Sustainable production of lignin nanoparticles (LNPs)

• Autor(a) principal: Almeida, Fábio Josué Sousa
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/37377
• topic: Lignin; Nanoparticles; Sustainable production; LNPs; LMPs; Antisolvent precipitation; Encapsulation

Lignin is an aromatic macromolecular component of lignocellulosic biomass and is generally obtained as by-product of bio-based industries (e.g. pulp and paper and second-generation biofuel companies). Since lignin is renewable, widely available and biocompatible, a sustainable valorization of this by-product must be found in the frame of bioeconomy and circular economy. In this sense, the production of lignin nanoparticles (LNPs) presents feasible prospects in lignin´s valorization. However, the production of LNPs is still in an early development stage and yet a challenging process. This work aimed at the sustainable production of lignin nanoparticles (LNPs) through the antisolvent precipitation method. In order to obtain lignin particles at nanometric scale different parameters were evaluated, including the methodology of LNP precipitation (Method A: addition of the antisolvent to the lignin solution; and Method B: addition of the lignin solution to the antisolvent), the lignin solvent (tetrahydrofuran – THF; ethanol – EtOH; ethylene glycol – EtGly; and -valerolactone - GVL), the flux addition (0.03/0.2/0.5/1 and 3 ml/min), the lignin solution/antisolvent ratios (1.1/2.8/5.6/11.1/22.2/27.7 and 33.3 v/v%) and the washing step (centrifugation or dialysis). Remarkably, Method A induced the formation of lignin microparticles (LMPs) (from 582.8 to 7820 nm), while desired LNPs (from 127.4 to 264.9 nm) were obtained with Method B for all studied solvents. Furthermore, the Zeta potential values of LNPs presented no significant variation between both methodologies (Method A= from -21.9 mV to -30.0 mV: Method B= from -20.6 mV to -29.5 mV). Regarding to the impact of the lignin solvent, EtOH induced the formation of the smallest LNPs (Method A=582.8 nm; Method B=127.4nm), while EtGly allowed the formation of the largest particles (Method A=7820 nm; Method B=264.9 nm) Furthermore, EtGly-based LNPs were characterized as heterogeneous (Method A PDI=0.505; Method B PDI=0.365), irregular, and highly aggregated when compared to GVL counterparts. Notably, GVL enabled the production of the most homogeneous (Method A PDI=0.057; Method B PDI=0.077) and spherical particles, while THF allowed the formation of cavities. After solvent screening on LNP´s formation, GVL and Method B were elected as the most promising towards low size, spherical and more homogenous LNPs. No significant impact of lignin solution addition rate was observed, while different ratios of lignin solution/antisolvent enabled substantial impact on LNP sizes and Zeta potential. For instance, decreasing ratios of lignin solution/antisolvent (1.1 v/v% of lignin solution), enabled reduction of LNP´s sizes and simultaneous decrease of Zeta potential to -34 mV. Regarding to washing method, dialysis enabled the formation of LNPs with lower size, lower aggregation and higher homogeneity compared to centrifuged LNPs. Yet, centrifuged LNPs presented lower zeta potential, indicating a more effective solvent removal. Finally, GVL-based LNPs were tested by the encapsulation of curcumin.