Sericin Promotes Fibroin Silk I Stabilization Across a Phase-Separation.

Natural silk spinning offers several advantages over the synthetic fiber spinning, although the underlying mechanisms of this process are yet to be fully elucidated. Silkworm silks, specifically B. mori, comprise two main proteins: fibroin, which forms the fiber, and sericin, a coextruded coating that acts as a matrix in the resulting nonwoven composite cocoon. To date, most studies have focused on fibroin's self-assembly and gelation, with the influence of sericin during spinning receiving little to no attention. This study investigates sericin's effects on the self-assembly of fibroin via their natural phase-separation. Through changes in sample opacity, FTIR, and XRD, we report that increasing sericin concentration retards the time to gelation and ß-sheet formation of fibroin, causing it to adopt a Silk I conformation. Such findings have important implications for both the natural silk spinning process and any future industrial applications, suggesting that sericin may be able to induce long-range conformational and stability control in silk fibroin, while being in a separate phase, a factor that would facilitate long-term storage or silk feedstocks.

Preparation of Silk Sericin/Lignin Blend Beads for the Removal of Hexavalent Chromium Ions.

In the present study, novel adsorbents having high adsorption capability and reusability were prepared using agricultural by-products: silk sericin and lignin. Silk sericin and lignin blend beads were successfully prepared using simple coagulation methods for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. A 1 M lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent system successfully dissolved both sericin and lignin and had sufficient viscosity for bead preparation. Compared to the conventional sericin bead adsorbent, sericin/lignin blend beads showed higher Cr(VI) adsorption capacity. The amount of lignin added to the adsorbent greatly affected the adsorption capacity of the beads, and a 50:50 sericin/lignin blend ratio was optimal. Adsorption behavior followed the Freundlich isotherm, which means the adsorption of Cr(VI) occurred on the heterogeneous surface. Cr(VI) adsorption capability increased with temperature because of thermodynamic-kinetic effects. In addition, over 90% of Cr(VI) ions were recovered from the Cr(VI) adsorbed sericin/lignin beads in a 1 M NaOH solution. The adsorption-desorption recycling process was stable for more than seven cycles, and the recycling efficiency was 82%. It is expected that the sericin/lignin beads could be successfully applied in wastewater remediation especially for hazardous Cr(VI) ions in industrial wastewater.

Structural characteristics and biological performance of silk fibroin nanofiber containing microalgae Spirulina extract.

Silk fibroin (SF) nanofiber scaffold containing microalgae Spirulina extract were prepared by electrospinning and the performance and functionality of the scaffold were evaluated. The viscosity and conductivity of the dope solution of Spirulina containing SF were examined for electrospinability and we found that the morphological structure of SF nanofiber is affected by the concentration of Spirulina extract added. The platelet adhesion and coagulation time test confirmed that the Spirulina containing SF nanofiber scaffold had excellent ability to prevent blood clotting or antithrombogenicity that is comparable to heparin. Low cytotoxicity and excellent cell adhesion and proliferation were also observed for Sprulina containing SF nanofiber scaffold by methylthiazolyldiphenyl-tetrazolium bromide assay and confocal fluorescence microscope using fibroblast and human umbilical vein endothelial cells. Based on these results, we believe SF nanofiber scaffold containing Spirulina extract has the potential to be used as tissue engineering scaffold that requires high hemocompatibility.

Lignin/PVA hydrogel with enhanced structural stability for cationic dye removal.

