Lignin nanoparticles are useful in multiple applications, but their opaqueness remains an obstacle in optical applications.

Lignin nanoparticles are useful in multiple applications, but their opaqueness remains an obstacle in optical applications. In a recent study, Henn et al. present a method to prepare optically clear lignin nanoparticle dispersions from acetylated lignin.

‘Optical coatings need to be transparent, but so far, even rather thin lignin particle films have been visible. We knew that small particles appear less turbid, so I wanted to see if I could make invisible particle films by pushing the particle size to a minimum,’ says doctoral researcher Alexander Henn from Aalto University.

Reference

Henn et al. 2023. Transparent lignin nanoparticles for superhydrophilic antifogging coatings and photonic films, Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2023.145965.

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Featured graph by Henn et al. /Aalto University (CC BY 4.0)

1. Introduction 2. Materials and methods 3. Results and discussion 4. Conclusions Declaration of Competing Interest Acknowledgments Appendix A. Supplementary data Data availability References Show full outline Figures (9) Unlabelled figure Fig. 1. Formation of water-dispersible lignin nanoparticles (LNPs) with fully and… Fig. 2. 3D-reconstructed images of fully-, partially-, and non-acetylated lignin… Fig. 3. Appearance, hydrophilicity, and antifogging properties of fully acetylated… Fig. 4. Microscopic appearance of mono- and multilayers of fully acetylated lignin… Fig. 5. Thin films of partially acetylated lignin nanoparticles as photonic films Show 3 more figures Extras (4) Download all Supplementary video 2 Supplementary video 3 Supplementary video 4 Supplementary data 1 Elsevier Chemical Engineering Journal Volume 475, 1 November 2023, 145965 Chemical Engineering Journal Transparent lignin nanoparticles for superhydrophilic antifogging coatings and photonic films Author links open overlay panelKarl Alexander Henn a, Sahar Babaeipour a, Susanna Forssell b, Paula Nousiainen a, Kristoffer Meinander a, Pekka Oinas b, Monika Österberg a Show more Add to Mendeley Share Cite https://doi.org/10.1016/j.cej.2023.145965 Get rights and content Under a Creative Commons license open access Highlights • Using lignin nanoparticles as transparent superhydrophilic antifogging coatings. • Preparing photonic lignin nanoparticle films with controllable colors. • Selective, quick, and direct lignin acetylation with conventional systems. • Scalable process for ≤ 100 nm lignin nanoparticle formation at high concentrations. Abstract Lignin nanoparticles are useful in multiple applications, but their opaqueness remains an obstacle in optical applications. In this study, we present a method to prepare optically clear lignin nanoparticle dispersions from acetylated lignin. Thin lignin nanoparticle films remained transparent when deposited on glass and other smooth surfaces, and monolayered particle films provided effective antifogging properties. The particles could also be used to prepare multilayered films with bright structural colors that could be controlled via the film-thickness and were retained in dry conditions. We also developed an improved energy- and cost-efficient esterification method for controlled and quick lignin acetylation. The reaction could be selectively controlled to acetylate only aliphatic groups or to also include phenolic groups. We show here that stable nanoparticle dispersions can be produced from acetylated lignin at very high initial lignin concentrations without the formation of aggregates. Both the very short reaction time and high possible lignin concentration make the process industrially feasible as shown with a preliminary techno-economic assessment. Graphical abstract of Transparent lignin nanoparticles for superhydrophilic antifogging coatings and photonic films by Henn et al./Aalto University (CC BY 4.0)