time and temperature results in a high network density of at least 3 crosslinks per 1000 carbons in only 2 minutes at 240 °C and at a curing agent stoichiometry of 3 wt%, which corresponds to merely 0.04 wt% elemental titanium. The here established crosslinking chemistry opens up a by-product free method for rapid curing of epoxy-functionalised polyethylenes.
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| 8. |
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| 9. |
- Pourrahimi, Amir Masoud, 1985, et al.
(författare)
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Alternative Concepts for Extruded Power Cable Insulation: from Thermosets to Thermoplastics
- 2024
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- The most common type of insulation of extruded high-voltage power cables is composed of low-density polyethylene (LDPE), which must be crosslinked to adjust its thermomechanical properties. A major drawback is the need for hazardous curing agents and the release of harmful curing byproducts during cable production, while the thermoset nature complicates reprocessing of the insulation material. This perspective explores recent progress in the development of alternative concepts that allow to avoid byproducts through either click chemistry type curing of polyethylene-based copolymers or the use of polyolefin blends or copolymers, which entirely removes the need for crosslinking. Moreover, polypropylene-based thermoplastic formulations enable the design of insulation materials that can withstand higher cable operating temperatures and facilitate reprocessing by remelting once the cable reaches the end of its lifetime. Finally, polyethylene-based covalent and non-covalent adaptable networks are explored, which may allow to combine the advantages of thermoset and thermoplastic insulation materials in terms of thermomechanical properties and reprocessability.
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