Sodium lignosulfonate used as water reducing agent

Ligosulfonate is a water-soluble multifunctional polymer electrolyte, is a lignosulfonate, with dispersing biological slime, dirt iron oxide, calcium phosphate ability, but also zinc ions, calcium ions to form a stable network compound.

Lignosulfonate and calcium lignosulfonate commonly used in the multi-purpose concrete waterproofing agent superplasticizer, concrete after adding water reducer, superplasticizer hydrophobic groups directed adsorbed on the surface of cement particles, hydrophilic groups pointing aqueous composition or adsorbed monomolecular film of molecules, the charge for the same cement particles are dispersed seemingly mutually exclusive, to release excess water from between the particles, in order to achieve the purpose of water reduction.

At the same time, due to the reduced interfacial tension and surface tension of water between the cement particles, while maintaining the same degree of fluidity, a corresponding reduction in water consumption, and thus also play a role in reducing water.

It can greatly reduce the hydration of concrete to reduce the porosity and increase the compactness of concrete, thereby greatly improving the strength and impermeability of concrete.

Lignosulfonate is a natural polymer having a molecular weight of 1,000 to 30,000. It was later extracted from the pulp of waste produced by the fermentation of alcohol, soda and then made mainly of calcium lignosulfonate, lignosulfonate, lignosulfonate and magnesium, among the most widely lignosulfonate calcium sulfite pulp waste is made.

This rich source of raw water reducing agent, manufacturing process is simple, inexpensive, more common in domestic applications, accounting for 80% of total water reducer. But its effect is not very good, there are air-entraining, retarding effect, belonging to the ordinary water reducer, early strength agent and the effect will be better.

In one study, increasing the molecular weight of the lignosulfonates through oxidation and sulfomethylation enhanced their plasticizing abilities in concrete from 161 (unmodified) to 185 mm at a dosage of 0.3 wt % lignosulfonates.

Another study stated that the fluidity of the oxidized and sulfomethylated product was comparable to that of commercial naphthalene sulfonate.

Increasing the molecular weight of kraft lignin by oxidation and sulfomethylation increased the adsorption of the modified kraft lignin on cement particles to 6 mg g−1 lignin dosage. This also increased the fluidity of the cement paste to 200 mm. In this case, the fluidity of unmodified kraft lignin was 70 mm and that of lignosulfonic acid was 190 mm at the same applied dosage.

By increasing the available functional groups through oxidation, the dispersing capabilities of lignosulfonates were increased dramatically. As mud dispersants, the oxidized lignosulfonates outperformed commercial products by at least 90 % based on gel point determination.

For gypsum dispersion, dispersion efficiency was improved by 50 % following oxidation of lignosulfonates. Increasing the thermal stability of lignosulfonates as a dispersant for drilling mud through hydroxymethylation allowed for values similar to those of the commercial additive ferric chromium lignin sulfonate.

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