Synthesis and properties of anionic cellulose ethers: influence of functional groups and molecular weight on flowability of concrete

The suitability of anionic cellulose ethers as superplasticizers and the effect of chemical structure on the fluidity of cement mixtures was investigated. To elucidate the influence of molecular weight and degree of cellulose backbone substitution, cellulose and hydroxyethyl cellulose with molecular weights <50,000 g/mol were synthesized by acid-catalyzed and oxidative degradation. Commercial as well as degraded samples were functionalized by carboxymethylation and sulfobutylation, controlling the degree of substitution (DS) by the molar ratio of reactants and by taking advantage of the high reactivity of sultones towards salts of carboxylic acids, even in aqueous solutions. The fluidizing effect of the cellulose ethers with anionic ‘cement-anchoring‘ groups was prescreened, measuring the static flow of cement pastes. The results indicated a high potential of sulfobutylated cellulose mixed ethers as dispersing agents for concrete. The fluidizing action increased with increasing DS and an optimum range of molecular weight between 100,000 and 150,000 g/mol was found.