The impact of the pulping process on the properties of lignin nanoparticles

Sammanfattning: Lignin valorization is a key component of the total utilization of biomass in the biorefinery industry. Lignin has seen some use in several different applications, but a breakthrough is still yet to happen, and there is still a need to find more areas where lignin can be used as an alternative feedstock or as the main component. Lignin nanoparticles (LNPs) could be an alternative route towards lignin valorization offering many areas of application. However, research around LNPs still has to overcome many challenges, primarily related to the complex structure of lignin, with composition and structure of lignin depending on its botanical origin and on the pulping process used to isolate the lignin from other components in biomass. This study investigates how spruce lignin originating from Kraft and Organosolv pulping will affect the properties of lignin nanoparticles. Particles from organosolv spruce lignin were prepared using a solvent exchange method with acetone/water as solvent and water as antisolvent. This resulted in spherical LNPs with hollow centers, sizes ranging from 104.6- 270.3 depending on initial lignin concentration and average zeta-potential of -35mV. Comparing Organosolv LPN’s with Kraft LNPs produced with the same experimental procedure, reviled that Organosolv LNPs were larger in and had lower absolute zeta potential, presumably due to the kraft lignin having higher phenolic-OH content. Furthermore, a larger comparison is made with LNPs from previous studies which indicated that LNP properties are further dependant Mw of lignin raw material, phenolic-OH content, and the method applied to produce the particles. In conclusion, this study proves that the pulping process used to isolate lining will affect the properties of NPs. But to strengthen and generalize this conclusion beyond the limitations of this study, more experimental data are needed, to further investigate the relationship between LNP properties and the properties of lignin raw material.