| 1. |
- Adu, Cynthia, et al.
(författare)
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Properties of cellulose nanofibre networks prepared from never-dried and dried paper mill sludge
- 2018
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Ingår i: Journal of Cleaner Production. - : Elsevier. - 0959-6526 .- 1879-1786. ; 197:1, s. 765-771
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Tidskriftsartikel (refereegranskat)abstract
- Paper mills yield large volumes of sludge materials which pose an environmental and economic challenge for disposal, despite the fact that they could be a valuable source for cellulose nanofibres (CNF) production. The aim of the study was to evaluate the production process and properties of CNF prepared by mechanical fibrillation of never-dried and dried paper mill sludge (PMS). Atomic force microscopy (AFM) showed that average diameters for both never-dried and dried paper sludge nanofibres (PSNF) were less than 50 nm. The never-dried and dried sludge nanofibres showed no statistical significant difference (p > 0.05) in strength 92 MPa, and 85 MPa and modulus 11 GPa and 10 GPa. The study concludes that paper mill sludge can be used in a dried state for CNF production to reduce transportation and storage challenges posed on industrial scale.
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| 2. |
- Aitomäki, Yvonne, et al.
(författare)
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Cellulose nanofibril nanocomposites processing
- 2013
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Ingår i: Production and Applications of Cellulose Nanomaterials. - Peachtree Corners, GA : TAPPI Press. - 9781595102249 ; , s. 271-274
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Bokkapitel (refereegranskat)abstract
- Impregnation of a preformed network of nanofibrils leads to high fibre volume fraction nanocomposites and with this good mechanical properties have been achieved. However, comparing nanofibrils composite made with different volume fractions and different matrices is difficult. In order to do this, and in doing so gain insight into the most promising approaches, methods of measuring reinforcing efficiencies are being developed. The results show that for matrices with low stiffness the stiffness reinforcing efficiency is high. However with high fibre volume fraction and high stiffness, this network effect may lead to a lack of exploitation of the properties of the nanofibrils. Alignment of the nanofibrils is also a key in effective reinforcement. In addition, upscaling of the impregnation process requires a good understanding of permeability and adaptation of existing permeability models for cellulose nanofibrils networks as well as experiments on their permeability are ongoing.
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| 3. |
- Aitomäki, Yvonne, et al.
(författare)
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Hydrogel state impregnation of cellulose fibre-phenol composites: Effects of fibre size distribution
- 2016
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Ingår i: ECCM 2016. - : European Conference on Composite Materials. - 9783000533877
-
Konferensbidrag (refereegranskat)abstract
- Whilst it has been well established that cellulose nanofibres (CNF) networks produce films that have high stiffness and strength, they are difficult to impregnate. Investigated in this study is whether by controlling the degree of nanofibrillation of cellulose, composites based on micro- and nano-size cellulose fibres can be made that are more easily manufactured and have better impregnation than solely cellulose nano-fibre based composites. To evaluate this, cellulose at different stages of ultrafine grinding, extracted at time intervals of 30, 60 and 290 mins, were used to make composites. To achieve good impregnation a novel strategy was used based on impregnation with phenol resin whilst the fibrillated cellulose is in a hydrogel state. The composites were subsequently dried and consolidated by hot press. The current results show that this method of impregnation is successful and the phenol matrix greatly improves the properties of the cellulose with a low degree of fibrillation. In general, as the degree of fibrillation and the proportion of nanofibres increases, the mechanical properties of the networks and their composites increase. The addition of the matrix appears to restrict the deformation of CNF network, increasing the modulus and yield strength but decreasing the ultimate strength. The method also appears to restrict the consolidation and voids remain in the composite, which reduces the modulus when compared to theoretical maximum values for this material. More work on the consolidation process is necessary to achieve the full potential of these composites.
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| 4. |
- Aitomäki, Yvonne, et al.
(författare)
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Impregnation of cellulose nanofibre networks with a thermoplastic polymer
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The emphasis of this study have been to study if impregnation of cellulose nanofibre networks can be made using a thermoplastic polymer as a matrix and to estimate the reinforcing efficiency of the cellulose nanofibres in this composite. A nanofibre network with higher porosity that water-dried nanofibre network was prepared from a cellulose waste byproduct (sludge). This was impregnated using a diluted solution of cellulose acetate butyrate polymer to produce a 60 wt. % CNF/CAB composite. This composite was characterized using microscopy and mechanical testing. High porosity is seen in the SEM images of the acetone-dried fibre network and SEM and film transparency was used to qualitatively assess the impregnation of the network. A significant improvement in the visible light transmittance was observed for the nanocomposite film compared to the nanofibre network as a result of the impregnation. The reinforcing efficiency was calculated based on a model of the nanocomposite and compared to other nanocomposites in the literature. The efficiency factor takes into account the volume fraction and the stiffness of the matrix. This showed that this CNF/CAB combination is similar in efficiency to CNF/PLA nanocomposites and more efficient that nanocomposites using when using stiffer matrices. It was also more efficient CNF nanocomposites based on Chitosan, which has the same stiffness. It is still however not as efficient as traditional glass polymer composites due to the random orientation of the fibres nor nanocomposites with very soft matrices due to the dominating network effect of the CNF in such composites. In conclusion, CAB impregnated cellulose nanofibre networks are promising biocomposite materials that could be used in applications where transparency and good mechanical properties are of interest. The key elements in the impregnation process of the nanocomposites were the use of a porous networks and a low viscosity thermoplastic resin solution.
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| 5. |
- Aitomäki, Yvonne, et al.
(författare)
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Light scattering in cellulose nanofibre suspensions : Model and experiments
- 2016
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Ingår i: Computers in Chemistry Proceeding from ACS National Meeting San Diego. - : American Chemical Society (ACS). ; , s. 122-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Here light scattering theory is used to assess the size distribution in a suspension of cellulose as it is fibrillated from micro-scaled to nano-scaled fibres. A model based on Monte carlo simulations of the scattering of photons by different sizes of cellulose fibres was used to predict the UV-IF spectrum of the suspensions. Bleached cellulose hardwood pulp was tested and compared to the visually transparent tempo-oxidised hardwood cellulose nanofibres (CNF) suspension. The theoretical results show that different diameter size classes exhibit very different scattering patterns. These classes could be identified in the experimental results and used to establish the size class dominating the suspension. A comparison to AFM/microscope size distribution was made and the results indicated that using the UV-IF light scattering spectrum maybe more reliable that size distribution measurement using AFM and microscopy on dried CNF samples. The UV-IF spectrum measurement combined with the theoretical prediction can be used even at this initial stage of development of this model to assess the degree of fibrillation when processing CNF.
