Towards a deep understanding of the biomass fractionation in respect of lignin nanoparticles formation

doi:10.21203/rs.3.rs-3417528/v1

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Towards a deep understanding of the biomass fractionation in respect of lignin nanoparticles formation

https://doi.org/10.21203/rs.3.rs-3417528/v1

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published 24 Nov, 2023

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In recent years, lignin-based nanomaterials have become increasingly relevant for researchers and producers of functional material applications due to their green and sustainable nature. However, there is still a challenge in controlling fabrication of lignin nanoparticles (LNPs). In the current study, we explored an environmentally friendly sequential hot water extraction with accelerated solvent extractor (ASE) to obtain a lignin-based fraction for the controllable production of LNPs. The lignin-based fractions are obtained from both Norway spruce heartwood (HW) and sapwood (SW) after sequential hot water extraction followed by separation with XAD 8 resin column and desorption with methanol (methanol fraction, MF). LNPs were successfully prepared from HWMF and SWMF with different physicochemical properties using acetonitrile/water binary solvent in an ultrasonic bath only within 1 min. The size of LNPs increased with the severity of wood ASE extraction, which is related to the reduction of β-O-4 bond, the increase of phenolic hydroxyl groups and the decrease of aliphatic hydroxyl groups in MF. However, no direct relationship between the size of LNPs and molar mass as well as carbohydrate content was found. The controllable preparation of LNPs was directly dependent on the ASE extraction conditions without complex chemical modification. This study presents a green method for controllable preparation of LNPs and provides a promising new value-added valorization pathway for lignin-based fractions (including lignin and lignin carbohydrate complex) from wood hot water extraction.

lignin

nanoparticles

sequential hot water extraction

heartwood

sapwood

Recently, the development of lignocellulosic biomass biorefinery and bio-based nanocomposites has played an increasingly important role in environmental pollution reduction and human sustainability[1–3]. As the dominant lignocellulosic feedstock available in the Nordic countries, Norway spruce has received the attention of many researchers[4, 5]. The efficient and high-value applications of lignocellulosic biomass are important in biorefineries, in which different treatment methods and further fractionation methods are proposed due to it being the most critical processing steps which will influence downstream application[6–8]. Among them, hot water extraction is attractive regarding its environmentally friendly potential.

Hot water extraction is a chemical-free process that usually removes most of the hemicelluloses, and some portion of lignin[9–11]. Most previous studies of Norway spruce hot water extraction have been focused on the valorization of hemicelluloses or cellulose[12]. The extracted hemicelluloses will be purified or modified as a raw material for further application, including hydrogels[13], barrier coating in packaging[14, 15] and etc. The disruption of the lignocellulosic biomass structure will increase cellulase accessibility and enhance the subsequent enzymatic hydrolysis and fermentation steps which facilitate the conversion of cellulose to bioethanol. In this case, lignin-based fractions (including lignin fraction and lignin carbohydrate complex) are usually ignored and underutilized[16]. Only a few attempts have been made to explore at the valorization of lignin-based fractions from hot water extraction[17, 18]. Zhang et al. investigated the lignin-rich fractions from hot water extraction and found that they exhibit good antioxidant activity[17]. The potential of lignin-carbohydrate hybrids obtained by hydrothermal treatment and solvent extraction as wood adhesives was investigated by Tarasov et al[18]. However, all biomass components utilization is the requirement of biorefinery for lignocellulosic biomass valorization, thus the utilization of lignin-based fractions after hot water extraction should not be neglected to make a full valorization lignocellulosic biomass[19, 20].

Lignin has been explored for prospective use to produce various materials for numerous applications[21], such as carbon materials for electrochemical energy storage[22] and polymer composite for packaging[23], biomedical[24, 25], 3D printing applications[26], etc. Nanomaterials, especially the preparation of lignin nanoparticles (LNPs) have received extensive attention due to their promising properties, including low cost, low density, renewable, degradable, and surface active as well as simple and flexible preparation. Moreover, the utilization of LNPs into nanocomposites could open new possibilities for the development of novel materials with outstanding properties (e.g., toughening, UV shielding, antibacterial properties)[27, 28]. There are many ways to prepare nanoparticles, and many studies are exploring the factors that affect the formation of nanoparticles, such as content of phenolic hydroxyl group[29, 30], molar mass[31], the content of carbohydrates in lignin[32], etc.

