Browsing by Author "Virtanen, Sanna"

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From wood to industrial polymeric biomaterials
(2018) Virtanen, Sanna
School of Chemical Technology | Doctoral dissertation (article-based)
Population growth, the dependence on fossil raw materials, and environmental problems caused by oil-based plastics have created a global need to search for alternative materials to replace conventional oil-based materials. Any effort to tackle such challenge, however, needs to meet the principles of sustainable development. Biodegradable and bio-based materials are promising candidates to support related bioeconomy strategies. Here, forest products are key players and, as such, this thesis targets the development of biocomposite materials by utilising wood as renewable source. The introduction of epoxy and silyl functional groups into wood-derived cellulose surface through chemical modiﬁcation seemed to provide an advantageous route to enhance cellulose nanoﬁbrils (CNF) dispersibility and compatibility with both polyvinyl alcohol (PVA) and polyurethane (PU) polymer matrices. The solution-casted PVA composites were developed by utilising the crosslinking reaction between the hydroxyl groups of PVA and epoxy groups of CNF. Using epoxidised CNF as reinforcement in PVA produced composites with outstanding mechanical properties already at low levels (0.5 to 1.5 wt.%). Additionally, the silylated CNF exhibit potential reinforcing additives already at low loadings in the water- and solvent-based two-component PU coatings by improving their strength, elasticity and abrasion resistance. The adhesion properties of the PU coatings to substrate were still retained when using the silylated CNF as additive. Modiﬁed wood-derived CNF provide fundamental improvements to PVA and PU properties, and are not only scientiﬁcally interesting but also industrially important. The study also demonstrates that moist, never-dried bleached softwood kraft pulp (BSKP) can be successfully melt compounded with polylactic acid (PLA) without chemical modiﬁcation, resulting in a composite with enhanced mechanical properties. By using BSKP with relatively high moisture content in feeding, the general drawbacks associated with ﬁbre cutting and degradation of PLA during melt processing were diminished. Also, the expensive and time-consuming stages involved in drying pulp ﬁbres can be curtailed by using this production route. The processability and properties of the PLA/BSKP composites facilitate their future industrialisation and unveil technically and economically feasible applications.
Mikro- ja nanofibrilloidun selluloosan reologia
(2015-12-07) Virtanen, Sanna
Kemiantekniikan korkeakoulu | Bachelor's thesis
Optimization of pulp drying line
(2020-06-16) Virtanen, Sanna
Kemian tekniikan korkeakoulu | Master's thesis
The aim of this thesis was to optimize pulp drying line and enhance tensile strength of pulp. The experimental part was divided into three parts: preliminary screening, screening experiment and optimization experiment. In the experimental part, tensile properties were tested using Valmet’s Paper Lab and fibre analysis was carried out using Valmet’s FS5. Addition to these, hornification was measured with WRV and internal bond strength was measured with a Scott bond tester. Experiments were carried out to bleached softwood kraft pulp. The objective of preliminary screening was to map pulp drying lines physical and chemical conditions from pulp storage tower to bale press and pinpoint equipment or process part that influences to pulp quality in a negative manner. Results showed that tensile index did not increase as expected in the press section. Screening experiment was based on the results of the preliminary screening and the literature review. The target was to investigate factors that affects tensile index in the press section. Plackett-Burman design was conducted for five factors: temperature, grammage, applied pressures of first, second and third presses. Results showed that applied pressures of second press and grammage were the main factors for tensile index. Results showed an indication that higher applied pressures could lead to increased tensile index and lower product hornification, as drying machine can be operated with milder temperatures. Optimization was based on the results of screening and observations that were made during the previous screening experiment. The objective of optimization experiment was to optimize the process with the first and second press pressures. Full factorial design was conducted. Results showed that applied pressures slightly increased tensile index. However, the increase in tensile strength was not significant enough to draw clear conclusions. Additional testing for hornification in the drying line is needed. Further studies are needed for applied pressures in the press section and their effects on hornification.