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| 6. |
- Aitomäki, Yvonne, et al.
(författare)
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Nanofibre distribution in composites manufactured with epoxy reinforced with nanofibrillated cellulose : model prediction and verification
- 2016
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Ingår i: IOP Conference Series. - 1757-8981 .- 1757-899X. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- In this study a model based on simple scattering is developed and used to predict the distribution of nanofibrillated cellulose in composites manufactured by resin transfer moulding (RTM) where the resin contains nanofibres. The model is a Monte Carlo based simulation where nanofibres are randomly chosen from probability density functions for length, diameter and orientation. Their movements are then tracked as they advance through a random arrangement of fibres in defined fibre bundles. The results of the model show that the fabric filters the nanofibres within the first 20 µm unless clear inter-bundle channels are available. The volume fraction of the fabric fibres, flow velocity and size of nanofibre influence this to some extent. To verify the model, an epoxy with 0.5 wt.% Kraft Birch nanofibres was made through a solvent exchange route and stained with a colouring agent. This was infused into a glass fibre fabric using an RTM process. The experimental results confirmed the filtering of the nanofibres by the fibre bundles and their penetration in the fabric via the inter-bundle channels. Hence, the model is a useful tool for visualising the distribution of the nanofibres in composites in this manufacturing process.
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| 7. |
- Aitomäki, Yvonne, et al.
(författare)
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Quantifying reinforcing efficiency of nanocellulose fibres
- 2013
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Ingår i: Processing of fibre composites-challenges for maximum materials performance. - Risö : Dept. of Wind Energy, Technical University of Denmark. - 9788792896513 ; , s. 149-160
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Konferensbidrag (refereegranskat)abstract
- Cellulose nanofibres are found in all plants and have the potential to provide a sustainable biobased material source. These nanofibres can be used for reinforcing polymers and thus as structural materials. Very promising results have been reported for different nanocomposites but to compete with existing materials, it is important to understand what progress has been made towards structural materials using nanocellulose. To do this the reinforcing efficiency of the stiffness and strength of nanocellulose in different nanocomposites has been calculated for a number of reported nanocellulose fibre based composites. For the stiffness this is done by back-calculating a reinforcing efficiency factor from a Halpin-Tsai model and laminate theory. For the strength efficiency, two models are used: a classic short fibre composite model and a network model. The results show that orientation is key to the stiffness efficiency, as shown by the high efficiency of aligned natural fibres. The stiffness efficiency is, as expected, high in soft matrices but in stiff matrices, the network effect of the nanofibres is possibility limiting their reinforcing potential. The strength efficiency results show that in all the nanocomposites evaluated the network model is closer to predicting strength than the short fibre composite model. The correlation between the network strength and the composite strength suggest that much of the stress transfer is from fibre to fibre and strong nanocomposites depend heavily on having a strong network. Also noted is that in composite processing a good impregnation of the nanofibers is also seen as an important factor in the efficiency of both strength and stiffness.
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| 8. |
- Aitomäki, Yvonne, et al.
(författare)
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Reinforcing efficiency and the manufacture nanocellulose fibre based composites by vacuum infusion
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Nanocomposites based on cellulose have received a rapidly rising attention over the last 10 years however the method of manufacturing these composites on a scale larger than that in the lab remains challenging. Another challenge is that low fraction nanocomposites, whilst they can show excellent improvement in polymer properties, have difficultly to compete with traditional fibre reinforced composites [1,2]. A commonly used liquid composite moulding method for producing composites is vacuum infusion and the possibility of trading glass fibre for nanocellulose networks sheets in this type of manufacturing could results in a upscale method for producing high volume fraction cellulose nanocomposites. CNF networks are stiff and strong but have high fibre packing and thus difficult to impregnate. This paper evaluates the effectiveness of increasing the porosity to improve their processability by VI.
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| 9. |
- Aitomäki, Yvonne, et al.
(författare)
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Reinforcing efficiency of nanocellulose in polymers
- 2014
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Ingår i: Reactive & functional polymers. - : Elsevier BV. - 1381-5148 .- 1873-166X. ; 85, s. 151-156
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose extracted from renewable sources, is a promising reinforcement for many polymers and is a material where strong interfibre hydrogen bonds add effects not seen in microfiber composites. Presented is a tool for comparing different nanocellulose composites based on estimating the efficiency of nanocellulose reinforcement. A reinforcing efficiency factor is calculated from reported values of elastic modulus and strength from various nanocellulose composites using established micromechanical models. In addition, for the strength, a network model is derived based on fibre-fibre bond strength within nanocellulose networks. The strength results highlight the importance of the plastic deformation in the nanocellulose composites. Both modulus and strength efficiency show that the network strength and modulus has a greater effect than that of the individual constituents. In the best cases, nanocellulose reinforcement exceeds all model predictions.
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| 10. |
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| 11. |
- Aitomäki, Yvonne, et al.
(författare)
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Vacuum infusion of cellulose nanofibre network composites : Influence of porosity on permeability and impregnation
- 2016
-
Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 95, s. 204-211
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Tidskriftsartikel (refereegranskat)abstract
- Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.
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| 12. |
- Aitomäki, Yvonne, et al.
(författare)
-
Vacuum Infusion of Nanocellulose Networks of Different Porosity
- 2015
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Ingår i: 20th International Conference on Composite Materials. - : ICCM.
-
Konferensbidrag (refereegranskat)abstract
- Cellulose nanofibres (CNF) have shown good potential as sustainable, biobased reinforcing materials in polymer composites. Addressing issues around the processing of these composites is an important part of establishing their use in different applications. Here, CNF networks of different porosity are made from nanofibrillated hardwood kraft pulp with the aim of increasing the impregnation of the CNF networks and to allow vacuum infusion to be used. Two different vacuum infusion strategies: in-plane and out of plane were used to infuse the CNF networks with a low viscosity epoxy. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated and compared to a micro-fibre based network. Using the out-of-plane permeability measurements and Darcy’s law, the fill-time was calculated and showed that the CNF network with 40% porosity had the lowest fill-time when an out-of-plane impregnation strategy is used. However this exceeded the gel-time of the epoxy system. In experiments, the resin reached the other side of the network but low transparency indicated that wetting was poor. The dry CNF preforms showed a very strong dependence on the porosity with both modulus and strength increasing rapidly at low porosity. Interestingly, the composite based on the 60% porosity network showed good wetting particularly with the in-plane infusion strategy, exhibiting a much more brittle fracture and a high yield strength. This shows that in CNF composites produced by VI, lowering the fibre volume content of the CNF composites gives better impregnation resulting in a lower ultimate strength but higher yield strength and no loss in modulus.