In this study, a lignin-based hydrogel for wastewater treatment was prepared by incorporating kraft lignin (KL) into a poly (vinyl alcohol) (PVA) matrix. The underwater structural stability of the KL-PVA hydrogel was guaranteed through physicochemical crosslinking, involving freeze-thaw process and chemical crosslinking reaction. The KL-PVA hydrogel displayed superior compressive characteristics compared to the original PVA hydrogel. This improvement was attributed to the chemical crosslinking and the reinforcing effect of the incorporated KL microparticles. The incorporation of anionic KL microparticles into the PVA three-dimensional network structure enhanced the cationic methylene blue (MB) and crystal violet (CV) adsorption efficiency of the prepared KL-PVA hydrogel. The MB adsorption results were well explained by pseudo-2nd order kinetics model and Langmuir isotherm model. Electrostatic forces, hydrogen bonding and π-π stacking interactions were the main adsorption mechanisms between cationic dyes and KL surfaces, indicating the potential of KL-PVA hydrogel as an effective adsorption material. Moreover, regulating the molecular weight of PVA not only prevented lignin leakage from the KL-PVA hydrogel but also elevated the KL content within the hydrogel, consequently improving its dye removal performance. For KL-PVA hydrogel with high molecular weight PVA, the MB and CV adsorption capacities were 193.8 mg/g and 190.0 mg/g, respectively.

Effect of hemicellulose hydrolysate addition on the dehydration and redispersion characteristic of cellulose nanofibrils.

Nanocellulose, owing to its environmentally friendly and unique attributes, is gaining traction in various industries. However, commercialization of nanocellulose faces challenges due to structural alterations during drying process, leading to irreversible aggregation. This study, inspired by wood's natural structure, introduces a cellulose nanofibril (CNF) drying system using hemicellulose hydrolysate (HH) as a capping agent. The addition of only 1 wt% of HH to the CNF suspension not only prevents aggregation among CNFs during dehydration and drying but also dramatically enhances the redispersion rate and dispersion stability of the dried CNFs. The redispersed CNF/HH suspension exhibits physicochemical properties comparable to the original CNF suspension before drying. This confirms that HH inhibits irreversible hydrogen bonding among CNFs, leading to the restoration of the nanostructure during redispersion. Moreover, HH in the CNF suspension after redispersion can be easily removed through a simple water rinsing process, highlighting HH as a highly suitable candidate for preventing aggregation of CNFs.

Glucaric Acid Production from Miscanthus sacchariflorus via TEMPO-Mediated Oxidation with an Efficient Separation System.

In this study, production and isolation of glucaric acid from lignocellulosic biomass were performed via potassium cation-based TEMPO-mediated oxidation for the ease of glucaric acid isolation. To optimize the oxidation conditions, response surface methodology (RSM) was adopted using standard glucose as the raw material. Among the oxidation conditions, the dosage of oxidant and pH of reaction affected the glucaric acid production, and the optimum conditions were suggested by RSM analysis: 5 °C of reaction temperature, 4.23 equiv dosage of KClO per mole of glucose, and pH of 12. Furthermore, glucaric acid was produced from lignocellulosic biomass-derived enzymatic hydrolysate from Miscanthus under optimum conditions. The impurities such as xylose and lignin in enzymatic hydrolysate inhibited the efficiency of glucose oxidation. As a result, more oxidant was required to produce sufficient glucaric acid from the enzymatic hydrolysate compared to standard glucose. The produced glucaric acid was simply isolated by controlling the pH in the form of glucaric acid monopotassium salt, which showed lower solubility in water, and the purity of isolated glucaric acid was over 99%. The overall mass balance of feedstock to glucaric acid was analyzed, suggesting that 86.38% (w/w) glucaric acid could be produced from initial glucan in feedstock.

Biodegradation in Composting Conditions of PBEAS Monofilaments for the Sustainable End-Use of Fishing Nets.

The development and utilization of biodegradable plastics is an effective way to overcome environmental pollution caused by the disposal of non-degradable plastics. Recently, polybutylene succinate co-butylene adipate co-ethylene succinate co-ethylene adipate, (PBEAS) a biodegradable polymer with excellent strength and elongation, was developed to replace conventional nylon-based non-degradable fishing nets. The biodegradable fishing gear developed in this way can greatly contribute to inhibiting ghost fishing that may occur at the fishing site. In addition, by collecting the products after use and disposing of them in composting conditions, the environmental problem such as the leakage of microplastics strongly can be prevented. In this study, the aerobic biodegradation of PBEAS fishing nets under composting conditions is evaluated and the resulting changes in physicochemical properties are analyzed. The PBEAS fishing gear exhibits a mineralization rate of 82% in a compost environment for 45 days. As a result of physicochemical analysis, PBEAS fibers show a representative decrease in molecular weight and mechanical properties under composting conditions. PBEAS fibers can be used as eco-friendly biodegradable fishing gear that can replace existing non-degradable nylon fibers, and in particular, fishing gear collected after use can be returned to nature through biodegradation under composting conditions.

