Potential of Lignosulphonate of Eucalyptus Lignin from Pulp Plant as Dispersant in Gypsum Paste

Eucalyptus lignin was isolated from kraft black liquor through acidification by using H2SO4. To effectively utilize black liquor waste from pulp plant, lignin was converted into sulphonated hydroxymethylated phenolized sulphuric acid lignin compound (SHP-SAL), which is soluble in water. SHP-SAL was obtained through the sequence of (1) phenolation of sulphuric acid lignin (SAL) into phenolized sulphuric acid lignin (P-SAL), (2) hydroxymethylation of P-SAL into hydroxymethylated phenolized sulphuric acid lignin (HP-SAL), and (3) sulphonation of HP-SAL into SHP-SAL. The derived lignin of SHP-SAL characterized by infrared spectrometry showed a significant absorption at 630 cm^-1, which indicates the presence of S−O bond, and absorption at 1118 and 1059 cm^-1, which are characteristics of C−O bonds in lignosulphonates. Assessment of SHP-SAL as a dispersant in gypsum paste was done according to C230-90 ASTM standard. The synthesized SHP-SAL has approximately 60% higher dispersability than those of commercial sodium lignosulphonate (comm. SLS) and commercial calcium lignosulphonate (comm. CLS). It is equal to the dispersability of sulphonated naphthalene formaldehyde (SNF), one of the high-performing sulphonate compounds.