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COST Action FP1105: effect of raw materials and pulping conditions on the characteristics of dissolved kraft lignins

Svärd, Antonia, Sevastyanova, Olena, Dobele, Galina, Jurkjane, Vilhemina, Brännvall, Elisabet
Holzforschung 2016 v.70 no.12 pp. 1105-1114
Eucalyptus, Picea, acid hydrolysis, byproducts, chemical structure, cooking, differential scanning calorimetry, gel chromatography, glass transition temperature, hydrolysates, kraft pulping, lignin, molecular weight, nuclear magnetic resonance spectroscopy, phosphorus, pyrolysis, raw materials, softwood, stable isotopes, sugars, sulfur, thermogravimetry, waste liquors
The composition, molecular weight (MW), and chemical structure of technical lignins as byproducts of pulping influence their application in terms of physical and chemical properties, reactivity, and performance. It is important to know how the analytical data of technical lignins are influenced by the wood species and the parameters of pulping. The present study focuses on kraft pulping and how the wood species (eucalyptus, pine, and spruce) and variable cooking times influence the characteristics of dissolved lignins. The black liquor (BL) was recovered after three different cooking times and the precipitated lignin was characterized by total acid hydrolysis including the determination of the acid insoluble part (Klason lignin, KL) and the sugars in the hydrolysate, elemental analysis, ³¹P NMR spectroscopy, analytical pyrolysis (Py-GC/MS), gel permeation chromatography (GPC), thermogravimetry (TG), and differential scanning calorimetry (DSC). The results indicate that the phenolic OH content, MW and glass transition temperature increased with longer cooking times for the softwood (SW) lignins. These lignins had also a higher MW (Mw 5500–8000 g mol⁻¹), than the eucalyptus lignin (Mw 2200–2400 g mol⁻¹). Eucalyptus lignin had higher sulfur content compared to SW.