The molecular structure of sodium lignosulfonate are:
- It is composed of a polydisperse lignin-based polymer backbone. Lignin is a complex polymer derived from trees.
- The polymeric backbone consists of phenylpropane units joined together irregularly in a cross-linked, non-linear structure.
- Some phenolic OH groups on the lignin polymer backbone selectively undergo sulfonation through sulfite pulping process.
- This leads to the incorporation of sulfonate functional groups (R-SO3-) onto the phenolic sites of the lignin polymer.
- The sulfonate groups ionize in water, imparting a permanent negative charge to the lignin polymer structure.
- Sodium ions (Na+) bond electrostatically with these sulfonate groups, making it soluble in water.
- This produces a highly hydrophilic, polyanionic structure able to strongly interact with water molecules.
- The polymer has a wide molecular weight distribution between 1000-50000 g/mol due to its complex natural origins.
- It exists as a mixture or family of polydisperse polymers rather than a uniform molecule.
- The irregular structure with pendant sulfonate groups contributes to its excellent dispersing, emulsifying and binding abilities in various applications.
key properties of sodium lignosulfonate:
- Chemical formula: C9H9O4S1Na1
- Appearance: Dark brown colored, water-soluble powder with sulfurous odor
- Molecular structure: Polydisperse polymer with sulfonated phenylpropane units
- Solubility: Highly soluble in water, insoluble in organic solvents
- Functional groups: Sulfonate (SO3-) groups make it highly hydrophilic
- Molecular weight: Average 200-500 g/mol, range 1000-50000 g/mol
- Dispersing ability: Good particle dispersion due to electrosteric stabilization
- Water reducing property: Increases workability of concrete without extra water
- Emulsifying property: Effectively stabilizes oil-water emulsions
- Binding ability: Binds particles through electrostatic and hydrogen bonding
- Flocculating ability: Agglomerates fine particles in wastewater treatment
- pH stability: Operates effectively in wide pH range of 2-12
- Thermal stability: Decomposes above 200°C
- Toxicity: non-toxic, biodegradable, considered GRAS
- Availability: Produced in bulk as pulp mill byproduct