The objective of the work is an investigation of the preparation of a sulphonated esparto grass lignin (SEL) and its behaviour as a plasticising–water-reducing agent for cement–water systems. SEL is prepared by extracting the lignin from the black liquor of a soda esparto grass pulping process and then sulphonating it with a mixture of sodium sulphite and formaldehyde.
Analyses and characterisation of SEL carried out with high-performance size exclusion chromatography (HPSEC), reversed phase chromatography (RPC), infrared spectrometry and chemical methods show that both the molecular weight average and the combined sulphur content are relatively high. HPSEC shows that SEL has a relatively more uniform molecular weight distribution (MWD) than the commercial products obtained from the sulphite wood pulping process. However, SEL could reduce the water content, improve the workability and compressive strength of mortars. SEL also permits a very low rate of slump loss of cements without excessive extension of the final set time. 36 refs.