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| 13. |
- Alemandar, Ayse, et al.
(författare)
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The effect of decreased fiber size in wheat straw/polyvinyl alchol composites
- 2009
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Ingår i: Journal of Biobased Materials and Bioenergy. - : American Scientific Publishers. - 1556-6560 .- 1556-6579. ; 3:1, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- The reinforcing potential of micro and nano-size fibers from wheat straw in polyvinyl alcohol (PVA) was studied. The microfibers were obtained by alkali treatment and disintegration process of wheat straw while nanofibers were obtained after applying further mechanical treatment of this alkali treated wheat straw. The results showed that the alkali treatment increased the α-cellulose content of the fibers from 38% to 73% due to hydrolysis of the hemicelluloses and lignin from the straw walls. The morphology and thermal properties of the micro and nano-size fibers were determined to show their potential as reinforcements. The transmission electron microscopy study showed that the size of the wheat straw fibers was decreased from micro to nano-size by the defibrillation process. Thermogravimetric analysis demonstrated the alkali treatment dramatically increased the thermal properties of the wheat straw fibers. The morphologies and thermal properties of the prepared composites were investigated by scanning electron microscopy and thermogravimetric analysis. The thermal stability of the nanofiber-reinforced composites increased with respect to the neat PVA. The mechanical properties of the composites increased significantly with the addition of microfibers and further increment was obtained with nanofibers. The tensile modulus increased from 2.1 GPa of pure PVA to 3 GPa with the addition of micro sized fibers and further to 3.8 GPa with the decreased fiber size to nano scale. The composites strength showed similar trend.
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| 14. |
- Alemdar, Ayse, et al.
(författare)
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Reinforcement capability of wheat straw fibers from micro to nano size
- 2007
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Ingår i: 9th International Conference on Wood & Biofiber Plastic Composites. - Madison, Wis : Forest Products Society. - 1892529505
-
Konferensbidrag (refereegranskat)abstract
- The goal of this study was to explore the reinforcement capability of micro and nano-size fibers from wheat straw. Microfibers were obtained by alkali treatment and disintegration processes of the wheat straw while nanofibers were obtained after applying further mechanical treatment of this alkali treated wheat straw. The morphology and thermal properties of both fiber types were determined to show their suitability as reinforcements. TEM images showed that the diameters of the wheat straw fibers were decreased from micro to nano-size by the defibrillation process. Thermogravimetric analysis showed the alkali treatment dramatically increased the thermal properties of the wheat straw fibers. The composites were produced using, respectively, the microfibers and nanofibers as reinforcement, with both polyvinyl alcohol (PVA) and cellulose acetate butyrate (CAB) as the matrix. The morphology and thermal properties of the composites were investigated by scanning electron microscopy and thermogravimetric analysis. The mechanical properties of the composites were compared with those of neat polymer matrix and found to be considerably improved.
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| 15. |
- Antlauf, Mathis, et al.
(författare)
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Thermal Conductivity of Cellulose Fibers in Different Size Scales and Densities
- 2021
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 22:9, s. 3800-3809
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Tidskriftsartikel (refereegranskat)abstract
- Considering the growing use of cellulose in various applications, knowledge and understanding of its physical properties become increasingly important. Thermal conductivity is a key property, but its variation with porosity and density is unknown, and it is not known if such a variation is affected by fiber size and temperature. Here, we determine the relationships by measurements of the thermal conductivity of cellulose fibers (CFs) and cellulose nanofibers (CNFs) derived from commercial birch pulp as a function of pressure and temperature. The results show that the thermal conductivity varies relatively weakly with density (ρsample = 1340–1560 kg m–3) and that its temperature dependence is independent of density, porosity, and fiber size for temperatures in the range 80–380 K. The universal temperature and density dependencies of the thermal conductivity of a random network of CNFs are described by a third-order polynomial function (SI-units): κCNF = (0.0787 + 2.73 × 10–3·T – 7.6749 × 10–6·T2 + 8.4637 × 10–9·T3)·(ρsample/ρ0)2, where ρ0 = 1340 kg m–3 and κCF = 1.065·κCNF. Despite a relatively high degree of crystallinity, both CF and CNF samples show amorphous-like thermal conductivity, that is, it increases with increasing temperature. This appears to be due to the nano-sized elementary fibrils of cellulose, which explains that the thermal conductivity of CNFs and CFs shows identical behavior and differs by only ca. 6%. The nano-sized fibrils effectively limit the phonon mean free path to a few nanometers for heat conduction across fibers, and it is only significantly longer for highly directed heat conduction along fibers. This feature of cellulose makes it easier to apply in applications that require low thermal conductivity combined with high strength; the weak density dependence of the thermal conductivity is a particularly useful property when the material is subjected to high loads. The results for thermal conductivity also suggest that the crystalline structures of cellulose remain stable up to at least 0.7 GPa.
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| 16. |
- Baş, Yağmur, et al.
(författare)
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Preparation and Characterization of Softwood and Hardwood Nanofibril Hydrogels: Toward Wound Dressing Applications
- 2023
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 24:12, s. 5605-5619
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogels of cellulose nanofibrils (CNFs) are promising wound dressing candidates due to their biocompatibility, high water absorption, and transparency. Herein, two different commercially available wood species, softwood and hardwood, were subjected to TEMPO-mediated oxidation to proceed with delignification and oxidation in a one-pot process, and thereafter, nanofibrils were isolated using a high-pressure microfluidizer. Furthermore, transparent nanofibril hydrogel networks were prepared by vacuum filtration. Nanofibril properties and network performance correlated with oxidation were investigated and compared with commercially available TEMPO-oxidized pulp nanofibrils and their networks. Softwood nanofibril hydrogel networks exhibited the best mechanical properties, and in vitro toxicological risk assessment showed no detrimental effect for any of the studied hydrogels on human fibroblast or keratinocyte cells. This study demonstrates a straightforward processing route for direct oxidation of different wood species to obtain nanofibril hydrogels for potential use as wound dressings, with softwood having the most potential.
