Public defence in Forest Products Chemistry, DI Saara Hanhikoski

Title of the thesis: Fractionation of softwood into lignin-containing fibres and fibrils and lignosulphonates through neutral sulphite pulping

Thesis defender: Saara Hanhikoski
Opponent: Prof. Bin Yang, Washington State University, United States
Custos: Prof. Tapani Vuorinen, Aalto University School of Chemical Engineering

Due to limited forest resources and growing economic and environmental pressures, the forest industry is exploring ways to enhance the comprehensive utilisation of wood and to produce higher value-added products. In the pulping industry, this means improving and developing processes to increase pulp yield and to utilise dissolved wood components as products instead of burning them for energy. This research explores semi-chemical pulping of softwood as a less-studied alternative process, aiming to produce high-yield fibres and to utilise dissolved wood components as useful by-products.

The research focused on sulphite pulping of Scots pine under neutral and slightly alkaline pH (NS pulping). Under the studied process conditions, pulp fibres were produced with yields comparable to those of industrial neutral sulphite semi-chemical (NSSC) pulp and approaching those of chemical pulp. A key advantage of softwood NS pulping is that it preserves high levels of the wood’s cellulose and hemicelluloses, even at lower pulp yields. At the same time, valuable compounds such as lignosulphonates and carboxylic acids were dissolved from the wood. These possible by-products, especially lignosulphonates, which are already used in commercial applications, support comprehensive and efficient utilisation of the wood raw material. Additionally, the pulp fibres could be easily fibrillated into nanoscale materials, even at different yield levels, which offers the possibility of using them as a cost-efficient source of lignin-containing cellulose nanofibrils.

This research demonstrates that NS pulping of softwood can be used to produce lignin-containing fibres and fibrils and lignosulphonates. The studied characteristics of these products also help identify their potential end-use applications. As the pulping industry seeks methods for more efficient utilisation of wood, semi-chemical pulping processes, such as NS pulping of softwood, offer a promising option.

Keywords: anthraquinone, galactoglucomannan, lignin-containing cellulose nanofibrils, lignosulphonate, neutral sulphite pulping, NSSC, semi-chemical pulping, softwood, spent liquor

Thesis available for public display 10 days prior to the defence at Aaltodoc.