Stefania Bertella

Lignin is an underutilized industrial byproduct with strong potential for sustainable applications. In organosolv pulping, lignin is dissolved into the spent liquor and can be recovered by antisolvent precipitation to form micro‐ and nanoscale particles. However, the relationship between mixing conditions and structural properties of the lignin particles remains poorly understood, limiting the controlled production of high‐value lignin products. By studying this precipitation process in situ using synchrotron X‐rays, we obtain information about the nanoscale structure of the particles and their formation. In the small‐angle X‐ray scattering experiment, structural units consistent in scale with lignin subunits reported in previous literature were initially observed. Later in the process, the precipitated lignin consisted of larger structural units in the size scale of 60–120 nm, which aggregated to form yet larger structures. An upper time limit of 1 second is obtained for this process. The aggregation and the relevant size scale is verified by scanning electron microscopy. Understanding the hierarchical structure formation in lignin precipitation promotes exploitation of lignin biomass at industrial scale.

Lignin, a widely available and renewable organic polymer, has several desirable properties and applications. However, as a by‐product of pulp and paper industry, it is mainly burned for energy. Limited understanding of the complex and heterogeneous structure and a shortage of tailored analysis methods hinder its utilization in higher value applications. This study describes and compares the use of two different static light scattering methods, laser diffraction and small‐angle light scattering (SALS), for studying lignin particle size in suspension. The results from laser diffraction showed that the selected particle concentration and absorption coefficient affect the measured sizes especially for particles <1 µm in diameter. For irregularly shaped particles with broad size distributions, sampling is the most important parameter affecting the results. SALS proved an efficient method for obtaining information on particle aggregation by providing primary particle sizes as well as aggregate sizes. Characterization of samples with spherical particles and narrow size distributions is straightforward with both laser diffraction and SALS, whereas the interpretation of results for more heterogeneous samples is less obvious. Static light scattering methods could make lignin particle size analysis more rapid and automated, thus enhancing lignin valorization, but should be applied carefully to avoid systematic errors.

Lignin valorization remains a significant roadblock in the development of green biorefineries. Currently, depolymerization strategies predominantly depend on energy- and resource-intensive thermochemical methods, while potential applications of the resulting bio-based products are often overlooked. Here, we demonstrate a scalable photocatalytic flow reactor for lignin deconstruction that operates at ambient conditions, along with a downstream process that yields commercially viable products at gram scale. An anthraquinone-based photocatalytic platform, when packed in a flow bed reactor, is demonstrated to selectively and nearly quantitatively cleave lignin’s -O-4 moieties, achieving a benchmark yield of 7.1 wt% for vanillin isolation. The utilization of residual oligomers as plasticizers for biobased polylactic acid resulted in improved mechanical properties and shape memory effects, while maintaining its suitability for conventional 3D printing. This aldehyde-oriented platform represents a key advancement that complements existing ketone-oriented photocatalytic approaches targeting valuable chemicals and products from lignin conversion, and it ultimately contributes to the holistic utilization of lignin.

Our ability to study and valorize the lignin fraction of biomass is hampered by the fundamental and still unmet challenge of precisely quantifying native lignin's structural features. Here, we developed a rapid elevated‐temperature ¹H−¹³C Heteronuclear Single‐Quantum Coherence Zero (HSQC₀) NMR method that enables this precise quantification of native lignin structural characteristics even with whole plant cell wall (WPCW) NMR spectroscopy, overcoming fast spin relaxation in the gel phase. We also formulated a Gaussian fitting algorithm to perform automatic and reliable spectral integration. By combining HSQC₀ measurements with yield measurements following depolymerisation, we can confirm the combinatorial nature of radical coupling reactions during biosynthesis leading to a random sequential organization of linkages within a largely linear lignin chain. Such analyses illustrate how this analytical method can greatly facilitate the study of native lignin structure, which can then be used for fundamental studies or to understand lignin depolymerization methods like reductive catalytic fractionation or aldehyde‐assisted fractionation.

