Lignin from Micro- to Nanosize: Applications

Abstract

Micro- and nanosize lignin has recently gained interest due to improved properties compared to standard lignin available today. As the second most abundant biopolymer after cellulose, lignin is readily available but used for rather low-value applications. This review focuses on the application of micro- and nanostructured lignin in final products or processes that all show potential for high added value. The fields of application are ranging from improvement of mechanical properties of polymer nanocomposites, bactericidal and antioxidant properties and impregnations to hollow lignin drug carriers for hydrophobic and hydrophilic substances. Also, a carbonization of lignin nanostructures can lead to high-value applications such as use in supercapacitors for energy storage. The properties of the final product depend on the surface properties of the nanomaterial and, therefore, on factors like the lignin source, extraction method, and production/precipitation methods, as discussed in this review.

Keywords: UV-blocker; antibacterial; biorefinery; drug carrier; lignin; microparticles; nanocomposites; nanoparticles; reinforcing.

Figure 1

Overview of potential and investigated applications of lignin from micro- to nanosize published in literature.

Figure 2

UV–Vis transmission spectra of Polyvinyl alcohol (PVA), Wheat gluten (WG) and Polylactic acid (PLA) polymer blend films with incorporated lignin nanoparticles (LNPs) and cellulose nanocrystals (CNCs). Adapted from [17,19,31,32], with permission from Elsevier.

Figure 3

Results of the antimicrobial liquid medium test of polylactic acid (PLA), polyvinyl alcohol (PVA) and chitosan (CH) polymer blends against different bacteria; (a) Pectobacterium carotovorum subsp. odoriferum (CFBP 1115); (b) Xanthomonas arboricola pv. pruni (CFBP 3894); (c) Pseudomonas syringae pv. tomato (CFBP 1323). Adapted from Yang et al. [17,32], with permission from Elsevier.

Figure 4

Proposed use cycle and principle of the bactericidal action of environmentally benign lignin-core nanoparticles (b) and the currently used silver nanoparticles (a). Reprinted by permission from Macmillan Publishers Ltd.: Nature Nanotechnology [66], Copyright 2015.

Figure 5

(A) 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging capacity; (B) reducing power; (C) superoxide radical scavenging activity; and (D) Dissolution profiles in water at room temperature of non-nanoscale lignin and nanoscale lignin. The antioxidant butylated hydroxyanisole (BHA) was used as control. Reprinted from [71], with permission from Elsevier.

Figure 6

A schematic representation of the preparation of lignin-coated microparticles and bare polystyrene (PS) microparticles based on a lignin-stabilized Pickering emulsion including recirculation of lignin. Reproduced from [83] with permission of The Royal Society of Chemistry.

Figure 7

Illustration of three cycles of CO₂-triggered emulsification and N₂-triggered demulsification of lignin-g-DEAEMA water/decane Pickering emulsion. Reproduced from [92] with permission of The Royal Society of Chemistry.

Figure 8

Schematic representation of the production procedure for reduced fluorescence carbon dots from lignosulfonate lignin in aqueous acidic media, including possible depolymerisation and formation reaction mechanisms in which sulfonate groups were neglected. Reprinted from [107], with permission from Elsevier.

Figure 9

Releasing rates of hydrophobic Coumarin-6 and hydrophilic SR101 for different lignin capsules. (a) Coumanrin-6 releasing rate of capsules produced by Chen et al. [126] at pH 4 and pH 7.4 (Adapted with permission from [126]. Copyright 2016 American Chemical Society) and capsules (PEG-LMC_5 and LMC_5) produced by Tortora et al. [125] (Adapted with permission from [125]. Copyright 2014 American Chemical Society); (b) SR101 releasing rate at different amounts of crosslinking agent TDI, pH values, temperatures and degradation by enzymes [124], published by The Royal Society of Chemistry.

Figure 10

(a) Release profile of 2-propylpyridine from lignin nanocarriers with varying morphology, core or surfactant. (b) Amount of 2-propylpyridine released after 24 h with and without enzymatic degradation of solid and core–shell nanocarriers with enzymes after 24 h. Reprinted with permission from [103]. Copyright 2017 American Chemical Society.

Figure 11

Tumor photographs of mice treated with different nanoparticles, pure Resveratrol and phosphate-buffered saline (PBS) as control. AL/RSV/Fe₃O₄, an LNP containing Resveratrol and Fe₃O₄ showed the best performance and could reduce the tumor size significantly. Adapted with permission from [138]. Copyright 2017 American Chemical Society.