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| 17. |
- Bátori, Veronika, 1980-
(författare)
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Fruit wastes to biomaterials : Development of biofilms and 3D objects in a circular economy system
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To address the current plastic pollution problem, the replacement of conventional plastics with bioplastics can be considered. Although the land use of crop cultivation for bioplastics is still negligible, there is an increasing interest in the utilisation of lignocellulosic waste products for the production of bioplastics. A latest trend in researching sources for bioplastic production focuses on the use of fruit and vegetable wastes because of their versatile polysaccharides. Among different fruit wastes, orange waste and apple pomace have been evaluated as raw materials in this thesis.The development of biofilms and 3D objects from the above-mentioned raw materials via the solution casting and compression moulding methods was investigated. Biocomposites are generally made from a bioplastic matrix and reinforcement, or a plastic reinforced with natural fibres. In the present study, pectin was used as a matrix, and cellulosic fibres wereused as reinforcement. Orange waste films had an opaque appearance with a yellowish colour and were very flexible, while the 3D objects had brown colour. The films had mechanical properties comparable with those of commodity plastics, such as 32 to 36 MPa tensile strength. The films were biodegradable under anaerobic conditions, and 3D objects showed good biodegradability in soil. Grafting of orange waste with maleic anhydride was performed in order to improve its properties, e.g. the hydrophilicity of the polysaccharides-based materials. Grafting reduced the density by 40 % and increased the hydrophobicity compared with unmodified orange waste. Further improvements included upgrading the film casting method and incorporating maleic anhydride in the recipe. The lowest amount of necessary maleic anhydride was determined (0.4 %), and the resulting films had a smoother and more uniform surface. The original methods were also applied to apple pomace in order to produce films and 3D objects. Films from apple pomace had an elongation of 55 %, a twofold increase compared to that of orange waste films containing maleic anhydride (28 %). Orange waste and apple pomace were also mixed for 3D object fabrication, achieving the highest strength of 5.8 MPa (ratio of 75 to 25, respectively) a threefold increase compared to that achieved with only orange waste alone (1.8 MPa).The results are promising‚ but further improvements, e.g. in respect to hydrophilicity and upscaling‚ are needed for orange waste and apple pomace to develop into raw materials for next-generation bioplastics.
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| 18. |
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| 19. |
- Bengtsson, Magnus, et al.
(författare)
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Durability and mechanical properties of silane cross-linkedwood thermoplastic composites
- 2007
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 67:13, s. 2728-2738
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Tidskriftsartikel (refereegranskat)abstract
- In this study, silane cross-linked wood-polyethylene composite profiles were manufactured by reactive extrusion. These composites were evaluated regarding their durability and mechanical properties in comparison with two non-cross-linked wood-polyethylene composites. An addition of only 2% w/w of silane solution during manufacturing was enough to achieve almost 60% degree of cross-linking after curing. The cross-linked composites showed flexural toughness superior to the non-cross-linked composites. The cross-linked composites also absorbed less moisture during a boiling test in water and this was an indirect evidence of improved interfacial adhesion. After accelerated weathering for 1000-3000 h the general trend was a decrease in flexural modulus and strength of both the non-cross-linked and cross-linked composites. The decrease in modulus seemed to be lower for the cross-linked composites while the decrease in strength seemed to be higher compared to the non-cross-linked composites. Weathering also resulted in a considerable colour fading of the composites. Water absorption-freeze-thaw cycling decreased the flexural modulus of non-cross-linked composites considerably while there was no statistical decrease in modulus for the cross-linked composites. There was only an insignificant decrease in strength for the composites after the water absorption-freeze-thaw cycling.
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| 20. |
- Bengtsson, Magnus, et al.
(författare)
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Extrusion and mechanical properties of highly filled cellulose fibre-polypropylene composites
- 2007
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 38:8, s. 1922-1931
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Tidskriftsartikel (refereegranskat)abstract
- This study focused on manufacturing of highly filled cellulose fibre-polypropylene composites and evaluation of the mechanical properties of the composites. Cellulose fibre reinforced polypropylene composites with up to 60 wt-% of fibres with and without coupling agent were manufactured by extrusion. In order to achieve consistent feeding of the fibres into the extruder a pelletization technique was used where the fibres were pressed into pellets. Two commercial grades of cellulose fibres were used in the study, bleached sulfite and bleached kraft fibres. Fibre dimension measurements showed that the pelletization process and extrusion at high fibre loading caused the most severe fibre breakage. Flexural testing showed that increased fibre loading made the composites stiffer but reduced the toughness. Addition of maleic anhydride grafted coupling agent increased the stiffness and strength of the composites significantly. In general, there was no significant difference in the mechanical properties between the composites with kraft and sulfite fibres. Scanning electron microscopy showed that addition of coupling agent improved the interfacial adhesion between the fibres and polypropylene matrix.
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| 21. |
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| 22. |
- Bengtsson, Magnus, et al.
(författare)
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Profile Extrusion and Mechanical Properties of Crosslinked Wood-Thermoplastic Composites
- 2006
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 27:2, s. 184-194
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Tidskriftsartikel (refereegranskat)abstract
- Challenges for wood-thermoplastic composites to be utilized in structural applications are to lower product weight and to improve the long-term load performance. Silane crosslinking of the composites is one way to reduce the creep during long-term loading and to improve the mechanical properties. In this study, silane crosslinked wood-polyethylene composites were produced by reactive extrusion and subsequently manufactured into rectangular profiles. The silane crosslinked composites were stored in a sauna at 90 °C to increase the degree of crosslinking. The toughness of the silane crosslinked composites was significantly higher than for the non-crosslinked composites. Improved adhesion between the wood and polyethylene phases is most likely the reason for the improved toughness of the crosslinked composites. There was no significant difference in flexural modulus between the crosslinked and non-crosslinked composites. In addition, impact testing showed that the impact strength of the crosslinked composites was considerable higher (at least double) than the non-crosslinked. The effect of temperature on the impact strength of the composites indicated slightly higher impact strength at _30 °C than at 0° and at 25 °C, and then an incrase in impact strength at 60 °C. Crosslinking also reduced the creep response during short-term loading. Moreover, scanning electron microscopy on the fracture surface of the crosslinked composites revealed good adhesion between the polyethylene and wood phases.
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| 23. |
- Bengtsson, Magnus, et al.