pH-sensitive cellulose/chitin nanofibrillar hydrogel for dye pollutant removal.

In this study, a pH-sensitive smart hydrogel was successfully prepared by combining a polyelectrolyte complex using biopolymeric nanofibrils. By adding a green citric acid cross-linking agent to the formed chitin and cellulose-derived nanofibrillar polyelectrolytic complex, a hydrogel with excellent structural stability could be prepared even in a water environment, and all processes were conducted in an aqueous system. The prepared biopolymeric nanofibrillar hydrogel not only enables rapid conversion of swelling degree and surface charge according to pH but can also effectively remove ionic contaminants. The ionic dye removal capacity was 372.0 mg/g for anionic AO and 140.5 mg/g for cationic MB. The surface charge conversion ability according to pH could be easily applied to the desorption of the removed contaminants, and as a result, it showed an excellent contaminant removal efficiency of 95.1 % or more even in the repeated reuse process 5 times. Overall, the eco-friendly biopolymeric nanofibrillar pH-sensitive hydrogel shows potential for complex wastewater treatment and long-term use.

Development of poly(butylene adipate-co-butylene succinate-co-ethylene adipate-co-ethylene succinate) (PBEAS) net twine as biodegradable fishing gear.

Nylon fishing nets have excellent strength and durability, but when lost at sea, their insufficient decomposition destroys habitats and spawning grounds, and pollutes the marine environment. This led to the development of poly(butylene succinate) (PBS) resin for biodegradable fishing gear based on aliphatic fibers. Prompted by the low stiffness and elastic recovery of PBS, we introduced two additional components into the molecular structure of PBS: adipic acid and ethylene glycol. These two new components were combined with succinic acid and 1,4-butanediol, the existing components of PBS, to synthesize poly(butylene adipate-co-butylene succinate-co-ethylene adipate-co-ethylene succinate) (PBEAS) resin via esterification and polycondensation reactions of a quaternary aliphatic copolyester. Although the molecular weight and molecular weight distribution of PBEAS are similar to those of PBS, it has excellent tensile strength, stiffness, elastic recovery, and biodegradability, with a low melting point for good production efficiency. These improvements are expected to allow PBEAS resin to be applied to gill nets for fish that require high stiffness, thereby expanding the use of biodegradable fishing gear.

Physicochemical characteristics of lignin-g-PMMA/PLA blend via atom transfer radical polymerization depending on the structural difference of organosolv lignin.

Lignin has different structural characteristics depending on the extraction conditions. In this study, three types of ethanol organosolv lignin (EOL) were produced under different extraction conditions involving the reaction temperature (140, 160, 180 °C), sulfuric acid concentration (0.5, 1, 1.5 %), and ethanol concentration (40, 60, 80 %) to compare the difference in properties when mixed with polylactic acid (PLA) matrix after atom transfer radical polymerization (ATRP). ATRP of EOL was conducted to improve its compatibility with PLA using methyl methacrylate (MMA) as a monomer. The molecular weight of each EOL increased significantly, and the glass transition temperature (Tg) decreased from approximately 150 to 110 °C. The EOL-g-PMMA copolymer exhibited a melting point (Tm), whereas EOL did not, implying that the thermoplasticity increased. The EOL-g-PMMA/PLA blend and film were prepared with 10 % of the copolymer in the PLA matrix. The tensile strength and strain of the blend were higher than those of unmodified organosolv lignin as the compatibility increased, and the UV transmittance was lower than that of neat PLA because of the UV protecting properties of EOL moiety.

