| 1. |
- Bek, Marko, et al.
(författare)
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Long-Term Creep Compliance of Wood Polymer Composites: Using Untreated Wood Fibers as a Filler in Recycled and Neat Polypropylene Matrix
- 2022
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:13
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Tidskriftsartikel (refereegranskat)abstract
- Neat (NPP) and recycled (RPP) polypropylene matrix materials were used to prepare wood–polymer composites with untreated wood fibers up to 40 wt.%. Long-term creep properties obtained through the time-temperature superposition showed superior creep resistance of composites with NPP matrix. In part, this is attributed to their higher crystallinity and better interfacial adhesion caused by the formation of a transcrystalline layer. This difference resulted in up to 25% creep compliance reduction of composites with NPP matrix compared to composites with recycled (RPP) polypropylene matrix, which does not form a transcrystalline layer between the fibers and polymer matrix. Despite the overall inferior creep performance of composites with RPP matrix, from the 20 wt.% on, the creep compliance is comparable and even surpasses the creep performance of unfilled NPP matrix and can be a promising way to promote sustainability.
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| 2. |
- D'Auria, Silvia, et al.
(författare)
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Polyethylene Based Ionomers as High Voltage Insulation Materials
- 2023
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Ingår i: Advanced Functional Materials. - 1616-3028 .- 1616-301X. ; 33:36
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Tidskriftsartikel (refereegranskat)abstract
- Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6·10−14 S m−1 at 70 °C and an electric field of 30 kV mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts.
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| 3. |
- Jan, Petra, et al.
(författare)
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Tribological behaviour of green wood-based unrecycled and recycled polypropylene composites
- 2023
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 524-525
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Tidskriftsartikel (refereegranskat)abstract
- In this study we evaluated the tribological performance of polypropylene composites with wood-flour fillers obtained as a by-product from the wood-processing industry, which were based on unrecycled and recycled polypropylene polymer matrices. The mechanical properties of polypropylene-wood composites with wood-filler loadings of 0–40 wt % were determined with tensile tests and their friction and wear behaviours were studied with dry reciprocating ball-on-disc sliding tests against 100Cr6 steel balls at room temperature. The addition of the wood fillers resulted in a significant improvement in the tribological performance compared to the neat, unrecycled, and recycled polypropylene materials: the friction coefficient decreased by up to 30%, while the wear resistance was improved by up to two orders of magnitude. While neat unrecycled polymers have better properties than recycled, addition of 40 wt % wood-filler content in both, recycled and unrecycled composites, resulted in almost the same level of coefficient of friction (∼0.25) and wear coefficient (2 × 10−6 mm3/(Nm) to 3 × 10−6 mm3/(Nm)). Even with the addition of as low as 5 wt % of wood fibres the wear resistance was improved for 63% and 43% for unrecycled and recycled composites, respectively, which indicates that the use of wood fillers could be a sustainable and cost-effective way to improve the polymer tribological performance, and could compensate for the normally poorer properties of recycled materials, making the recycled polypropylene-wood composites a suitable sustainable choice for tribological applications.
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| 4. |
- Kádár, Roland, 1982, et al.
(författare)
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Challenges in nano-structured fluid flows for assembly into hierarchical biomaterials
- 2023
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Ingår i: AIP Conference Proceedings. - 0094-243X .- 1551-7616. - 9780735445475 ; 2997
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Konferensbidrag (refereegranskat)abstract
- Hierarchical biomaterials have their place in the context of developing novel material systems particularly in the framework of sustainability. The key to their development is in controlling their assembly into hierarchical orders at various lengthscales. Thus, flow can be an asset in e.g. controlling orientation, however, resolving the hierarchical orientation dynamics of such systems remains a challenge. We focus here mainly on cellulose nanocrystals water-based suspensions, however, the outline is representative of numerous nanostructured fluids.
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| 5. |
- Kušter, Monika, et al.
