The colloidal behaviour of kraft lignin and lignosulfonates
Date
1986
Authors
Nyman, V.
Rose, G.
Ralston, J.
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Colloids and Surfaces, 1986; 21(C):125-147
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Pinus radiata Kraft lignin (PKL), Eucalyptus regnans Kraft lignin (EKL) and Eucalyptus regnans NSSC lignosulfonic acid (LSA) have been isolated and purified. The PKL and LSA samples have been fractionated by gel permeation chromatography and their molecular weights verified by light scattering. Molecular weights range from 104 to 2.5 × 105. Coagulation studies of these lignins, as well as two commercial products (Indulin AT and Ufoxane 3A), performed in the presence of salt indicate that the lignins behave as colloids which are sterically stabilized, particularly at high pH. Lignin specifically adsorbs onto solid Ca(OH)2 at pH 12.2 and reverses the sign of the zeta potential. PKL, EKL, Indulin AT and LSA have been potentiometrically titrated. The variation of apparent dissociation constant with degree of dissociation is markedly different from that of classic polyelectrolytes. Aggregation effects occur at low α, and surface chain extension and ionization at high α. Most of the lignins have an intrinsic dissociation constant (pKo) equivalent to that of a carboxyl group. Free energy data and pKo vary with ionic strength in a manner which reflects the different chemical structures of the two main classes of lignin.
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Copyright 1986 Elsevier