Like lignin, the basic component of lignosulfonate is benzyl propane derivatives. The sulfonic acid group determines its good water solubility, soluble in aqueous solutions of various pH values, but insoluble in organic solvents such as ethanol and acetone.
Lignosulfonates have both C3-C6 hydrophobic skeletons and hydrophilic groups, such as sulfonic acid groups, carboxyl groups, etc., and belong to anionic surfactants, but the structural characteristics and molecular weight distribution of lignosulfonates determine them in many aspects. The uses are different from other synthetic surfactants, listed below.
(1) There are many hydrophilic groups on the surface-active lignosulfonate molecule, and there is no linear alkane chain, so its oil solubility is very weak, its hydrophilicity is strong, and its hydrophobic skeleton is spherical, which cannot be as low as the surface activity of ordinary molecules. The agent has a neat phase interface arrangement state, so although the surface tension of the solution can be reduced, it has a small inhibitory effect on the surface tension and does not form micelles.
(2) Adsorption and dispersion Adding a small amount of lignosulfonate to the viscous slurry can reduce the viscosity of the slurry; adding it to a relatively dilute suspension can reduce the sedimentation speed of the suspended particles. This is because lignosulfonates are strongly lyophilic and negatively charged, forming anionic groups in aqueous solutions. When adsorbed on various organic or inorganic particles, the particles maintain a stable dispersion state due to the mutual repulsion between the anionic groups; further research results show that the adsorption and dispersion of lignosulfonate is caused by electrostatic repulsion and microscopic The lubrication of microbubbles is caused by their dispersion. The main reason is that the dispersing effect of lignosulfonate varies with molecular weight and suspension system. Generally, the fraction with molecular weight of 5000-4000 has better dispersion effect.
(3) Chelated lignosulfonates contain more phenolic hydroxyl groups, alcoholic hydroxyl groups, carboxyl groups and carbonyl groups, in which the unshared electron pairs on oxygen atoms can form coordination bonds with metal ions, resulting in chelation, resulting in lignin of metal chelates, thus possessing new properties. For example, lignosulfonates can be chelated with iron ions, chromium ions, etc. to prepare oil drilling mud diluents. The chelation effect also makes it have certain corrosion and scale inhibition effect, which can be used as a water treatment agent.
(4) Adhesion In natural plants, lignin is like a binder, distributed around the fiber and between the small fibers inside the fiber, inlaid between the fibers and the small fibers, making it a strong skeleton structure. The reason why trees cannot fall tens of meters or even hundreds of meters is because of the cohesion of lignin. The lignosulfonate separated from the black liquor can restore the original cohesive force after modification treatment, while the enamel and its derivatives in the waste liquor help to enhance its cohesion through mutual synergy. Effect.
(5) Foaming performance The foaming performance of lignosulfonate is similar to that of general polymer surfactants, and it has the characteristics of low foaming ability but good foam stability, and the foaming performance of lignosulfonate is used for its application. Performance will have some impact. For example, when it is used as a water reducing agent for commercial concrete, on the one hand, due to the lubricating effect of lignosulfonate, air bubbles are generated, which increases the fluidity of commercial concrete and changes the workability. OK; on the other hand, foamability increases the air entrainment of commercial concrete and reduces strength. When used as air-entraining water reducing agent, it is beneficial to improve the frost resistance and durability of commercial concrete.
Since lignosulfonates are derived from pulp waste liquor, the pulping process also affects their structure and properties. For example, the surface activity and adsorption-dispersion properties of lignosulfonates increased with increasing cooking time. ; Molecular weight, cooking process conditions, black liquor extraction equipment and purification methods, wood types, etc. also have a certain influence on its structure and performance.