Biodegradable and hydrophobic nanofibrous membranes produced by solution blow spinning for efficient oil/water separation.

The development of nanofibrous oil-water separation materials is explosively progressing, but the remarkably low productivity is the main factor hindering their practical application. In this study, biodegradable polybutylene succinate (PBS) nanofibers with excellent productivity (27.0 g/h per nozzle) were successfully fabricated using the solution blow spinning (SBS) process, breaking away from the conventional electrospinning method. The prepared PBS nanofibers exhibited extremely thin fiber diameters (130 nm) with high porosity (97.4%). Without any chemical modification or inorganic/organic hybrid materialization, the PBS nanofibrous membrane showed excellent oil adsorption capacity (minimum: 18.7 g/g and maximum: 38.5 g/g) and separation efficiency; water and oil mixtures (99.4-99.98%) and emulsions (98.1-99.5%) compared to conventional organic polymer-based nanofibers. In terms of disposal after use, this biodegradable nanofibrous membrane was able to return to nature through hydrolysis and biodegradation processes.

Fabrication of transparent cellulose nanofibril composite film with smooth surface and ultraviolet blocking ability using hydrophilic lignin.

Ecofriendly multifunctional films with only biomass-based components have gathered significant interest from researchers as next-generation materials. Following this trend, a TEMPO-oxidized cellulose nanofibril (TOCNF) film containing hydrophilic lignin (CL) was fabricated. To produce the lignin, peracetic acid oxidation was carried out, leading to the introduction of carboxyl groups into the lignin structure. By adding hydrophilic lignin, various characteristics (e.g., surface smoothness, UV protection, antimicrobial activity, and barrier properties) of the TOCNF film were enhanced. In particular, the shrinkage of CNF was successfully prevented by the addition of CL, which is attributed to the lower surface roughness (Ra) from 18.93 nm to 4.99 nm. As a result, the smooth surface of the TOCNF/CL film was shown compared to neat TOCNF film and TOCNF/Kraft lignin composite film. In addition, the TOCNF/CL film showed a superior UV blocking ability of 99.9 % with high transparency of 78.4 %, which is higher than that of CNF-lignin composite films in other research. Also, water vapor transmission rate was reduced after adding CL to TOCNF film. Consequently, the developed TOCNF/CL film can be potentially utilized in various applications, such as food packaging.

Effect of chemically modified lignin addition on the physicochemical properties of PCL nanofibers.

In this study, a chemically modified lignin additive was successfully prepared to improve the physicochemical properties of biodegradable polycaprolactone (PCL)-based nanofibers. The molecular weight and surface functional group characteristics of lignin were effectively controlled through a solvent fractionation process using ethanol. Then, PCL-g-lignin was successfully synthesized by using ethanol-fractionated lignin as a platform for the PCL grafting process. Finally, PCL/PCL-g-lignin composite nanofibers were simply prepared by adding PCL-g-lignin to the PCL doping solution and performing a solution blow spinning process. The addition of PCL-g-lignin could dramatically improve the physical and chemical properties of PCL nanofibers, and in particular, the tensile strength (0.28 MPa) increased by approximately 280 % compared to the conventional PCL. In addition, the lignin moiety present in PCL-g-lignin was able to impart UV blocking properties to PCL nanofibers, and as a result, it was possible to effectively suppress the photolysis phenomenon that occurred rapidly in existing PCL nanofibers. Therefore, PCL-g-lignin may be widely used not only as a reinforcing agent of existing biodegradable nanofibers but also as a functional additive for UV protection.

Biodegradation behavior of acetylated lignin added polylactic acid under thermophilic composting conditions.

