Browsing by Author "Korhonen, Oona"

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All-cellulose composite aerogels and cryogels
(2020-10) Korhonen, Oona; Budtova, Tatiana
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Porous all-cellulose composites were prepared from pulps dissolved in 8 wt-% NaOH-water and dispersed softwood kraft fibers. Freeze-drying and drying with supercritical CO2 were used to vary the morphology of the composites. As cellulose dissolution in NaOH-water is known to be limited by pulp degree of polymerization, the latter was varied to obtain different amounts of non-dissolved fractions in solution. The goal of the work was to understand the influence of fibers originating from the incomplete dissolution and/or from added kraft fibers on the morphology and properties of porous all-cellulose composites. Density, porosity, pore volume, specific surface area and mechanical properties under compression were determined and correlated with the composite formulations and morphology.
All-cellulose composites from alfa and wood fibers
(2019-01-01) Labidi, Khaled; Korhonen, Oona; Zrida, Montassar; Hamzaoui, Ahmed Hichem; Budtova, Tatiana
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
All-cellulose composites (ACCs) in which both matrices and reinforcing fibers are made from lignocellulose were successfully obtained from alfa (Stipa tenacissima L) and wood (Genus Betula) fibers. Matrices were prepared either from alfa or wood pulps that were dissolved in 8 wt% NaOH-water, while reinforcing fibers were alfa in both matrices. Prior to the dissolution, alfa and wood pulps were acid hydrolyzed in order to decrease cellulose degree of polymerization to 149 and 145, respectively. The degree of cellulose dissolution was 95–96% for both alfa and wood dissolving pulps. X-ray diffraction (XRD) analysis confirmed the coexistence of cellulose I and II. The adhesion between the reinforcing fibers and both matrices was investigated using Scanning Electron Microscopy (SEM) and was found to be excellent. The density of ACCs decreased with the increase of the reinforcing fiber content for both types of matrices and ranged from 0.6 to 1.0 g.cm−3 leading to remarkably low-density ACCs. Young's modulus reached 3.8 and 4.2 GPa for the composites based on alfa and wood dissolving pulps, respectively, while yield stress reached 16 and 13.9 MPa, respectively.
All-cellulose composites via short-fiber dispersion approach using NaOH–water solvent
(2019-05-30) Korhonen, Oona; Sawada, Daisuke; Budtova, Tatiana
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Abstract: All-cellulose composites were prepared by dispersing short softwood kraft fibers in dissolving pulp-8 wt% NaOH–water. The degree of polymerization of the dissolving pulp used for the matrix and the concentration of reinforcing fibers were varied. Morphology, density, crystallinity, cellulose I content and mechanical properties of the composites were investigated. A special attention was paid on the presence of non-dissolved fibers originating from incomplete dissolution of pulp in 8 wt% NaOH–water thus decreasing the actual concentration of dissolved cellulose in matrix solution. This “lack of matter” induced the formation of pores, which strongly influenced the morphology of composites. Density was shown to be the main parameter contributing to the mechanical properties of the prepared all-cellulose composites. The results demonstrate the complexity of the system and the need in taking into account the dissolution power of the solvent. Graphical abstract: Morphology of all-cellulose composites: matrix is from low-DP dissolving pulp (a) and from high-DP pulp (b).[Figure not available: see fulltext.].
Elävät radikaalipolymerointimenetelmät selluloosan oksakopolymeroinnissa
(2013-12-02) Korhonen, Oona
Kemiantekniikan korkeakoulu | Bachelor's thesis
Eucalyptus soda/kraft process and production of sulfur-free lignin as an alternative to kraft process
(2015-12-15) Korhonen, Oona
Kemian tekniikan korkeakoulu | Master's thesis
Gelation of cellulose-NaOH solutions in the presence of cellulose fibers
(2019-08-01) Korhonen, Oona; Budtova, Tatiana
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
It is well known that when cellulose is dissolved in aqueous NaOH-based solvent, solutions are gelling with increasing time and temperature. The goal of this work was to understand if the presence of non-dissolved cellulose fibers influences gelation behavior of the whole system. One of the motivations is to control gelation when making all-cellulose composites with short fibers dispersed in cellulose-NaOH-water solutions. Gelation kinetics of cellulose(dissolving pulp)-NaOH-water solutions with added softwood kraft fibers were investigated using dynamic rheology. Fiber concentration, dissolving pulp degree of polymerization and solution temperature were varied. In all cases the addition of kraft fibers accelerates gelation and increases modulus at gel point while the presence of “inert” carbon fibers does not influence solution gelation kinetics. It was suggested that acceleration of gelation and reinforcement of cellulose gels is due to the interactions between dissolved and non-dissolved cellulose.
Short-Fiber Reinforced All-Cellulose Composites Using Aqueous NaOH Solution
(2020) Korhonen, Oona
School of Chemical Technology | Doctoral dissertation (article-based)
The demand for producing materials utilizing renewable resources instead of petroleum has increased with environmental concerns. This dissertation focuses on all-cellulose composites produced via short-fiber dispersion approach using commercial pulps as raw material and NaOH (aq) as cellulose solvent. The goal was to study the complete process of all-cellulose composite preparation and to understand how the pulp characteristics, special features of NaOH (aq) solvent and the processing parameters affect the material's properties. The influence of incomplete dissolution on the gelation properties of cellulose-NaOH systems was determined, different drying methods for all-cellulose composite production were studied and the effect of layer-by-layer hydrophobization treatment on the properties of these materials was examined. NaOH was found to be a suitable solvent for the production of all-cellulose composites if a sufficient concentration of dissolved cellulose in the matrix is achieved. The presence of non-dissolved cellulose in the cellulose-NaOH solution was found to reinforce the formed gels, but to accelerate gelation of the system, which should be taken into account for successful manufacturing. Density was found to be the main contributor to the mechanical performance of all-cellulose composites. Drying under compression resulted in materials with maximum Young's modulus of 8 GPa and tensile strength 53 MPa. In the case of porous all-cellulose composites prepared via supercritical drying, the addition of fibers significantly decreased the specific surface area. The best performance was found for the system containing only non-dissolved fiber fragments, which provided the reinforcement (compressive modulus 8 MPa), without sacrificing the high specific surface area (335 m2/g). Freeze-drying resulted in stronger materials, but surface area was significantly lower due to larger pores in the matrix. Additionally, the origin of the reinforcement (non-dissolved fragments or added fibers) was shown to have less influence on the composite's properties compared to fiber concentration. Layer by layer deposition of cationic starch and carnauba wax was shown to result in surface hydrophobized all-cellulose composites. Process optimisation was performed to obtain high water contact angle (122 °) while maintaining the composite mechanical properties. Overall, the results obtained in this work show that the properties of short-fiber reinforced all-cellulose composites can be altered and controlled, therefore allowing to design these materials to fulfil the requirements for various applications.