Welcome to this Licentiate seminar in Chemical Engineering with our PhD student Ran Duan. The title of the thesis is: On Shaping Mechanical Properties of Lignocellulosic Materials by Benign Chemical Processing.
In this licentiate thesis some different benign chemical approaches to change and shape mechanical properties of lignocellulosic materials were studied. Selective removal of lignin from lignocellulosic pulp by a switchable ionic liquid was investigated in order to determine the role of lignin for the strength properties of hand sheets and fibres in the first paper. In the second paper, lightweight polysaccharide-based foams were synthesized, characterised and tested for their water absorption capacity. Lastly, the effect of green-solvent plasticisation on lignocellulosic mechanical material properties was studied.
To selectively remove lignin from high-temperature chemi-thermomechanical pulp (HT-CTMP), we were using switchable ionic liquid (SIL) prepared from an organic superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)), monoethanol amine (MEA), and SO2. The relation between lignin content and tensile stress-displacement properties for the labsheets made from the treated HT-CTMP was studied with zero and short span tester. The tensile strength of the fibres that was measured indirectly revealed that the SIL treatment had a small influence on the strength properties.
Lightweight polysaccharide-based foams with bulk densities in the range of 10−25 kg/m3 and water absorption capacities between 30 to 80 times were synthesized in a two-step process. Esterification of cellulose was first made with citric anhydride followed by chemical crosslinking with chitosan through amide bond formation. Different low-cost and non-toxic organic acids were utilized as catalysts in the first step and the effects of the different reaction conditions on water absorbency and weight loss of the freeze-casted polysaccharide-citrate-chitosan foams were determined. Physical properties, such as pore-size distributions, compressive stress-strain curves of the foams were also determined.
Kraftliner sheets were plasticised by partial dissolution with sodium hydroxide and urea at −10 °C. Several layers of kraftliner were successfully "welded" together after regenerating the cellulose by hot pressing or anti-solvent infusion. The mechanical properties were evaluated by short span compression strength and 2-point bending stiffness. By using NaOH/urea for both single and laminated kraftliner sheets, the treated samples had around 50% higher short span compression strength compared with the sheets treated with water. The plasticised single layer sheet also showed a 30% higher 2-point bending stiffness than the sample treated with water.
Opponent will be Docent Daniel Söderberg, KTH.