(författare)
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Silane crosslinked wood plastic composites : Processing and properties
- 2006
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 66:13, s. 2177-2186
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Tidskriftsartikel (refereegranskat)abstract
- The focus of the study has been to produce silane crosslinked wood plastic composites in a compounding process. Silane crosslinking is one way to improve the mechanical and long-term properties of wood plastic composites. Silane crosslinked composites with different amounts of vinyltrimethoxy silane were produced in a compounding process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Gel content and swelling experiments showed that the highest degree of crosslinking was found in the composites stored in a sauna. The crosslinked composites showed toughness, impact strength and creep properties superior to those composites to which no silane was added. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. Differential scanning calorimetry measurements of the composites showed a lower crystallinity in the crosslinked samples than in the non-crosslinked.
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| 24. |
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| 25. |
- Bengtsson, Magnus, et al.
(författare)
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The effect of crosslinking on the properties of polyethylene/wood flour composites
- 2005
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 65:10, s. 1468-1479
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the possibility of using silane technology in crosslinking composites of wood flour and polyethylene has been investigated. Composites of vinyltrimethoxy silane grafted high density polyethylene and wood flour were produced by compounding in a twin-screw extruder. Gel content analysis with p-xylene extraction revealed higher gel content in the samples where wood flour was added compared to neat crosslinked matrix. Mechanical analysis of the crosslinked composites showed increased tensile strength with increasing amount of wood flour, which might be an indication of improved adhesion between the matrix and the wood flour. The stiffness increased with increasing amount of wood flour with accompanied decrease in strain at break. Dynamic mechanical thermal analysis of crosslinked plastics and composites showed no significant shift in the γ-transition towards higher temperature for the composites compared to neat plastic. Short-term creep experiments showed reduced creep deformation with increasing amount of wood flour. Crosslinking of the composites reduced the creep deformation further. A boiling test in water followed by tensile testing showed that the crosslinked composites were less susceptible to water uptake compared to the non-crosslinked. Moreover, the decrease in tensile strength of the crosslinked composites was not as significant as for the non-crosslinked composites. Scanning electron microscopy revealed good compatibility and adhesion between the plastic and the wood flour for crosslinked composites.
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| 26. |
- Bengtsson, Magnus, et al.
(författare)
-
The use of silane technology in crosslinking polyethylene/wood flour composites
- 2006
-
Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 37:5, s. 752-765
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the use of silane technology in crosslinking polyethylene-wood flour composites have been investigated. Composites were produced in a one-step process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Crosslinked composites showed improved toughness and creep properties compared to non-crosslinked composites. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. FTIR was used to study the crosslinking reaction in the samples. X-ray mapping of the silicon signal was also performed to locate the silane in the composites. This study provides a basis for proposing, that part of the silane is grafted onto polyethylene and wood thereby creating a crosslinked network in the matrix with chemical bonds (covalent and hydrogen bonding) to wood. The other part of the silane remains un-reacted and blends into the system.
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| 27. |
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| 28. |
- Berglund, Linn
(författare)
-
From bio-based residues to nanofibers using mechanical fibrillation for functional biomaterials
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bio-based resource utilization in different forms has been driven by societal, industrial and academic research interests towards the development of “green”, sustainable materials from renewable sources. Within this context, exploiting biomass from different industrial residues is further advantageous from an environmental and economic point of view, leading to minimization of residues by means of waste treatment and to the development of high-addedvalue- products. Breaking down the cell wall structure to its smallest structural components is one means of turning bio-based residues into high-value products, leaving us with nanofibers. The aim of this work has been to understand how these nanofibers can be liberated from various cellulosic sources using mechanical fibrillation and how they can be assembled into functional hydrogels.The production of bio-based nanofibers as a sustainable bio-based material is in the early stages of commercialization and considerable research has been devoted to explore different methods of reaching nanoscale. However, the extraction process by chemical and/or mechanical means is still associated with a relatively high energy demand and/or cost. These are key obstacles for use of the material in a wide range of applications. Another challenge is that methods to characterize nanofiber dimensions are still being developed, with few options available as online measurements for assessing the degree of fibrillation. Allowing for assessment during the fibrillation process would enable not only optimization towards a more energy efficient fibrillation, but also matching of the nanofiber quality to its intended function, since different applications will require widely different nanofiber qualities. Energy-efficient fibrillation and scalability from industrial residues were explored using upscalable ultrafine grinding processes.Nanofibers from various industrial bio-residues and wood were prepared and characterized, including the development of a method for evaluation of the fibrillation process online via viscosity measurements as an indication of the degree of fibrillation down to nanoscale. Furthermore, the correlation of viscosity to that of the strength of the nanopapers (dried fiber networks) was evaluated for the different raw materials.Switchable ionic liquids (SIL) were tested as a green pretreatment for delignification, without bleaching of wood prior to fibrillation, with the aim to preserve the low environmental impact that the raw material source offers.In order to employ the hydrophilic nature and strong network formation ability of the fibrillated nanofibers, they were utilized in the preparation of functional biomaterials in the form of hydrogels. Firstly, brewer’s spent grain nanofibers were used to promote and reinforce hydrogel formation of lignin-containing arabinoxylan, resulting in a hydrogel completely derived from barley residues. In addition, alginate-rich seaweed nanofibers from the stipe (stem-like part of the seaweed) were used directly after fibrillation as an ink and hydrogels were formed via 3D printing.
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| 29. |
- Berglund, Linn, et al.
(författare)
-
Production potential of cellulose nanofibers from industrial residues : Efficiency and nanofiber characteristics
- 2016
-
Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 92, s. 84-92
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate the production potential of cellulose nanofibers from two different industrial bio-residues: wastes from the juice industry (carrot) and the beer brewing process (BSG). The mechanical separation of the cellulose nanofibers was by ultrafine grinding. X-ray diffraction (XRD) and Raman spectroscopy revealed that the materials were mechanically isolated without significantly affecting their crystallinity. The carrot residue was more easily bleached and consumed less energy during grinding, using only 0.9 kWh/kg compared to 21 kWh/kg for the BSG. The carrot residue also had a 10% higher yield than the BSG. Moreover, the dried nanofiber networks showed high mechanical properties, with an average modulus and strength of 12.9 GPa and 210 MPa, respectively, thus indicating a homogeneous nanosize distribution. The study showed that carrot residue has great potential for the industrial production of cellulose nanofibers due to its high quality, processing efficiency, and low raw material cost
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| 30. |
- Berglund, Linn, et al.
(författare)
-
Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial
- 2018
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 8:67, s. 38219-38228
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.
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| 31. |
- Berglund, Linn, et al.
