Chemical Transformation of Lignosulfonates to Lignosulfonamides with Improved Thermal Characteristics

Abstract

Lignin is an abundantly occurring aromatic biopolymer that receives increasing attention as, e.g., a biofiller in polymer composites. Though its structure depends on the plant source, it is a valuable component showing biodegradability, antioxidant, and ultra-violet (UV) absorption properties. Lignosulfonates, a by-product of the paper and pulping industries formed as a result of the implementation of the sulfite process, have been used in the presented study as a raw material to obtain a sulfonamide derivative of lignin. Hereby, a two-step modification procedure is described. The obtained materials were investigated by means of FTIR, WAXD, SS-NMR, SEM, and TGA; the results of spectroscopic investigations confirm the formation of a sulfonamide derivative of lignin via the proposed modification method. The obtained modified lignin materials showed significantly improved thermal stability in comparison with the raw material. The internal structure of the lignosulfonate was not altered during the modification process, with only slight changes of the morphology, as confirmed by the WAXD and SEM analyses. The manufactured sulfonamide lignin derivatives show great promise in the potential application as an antibacterial filler in advanced biopolymeric composites.

Synthesis and Characterization of Thermally Stable Lignosulfonamides

“…The formation of sulfonamide from the sulfonyl group may inhibit desulfonation and shift it toward higher temperatures, resulting in enhanced thermal properties of the obtained sulfonamide derivatives of lignin. Similar observations were made in our previous work, in which we investigated lignosulfonamides obtained using chlorosulfonic acid [ 71 ].…”

“…This method employed the acidolysis of sodium lignosulfonate in hydrochloric acid (HCl), as described in our previous paper [ 71 ]. 200 g of ligS dried under as-above conditions was used to obtain powdered lignosulfonic acid (ligH), which was later reacted with phosphorus pentachloride, yielding lignosulfonyl chloride (ligH-PCl5).…”

“…All of the obtained lignosulfonyl chlorides were subjected to the second step of the employed modification procedure, i.e., reaction with the dihexylamine, as it was described in our previous work [ 71 ]. In three flasks, NaOH solution, dihexylamine, and the corresponding lignosulfonyl chlorides were reacted.…”

“…In this work, we present another method of lignin modification, a continuation of our previous research [ 71 ]. In the proposed two-step method, the sulfonyl groups present in the sodium lignosulfonate structure undergo a reaction with two different chlorinating agents, thionyl chloride and phosphorus pentachloride, to obtain lignosulfonyl chloride, which is subsequently reacted with a secondary amine.…”

Chemical and Physical Modification of Lignin for Green Polymeric Composite Materials

“…Lignocellulosic biomass constitutes the most abundant source of renewable biomass, which consists mainly of three biopolymeric elements-cellulose, hemicelluloses, and lignin, which form complex, interpenetrating structures in plant organisms [1][2][3][4][5]. Both cellulose and hemicellulose fractions are comprised of polysaccharides [1][2][3][6][7][8], whereas lignin is an aromatic macromolecule composed of three phenylpropane units, originating from three aromatic alcohol precursor components (monolignols), namely p-coumaryl, coniferyl, and sinapyl alcohols (Figure 1) [9].…”