Abstract
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 cross-linked 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 °C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).
Highlights
Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin
Bisphenol A diglycidyl ether (BADGE) in acetone-water (3:1, w/w). (2) Rapid coprecipitation of softwood Kraft lignin (SKL) and BADGE solution against water to form BADGE-SKL hyLNPs. (3a) Intraparticle cross-linking of the hybrid LNPs (hy-LNPs) (BADGE ≤ 20 wt %) in the dispersion state and covalent surface functionalization of the stabilized particles with glycidyl trimethylammonium chloride (GTMA) at pH 12 via epoxy chemistry. (3b) Heat-induced release of BADGE from the hy-LNPs (BADGE ≥30 wt %), allowing both inter- and intraparticle cross-linking for application as a waterborne wood adhesive
Combined with the 31P NMR results (Figure 2b and Table 1), one can deduce that the precipitation was caused by the reaction of the carboxylic OH of SKL to BADGE that reduced the surface charge of the particles. These hy-LNP dispersions (BADGE content ≥30 wt %) were stable upon storage at 4 °C for 110 days (Figure S2c), since the oxiranecarboxyl reaction was thermodynamically disfavored at a low temperature. These results suggested that the hy-LNPs with BADGE content ≤20 wt % were suitable for intraparticle crosslinking in dispersion state
Summary
Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. 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. The hy-LNPs with a BADGE content ≤20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. (3a) Intraparticle cross-linking of the hy-LNPs (BADGE ≤ 20 wt %) in the dispersion state and covalent surface functionalization of the stabilized particles with glycidyl trimethylammonium chloride (GTMA) at pH 12 via epoxy chemistry. Nypelö et al.[37] crosslinked Kraft lignin with epichlorohydrin via a water-in-oil microemulsion template to form intraparticle-cross-linked
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
