## 1 Introduction  
Ligmin is the second most abundant natural polymer, composed of three different C6C3 types of monolignols (p-couranyl, coniferyl, and sinapyl alcohol) with various interunit linkages such as \(\beta\)-O-4, \(\beta\)-5, and biphenyl [1]. Native lignin has complex and three-dimensional amorphous structures with a high degree of condensation, which allows the lignin to resist physical, chemical, and/or biological forces. Due to this resistance, the utilization of lignin in high value-added products is very difficult [2]. Most lignins are produced as a waste by the pulp industry (70 million tons per year), but they are also expected to be a byproduct from sugar-based biofuels and bioproducts (less than 10 million tons per year) [3, 4]. However, only 2% of lignin byproducts are used as a value-added product, which traditionally has been used as a stabilizer for plastics and rubber [5, 6], phenolic resins [7] and automotive brakes [8]. Production research on aromatic chemicals, carbon fibers, and thermoplastic or fusible materials from various lignins has also been performed. All of the lignin uses mentioned so far require proper conversion process conditions, but it is also important to select suitable raw lignin materials because their structural features significantly influence the yield and characteristics of the target products. An in-depth study of the structural features of lignin must be conducted before its widespread utilization. A drug delivery system is generally designed to improve the pharmacological and therapeutic profile of a drug molecule inside the body of humans or animals [9]. The global drug delivery systems market was valued at 510 billion USD in 2016 and it is anticipated that the market will expand at a compound annual growth rate (CAGR) of 7% from 2017 to 2025 to reach approximately 900 billion USD. Conventional drug delivery systems have many problems that may be potentially overcome by methods that can enhance solubility and sustained release of drugs. Nanoparticle-based drug delivery systems show promise as active vectors due to their drug-release ability. Their subcellular size allows higher intracellular uptake than other particulate systems and they can improve the stability of active drugs or other substances. Among them, the nanocapsule is a vesicular system in which a drug is confined in a space consisting of an inner liquid core encapsulated by a polymeric membrane. Polymers used for drug encapsulation are preferably produced from natural compounds. Thus many biopolymers, such as polysaccharides, lipids, and proteins, have been studied in detail regarding application to release substances. However, studies of lignin for biomedical applications, especially for drug release, are rare. Lignin is the most abundant phenolic biopolymer in nature, with great biocompatibility. To assert the potential use of lignin capsules in biomedical fields, in vitro cytotoxicity studies of capsules were performed and positive results were achieved [10; 11]. Meanwhile, in recent years, most nanoparticle/nanocapsule production techniques are based on the nanoprecipitation process [12]. Studies regarding various parameters that control particle size and drug loading for nanocapsules prepared by nanoprecipitation were also performed. However, few studies investigate the effect of structural characteristics of lignin, an important parameter that could explain the enormous effect on properties (particle size and encapsulation efficiency) of nanoparticles [13]. In this study, we aimed to clarify the effect of lignin molecular weight on the formation of nanoparticles and related properties. To determine the effects of molecular weight on particle size, shape, and colloidal properties, six different fractions with a remarkable molecular weight difference from lignin were obtained by sequential solvent extraction [14; 15]. Lignin nanoparticles were synthesized by nanoprecipitation and recovered by centrifugation and freeze-drying.