The production of lignin nanoparticles (LNPs) has opened new routes to 18 utilization of lignin in advanced applications. The existing challenge, however, is to 19 develop a production method that can easily be adapted on an industrial scale. In this 20 study, we demonstrated a green and rapid method of preparing LNPs directly from a 21 sulfur-free alkaline pulping liquor by combining acid-precipitation and ultrasonication. The 22 combined method produced spherical LNPs, with hierarchical nanostructure and highly 23 negative surface charge, within only 5-min of sonication. The mild, rapid sonication was 24 achieved by sonicating directly without prior drying the acid-precipitated and dialyzed 25 lignin. Optimization of the method revealed the potential for minimizing acid consumption, 26 shortening the dialysis time, and processing directly the alkaline liquor with as much as Page 2 of 54 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering 3 27 20 wt% lignin. The isolated LNPs were stable during storage for 180 days, at a pH range 28 of 4-7 and in a dispersing medium below 0.1 M NaCl. The LNPs also displayed excellent 29 emulsifying properties, stabilizing oil-in-water emulsions. Thus, this simple and energyefficient method opens a sustainable, straightforward and scalable route to production of 31 solvent-free LNPs, with high potential as interface stabilizers of multi-phase systems in 32 the food and medical industries. 33 34 INTRODUCTION 35 Lignin, with its highly irregular polyphenolic structure, is the most abundant natural 36 aromatic polymer on Earth. 1 Representing 15-40% of the dry weight of lignocellulosics, 2 37 lignin is one of the major by-products in the pulp and paper industries, with an estimated 38 global production of 50 million tons per year. 3,4 Lignin production is expected to 39 continuously increase as the demand for second-generation biofuel, i.e. biofuels from 40 nonfood sources, is realized. In the USA alone, the mandate to produce 79 billion liters 41 of second-generation biofuels by 2022 translates into the production of 62 million tons of

Wood hemicelluloses have an excellent capacity to form and stabilize oil-in-water emulsions. Galactoglucomannans (GGM) from spruce and glucuronoxylans (GX) from birch provide multifunctional protection against physical breakdown and lipid oxidation in emulsions. Phenolic residues, coextracted with hemicelluloses using the pressurized hot water (PHWE) process, seem to further enhance emulsion stability. According to hypothesis, phenolic residues associated with hemicelluloses deliver and anchor hemicelluloses at the emulsion interface. This study is the first to characterize the structure of the phenolic residues in both GGM-and GX-rich wood extracts and their role in the stabilization of emulsions. PHWE GGM and GX were fractionated by centrifugation to obtain concentrated phenolic residues as one fraction (GGM-phe and GX-phe) and partially purified hemicelluloses as the other fraction (GGM-pur and GX-pur). To evaluate the role of each fraction in terms of physical and oxidative stabilization, rapeseed oil-in-water emulsions were prepared using GGM, GX, GGM-pur, and GX-pur as stabilizers. Changes in droplet-size distribution and peroxide values were measured during a 3-month accelerated storage test. The results for fresh emulsions indicated that the phenolic-rich fractions in hemicelluloses take part in the formation of emulsions. Furthermore, results from the accelerated storage test indicated that phenolic structures improve the long-term physical stability of emulsions. According to measured peroxide values, all hemicelluloses examined inhibited lipid oxidation in emulsions, GX being the most effective. This indicates that phenolic residues associated with hemicelluloses act as antioxidants in emulsions. According to chemical characterization using complementary methods, the phenolic fractions, GGM-phe and GX-phe, were composed mainly of lignin. Furthermore, the total carbohydrate content of the phenolic fractions was clearly lower compared to the starting hemicelluloses GGM and GX, and the purified fractions GGM-pur and GX-pur. Apparently, the phenolic structures were enriched in the GGM-phe and GX-phe fractions, which was confirmed by NMR spectroscopy as well as by other characterization methods. The frequency of the main bonding pattern in lignins, the β-O-4 structure, was clearly very high, suggesting that extracted lignin remains in native form. Furthermore, the lignin carbohydrate complex of γ-ester type was found, which could explain the excellent stabilizing properties of PHWE hemicelluloses in emulsions.

Lignin is an abundant natural feedstock that offers great potential as a renewable substitute for fossil-based resources. Its polyaromatic structure and unique properties have attracted significant research efforts. The advantages of an enzymatic over chemical or thermal approach to construct or deconstruct lignins are that it operates in mild conditions, requires less energy, and usually uses non-toxic chemicals. Laccase is a widely investigated oxidative enzyme that can catalyze the polymerization and depolymerization of lignin. Its dual nature causes a challenge in controlling the overall direction of ligninlaccase catalysis. In this Review, the factors that affect laccasecatalyzed lignin polymerization were summarized, evaluated, and compared to identify key features that favor lignin polymerization. In addition, a critical assessment of the conditions that enable production of novel lignin hybrids via laccase-catalyzed grafting was presented. To assess the industrial relevance of laccase-assisted lignin valorization, patented applications were surveyed and industrial challenges and opportunities were analyzed. Finally, our perspective in realizing the full potential of laccase in building lignin-based materials for advanced applications was deduced from analysis of the limitations governing laccase-assisted lignin polymerization and grafting.

Centrifuging softwood extracts separated the hemicellulose-rich fraction and lignin-rich micro- and nanoparticles. The hemicellulose-rich fraction and lignin-rich nanoparticles formed stable emulsions.

Laccases (EC 1.10.3.2) are multicopper oxidases able to oxidize phenolic compounds such as lignin-related polyphenols. Since the discovery that so-called mediators effectively extend the family of laccase substrates, direct interactions between lignin-like materials and laccase have gained much less attention. In this work, the aim was to characterize oxidation products formed in direct laccase-catalyzed oxidation of different guaiacylic and syringylic lignin model compounds with two different laccases: a low redox potential Melanocarpus albomyces laccase and a high redox potential Trametes hirsuta laccase. By following the formation of different, mainly biphenylic (5-5) and benzylic oxidation products, it was found that although both of these enzymes generated practically the same pattern of products with particular types of syringyl and guaiacyl compounds, in some cases a clear difference in the rates of their formation was observed. The results also confirm further to the suggestions that syringylic compounds are able to act as mediators in their own oxidation reactions and also that in some instances acetylation of phenolic material may produce altered, unexpected structures.