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.
Highlights
Lignin is a naturally occurring, branched aromatic polymer, co-existing in plant organisms with cellulose and hemicelluloses, and, due to its abundance, it is the most common macromolecule comprised of the aromatic moieties [1,2,3]
Sodium lignosulfonate was modified via a two-step chemical route using chlorosulfonic acid and dihexylamine to yield a sulfonamide derivative of lignin
Thermal stability of the modified lignin is considerably improved in relation to the raw materials, especially when looking at changes of the T5% temperature—the final modified material showed an improvement of the said parameter of 115 ◦C in comparison with the raw material (219 ◦C vs. 104 ◦C, respectively)
Summary
Lignin is a naturally occurring, branched aromatic polymer, co-existing in plant organisms with cellulose and hemicelluloses, and, due to its abundance, it is the most common macromolecule comprised of the aromatic moieties [1,2,3]. The dependency of the lignin structure on the source of acquisition, as well as the difficulties with the repeatability of its properties, hinders the potential application possibilities. Only 5% of lignin is explored in low-value uses or used as a resource for energy production and recovery [8]; there is a growing interest in its application as a renewable source of aromatic hydrocarbons [7,9,10]. The extraction using alcohols is possible; it only yields a fraction of the lignin from a plant source, namely, the alcohol-soluble constituents [7,11]
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