The key difference between Kraft lignin and lignosulfonate is that Kraft lignin can induce reinforcement and increase glass transition and water solubility, whereas lignosulfonate can have a plasticizing effect on mechanical properties.
There are different types of lignin, such as soda lignin, Kraft lignin, hydrolyzed lignin, organosolv lignin, and lignosulfonates.
CONTENTS
1. Overview and Key Difference
2. What is Kraft Lignin
3. What is Lignosulfonate
4. Kraft Lignin vs Lignosulfonate in Tabular Form
5. Summary – Kraft Lignin vs Lignosulfonate
What is Kraft Lignin?
Kraft lignin is a type of industrial lignin that is obtained from Kraft pulp. This pulp accounts for about 85% of the total lignin production in the world. The method known as the “Kraft pulp method” is the main method for the conversion of coniferous wood to pulp. This pulping method yields comparatively higher results than alkaline pulping methods.
Typically, Kraft lignin is completely soluble in alkaline solvents such as NaOH. Indulin AT is a type of kraft lignin. It is also soluble in DMSO, DMF, and ethylene glycol. However, the solubility of this substance in acetone, ethanol, and THF is poor. It is also poorly soluble in water.
We can extract kraft lignin from black liquor that is generated during wood digestion. Currently, there are some water-soluble kraft lignin types that have been prepared chemically. The method includes the preparation of a purified form of CO2-precipitated softwood kraft lignin. This forms a stable aqueous solution at a pH value of 8.9.
What is Lignosulfonate?
Lignosulfonate is a water-soluble anionic polyelectrolyte polymer that comes as a byproduct of the production of wood pulp, which involves acidic cleavage of ether bonds. These ether bonds connect a number of constituents of lignin. Lignosulfonates are abbreviated as LS. There are other forms of sulfonated lignin (SL) types that are also lignin byproducts made mainly in the Kraft process. Both lignosulfonates and sulfonate lignin have similar uses and are often confusing terms. However, sulfonated lignin is comparatively much cheaper. Moreover, both these types appear as free-flowing powders with different colors: LS is light brown while SL is dark brown.
Figure 01: The Preparation of Lignosulfonate
Often, lignosulfonates show a broad range of molecular masses ranging from 1 000 to 140 000 Da. Comparatively, other types of lignin have smaller values for molecular mass, ranging from 2 000 to 3 000 Da. Lignosulfonate is nontoxic and noncorrosive; it is also biodegradable. Furthermore, we can add a range of modifications to this substance through oxidation, hydroxymethylation, sulfomethylation, and a combination of the two.
What is the Difference Between Kraft Lignin and Lignosulfonate?
There are different types of lignin, such as soda lignin, Kraft lignin, hydrolyzed lignin, organosolv lignin, and lignosulfonates. Kraft lignin is a type of industrial lignin that is obtained from Kraft pulp while lignosulfonate is a water-soluble anionic polyelectrolyte polymer that is a byproduct of the production of wood pulp. The key difference between Kraft lignin and lignosulfonate is that Kraft lignin can induce reinforcement and increase glass transition and water solubility, whereas lignosulfonate can have a plasticizing effect on mechanical properties.
The below infographic presents the differences between Kraft lignin and lignosulfonate in tabular form for side-by-side comparison.
Summary – Kraft Lignin vs Lignosulfonate
Kraft lignin is a type of industrial lignin that is obtained from Kraft pulp. Lignosulfonate is a water-soluble anionic polyelectrolyte polymer that comes as a byproduct of the production of wood pulp, which involves acidic cleavage of ether bonds. The key difference between Kraft lignin and lignosulfonate is that Kraft lignin can induce reinforcement and increase glass transition and water solubility, whereas lignosulfonate can have a plasticizing effect on mechanical properties.
Reference:
1. Duval, Antoine, et al. “Comparison of Kraft Lignin and Lignosulfonates Addition to Wheat Gluten-Based Materials: Mechanical and Thermal Properties.” Industrial Crops and Products, Elsevier, 27 May 2013.
Image Courtesy:
1. “Ligninsulfonate Formation V2” By Jü – Own work (CC BY-SA 4.0) via Commons Wikimedia