Acetylated lignin (AL) can improve compatibility with commercial plastic polymers compared to existing lignin and can be used as an effective additive for eco-friendly biocomposites. For this reason, AL can be effectively incorporated into polylactic acid (PLA)-based biocomposites, but its biodegradation properties have not been investigated. In this study, biodegradation experiments were performed under mesophilic and thermophilic conditions to determine the effect of AL addition on the biodegradation characteristics of PLA-based biocomposites. As a result, the PLA-based biocomposite showed a faster biodegradation rate in a thermophilic composting environment, which is higher than the glass transition temperature of PLA, compared to a mesophilic environment. 16S rDNA sequencing results showed that differences in microbial communities depending on mesophilic and thermophilic environments strongly affected the biodegradation rate of lignin/PLA biocomposites. Importantly, the addition of AL can effectively delay the thermophilic biodegradation of PLA biocomposites. As a result of tracking the changes in physicochemical properties according to the biodegradation period in a thermophilic composting environment, the main biodegradation mechanism of AL/PLA biocomposite hydrolysis. It proceeded with cleavage of the PLA molecular chain, preferential biodegradation of the amorphous region, and additional biodegradation of the crystalline region. Above all, adding AL can be proposed as an effective additive because it can minimize the decline in the mechanical properties of PLA and delay the biodegradation rate more effectively compared to existing kraft lignin (KL).

Enhancement of elongation at break and UV-protective properties of poly(lactic acid) film with cationic ring opening polymerized (CROP)-lignin.

In this study, the intrinsic brittleness of poly(lactic acid) (PLA) was overcome by chemical modification using ethyl acetate-extracted lignin (EL) via cationic ring-opening polymerization (CROP). The CROP was conducted to promote homopolymerization under starvation of the initiator (oxyrane). This method resulted in the formation of lignin-based polyether (LPE). LPE exhibited enhanced interfacial compatibility with nonpolar and hydrophobic PLA owing to the fewer hydrophilic hydroxyl groups and a long polyether chain. In addition, because of the UV-protecting and radical-scavenging abilities of lignin, LPE/PLA exhibited multifunctional properties, resulting in improved chemical properties compared with the neat PLA film. Notably, one of the LPE/PLA films (EL_MCF) exhibited excellent elongation at break of 297.7 % and toughness of 39.92 MJ/m3. Furthermore, the EL_MCF film showed superior UV-protective properties of 99.52 % in UVA and 88.95 % in UVB ranges, both significantly higher than those of the PLA film, without sacrificing significant transparency in 515 nm. In addition, the radical scavenging activity improved after adding LPE to the PLA film. These results suggest that LPEs can be used as plasticizing additives in LPE/PLA composite films, offering improved physicochemical properties.

Highly efficient Cr(VI) remediation by cationic functionalized nanocellulose beads.

Applications of nanocellulose as a water treatment material are being actively pursued based on its interesting properties, such as renewability, large specific surface area, hydrophilic surface chemistry, and biodegradability. This study used carboxymethyl cellulose nanofibrils (CMCNFs) to prepare a typical bead-type adsorbent with improved structural stability as an actual water treatment restoration material. In addition, a cationized nanocellulose adsorbent was prepared by introducing polyethyleneimine (PEI) on the surface of the CMCNF (P/CMCNF), the removal efficiency of Cr(VI) was evaluated, and its mechanism was elucidated. As a result, the P/CMCNF beads showed an excellent Cr(VI) removal capacity of 1302.3 mg/g, the best result among cellulose-based adsorption materials. Cr(VI) was effectively removed by electrostatic attractions combined with chemical reduction and chelation mechanisms. Furthermore, the macrobead fabrication and PEI surface modification process improved the underwater stability of the P/CMCNF, and it showed excellent reuse efficiency.

Thermoplasticity reinforcement of ethanol organosolv lignin to improve compatibility in PLA-based ligno-bioplastics: Focusing on the structural characteristics of lignin.

