Stabilisation of kraft lignin solutions by surfactant additions

The colloidal stability of kraft lignin (KL) and some various KL-surfactant mixtures in aqueous alkaline solutions, pH 10.0-11.50, was tuned and inves tigated at high ionic strengths, 0.5-1.1 M, and elevated temperatures, 70 a nd 150 degreesC. The main techniques used were Quasi-Elastic Light-Scatteri ng (QELS) and turbidity measurements, together with sample inspection by th e naked eye. Samples without surfactant additions and samples containing va rious alkyl sulfonates showed a comparably low colloidal stability, whereas in mixtures containing sodium salts of bile acids, the stability was found greatly improved. The efficiency of different bile salts was investigated and it was found that the overall best solution stability is obtained in mi xtures of KL and sodium taurodeoxycholate (STDC). STDC showed a relatively good stabilising effect also at very high temperatures (150 degreesC). Furt hermore, in already aggregated KL solutions, additions of STDC were found t o cause 'de-aggregation' and the number of formed aggregates was dramatical ly decreased. From the outcome of the investigation, it can be concluded th at by introducing surfactants, and maybe other designed additives too, new possibilities in controlling the colloidal stability of KL at rough solutio n conditions are given. (C) 2001 Elsevier Science BN. All rights reserved.