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.

Every year, the pulp and wood-processing industry produces large side streams of bark, the valorisation of which is desirable for both economic and environmental reasons. We investigated organosolv extraction of antioxidants from Picea abies bark using various ratios of ethanol/water with the goal of obtaining high yields of these desirable compounds. The resulting extracts were analysed (I) for their total contents of phenols (TPC), flavonoids (TFC) and tannins (TTC), and (II) for their antioxidant activity using the DPPH radical scavenging method. The highest total yield of bark extract (14.78%) and the highest concentrations of dry extracts of TPC (324.80 mg g⁻¹), TFC (62.55 mg g⁻¹) and TTC (83.63 mg g⁻¹) were obtained under mild conditions (100 °C extraction temperature and an ethanol/water solvent ratio of 50%, v/v). DPPH antioxidant activity index (AAI) ranged from 0.68 (pure water extract) to 1.31. This antioxidant effect was increased to 1.59 by adding oligolignin from the organosolv process. In the extracts, gas chromatography–mass spectrometry (GC–MS) found nine aromatic carboxylic acids, including phenolic acids and the flavonoid compounds quercetin and (+)-catechin. Our environmentally friendly approach will form the basis for pilot plant and industrial applications.

Biodiesel is considered valuable to reduce dependency on petrofuels. This work aimed to synthesize biodiesel from Silybum marianum using synthesized ZnO nanoparticles as a catalyst. The synthesized ZnO nanoparticles were examined by scanning electron microscopy and X-ray diffraction for confirmation. The synthesized biodiesel was confirmed by ASTM D-6751, H and C-NMR, GC-MS, and FT-IR spectroscopy. The optimum biodiesel yield of 91% was obtained with an oil-to-methanol ratio of 1:24, 15 mg of catalyst concentration, 60 °C temperature, and 45 min of reaction time. Fuel properties were determined according to the ASTM-defined methods and found within the defined limits of ASTM D-6751. ¹H-NMR and ¹³C-NMR showed characteristic peaks at 3.667 ppm, 2.000–2.060 ppm, 0.858–0.918 ppm, 5.288–5.407 ppm, 24.93–34.22 ppm, 172.71, 173.12, 130.16 ppm, and 128.14 ppm, respectively, which confirm biodiesel synthesis. The FAMEs composition of biodiesel was determined by GC-MS, which recognized 19 peaks for different types of FAMEs. FT-IR spectroscopy showed two main peaks, first in the range of 1725–1750 cm⁻¹ and second in the range of 1000–1300 cm⁻¹, which confirmed that the transesterification process had completed successfully. The physicochemical characteristics of Silybum marianum confirm that it is a suitable source to produce biodiesel on an industrial scale.