(författare)
-
Seaweed-Derived Alginate–Cellulose Nanofiber Aerogel for Insulation Applications
- 2021
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:29, s. 34899-34909
-
Tidskriftsartikel (refereegranskat)abstract
- The next generation of green insulation materials is being developed to provide safer and more sustainable alternatives to conventional materials. Bio-based cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties; however, their high flammability restricts their application. In this study, the design concept for the development of a multifunctional and non-toxic insulation material is inspired by the natural composition of seaweed, comprising both alginate and cellulose. The approach includes three steps: first, CNFs were separated from alginate-rich seaweed to obtain a resource-efficient, fully bio-based, and inherently flame-retardant material; second, ice-templating, followed by freeze-drying, was employed to form an anisotropic aerogel for effective insulation; and finally, a simple crosslinking approach was applied to improve the flame-retardant behavior and stability. At a density of 0.015 g cm–3, the lightweight anisotropic aerogels displayed favorable mechanical properties, including a compressive modulus of 370 kPa, high thermal stability, low thermal conductivity (31.5 mW m–1 K–1), considerable flame retardancy (0.053 mm s–1), and self-extinguishing behavior, where the inherent characteristics were considerably improved by crosslinking. Different concentrations of the crosslinker altered the mechanical properties, while the anisotropic structure influenced the mechanical properties, combustion velocity, and to some extent thermal conductivity. Seaweed-derived aerogels possess intrinsic characteristics that could serve as a template for the future development of sustainable high-performance insulation materials.
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| 32. |
- Berglund, Linn, et al.
(författare)
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Self-Assembly of Nanocellulose Hydrogels Mimicking Bacterial Cellulose for Wound Dressing Applications
- 2023
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 24:5, s. 2264-2277
-
Tidskriftsartikel (refereegranskat)abstract
- The self-assembly of nanocellulose in the form of cellulose nanofibers (CNFs) can be accomplished via hydrogen-bonding assistance into completely bio-based hydrogels. This study aimed to use the intrinsic properties of CNFs, such as their ability to form strong networks and high absorption capacity and exploit them in the sustainable development of effective wound dressing materials. First, TEMPO-oxidized CNFs were separated directly from wood (W-CNFs) and compared with CNFs separated from wood pulp (P-CNFs). Second, two approaches were evaluated for hydrogel self-assembly from W-CNFs, where water was removed from the suspensions via evaporation through suspension casting (SC) or vacuum-assisted filtration (VF). Third, the W-CNF-VF hydrogel was compared to commercial bacterial cellulose (BC). The study demonstrates that the self-assembly via VF of nanocellulose hydrogels from wood was the most promising material as wound dressing and displayed comparable properties to that of BC and strength to that of soft tissue.
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| 33. |
- Berglund, Linn, et al.
(författare)
-
Switchable ionic liquids enable efficient nanofibrillation of wood pulp
- 2017
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 24:8, s. 3265-3279
-
Tidskriftsartikel (refereegranskat)abstract
- Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.
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| 34. |
- Berglund, Linn, et al.
(författare)
-
Toward eco-efficient production of natural nanofibers from industrial residue : Eco-design and quality assessment
- 2020
-
Ingår i: Journal of Cleaner Production. - : Elsevier. - 0959-6526 .- 1879-1786. ; 255
-
Tidskriftsartikel (refereegranskat)abstract
- Conversion of bio-based industrial residues into high value-added products such as natural nanofibers is advantageous from an environmental and economic perspective, promoting resource efficiency along with the utilization of renewable materials. However, in order to employ the benefits of the raw material; its eco-efficient production should further be developed. Within this context, eco-design optimization through life cycle assessment (LCA) combined with life cycle costing (LCC) were applied to target eco-efficient production of natural nanofibers from carrot residue, along with quality assessment. The initial production steps included pretreatment combined mechanical nanofibrillation via ultrafine grinding, where the largest contributors to the environmental impact were identified as chemicals and energy. These were targeted by omitting the alkali pretreatment step and instead applying direct bleaching prior to nanofibrillation. After eco-design optimization, the yield increased while the energy, chemical, and water use significantly decreased. Therefore, a reduced environmental impact of more than 75% each for carbon footprint, freshwater ecotoxicity, and human toxicity was shown, along with a cost reduction of more than 50%. The use of carrot residue displayed an efficient conversion into natural nanofibers that was further promoted with the use of eco-design, yet with sustained functionality and nanoscaled dimensions, thus promoting resource-efficiency and natural nanofiber implementation in a wide range of promising bio-based applications.
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| 35. |
- Berglund, Linn, et al.
(författare)
-
Utilizing the Natural Composition of Brown Seaweed for the Preparation of Hybrid Ink for 3D Printing of Hydrogels
- 2020
-
Ingår i: ACS Applied Bio Materials. - : American Chemical Society (ACS). - 2576-6422. ; 3:9, s. 6510-6520
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to utilize the natural composition of brown seaweed by deriving alginate and cellulose concurrently from the stipe (stem-like) and blade (leaf-like) structures of the seaweed; further, this is followed by fibrillation for the direct and resource-efficient preparation of alginate/cellulose nanofiber (CNF) hybrid inks for three-dimensional (3D) printing of hydrogels. The efficiency of the fibrillation process was evaluated, and the obtained gels were further studied with regard to their rheological behavior. As a proof of concept, the inks were 3D printed into discs, followed by cross-linking with CaCl2 to form biomimetic hydrogels. It was shown that the nanofibrillation process from both seaweed structures is very energy-efficient, with an energy demand lower than 1.5 kW h/kg, and with CNF dimensions below 15 nm. The inks displayed excellent shear-thinning behavior and cytocompatibility and were successfully printed into 3D discs that, after cross-linking, exhibited an interconnected network structure with favorable mechanical properties, and a cell viability of 71%. The designed 3D biomimetic hydrogels offers an environmentally benign, cost-efficient, and biocompatible material platform with a favorable structure for the development of biomedical devices, such as 3D bio printing of soft tissues.
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| 36. |
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| 37. |
- Bondeson, Daniel, et al.
