Lignin modifications and perspectives towards applications of phenolic foams: A Review

Abstract

Lignin is a complex natural polymer and by-product of the pulp and paper industry. Currently, the increasing interest in bio-based products has motivated the search for alternative renewable feedstocks that can sustainably replace synthetic polymers. Because of the phenolic functionalities of lignin, this natural polymer has attracted interest for application in biomaterials. Among various products, polymeric foams stand out as a potential product in which lignin incorporation has resulted in improved mechanical and thermal properties. This paper reviews the state of lignin foam development, with emphasis placed on phenol-lignin types.

Lignosulphonates as an Alternative to Non-Renewable Binders in Wood-Based Materials

“…A recent study has suggested that lignin substructures such as β-O-4 , β-5 /α-O-4 , β-β', and α-carbonyl react with phenol, thus increasing the amount of phenolic hydroxyl groups present in the structure. This work also considered the ortho and para positions for lignin phenolation and the presence of more substructures, shown in Figure 8, because of the elimination of formaldehyde from the γ-carbon [71]. Phenolation is frequently used for the modification of lignosulphonates since it increases the content of phenolic hydroxyl groups, while reducing molecular weight, thus simplifying their structure.…”

“…Phenolation reactions result in the attachment of phenol onto lignin. These reactions can occur in alkaline or acidic mediums [ 71 ].…”

“…A recent study has suggested that lignin substructures such as β-O-4′, β-5′/α-O-4′, β-β’, and α-carbonyl react with phenol, thus increasing the amount of phenolic hydroxyl groups present in the structure. This work also considered the ortho and para positions for lignin phenolation and the presence of more substructures, shown in Figure 8 , because of the elimination of formaldehyde from the γ-carbon [ 71 ].…”

“…Phenolation is frequently used for the modification of lignosulphonates since it increases the content of phenolic hydroxyl groups, while reducing molecular weight, thus simplifying their structure. The removal of the sulfonic acid group after phenolation has also been reported [ 71 ].…”

“…The final product has a lower molecular weight. In lignin’s case, hydrolysis can occur in an alkaline or acidic medium under sub or supercritical conditions [ 15 , 71 ].…”