| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
- Berglund, Linn
(författare)
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From bio-based residues to nanofibers using mechanical fibrillation for functional biomaterials
- 2019
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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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| 7. |
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| 8. |
- Butchosa Robles, Núria, 1984-
(författare)
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Tailoring Cellulose Nanofibrils for Advanced Materials
- 2014
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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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| 9. |
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Cellulose nanocomposites : processing, characterization and properties
- 2005
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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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| 10. |
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