(författare)
-
All cellulose nanocomposites produced by compounding extrusion
- 2007
-
Ingår i: Journal of Biobased Materials and Bioenergy. - : American Scientific Publishers. - 1556-6560 .- 1556-6579. ; 1:3, s. 367-371
-
Tidskriftsartikel (refereegranskat)abstract
- A transparent biobased nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC), was produced by melt extrusion. The cellulose nanowhiskers were prepared from commercially available microcrystalline cellulose (MCC) by hydrochloric acid hydrolysis. The plasticizer, TEC, was solved in the whisker suspension and this suspension was pumped into the extruder during the compounding process. Scanning electron microscopy, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposite. The tensile modulus and strength indicated an improvement with 300% and 100%, respectively, compared to neat CAB but the elongation at break was decreased. Further more, the softening temperature of CAB was extended for the nanocomposite. Results from DMTA showed that the tanδ peak temperature was shifted by 31 °C, from 117 °C to 148 °C with addition of CNW in CAB. The extrusion process with liquid feeding was shown to be successful for this material combination. AbstractA transparent biobased nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC), was produced by extrusion compounding. The cellulose nanowhiskers were prepared from commercially available microcrystalline cellulose (MCC) by hydrochloric acid hydrolysis. The plasticizer, TEC, was solved in the whisker suspension and this suspension was pumped into the extruder during the compounding process. Scanning electron microscopy, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposite. The tensile modulus and strength were improved with 300% and 100%, respectively, compared to neat CAB but the elongation at break was decreased. Further more, the softening temperature of CAB was extended for the nanocomposite. Results from DMTA showed that the tan d peak temperature was shifted by 31 ˚C, from 117 °C to 148 ˚C with addition of CNW in CAB.
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| 38. |
- Bondeson, Daniel, et al.
(författare)
-
Bio-nanocomposites based on cellulose whiskers
- 2006
-
Ingår i: 6th Global Wood and Natural Fibre Composites Symposium. - : Lehrstuhl Kunststoff- und Recyclingtechnik. - 8360140871
-
Konferensbidrag (refereegranskat)
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| 39. |
- Bondeson, Daniel, et al.
(författare)
-
Dispersion and characteristics of surfactant modified cellulose whiskers nanocomposites
- 2007
-
Ingår i: Composite interfaces (Print). - : Informa UK Limited. - 0927-6440 .- 1568-5543. ; 14:7-9, s. 617-630
-
Tidskriftsartikel (refereegranskat)abstract
- Biodegradable nanocomposites based on 5 wt% cellulose nanowhiskers (CNW) and polylactic acid (PLA) were prepared using an extrusion process. An anionic surfactant (5, 10, and 20 wt%) was used to improve the dispersion of the CNW in the PLA matrix. The results showed that increased surfactant content resulted in improved dispersion but at the same time degraded the PLA matrix. The results from mechanical testing showed a maximum modulus for the composite with 5 wt% surfactant and as the surfactant content increased, the CNW dispersion improved and the tensile strength and elongation at break was improved compared to its unreinforced counterpart.
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| 40. |
- Bondeson, Daniel, et al.
(författare)
-
Optimization of the Isolation of Nanocrystals from Microcrystalline Cellulose by Acid Hydrolysis
- 2006
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 13:2, s. 171-180
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as the starting material. The processing parameters have been optimized by using response surface methodology. The factors that varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between 200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight).
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| 41. |
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| 42. |
- Bondeson, Daniel, et al.
(författare)
-
Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol
- 2007
-
Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 38:12, s. 2486-2492
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.
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| 43. |
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| 44. |
- Butchosa Robles, Núria, 1984-
(författare)
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Tailoring Cellulose Nanofibrils for Advanced Materials
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose nanofibrils (CNFs) are nanoscale fibers of high aspect ratio that can be isolated from a wide variety of cellulosic sources, including wood and bacterial cellulose. With high strength despite of their low density, CNFs are a promising renewable building block for the preparation of nanostructured materials and composites. To fabricate CNF-based materials with improved inherent rheological and mechanical properties and additional new functionalities, it is essential to tailor the surface properties of individual CNFs. The surface structures control the interactions between CNFs and ultimately dictate the structure and macroscale properties of the bulk material. In this thesis we have demonstrated different approaches, ranging from non-covalent adsorption and covalent chemical modification to modification of cellulose biosynthesis, to tailor the structure and surface functionalities of CNFs for the fabrication of advanced materials. These materials possess enhanced properties such as water-redispersibility, water absorbency, dye adsorption capacity, antibacterial activity, and mechanical properties.In Paper I, CNFs were modified via the irreversible adsorption of carboxymethyl cellulose (CMC). The adsorption of small amounts of CMC onto the surface of CNFs prevented agglomeration and co-crystallization of the nanofibrils upon drying, and allowed the recovery of rheological and mechanical properties after redispersion of dried CNF samples.In Paper II, CNFs bearing permanent cationic charges were prepared through quaternization of wood pulp fibers followed by mechanical disintegration. The activation of the hydroxyl groups on pulp fibers by alkaline treatment was optimized prior to quaternization. This optimization resulted in individual CNFs with uniform width and tunable cationic charge densities. These cationic CNFs demonstrated ultrahigh water absorbency and high adsorption capacity for anionic dyes.In Paper III, via a similar approach as in Paper II, CNFs bearing polyethylene glycol (PEG) were prepared by covalently grafting PEG to carboxylated pulp fibers prior to mechanical disintegration. CNFs with a high surface chain density of PEG and a uniform width were oriented to produce macroscopic ribbons simply by mechanical stretching of the CNF hydrogel network before drying. The uniform grafted thin monolayer of PEG on the surface of individual CNFs prevented the agglomeration of CNFs and facilitated their alignment upon mechanical stretching, thus resulted in ribbons with ultrahigh tensile strength and modulus. These optically transparent ribbons also demonstrated interesting biaxial light scattering behavior.In Paper IV, bacterial cellulose (BC) was modified by the addition of chitin nanocrystals (ChNCs) into the growing culture medium of the bacteria Acetobacter aceti which secretes cellulose in the form of entangled nanofibers. This led to the in situ incorporation of ChNCs into the BC nanofibers network and resulted in BC/ChNC nanocomposites exhibiting bactericidal activity. Further, blending of BC nanofibers with ChNCs produced nanocomposite films with relatively lower tensile strength and modulus compared to the in situ cultivated ones. The bactericidal activity increased significantly with increasing amount of ChNCs for nanocomposites prepared by direct mixing of BC nanofibers and ChNCs.In Paper V, CNFs were isolated from suspension-cultured wild-type (WT) and cellulose-binding module (CBM) transformed tobacco BY-2 (Nicotiana tabacum L. cv bright yellow) cells. Results from strong sulfuric acid hydrolysis indicated that CNFs from transgenic cells overexpressing CBM consisted of longer cellulose nanocrystals compared to CNFs from WT cells. Nanopapers prepared from CNFs of transgenic cells demonstrated significantly enhanced toughness compared to CNFs of WT cells.