(författare)
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Effect of Al-Cu-Fe Quasicrystal Particles on the Reinforcement of a Polymer–Matrix Composite: From Surface to Mechanical Properties
- 2024
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Ingår i: Crystals. - 2073-4352. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- We examined the effect of Al59Cu25Fe13B3 (at.%) quasicrystalline (QC) reinforcement particles on the mechanical and surface properties of a polymer-matrix composite by applying a technical polymer polyphthalamide (PPA). The observed increase in the tensile Young’s modulus ranged from 1810 MPa for the pure polymer to 4114 MPa for the composite with a QC filling of 35 vol.%. The elongation at fracture decreased with the filling fraction, being equal to 16.9% for a pure polymer and dropping to 4.8% for the composite with a QC filling of 35 vol.%. The same trend was noticeable with flexural Young’s modulus, which ranged from 100 MPa for a pure polymer to 125.5 MPa for the composite with 35 vol.% of QC. It was found that the increase in the mechanical strength led to a simultaneous increase of brittleness, which was reflected in a decrease of the impact strength for a pure polymer from 98.5 kJ/m2 to 42.4 kJ/m2 for composites with a QC filling of 35 vol.%. In contrast, when filled with 5 vol.% of QC, the impact strength increased by 8%. The friction coefficient against 100C6 steel dropped from 0.15 for pure PPA down to 0.10 for 5 vol.% of the QC filling, followed by an increase to 0.26 for further QC fillings up to 35 vol.%. Interestingly, a local minimum of friction was achieved at filling factors between 5 to 20 vol.% of QC. Independently, a clear surfenergy minimum was also found for the composite material with 20 vol.% of QC filling associated with a net drop in the polar component of the surfenergy. Surfenergy refers to the surface energy related to the top of the oxide layer under ambient conditions. We hypothesise that this is related to the percolation threshold at about 13 vol.% QC, reflected in the observed behaviour of both the friction coefficient and surfenergy. For the pure QC annealed in air for 1 h at 500 °C significant wear tracks were observed accompanied by a wear debris formation. On the other hand, a pure polymer exhibited slightly visible wear tracks with no apparent debris formation, and for the composites with different QC filling factors, the wear traces were barely visible with negligible debris formation.
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| 6. |
- Nygård, K., et al.
(författare)
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ForMAX – a beamline for multiscale and multimodal structural characterization of hierarchical materials
- 2024
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 31:Pt 2, s. 363-377
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Tidskriftsartikel (refereegranskat)abstract
- The ForMAX beamline at the MAX IV Laboratory provides multiscale and multimodal structural characterization of hierarchical materials in the nanometre to millimetre range by combining small- and wide-angle X-ray scattering with full-field microtomography. The modular design of the beamline is optimized for easy switching between different experimental modalities. The beamline has a special focus on the development of novel fibrous materials from forest resources, but it is also well suited for studies within, for example, food science and biomedical research.
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| 7. |
- Pashazadehgaznagh, Sajjad, 1994, et al.
(författare)
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An Intriguing Array of Extrudate Patterns in Long-Chain Branched Polymers During Extrusion
- 2023
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Ingår i: Macromolecular Materials and Engineering. - 1439-2054 .- 1438-7492. ; 308:8
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Tidskriftsartikel (refereegranskat)abstract
- The present study highlights a range of surface and volume extrudate patterns that can be detected during the extrusion flow of long-chain branched polymers. Thus, four linear low-density polyethylenes (LDPEs) have been extruded using a single-screw extruder coupled to an inline optical imaging system. The selected LDPEs are selected to outline the influence of molecular weight and long-chain branching on the types of melt flow extrusion instabilities (MFEI). Through the inline imaging system, space–time diagrams are constructed and analyzed via Fourier-transformation using a custom moving window procedure. Based on the number of characteristic frequencies, peak broadness, and whether they are surface or volume distortions, three main MFEI types, distinct from those typically observed in linear and short-chain branched polymers, are identified. The higher molecular weight, low long-chain branching LDPEs exhibited all three instability types, including a special type volume instability. Independently of the molecular weight, higher long-chain branching appeared to have a stabilizing effect on the transition sequences by suppressing volume extrudate distortions or limiting surface patters to a form of weak intensity type.
