Characterization of black liquors from kraft pulping of first-thinning Scots pine (Pinus sylvestris L.)

Abstract

Abstract Formation of hydroxy acids and soluble lignin fragments was investigated during conventional kraft pulping of first-thinning Scots pine (Pinus sylvestris L.) stem wood and its long-fiber outer part and short-fiber inner part. The results indicate that there are characteristic differences in the formation of hydroxy acids in these specific tissues, due to the slightly different contents of cellulose, hemicelluloses, and lignin. Notable are the differences in the formation of xylan-derived acids (2-hydroxybutanoic and xyloisosaccharinic acids) and glucomannan- and cellulose-derived acids (3,4-dideoxy-pentonic and glucoisosaccharinic acids). In contrast, no significant differences were found in the average molecular masses of the dissolved lignins in these black liquors. Finally, the black liquor from the outer part of first-thinning pine was shown to have similar properties as the black liquor from the reference mature wood material.