Browsing by Author "Borghei, Maryam, Dr., 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.
Nanocellulose Interactions with Protein and Water in Advanced Sensing Systems
(2022) Solin, Katariina
School of Chemical Engineering | Doctoral dissertation (article-based)
In this work, cellulosic nanomaterials were investigated for application as fluidic and sensing platforms. These platforms were used for humidity measurement, biosensors, and immunoassays, which are relevant to the areas of diagnostics, printed electronics, and smart packaging. A systematic investigation was carried out to study the interactions between water and protein molecules with cellulosic materials, which was facilitated by advanced techniques such as quartz microgravimetry, surface plasmon resonance, and confocal microscopy. Humidity responsive and electroactive composite films were developed using hybrid materials composed of nanocellulose and carbon nanotubes. The changes in relative humidity of air were monitored by measuring the shift in electroacoustic admittance and electrical resistivity of composite films upon water uptake. Other systems that incorporated mineral particles and nano-and microcellulose were used for lateral flow assays (LFA) based on fluidic wicking. For this purpose, inkjet printing was used to produce hydrophobic channel sidewalls on nanopaper. Alternatively, stencil printing of the fluid-wicking element was applied on hydrophobic supports. These wicking systems showed the potential as new types of LFA devices with excellent sensitivity. Glucose, non-specific protein, and antigen detection were demonstrated by colorimetric sensing at clinically relevant concentrations. A new type of cellulose nanomaterial, cellulose II nanoparticles, was introduced as a substrate for controlled protein adsorption. The interactions and protein accessibility to surfaces treated with such cellulose II nanoparticles, which formed a hydrogel film, were investigated in detail. Cationic cellulose II nanoparticles (NPcat) showed one of the highest levels of accessibility recorded, following both specific and non-specific protein interactions, and suggested NPcat suitability as a new immobilizing agent for biomolecular sensing. Oppositely charged anionic cellulose II nanoparticles (NPan) were used for surface passivation and indicated a great potential as a blocking agent that can be deposited on substrates to minimize non-specific molecular interactions. Both cellulose nanospheres, NPcat and NPan were deployed in protein-accessible and protein-repellent materials, respectively, and facilitated the design of a rapid antigen sensing system for SARS-CoV-2 nucleocapsid.