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| 8. |
- Pashazadehgaznagh, Sajjad, 1994, et al.
(författare)
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Mapping surface defects in highly-filled wood fiber polymer composite extrusion from inline spectral analysis
- 2023
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Ingår i: Composites Science and Technology. - 0266-3538. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- Surface defects in highly-filled wood polymer composites (WPCs) are mapped in single-screw extrusion via inline optical spectral analysis for the first time. The effects of wood fiber content and drying on the dynamics of surface defects are spatio-temporally resolved via space–time inline optical imaging. Surface tearing appeared from the lowest shear rates investigated followed by a gradual decay in spectral intensity with increasing shear rates/slip velocities. This is accompanied by broadening of the surface tearing characteristic frequency while the average wavelength is estimated to remain constant within the experimental conditions. Increasing shear rates, drying and increasing wood fiber content showed mitigating effects on surface tearing. However, surface tearing in undried samples was still present even at the highest shear rates and high wall slip velocities. A regime where the extrudate surface is dominated by bubbles at high shear rates and low wood fiber contents in undried WPCs was identified.
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| 9. |
- Podmiljšak, Benjamin, et al.
(författare)
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Additive-manufactured anisotropic magnets for harsh environments
- 2023
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Ingår i: Journal of Magnetism and Magnetic Materials. - 0304-8853. ; 586
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Tidskriftsartikel (refereegranskat)abstract
- We describe the fabrication of SrFe12O19-based filaments, using polyphenylene sulphide (PPS) as the binder for the magnetic particles, and the subsequent printing of this filament with a 3D printer. PPS is an ideal polymer for applications in harsh environments, making it applicable for the automotive industry, where it is widely used with injection moulding. However, 3D printing this polymer introduces a major challenge. Because PPS is more difficult to extrude than polyamide, the filling factor in this study was set to 70 wt. %, which is lower than when used in injection moulding (close to 90 wt. %). The filament with a diameter of 2.75 mm was printed into a disk-shaped magnet with a diameter of 10 mm and a height of 4 mm using a HAGE 3D printer that uses a belt system for the filament extrusion. The magnets were printed onto a glass surface and onto a bulk Nd-Fe-B permanent magnet with an external magnetic field, parallel to the printer’s z-axis. Printing in the presence of a magnetic field was found to increase the magnet’s remanent magnetization by 61%, compared to an isotropic print. Without an external magnetic field we achieved a remanence of 23.9 emu/g for the 70 wt.% filling fraction, while when printing in a magnetic field, the value of the remanence improved to 39.7 emu/g because of the improved magnetic texture.
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| 10. |
- Ruan, Hengzhi, 1995, et al.
(författare)
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Biomimetic Antibacterial Gelatin Hydrogels with Multifunctional Properties for Biomedical Applications
- 2023
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Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 15:47, s. 54249-54249–54265
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Tidskriftsartikel (refereegranskat)abstract
- A facile novel approach of introducing dopamine and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide via dopamine-triggered in situ synthesis into gelatin hydrogels in the presence of ZnSO4 is presented in this study. Remarkably, the resulting hydrogels showed 99.99 and 100% antibacterial efficiency against Gram-positive and Gram-negative bacteria, respectively, making them the highest performing surfaces in their class. Furthermore, the hydrogels showed adhesive properties, self-healing ability, antifreeze properties, electrical conductivity, fatigue resistance, and mechanical stability from −100 to 80 °C. The added multifunctional performance overcomes several disadvantages of gelatin-based hydrogels such as poor mechanical properties and limited thermostability. Overall, the newly developed hydrogels show significant potential for numerous biomedical applications, such as wearable monitoring sensors and antibacterial coatings.
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