However, the well controllable preparation of LNPs is still a challenge including the shape and size of particles. Previously, most of the lignin raw materials used for LNPs preparation are kraft lignin[33, 31] or organosolv lignin[16]. However, due to the complex structure of theses lignins, complicated treatments such as purification (remove sulphur), and fractionation are needed to obtain lignin fraction meeting the requirement for the controlled preparation of LNPs. Norway spruce sapwood (SW) contains less lignin and more cellulose than heartwood (HW) according to Bertaud et al[34]. Considering the chemical composition differences between of HW and SW will influence the properties of the extracted lignin fraction. Therefore, lignin-based fraction from Norway spruce HW and SW were both extracted using sequential hot water extraction, and the influence of the extraction conditions on the formation of LNPs in acetonitrile/water binary solvent was investigated. The isolated lignin-based fractions were characterized by gas chromatography (GC), Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC) equipped with a multiangle light scattering detector (MALS) and a differential refractive index concentration (RI) detector, thermogravimetric (TG), and nuclear magnetic resonance (2D HSQC, ¹³C NMR and ³¹P NMR) to analyze their structural differences in terms of carbohydrate composition, substructures, molar mass and molar mass dispersity, thermal degradation properties and content of hydroxyl groups. Moreover, the formed LNPs were systematically characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and force tensiometer.

2.1 Materials

Fresh and healthy Norway spruce was applied as the raw material, which was collected from South-West Finland. The wood disk was divided into sapwood (SW) and heartwood (HW) (Fig. 1) and cut into small knot-free pieces and then ground into wood sawdust with a particle size < 1 mm. Wood sawdust (screened below 60 mesh) was pre-extracted with acetone in a Soxhlet apparatus and air-dried before hot water extraction. Acetonitrile used in this study was chromatographic grade.

2.2 Methanol fraction (MF) isolation

Lignin-based fraction (MF) was obtained during separation of ASE extracts with XAD 8 resin column according to previous publication with some modifications[17]. The detailed scheme is shown in Fig. 1.

Deionized water was used as a solvent in an accelerated solvent extractor (ASE 350, DIONEX, CA, USA) for sequential hot water extraction. Approximately 20 g of extractive-free sawdust was used for a continuous ASE extraction at following conditions (160°C for 20 min, 160°C for 40 min, and 180°C for 10 min). After the oxygen-free extraction, the extracted solution (hydrolysates) was purged from the extraction cell with nitrogen. The ASE water extracts were collected separately and labelled as SWH1/HWH1, SWH2/HWH2, and SWH3/HWH3.

Lignin separation was then carried out on a column packed with XAD-8 resin[35]. Prior to separation, the column was pre-washed and conditioned with acidified water at pH 2 (HCl). The pH of ASE water extracts was adjusted to 2 before being passed through the column. The XAD-8 resin allows the hydrophilic substances (carbohydrates) to pass through the column while the hydrophobic component (i.e., lignin) gets adsorbed onto the XAD-8 resin. Afterward, the column was washed with methanol to desorb lignin-based substances. The MF was collected separately and given the names SWMF1/HWMF1, SWMF2/HWMF2, and SWMF3/HWMF3 for further LNPs preparation.

2.3 Lignin nanoparticles (LNPs) preparation

LNPs were rapidly prepared from MF in an acetonitrile-water system[36]. In general, 6 mL of mixture solution (acetonitrile/water, v/v = 2:1) was added into a 30 mg of dried MF sample and treated in ultrasonic bath for 1 min. Then LNPs dispersions were obtained, and the residual acetonitrile was removed by dialysis.

