Fabrication of hollow polymer microcapsules and removal of emulsified oil from aqueous environment using soda lignin nanoparticles

Abstract

Lignin-based materials have been explored as a way to minimize dependence on petroleum products and consolidate valorization schemes of lignocellulosic biomass. Soda lignins have peculiar properties and can generate lignin nanoparticles (LNP) with the potential ability to solve emulsification/demulsification problems. The present study focuses on the use of soda LNPs for fabrication of polymer microcapsules via Pickering emulsion template and for removing emulsified oil from aqueous environment. Structural characteristics of lignins recovered from corn cob (CC) and green coconut fibre (GCF) were evaluated after analyses of chemical composition, thermal degradation and infrared spectroscopy. Both LNPs were obtained by pH-shifting method and showed low absolute values of zeta potential. LNPs provided good emulsification capacity (emulsification index > 40 % at 5.00 g/L LNP) and micrometer-scale droplets in oil-water Pickering emulsions. LNPs have been successful as a stabilizing agent in the preparation of microcapsules of poly(methyl methacrylate) (PMMA) and polycaprolactone (PCL), in which size was strongly dependent on the LNP concentration. Hollow PCL microcapsules were manufactured by stabilization with GCF-LNP, but did not show to be stable in experiments involving CC-LNP. In addition, the tendency of soda LNPs to form aggregates was used as a mechanism to remove emulsified oil, which made it possible to remove up to 90.6 % for CC-LNP and 94.4 % for GCF-LNP experiments.