Lignin is the second most abundant renewable natural polymer that occurs on Earth, and as such, it should be widely utilised by industries in a variety of applications. However, these applications and possible research seem to be limited or prevented by a variety of factors, mainly the high heterogeneity of lignin. Selective modifications of the structure and of functional groups allow better properties in material applications, whereas the separation of different qualitative lignin groups permits selective application in industry. This review is aimed at modification of the lignin structure, increasing the hydrophobicity of the produced materials, and focusing on several perspective modifications for industrial-scale production of lignin-based polymers, as well as challenges, opportunities, and other important factors to take into consideration.

Lignin is the second most abundant biopolymer in the world. Due to its complex structure, lignin can be considered a valuable source of energy and different chemicals. In addition, using different reactive sites on lignin, it is possible to prepare different value-added products, such as resins, polyurethanes, and many more. Different functional groups are presented on the lignin macromolecule and can be modified via different pathways. Hydroxyl groups are the most promising reactive sites for lignin modifications. Both modified and unmodified lignins could be used for preparing different biomaterials. This paper shows several possible applications of lignin. The main goal of this publication is to show the possible valorization of lignin in different value-added products throughout the actual market prices of non-biobased materials. This review proves that lignin has unquestionable advantages in material technology and can replace different substances which will lead to a higher potential market value of lignins and could create new bio-based materials compared with the actual prices of commercially available materials. Nowadays, it is easier to use lignin as an energy source even though a lot of lignin modifications and conversion processes are still under development and need more time to become more relevant for industrial applications. Information in the presented paper should reveal to the reader the importance and economic benefits of using lignin as a value-added compound in different applications.

Lignin has great potential for utilization as a green raw material or as an additive in various industrial applications, such as energy, valuable chemicals, or cost-effective materials. In this study, we assessed a commercial form of lignin isolated using LignoBoost technology (LB lignin) as well as three other types of lignin (two samples of non-wood lignins and one hardwood kraft lignin) isolated from the waste liquors produced during the pulping process. Measurements were taken for elemental analysis, methoxyl and ash content, higher heating values, thermogravimetric analysis, and molecular weight determination. We found that the elemental composition of the isolated lignins affected their thermal stability, activation energies, and higher heating values. The lignin samples examined showed varying amounts of functional groups, inorganic component compositions, and molecular weight distributions. Mean activation energies ranged from 93 to 281 kJ/mol. Lignins with bimodal molecular weight distribution were thermally decomposed in two stages, whereas the LB lignin showing a unimodal molecular weight distribution was decomposed in a single thermal stage. Based on its thermal properties, the LB lignin may find direct applications in biocomposites where a higher thermal resistance is required.

Deep eutectic solvent-like (DES-like) mixtures re-emerged in green chemistry nineteen years ago and yet have led to a large number of publications covering different research areas and different application industries. DES-like mixtures are considered a special class of green solvents because of their unique properties, such as high solubilization ability, remarkable biocompatibility, low production cost, low volatility, relatively simple synthesis methods, and considerable stability. Several studies have been published that analyze the effect of acidity/alkalinity and water content in DES-like mixtures on their physicochemical properties and behavior. This work summarizes the characterization of green solvents and, subsequently, the influence of various factors on the resulting pH values of green solvent systems. Part of this work describes the influence of water content in DES-like mixtures on their physical and chemical properties. The acidity/alkalinity effect is very important for green solvent applications, and it has the main impact on chemical reactions. As the temperature increases, the pH of DES-like mixtures decreases linearly. The type of hydrogen bond donors has been shown to have an important effect on the acidity of DES-like mixtures. The water content also affects their properties (polarity, solubilization capacity of DES-like mixtures).