| 1. |
- Forsgren, Lilian, 1990, et al.
(författare)
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The thermo-oxidative durability of polyethylene reinforced with wood-based fibres
- 2020
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Ingår i: Polymer degradation and stability. - : Elsevier Ltd. - 0141-3910 .- 1873-2321. ; 181
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Tidskriftsartikel (refereegranskat)abstract
- Aiming at better understanding the ageing behaviour of cellulose composites, the accelerated thermo-oxidative ageing of polyethylene reinforced with two types of wood-based cellulose fibres was studied. Materials were prepared by extrusion mixing of either un-stabilized or stabilized polyethylene reinforced with 5 and 20 vol % cellulose content. The materials were extruded into strips and then aged at 90°C in circulating air. The effect of accelerated ageing up to 31 days was assessed by oxidation induction time and mechanical properties in tension. The results indicated that the added cellulose fibres did not increase the degradation of the composites during this ageing. Reinforcement with 20 % cellulose fibre having a 28 % lignin content together with 0.005 % Irganox 1010 antioxidant resulted in a remarkable improvement in the resistance against accelerated thermo-oxidation, compared to the pure polyethylene with added antioxidant. The findings of increased lifetime of LDPE by addition of wood-based reinforcement is of great interest, since the durability aspect is crucial to understand and predict before usage in commercial applications and especially as structural composites.
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| 2. |
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| 3. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Composites with surface-grafted cellulose nanocrystals (CNC)
- 2019
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 54:4, s. 3009-3022
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100 °C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10 wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10 wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups.
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| 4. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Injection Molding and Appearance of Cellulose-Reinforced Composites
- 2019
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Ingår i: Polymer Engineering and Science. - : John Wiley and Sons Inc.. - 0032-3888 .- 1548-2634. ; 60:1, s. 5-12
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Tidskriftsartikel (refereegranskat)abstract
- Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness.
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| 5. |
- Forsgren, Lilian, 1990
(författare)
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Physical properties of dispersions and composites containing surface-grafted cellulose nanocrystals
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The needs and requests from the society for non-fossil-based materials as well as more lightweight products are constantly increasing. The increasing awareness of the sustainability of the resources available paralleled by a growing population, point to a need for changes, if the population also aim for constantly higher standard of living. Cellulose is a renewable material, produced by all plants on earth through photosynthesis using solar energy. It has promising properties, being the supportive and stiff structure in plants and trees, and has been widely used throughout history as a construction material and in everyday life. The smallest entity of the cellulose fibre, the cellulose nanocrystals (CNC), exhibit even greater promising properties with their low weight, high aspect ratio and high specific stiffness in combination with biodegradability and renewability. Using CNC as reinforcements in a polymer matrix reduces in principle the need for fossil-based materials and reduces also the weight of the component. There are however some challenges, the hydrophilic nature of cellulose and the hydrophobic nature of most polymers causing low adhesion and poor dispersion. The temperatures needed for most thermoplastic processes also exceed the onset temperature for thermal degradation of cellulose, about 150-200 °C. Here, azetidinium salts have been used to graft three different functional groups onto the CNC surface, aiming at improving the thermal stability of the CNC but also the compatibility between a polymer matrix and CNC in a composite material. The focus in the first part of the study was to evaluate the properties of and interactions between the grafted groups in aqueous dispersions of surface-treated CNC. This was followed by manufacturing of composites using dispersion mixing of CNC and an ethylene-acrylic acid copolymer and compression moulding of plaques. The composites were then evaluated in terms of mechanical properties and thermal stability. The surface-grafting resulted in a large increase in thermal stability of the CNC; the onset temperature for thermal degradation increased from 150 °C to 250 °C. The addition of CNC also had a strong influence on the mechanical properties of the composites, e. g. resulting in an up to three times higher elastic modulus when adding 10 weight-% CNC. Several experimental methods indicated enhanced interactions either between the grafted groups and/or between the polymer matrix and the grafted groups.
