Browsing by Author "Rojas, Orlando, Prof., Aalto University, Finland"

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Functional fibres by Wet-spinning of Bio-based Colloids
(2020) Wang, Ling
School of Chemical Engineering | Doctoral dissertation (article-based)
Chitin nanofibrils (ChNF), TEMPO-oxidized cellulose nanofibrils (TOCNF), lignocellulose nanofibrils (LCNF), and lignin were isolated from marine and plant biomass. Microfibres were synthesized by wet spinning of aqueous suspensions of the respective bio-based colloid. The influence of coagulant type in wet spinning as well as the properties of the microfibers obtained from TOCNF and ChNF were studied. In general, fibres coagulated via ion exchange demonstrated better mechanical properties and water/moisture stability. Meanwhile, a clear difference was found in thermal properties: TOCNF microfibres coagulated in aqueous electrolyte presented better thermal stability compared to those coagulated in organic solvents. All the TOCNF and ChNF microfibres were biocompatible as shown by in vitro tests, which indicate prospective applications in the biomedical fields. Lignin-based fibres were manufactured from either LCNF or aqueous lignin suspensions in the presence of TOCNF. An increased lignin loading resulted in microfibres of lower mechanical strength and better thermostability. Carbon microfibres were obtained by one-step carbonization. The higher lignin content in the precursor led to carbon microfibres at higher mass yields and displaying smoother surfaces and higher electroconductivity. The measured electroconductivity (up to 103 S/cm) make them suitable for microelectrodes and wearable electronics. Moreover, the carbon microfibres developed from LCNF suspensions were demonstrated in uses as fibre-shaped supercapacitors, which showed a promising performance. A prototype system for continuous wet-spinning was developed to increase the spinning rate and to optimize the process. This work highlights the use of renewable bioresources in the production of microfibers with no need for molecular dissolution. Thus, the wet-spinning technique is shown as a feasible and versatile approach to produce microfibres, furthering their potential in functional materials. Biobased colloids are suitable alternatives for adoption in fibre production, replacing petroleum-based precursors and opening new opportunities for green processing.
Functional Materials from Nanocellulosic Networks and Uses in Water Purification
(2020) Lehtonen, Janika
School of Chemical Engineering | Doctoral dissertation (article-based)
Due to their nano-scaled dimensions and mechano-chemical versatility, nanocelluloses have generated interest in the production of various types of bioproducts. However, the full potential of these materials and their applications, which are strongly coupled to their structural features, is yet to be realized. In this thesis, two types of nanocelluloses, cellulose nanofibrils (CNF) and bacterial nanocellulose (BNC), are introduced to achieve different types of porous networks and functional materials. The performance of CNF and CNF-based materials is investigated in applications related to water purification. Composites incorporating cationic CNF and silver nanoparticles are studied for use in drinking water disinfection. Phosphorylated CNF is implemented for the removal of uranium from water via batch adsorption. With BNC, the opportunities provided by biological fabrication of nanofibrous materials are considered in the synthesis of 2D membranes as well as intricate 3D structures. The impact of physico-chemical modifications of the fibrous networks in the BNC membranes are investigated to give insights on their potential use in pressure-driven filtration. To produce 3D structures from BNC, a simple method is developed utilizing hydrophobic particles for stabilization of air-water interfaces. Utilizing this method, capsules were produced and applied as sensors and enzymatic reactors in aqueous media. This thesis provides insights and novel pathways for the production and application of porous nanocellulose-based structures. They are expected to contribute to the development of future functional materials, for instance in the field of water purificaton.
Structuring of Nanocelluloses in 3-D Functional Materials
(2022) Ajdary, Rubina
School of Chemical Engineering | Doctoral dissertation (article-based)
This thesis investigates fundamental and practical aspects of the materials and methods used to assemble 3D structures from bio-based materials using mono- to multi-component systems through bottom-up and other processes. Fused Deposition Molding (FDM) and Direct Ink Writing (DIW) were used to fabricate structures with controlled geometries and properties. Nanocellulose from both microorganisms and wood featured promising biocompatibility and was investigated as primary subjects for the studies. We discuss the rheological requirements to process hydrogels by direct ink writing and address the effect of compositions and water interactions in the swelling of 3D-printed materials. The essential factors associated with cellular activities in biomedical applications were considered. The shear-thinning behavior of nanocellulose hydrogels facilitated the printability of the inks into defined shapes, which were investigated by using a wide range of needle sizes, lengths, and profiles. We discuss the effect of printing parameters and post-processing techniques on structural fidelity and properties. The nanocellulose-based mono and multi-component functional structures presented the advantages of inexpensive and fast production, dimensional retention and stability, ease of drying and rewetting process, thus facilitating packaging, transportation, and material sterilization while displaying excellent compatibility with cells. Material characterizations (for example, morphology, microstructure, mechanical performance, shrinkage, swelling, and degradation) were studied to define suitable applications for the developed structures. Our findings in this thesis are expected to facilitate future work to address standing challenges in constructing 3-dimensional bio-based materials.