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| 45. |
- Butylina, Svetlana, et al.
(författare)
-
Cellulose Nanocomposite Hydrogels : From Formulation to Material Properties
- 2020
-
Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(vinyl alcohol) (PVA) hydrogels produced using the freeze-thaw method have attracted attention for a long time since their first preparation in 1975. Due to the importance of polymer intrinsic features and the advantages associated with them, they are very suitable for biomedical applications such as tissue engineering and drug delivery systems. On the other hand, there is an increasing interest in the use of biobased additives such as cellulose nanocrystals, CNC. This study focused on composite hydrogels which were produced by using different concentrations of PVA (5 and 10%) and CNC (1 and 10 wt.%), also, pure PVA hydrogels were used as references. The main goal was to determine the impact of both components on mechanical, thermal, and water absorption properties of composite hydrogels as well as on morphology and initial water content. It was found that PVA had a dominating effect on all hydrogels. The effect of the CNC addition was both concentration-dependent and case-dependent. As a general trend, addition of CNC decreased the water content of the prepared hydrogels, decreased the crystallinity of the PVA, and increased the hydrogels compression modulus and strength to some extent. The performance of composite hydrogels in a cyclic compression test was studied; the hydrogel with low PVA (5) and high CNC (10) content showed totally reversible behavior after 10 cycles.
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| 46. |
- Butylina, Svetlana, et al.
(författare)
-
Properties of as-prepared and freeze-dried hydrogels made from poly(vinyl alcohol) and cellulose nanocrystals using freeze-thaw technique
- 2016
-
Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 81, s. 386-396
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Tidskriftsartikel (refereegranskat)abstract
- Poly(vinyl alcohol), PVA hydrogels are potential materials for biomedical and biotechnogical applications. However, their low mechanical properties restrict their use. In this study, the effect of PVA concentration, addition of nanocrystalline cellulose, CNC, number of freeze-thaw cycles and freeze-drying stage on properties of resulting hydrogels were investigated. The results showed that increase in PVA concentration and the addition of CNC improved the compressive properties of the hydrogels. Overall, increase in number of freeze-thaw cycles from 3 to 5 did not show any improvements in properties of hydrogels. Concentration of PVA had great effect on morphology of freeze-dried hydrogels. The CNC reduced crystallinity of PVA/CNC hydrogels as compared to PVA hydrogels. Rehydrated PVA and PVA/CNC hydrogels had higher compressive characteristics than their as-prepared analogues. In general, an improvement of compressive properties of hydrogels was achieved via reduction of their water content. In case of 5% PVA hydrogel, an addition of CNC was found to be beneficial because it increased degree of swelling and water content on rehydration.
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| 47. |
-
Cellulose nanocomposites : processing, characterization and properties
- 2005
-
Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The book will deal with new nanostructured composites, where both the reinforcement and the matrix are bio based. Cellulose combined with natural polymers led to the development of a new class of biodegradable and environmental friendly bionanocomposites. This new family of nanocomposites is expected to have remarkable improvement of material properties when compared with the matrix polymers or conventional micro- and macro-composite materials. Such improvements in properties typically include a higher modulus and strength, improved barrier properties, increased heat distortion temperature. This new class of renewable nanocomposites is expected to capture new market in transportation, medical and packaging applications. This book will include the raw materials which can be used for making these composites, separation/isolation technologies of cellulose based reinforcements from diverse natural resources and it will also include a brief overview of the recent advancements in the surface chemistry of nanocellulose. Characterization methods such as atomic force microscope (AFM), transmission electron microscope (TEM) and scanning electron microscope (SEM), Raman Spectroscopy, for the nano scale cellulose reinforcements and for the bio-nanocomposites will be discussed. Further, different processing methods for nanocomposites and their mechanical, thermal properties, barrier properties will be included. This will be the first book on the topic of cellulose based Nanocomposites! This is a relatively new research field and there are no books available on this topic. There is a growing interest on biopolymer based nanocomposites in developed and developing world (Japan, USA, Europe, China, South Africa, Australia) and especially if the nanocomposites are based totally on renewable raw materials. We can see several ongoing research projects on this topic in Europe and North America, and there is an emerging research trend for developing micro-and nano-fibre reinforced biopolymers.
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| 48. |
- Deepa, B., et al.
(författare)
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Utilization of various lignocellulosic biomass for the production of nanocellulose : a comparative study
- 2015
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 22:2, s. 1075-1090
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose was successfully extracted from five different lignocellulosic biomass sources viz. banana rachis, sisal, kapok, pineapple leaf and coir using a combination of chemical treatments such as alkaline treatment, bleaching and acid hydrolysis. The shape, size and surface properties of the nanocellulose generally depend on the source and hydrolysis conditions. A comparative study of the fundamental properties of raw material, bleached and nanocellulose was carried out by means of Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, birefringence, X-ray diffraction, inverse gas chromatography and thermogravimetric analysis. Through the characterization of the nanocellulose obtained from different sources, the isolated nanocellulose showed an average diameter in the range of 10–25 nm, high crystallinity, high thermal stability and a great potential to be used with acid coupling agents due to a predominantly basic surface. This work provides an insight into the effective utilization of a variety of plant biomass as a potential source for nanocellulose extraction.
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| 49. |
- Duchemin, Benoit, et al.
(författare)
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All-cellulose composites by partial dissolution in the ionic liquid 1-butyl-3-methylimidazolium chloride
- 2009
-
Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 40:12, s. 2031-2037
-
Tidskriftsartikel (refereegranskat)abstract
- Fully bio-based and biodegradable all-cellulose composites were prepared in the form of films by partial dissolution of two cellulose sources: a commercially available microfibrillated cellulose (MFC) and filter paper (FP). The solvent selected for this work was the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl). Both cellulose sources were partially dissolved at 80 °C and consolidated by partial dissolution, resulting in excellent mechanical properties. X-ray diffraction and electron microscopy demonstrated that partial dissolution was a viable path to transform FP into a continuous paracrystalline matrix reinforced with cellulose I crystallites. In contrast, partially dissolved MFC was not as thoroughly dissolved and large amounts of undissolved material were still visible along the center line of the films after the longest dissolution times. Consequently, partially dissolved MFC retained its initially high crystallinity. The degree of polymerization of the materials after dissolution was significantly reduced.
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|
| 50. |
|
|