Our ability to study and valorize the lignin fraction of biomass is hampered by the fundamental and still unmet challenge of precisely quantifying native lignin's structural features. Here, we developed a rapid elevated‐temperature ¹H−¹³C Heteronuclear Single‐Quantum Coherence Zero (HSQC₀) NMR method that enables this precise quantification of native lignin structural characteristics even with whole plant cell wall (WPCW) NMR spectroscopy, overcoming fast spin relaxation in the gel phase. We also formulated a Gaussian fitting algorithm to perform automatic and reliable spectral integration. By combining HSQC₀ measurements with yield measurements following depolymerisation, we can confirm the combinatorial nature of radical coupling reactions during biosynthesis leading to a random sequential organization of linkages within a largely linear lignin chain. Such analyses illustrate how this analytical method can greatly facilitate the study of native lignin structure, which can then be used for fundamental studies or to understand lignin depolymerization methods like reductive catalytic fractionation or aldehyde‐assisted fractionation.

Concerns over the sustainability and end‐of‐life properties of fossil‐derived surfactants have driven interest in bio‐based alternatives. Lignocellulosic biomass with its polar functional groups is an obvious feedstock for surfactant production but its use is limited by process complexity and low yield. Here, we present a simple two‐step approach to prepare bio‐based amphiphiles directly from hemicellulose and lignin at high yields (29 % w/w based on the total raw biomass and >80 % w/w of these two fractions). Acetal functionalization of xylan and lignin with fatty aldehydes during fractionation introduced hydrophobic segments and subsequent defunctionalization by hydrogenolysis of the xylose derivatives or acidic hydrolysis of the lignin derivatives produced amphiphiles. The resulting biodegradable xylose acetals and/or ethers, and lignin‐based amphiphilic polymers both largely retained their original natural structures, but exhibited competitive or superior surface activity in water/oil systems compared to common bio‐based surfactants.

Concerns over the sustainability and end‐of‐life properties of fossil‐derived surfactants have driven interest in bio‐based alternatives. Lignocellulosic biomass with its polar functional groups is an obvious feedstock for surfactant production but its use is limited by process complexity and low yield. Here, we present a simple two‐step approach to prepare bio‐based amphiphiles directly from hemicellulose and lignin at high yields (29 % w/w based on the total raw biomass and >80 % w/w of these two fractions). Acetal functionalization of xylan and lignin with fatty aldehydes during fractionation introduced hydrophobic segments and subsequent defunctionalization by hydrogenolysis of the xylose derivatives or acidic hydrolysis of the lignin derivatives produced amphiphiles. The resulting biodegradable xylose acetals and/or ethers, and lignin‐based amphiphilic polymers both largely retained their original natural structures, but exhibited competitive or superior surface activity in water/oil systems compared to common bio‐based surfactants.

Transmission of viruses through contact with contaminated surfaces is an important pathway for the spread of infections. Antiviral surface coatings are useful to minimize such risks. Current state-of-the-art approaches toward antiviral surface coatings either involve metal-based materials or complex synthetic polymers. These approaches, however, even if successful, will have to face great challenges when it comes to large-scale applications and their environmental sustainability. Here, an antiviral surface coating was prepared by spin-coating lignin, a natural biomass residue of the paper production industry. We show effective inactivation of herpes simplex virus type 2 (>99% after 30 min) on a surface coating that is low-cost and environmentally sustainable. The antiviral mechanism of the lignin surface was investigated and is attributed to reactive oxygen species generated upon oxidation of lignin phenols. This mechanism does not consume the surface coating (as opposed to the release of a specific antiviral agent) and does not require regeneration. The coating is stable in ambient conditions, as demonstrated in a 6 month aging study that did not reveal any decrease in antiviral activity. This research suggests that natural compounds may be used for the development of affordable and sustainable antiviral coatings.

Lignin was simultaneously extracted and functionalized with non-native groups in one step from biomass. These groups were then used to increase lignin's reactivity towards phenolation in both acidic and basic conditions in order to improve its incorporation into materials.