Direct Preparation of Hollow Nanospheres with Kraft Lignin: A Facile Strategy for Effective Utilization of Biomass Waste

Abstract

This work discusses the preparation and characterization of hollow nanospheres based on kraft lignin (KL). Kraft lignin is a by-product of the papermaking industry and an abundant renewable resource. It was determined that adding water to a KL/THF solution induced KL to form hollow nanospheres via self-assembly. Scanning electron microscopy and transmission electron microscopy confirmed the hollow nanosphere morphology. The shell thickness of the hollow nanospheres was tunable by adjusting the initial KL concentration in THF, making the nanospheres a potential material for the encapsulation and controlled release of guest molecules. Ultraviolet (UV) and Fourier transform infrared (FTIR) spectroscopy confirmed the π-π stacking of aromatic rings as an important and distinctive mechanism for the formation of hollow KL nanospheres. The nanospheres were obtained simply and inexpensively, and they exhibited the characteristics of biocompatibility, biodegradability, and low toxicity. These advantages make hollow KL nanospheres attractive for applications in nanoscience and nanotechnology. This study developed an economically feasible and facile strategy for the effective use of biomass waste in sustainable chemistry.

Scaling Up Production of Colloidal Lignin Particles

“…This is reflected in the observed inverse correlation between the addition rate and average particle size when adding water into lignin solution (Fig 2A-B). The mechanism involving an emulsion like intermediate stage could also better explain the reported formation of hollow lignin spheres (Li et al 2016a, Xiong et al 2017a) when low concentration of lignin is used. Fig 2 -Influence of solvent shfiting technique on average particle size of CLPs.…”

“…Use of THF as a solvent system for lignin dissolution prior to the CLP formation has been found efficient in previous studies (Lievonen et al 2016;Li et al 2016a;Xiong et al 2017a;Xiong et al 2017b), while there are also alternative solvent systems for CLP formation, such as acetone (Appendix 1). Unlike in the studies where pure THF solvent was used, we have applied THF-water (3:1) mixture as solvent for lignin.…”

“…In general, the boundaries for solute concentrations that can be used for nanoprecipitation are in range of few mass percentages, depending on the system (Aubry et al 2009;Schubert et al 2011). Lignin concentrations between 0.05 to 1 wt% have been demonstrated so far to produce CLPs from THF solutions (Lievonen et al 2016;Xiong et al 2017a;Xiong et al 2017b), with low concentrations below 0.2 wt% producing hollow sphere structures (Li et al 2016a, Xiong et al 2017a. We have mapped the influence of lignin concentration to the characteristics of formed particles (Fig 4) in THF-water system, and our results agree with existing literature (Lepeltier et al 2014;Lievonen et al 2016;Xiong et al 2017b) that the particle size grows with increasing polymer concentration of the feed solution.…”

“…Typically this done by adding water (a non-solvent) into lignin solution in organic solvent (a solvating solvent, such as THF). (Lievonen et al 2016;Li et al 2016a;Li et al 2016b;Yearla, Padmasree 2016;Richter et al 2016;Xiong et al 2017a;Xiong et al 2017b;Tian et al 2017) The resulting particles commonly have spherical shape, diameter of above hundred nanometers, and negative surface charge, providing them with stability in aqueous dispersions. Particle properties, such as morphology, particle size and surface charge are largely determined by the applied parameters of the formation process, such as solvent system, concentration and characteristics of the lignin polymer, and technique applied for implementation of the solvent shifting process.…”

“…Particle properties, such as morphology, particle size and surface charge are largely determined by the applied parameters of the formation process, such as solvent system, concentration and characteristics of the lignin polymer, and technique applied for implementation of the solvent shifting process. (Lievonen et al 2016;Li et al 2016a;Li et al 2016b;Yearla, Padmasree 2016;Richter et al 2016;Xiong et al 2017a;Xiong et al 2017b;Tian et al 2017) Adsorptionbased processes utilizing synthetic polymers (Lievonen et al 2016;Richter et al 2016) or proteins (Leskinen et al 2016) can be used for further tailoring of the surface chemistry of the CLPs. Even magnetization of the particles has been introduced for high-end applications, such as drug delivery (Lintinen et al 2016;Figueiredo et al 2017).…”