| 1. |
- Liu, Dongming, et al.
(författare)
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Cellulose nanofibril core-shell silica coatings and their conversion into thermally stable nanotube aerogels
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 3:30, s. 15745-15754
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Tidskriftsartikel (refereegranskat)abstract
- A facile water-based one-pot reaction protocol for obtaining 20 nm thick uniform silica coatings on cellulose nanofibrils (CNFs) is herein presented for the first time. The fully covering silica shells result in the thermal stability of the CNFs improved by ca. 70 degrees C and 50 degrees C under nitrogen and oxygen atmospheres, respectively. Heating of the core-shell hybrid fibres to 400 degrees C results in complete degradation/removal of the CNF cores, and demonstrates an inexpensive route to large-scale preparation of silica nanotubes with the CNFs used as templates. The key to a uniform condensation of silica (from tetraethyl orthosilicate) to cellulose is a reaction medium that permits in situ nucleation and growth of the silica phase on the fibrils, while simultaneously matching the quantity of the condensed silica with the specific surface area of the CNFs. Most coatings were applied to bundles of 2-3 associated CNFs, which could be discerned from their negative imprint that remained inside the silica nanotubes. Finally, it is demonstrated that the coated nanofibrils can be freeze-dried into highly porous silica/cellulose aerogels with a density of 0.005 g cm(-3) and how these hybrid aerogels preserve their shape when extensively exposed to 400 degrees C in air (>6 h). The resulting material is the first reported silica nanotube aerogel obtained by using cellulose nanofibrils as templates.
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| 2. |
- Pallon, Love K. H., et al.
(författare)
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Formation and the structure of freeze-dried MgO nanoparticle foams and their electrical behaviour in polyethylene
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:14, s. 7523-7534
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Tidskriftsartikel (refereegranskat)abstract
- Electrically insulating low-density polyethylene (LDPE) nanocomposites based on dispersed MgO nanoparticle foams are reported. The foams were obtained via freeze-drying aqueous suspensions of precipitated ca. 40 nm wide and 10 nm thick Mg(OH)(2) nanoparticles and dewatering (calcining) at 400 degrees C, resulting in a 25 times more voluminous powder compared to conventionally dried nanoparticles. This powder handling prior to extrusion melt-processing greatly facilitated the nanocomposite preparation since no particle grinding was necessary. Large quantities of particles were prepared (>5 g), and the nanoparticle foams showed improved dispersion in the LDPE matrix with 70% smaller aggregate sizes compared to the conventionally dried and ground nanopowders. The nature of the nanoparticle foams was evaluated in terms of their dispersion on Si-wafers using ultrasonication as a dispersing aid, which showed to be detrimental for the nanoparticle separation into solitary particles and induced severe aggregation of the calcined nanoparticles. The grind-free MgO nanoparticles/LDPE-composite was evaluated by electrical measurement. The prepared composite showed an initial ca. 1.5 orders of magnitude lower charging current at 10(2) s, and a 4.2 times lower charging current after 16 hours compared to unfilled LDPE. The results open a way for improved insulation to be implemented in the future high-voltage cable system and present a new promising nanoparticle powder handling technique that can be used on a large scale.
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| 3. |
- Pallon, L. K. H., et al.
(författare)
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The impact of MgO nanoparticle interface in ultra-insulating polyethylene nanocomposites for high voltage DC cables
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:22, s. 8590-8601
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Tidskriftsartikel (refereegranskat)abstract
- Low density polyethylene (LDPE) nanocomposites with a reduced conductivity of two orders of magnitude are reported as a novel insulation material for high voltage distribution of renewable energy. The key to the high insulation capacity was to provide 70 nm hexagonal MgO nanoparticles with relatively tong, preferably 18 units long, hydrocarbon functional silsesquioxane coatings. This rendered the surface of the particles completely hydrophobic and also served as a protective layer against adsorption of polar low molecular weight atmospheric substances (H2O and CO2). The elimination of trace amounts of water, in combination with the provided carbon functionality, dramatically improved the dispersion of MgO nanoparticles. The lowest volume conductivity was ca. 7 x 10(-16) s m(-1) for 3 wt% surface coated nanoparticles. Extensive electron microscopy characterization was further used to relate the measured volume conductivity, acquired under conditions that resemble 800 kV high voltage direct current (HVDC) cables, to the distribution of the nanoparticles in the polymer matrix. The results show that an appropriate surface-modification approach yielded uniformly dispersed MgO nanoparticles up to contents as high as 9 wt%, with maintained 10-100 times reduced volume conductivity. Simulations of the MgO nanoparticles distribution revealed that the required interaction radius of the MgO-phase was 775 nm, setting a lower limit of particle amount to effectively work as electrical insulation promoters. The reduced volume conductivity values and scalable processing chemistry reported allow for the production of the next generation insulation material for HVDC cables.
