Public defence in Bioproduct Technology, M.Sc.(Tech.) Elina Warsta

Title of the thesis: Reactions of neutral sodium sulphite solutions with chemical components of wood and wood pulps

Thesis defender: Elina Warsta
Opponent: Prof. Merima Hasani, Chalmers University, Sweden
Custos: Prof. emeritus Tapani Vuorinen, Aalto University School of Chemical Engineering

In the dissertation, the reactions of neutral sodium sulphite solutions with wood, wood pulps, and their chemical components were investigated. Lignin, cellulose, and hemicelluloses are the main chemical components of wood.

A spectroscopic method was developed to evaluate the phenolic content of lignin using several lignin model compounds and wood pulp samples. The developed UV resonance Raman (UVRR) spectroscopic method was applied to structural studies of wood pulp samples and to assess the effects of neutral sulphite treatment on lignin reactions. In addition to lignin reactions and dissolution, it was observed that sulphite treatment at high temperature also cleaved cellulose chains.

The method developed in this work facilitates lignin analytics and enables a faster, non-destructive approach to analyzing samples and lignin reactivity compared with traditional chemical methods. A large proportion of lignin is burned for energy as process liquors in chemical forest industry; therefore, the development of lignin analytics is an essential part of increasing industrial value addition.

Neutral sulphite pulping is a pulping method that has been utilized only to a limited extent. In this study, the effects of neutral sulphite treatment on fibre properties were examined, and potential application areas were considered. The results indicate the possibility of producing higher-yield pulps compared with the prevailing kraft (sulphate) process, as well as potential for applications in bio-based materials that require tunable hydrophilicity and interaction with water. Sulphonated cellulose can be used, for example, in the concrete industry as a viscosity-increasing agent or as a so-called superplasticizer, which acts on the surface of cement particles, causing dispersion and reducing coagulation. Cellulose sulphonic acid can also be used as a solid acid catalyst in the chemical industry, for example in biodiesel production. Traditional homogeneous catalysts are challenging due to toxic and corrosive reagents, complex preparation, wastewater neutralization requirements, long reaction times, and high operating temperatures.

Key words: bisulphite, carbonyl group, cellulose, chemical pulping, chemithermomechanical pulp, hemicellulose, kraft pulp, lignin, phenolic group, softwood, sulphite, sulphonic acid group, ultraviolet resonance Raman spectroscopy

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.

Yhteystiedot: elina.warsta@upm.com