Commonly, lignin macromolecules have limitations in application to the thermoplastics industries due to poor dispersibility and interfacial compatibility within ligno-bioplastics. In this study, the dispersibility and interfacial compatibility of ethanol organosolv lignin (EOL) in PLA-based ligno-bioplastic were improved by enhancing the thermoplasticity via oxypropylation. Further, three types of EOLs extracted from different severity conditions were applied to investigate the effect of the structural characteristics of EOLs on the changes in the thermal properties. The thermal properties of oxypropylated EOL were dependent on the structural characteristics of the initial EOL as well as the degree of polymerization of propylene oxide. The thermoplasticity of EOLs extracted under mild condition was effectively increased as a new Tg and melting were observed. Based on increased thermoplasticity, the dispersibility and interfacial compatibility of EOL within PLA-based ligno-bioplastic were successfully improved, which compensates for the deterioration in mechanical strength of ligno-bioplastic due to the addition of unmodified EOL. Therefore, oxypropylation of EOL with suitable structural characteristics promises improved availability as a thermoplastic material.

Eco-friendly alkaline lignin/cellulose nanofiber drying system for efficient redispersion behavior.

Although nanocellulose is an eco-friendly, high-performance raw material provided by nature, the agglomeration of nanocellulose that occurs during the drying process is the biggest obstacle to its advanced materialization and commercialization. In this study, a facile and simple nanocellulose drying system was designed using lignin, which is self-assembled together with cellulose in natural wood, as an eco-friendly additive. The addition of lignin not only minimized aggregation during the drying and dehydration process of nanocellulose but also ensured excellent redispersion kinetics and stability. In addition, the added lignin could be removed through a simple washing process. Through FTIR, XRD, TGA, tensile and swelling tests, it was confirmed that the addition of lignin enabled the reversible restitution of the nanocellulose physicochemical properties to the level of pristine never-dried nanocellulose in drying, redispersion, and polymer processing processes.

Cationic surface-modified regenerated nanocellulose hydrogel for efficient Cr(VI) remediation.

Because nanocellulose has a large specific surface area and abundant hydroxyl functional groups due to its unique nanomorphology, interest increases as an eco-friendly water treatment material. However, the distinctive properties of nanocellulose, which exists in a dispersion state, strongly hamper its usage in practical water treatment processes. Additionally, nanocellulose shows low performance in removing anionic pollutants because of its anionic characteristics. In an effort to address this challenge, regenerated cellulose (RC) hydrogel was fabricated through cellulose's dissolution and regeneration process using an eco-friendly aqueous solvent system. Subsequently, a crosslinking process was carried out to introduce the cationic functional groups to the RC surface PEI coating (P/RC). As a result, the PEI surface cationization process improved the mechanical rigidity of RC and showed an excellent Cr(VI) removal capacity of 578 mg/g. In addition, the prepared P/RC maintained more than 90% removal efficiency even after seven reuses.

Aquatic polymer-based edible films of fish gelatin crosslinked with alginate dialdehyde having enhanced physicochemical properties.

Fish-derived gelatin (FG), a raw material for edible films, has recently been spotlighted as an alternative source of mammalian gelatin. However, its low stability under moisture conditions and weak mechanical properties limit its application. In this study, a water-stable and mechanically robust FG film was prepared using alginate dialdehyde (ADA) as an eco-friendly crosslinking agent. The crosslinking process of FG with ADA was easily recognized by the change in the color of the FG/ADA composite film, and the browning index of the FG/ADA film could be correlated well with the actual crosslinking degree. The mechanical strength and Young's modulus of the FG/ADA composite film increased significantly with an increase in the content of the ADA crosslinker. In the case of FG/ADA10, the tensile strength and Young's modulus increased by 400 and 600 %, respectively, compared to those of FG. Remarkably, the FG-ADA crosslinking process greatly decreased the vulnerability of FG in moisture environments. Consequently, the FG/ADA10 film remained stable for 30 days under wet environment. In addition, the FG-ADA crosslinking process could enhance the antioxidative capacity of the FG/ADA edible film. According to this study, FG/ADA composite films fabricated in an effective manner using polymers derived from aquatic species like gelatin from fish and ADA from algae could have practical applications in the edible film-based packaging industry.