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| 4. |
- Pourrahimi, A. M., et al.
(författare)
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Heat treatment of ZnO nanoparticles : new methods to achieve high-purity nanoparticles for high-voltage applications
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:33, s. 17190-17200
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Tidskriftsartikel (refereegranskat)abstract
- Novel methods based on orienting and coating of ZnO nanoparticles were studied in order to obtain uniform, nano-sized and ultra-pure ZnO grains/particles after heat treatment. A 1 nm zinc-hydroxy-salt complex layer on the nanoparticle surfaces was revealed by thermogravimetry and infrared spectroscopy. This 'phase' gradually decomposed into ZnO during the heat treatment while sintering occurred above 600 degrees C, as revealed by scanning-and transmission-electron microscopy. The c-axis alignment of the nanoparticles provided smaller pores than those associated with non-oriented nanoparticles, presenting the means to obtain high-density ceramics. The orientation resulted in a smaller grain size after heat treatment than that of the nonaligned nanoparticles. Another method that involved three steps - silane coating, heat treatment and silica layer etching - was used to remove the ionic species from the nanoparticle surface while preserving its hydroxylated surface. These ultra-pure nanoparticles are expected to be key components in the development of HVDC insulation polyethylene nanocomposites.
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| 5. |
- Strain, I. N., et al.
(författare)
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Electrospinning of recycled PET to generate tough mesomorphic fibre membranes for smoke filtration
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:4, s. 1632-1640
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Tidskriftsartikel (refereegranskat)abstract
- Tough fibrous membranes for smoke filtration have been developed from recycled polyethylene terephthalate (PET) bottles by solution electrospinning. The fibre thicknesses were controlled from 0.4 to 4.3 mu m by adjustment of the spinning conditions. The highest fibre strength and toughness were obtained for fibres with an average diameter of 1.0 mu m, 62.5 MPa and 65.8 MJ m(-3), respectively. The X-ray diffraction (XRD) patterns of the fibres showed a skewed amorphous halo, whereas the differential scanning calorimetry (DSC) results revealed an apparent crystallinity of 6-8% for the 0.4 and 1 mu m fibres and 0.2% crystallinity for the 4.3 mu m fibres. Heat shrinkage experiments were conducted by exposing the fibres to a temperature above their glass transition temperature (T-g). The test revealed a remarkable capability of the thinnest fibres to shrink by 50%, which was in contrast to the 4.3 mu m fibres, which displayed only 4% shrinkage. These thinner fibres aka showed a significantly higher glass transition temperature (+15 degrees C) than that of the 4.3 mu m fibres. The results suggested an internal morphology with a high degree of molecular orientation in the amorphous segments along the thinner fibres, consistent with a constrained mesomorphic phase formed during their rapid solidification in the electric field. Air filtration was demonstrated with cigarette smoke as a model substance passed through the fibre mats. The 0.4 mu m fibres showed the most effective smoke filtration and a capacity to absorb 43x its own weight in smoke residuals. whereas the 1 mu m fibres showed the best combination of filtration capacity (32x) and mechanical robustness. The use of recycled PET in the form of nanofibres is a novel way of turning waste into higher-value products.
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| 6. |
- Wu, Qiong, et al.
(författare)
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Highly porous flame-retardant and sustainable biofoams based on wheat gluten and in situ polymerized silica
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:48, s. 20996-21009
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a novel type of flame-retardant biohybrid foam with good insulation properties based on wheat gluten and silica, the latter polymerized in situ from hydrolysed tetraethyl orthosilicate (TEOS). This led to the formation of intimately mixed wheat gluten and silica phases, where, according to protein solubility measurements and infrared spectroscopy, the presence of silica had prohibited full aggregation of the proteins. The foams with "built-in" flame-retardant properties had thermal insulation properties similar to those of common petroleum- and mineral-based insulation materials. The foams, with a porosity of 87 to 91%, were obtained by freeze-drying the liquid mixture. Their internal structure consisted of mainly open cells between 2 and 144 mu m in diameter depending on the foam formulation, as revealed by mercury intrusion porosimetry and scanning electron microscopy. The foams prepared with >= 30% TEOS showed excellent fire-retardant properties and fulfilled the criteria of the best class according to UL94 fire testing standard. With increasing silica content, the foams became more brittle, which was prevented by cross-linking the materials (using gluteraldehyde) in combination with a vacuum treatment to remove the largest air bubbles. X-ray photoelectron and infrared spectroscopy showed that silicon was present mainly as SiO2 .
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