Lignosulfonates

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Lignosulfonates (LS) are water-soluble anionic polyelectrolyte polymers: they are byproducts from the production of wood pulp using sulfite pulping.^[1] Most delignification in sulfite pulping involves acidic cleavage of ether bonds, which connect many of the constituents of lignin.^[2] Sulfonated lignin (SL) refers to other forms of lignin by-product, such as those derived from the much more popular Kraft process, that have been processed to add sulfonic acid groups. The two have similar uses and are commonly confused with each other, with SL being much cheaper.^[3] LS and SL both appear as free-flowing powders; the former is light brown while the latter is dark brown.^[1]

Lignosulfonates have very broad ranges of molecular mass (they are very polydisperse). A range of from 1,000 to 140,000 Da has been reported for softwood lignosulfonates with lower values reported for hardwoods. Sulfonated Kraft lignin tends to have smaller molecules at 2,000–3,000 Da.^[1] SL and LS are non-toxic, non-corrosive, and biodegradable. A range of further modifications may be applied to LS and SL, including oxidation, hydroxymethylation, sulfomethylation, and a combination thereof.^[3]