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| 6. |
- Forsgren, Lilian, 1990
(författare)
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Processing and properties of thermoplastic composites containing cellulose nanocrystals or wood-based cellulose fibres
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose nanocrystals (CNC) were surface modified with dialkylamines to increase the compatibility between the CNC and the polymeric matrix, and promising results were obtained, with a 300 % stiffness increase when the mixed dispersion was compression moulded on a laboratory scale. The manufacturing process was up-scaled using water-assisted mixing in a twin-screw extruder (TSE) followed by a second compounding step and injection moulding (IM). The composites were successfully produced using conventional melt-processing techniques but these did not show the same improvement in mechanical performance, probably due to the formation of CNC aggregates. There were indications of network formation when CNC was added, especially in the case of surface-modified CNC. Cellulose fibres and thermomechanical pulp were used as reinforcement in similar types of polymer matrices and the mixtures were similarly processed by TSE and IM. These materials were characterized with regard to appearance and durability. The discoloration of the composites due to excessive heat during processing did not significantly affect their mechanical properties, and the addition of the cellulose-based reinforcement to the polymer did not reduce its resistance to thermo-oxidative degradation compared to that of the pure matrix. In fact, the resistance to degradation was increased when lignin was present in the reinforcing element, showing a synergistic effect together with the added anti-oxidant. Superior properties were expected for the CNC composites compared to those of the larger cellulose fibre reinforcements, but in continuous production the stiffening effects were similar regardless of reinforcement type. These results confirm that the processing method and properties strongly affect the final properties of the composite.
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| 7. |
- Forsgren, Lilian, 1990, et al.
(författare)
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Water-assisted extrusion and injection moulding of composites with surface-grafted cellulose nanocrystals – An upscaling study
- 2021
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- The large-scale surface modification of cellulose nanocrystals (CNC) was carried out to produce CNC-containing composites, in a scale of 3 kg, using industrial-scale melt processing techniques such as twin-screw extrusion and injection moulding. Two different polymer matrices, ethylene-acrylic acid copolymer (EAA) and low-density polyethylene (LDPE), were reinforced with 10 wt% unmodified cellulose nanocrystals (CNC) or surface-treated CNC, where a 2-hydroxyproyl-N-diallyl group had been grafted onto the sulphate half-ester groups on the CNC surfaces. This was achieved by mixing an aqueous CNC dispersion and the polymer pellets directly in the twin-screw extruder followed by a second dry compounding step prior to shaping by injection moulding. The injection-moulded materials were characterized with respect to their mechanical properties and thermal stability. The addition of 10 wt % CNC resulted in all cases in an increase in the yield strength and stiffness by 50–100%, most significantly for the EAA based composites. There were indications of the presence of a stable interphase and a percolating network in the EAA-based materials, according to dynamic-mechanical measurements. A reduction in thermal stability was observed for the melt-processed samples containing diallyl-modified CNC and discoloration in the EAA based samples.
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| 8. |
- Sahlin, Karin, 1991, et al.
(författare)
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Nanocellulose in biocomposites
- 2016
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Ingår i: Proc Materials for Tomorrow 2016. ; , s. Nr 41-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Sahlin, Karin, 1991, et al.
(författare)
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Surface treatment of cellulose nanocrystals (CNC): effects on dispersion rheology
- 2018
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 25:1, s. 331-345
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanocrystals (CNC) were surface modified by grafting azetidinium salts onto the sulphate ester groups on the cellulosic surfaces. The modified CNC were characterized using NMR, FTIR spectroscopy, conductometric titration and measurement of the zeta-potential. Thermal gravimetrical analysis revealed that the onset temperature for the thermal degradation was shifted upwards by almost 100 degrees C as a result of the surface grafting. The rheological properties of dispersions based on unmodified and modified CNC were evaluated in detail. Two solids contents were studied; 0.65 and 1.3 wt%. In general, the grafting of the salts significantly increased the shear viscosity at a given shear rate as well as the storage and loss moduli of the dispersions. The CNC concentration at the gel point (network formation) decreased in a corresponding manner when the nanocellulosic particles were surface modified. This may be associated with pronounced hydrophobic attractive interactions between the grafted substituents.
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| 10. |
- Venkatesh, Abhijit, 1989, et al.
(författare)
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Water-assisted melt processing of cellulose biocomposites with poly(ε-caprolactone) or poly(ethylene-acrylic acid) for the production of carton screw caps
- 2022
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 139:6
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Tidskriftsartikel (refereegranskat)abstract
- Composites in 25 kg batches were compounded of cellulose nanocrystals (CNC) and thermomechanical pulp (TMP) and shaped into caps at industrial facilities on a pilot-plant scale. Some of the material was also injection molded into plaques to compare the effect of laboratory-scale and pilot-scale compounding of poly(ethylene-co-acrylic acid) (EAA7) and poly(caprolactone) composites reinforced with 10 wt% CNC and TMP. The materials compounded under laboratory-scale conditions showed a different morphology, improved mechanical properties, and a higher viscosity, than the materials compounded on a pilot-scale. In some cases, the rheological properties of the melts indicated the presence of a relatively strong percolating cellulosic network, and the interphase region between the cellulose and the matrix appears to be important for the mechanical performance of the composites. After the compounding on a pilot scale, both the length and width of the pulp fibers was reduced. The TMP provided better reinforcement than the CNC possibly due to the higher aspect ratio.
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