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    Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives

    Year: 2021

    Journal: ACS Nano, Volume 15, MAR 23, page 4811–4823

    Authors: Zou, Tao; Sipponen, Mika Henrikki; Henn, Alexander; Osterberg, Monika

    Organizations: Novo Nordisk Foundation (SUSCELL project) [NNF17OC0027658]; FinnCERES Materials Bioeconomy Ecosystem

    Keywords: hybrid lignin nanoparticle; intraparticle cross-linking; interparticle cross-linking; covalent surface functionalization; lignin-epoxy adhesive; colloidal lignin particle

    Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content <= 20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally crosslinked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content >= 30% allowed both inter- and intraparticle cross-linking at >150 degrees C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).
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