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Functional surfaces, fi lms, and coatings with lignin – a critical review
Cite this: RSCAdv. , 2023, 13 , 12529
Jost Ruwoldt,* Fredrik Heen Blindheim and Gary Chinga-Carrasco
Lignin is the most abundant polyaromatic biopolymer. Due to its rich and versatile chemistry, many applications have been proposed, which include the formulation of functional coatings and fi lms. In addition to replacing fossil-based polymers, the lignin biopolymer can be part of new material solutions. Functionalities may be added, such as UV-blocking, oxygen scavenging, antimicrobial, and barrier properties, which draw on lignin's intrinsic and unique features. As a result, various applications have been proposed, including polymer coatings, adsorbents, paper-sizing additives, wood veneers, food packaging, biomaterials, fertilizers, corrosion inhibitors, and antifouling membranes. Today, technical lignin is produced in large volumes in the pulp and paper industry, whereas even more diverse products are prospected to be available from future biore fi neries. Developing new applications for lignin is hence paramount – both from a technological and economic point of view. This review article is therefore summarizing and discussing the current research-state of functional surfaces, fi lms, and coatings with lignin, where emphasis is put on the formulation and application of such solutions.
Received 22nd December 2022 Accepted 3rd March 2023
DOI: 10.1039/d2ra08179b
rsc.li/rsc-advances
Technical lignin is the product of biomass separation processes and hence di ff ers from natural or pristine lignin, as it is found in lignocellulose biomass. 3 The composition and properties of technical lignin are largely determined by their botanical origin, extraction process, puri cation, and potential chemical modi cation. 4 Presently, there are some 50 – 70million tons technical lignin available from pulping or biore nery operations. Most is burned to produce energy in biore nery processes and only approx. 2% is sold commercially. 5 Technical lignin isolated from pulping processes includes Kra and soda lignin from alkali pulping, lignosulfonates from sul te pulping, and organosolv lignin from solvent pulping. 6 The two main types of technical lignin are lignosulfonates (approx. 1 million Dr Fredrik Heen Blindheim is a Postdoctoral researcher at RISE PFI. He received a PhD in Organic Chemistry at the Norwegian University of Science and Technology, specializing in medicinal chemistry and the development of small-molecule bacterial kinase inhibitors. In his current position, he works with chemical modi cation, quanti cation, and character- ization of technical lignins for green applications in industry. His main interests are in organic synthesis and spectroscopic analysis.
1. Introduction Lignin is the second most abundant biopolymer on earth, a er cellulose. Natural lignin is synthesized from the three mono- lignol precursors, namely p -hydroxyphenyl (H unit), guaiacyl (G unit), and syringyl (S unit) phenylpropanoid. 1 Lignin from so wood consists primarily of G units, whereas hardwood lignin contains both G and S units. 2 Moreover, lignin from annual plants, such as grass or straw, can contain all three monolignol units.
RISE PFI AS, Høgskoleringen 6B, Trondheim 7491, Norway. E-mail: jostru.chemeng@ gmail.com
Dr Jost Ruwoldt is a research scientist at RISE PFI, Norway. He graduated with a PhD in Chemical Engineering from the Norwegian University of Science and Technology (NTNU) in 2018, and an MSc in Chemical and Bioprocess Engineering from Hamburg University of Technology (TUHH) in 2015. His current work includes lignin technology, thermoforming of wood pulp, and biomass
conversion and utilization. In addition to his work at RISE PFI, he is a visiting researcher and lecturer at TU Berlin, Germany.
RSCAdv. , 2023, 13 , 12529 – 12553 | 12529
© 2023 The Author(s). Published by the Royal Society of Chemistry
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