Dispersing agents for cement based on modified polysaccharides

In this paper, starch and cellulose anionic derivatives are investigated with the objective to obtain new biodegradable dispersing agents for mortar and concrete mixtures. For that purpose, different starch and cellulose materials were partially depolymerized, giving limit-dextrins with DPw 50-300 and level-off-DP (LODP) celluloses with DPw 30-150. The subsequent hydroxyethylation, carboxymethylation, or sulfoethylation of these partially hydrolyzed polysaccharides occurred in 2-propanol, whereas the sulfation was carried out in dimethyl sulfoxide. The molecular weights of the samples were characterized by means of GPC, the chemical structure and functionalization pattern by means of NMR spectroscopy, and the theological behavior of the sample solution was also determined. The dispersant products were tested as mortar and concrete admixtures. As a result, it could be shown that partially hydrolyzed and sulfoethylated amylomaize starch (70 % amylose) provides the most efficient dispersing agent. The results were comparable to those of superplasticizers (i.e., polycarboxylate ethers). (c) 2004 Elsevier Ltd. All rights reserved.