2.4 Analytical methods

Molar mass analysis. Dry MF samples were dissolved in DMSO/0.05 M LiBr to a concentration of 10 mg/mL and analyzed by size exclusion chromatography (SEC) in tandem with a multiangle light scattering detector (MALS), and differential refractive index (RI) detector (DAWN 8 and Optilab by Wyatt Technology). The columns were Jordi Gel GBR Glucose guard column (8 mm x 50 mm) and Jordi Gel GBR Glucose Mixed Bed column (10 mm x 250 mm). The eluent flow rate was kept at 0.5 mL/min, and the column temperature was 60°C. All the data was collected and processed by ASTRA software (version 7.3.2). A dn/dc value of 0.15 mL/g was used for calculation[37].

Carbohydrate analysis. Acid methanolysis and GC-FID were applied to characterize the chemical composition of hemicelluloses in the MF samples[38]. 10 mg of MF sample was weighed (± 0.01 mg) in a pear-shaped flask and methanolyzed with 2 M HCl in dry methanol at 105°C for 4 h. After that, the flask was cooled down and the content was neutralized with 150 µL of pyridine. 1.0 mL of the internal standard (0.1 mg/mL of resorcinol in methanol) was added to the samples and the solvent was evaporated with a nitrogen flow. Then the sample was additionally dried in a vacuum oven at 40°C and silylated with 150 µL of pyridine, 150 µL of hexamethyldisilazane (HMDS), and 70 µL of trimethylchlorosilane (TMCS) overnight. The TMS-derivatives of sugar and uronic acid units were analyzed with a GC (PerkinElmer AutoSystemXL) equipped with a flame ionization detector on a capillary columns HP-1 (25 m×0.20 mm; film thickness 0.11 µm).

NMR analysis. NMR spectra were recorded on a 500 MHz Bruker instrument at 25°C. Two-dimensional heteronuclear single-quantum coherence (HSQC) spectra were performed using the Bruker standard pulse program hsqcedetgpsisp2.3. 80 mg of MF samples were dissolved in 0.7 mL of DMSO-d6 and placed into a 5 mm NMR tube, referenced at 39.5/2.5 ppm. The quantitative ³¹P NMR analyzes were performed according to previous literature[32, 39]. 20 mg of MF samples was dissolved in 300 µL of A solvent (anhydrous pyridine and deuterated chloroform (CDCl₃) 1.6:1, v/v), and 100 µL of dimethylformamide (DMF) under stirring. After complete dissolution, 100 µL of endo-N-hydroxyl-5-norbornene-2,3-dicarboximide (0.12 M in pyridine/CDCl₃ 1.6:1, v/v) was added as an internal standard, and 50µL of chromium (III) acetylacetonate solution (11.4 mg/mL in pyridine/CDCl₃ 1.6:1, v/v) was added as relaxation reagent. Finally, the mixture was reacted with 100 µL of the phosphorylating reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholate and was transferred into a 5mm NMR tube for NMR analysis. Detailed information on quantitative ¹³C NMR is given in the Supporting Information.

FTIR analysis. FT-IR analysis was performed by potassium bromide (KBr) pellet method using a weight ratio of 1:100 (sample/KBr) in the range of 4000 − 400 cm^− 1 with a Thermo Scientific Nicolet iS50 FTIR spectrophotometer.

Thermogravimetric (TG) analysis. Thermogravimetric analysis was performed with a thermogravimetric analyzer (Discovery SDT 650, TA instruments). The MF samples were heated from room temperature to 900°C at a heating rate of 10°C/min in a nitrogen atmosphere at a flow rate of 100 mL/min.

TEM analysis. A JEM-1400 PLUS microscope (JEOL Ltd., Japan) operating at 80 kV was used to obtain TEM images of LNP samples in bright-field mode.

Particle size and zeta potential analysis. Measurements of size and zeta potential of LNPs were carried out using a Malvern Zetasizer nano series at 25°C. Triplicate measurements were performed on each sample to check the reproducibility. The data was analyzed using the Zetasizer Software.

Surface tension analysis. The surface tension of the LNPs solution (0.1 mg/mL) against air was measured with a force tensiometer-K100 using a Wilhelmy plate (Krüss, Germany) at 25°C[18].

3.1 The morphology and properties of LNPs prepared from lignin-based fractions (MF)

During the entire process, the sequential hot water extraction was performed to tailor the subsequent controllable LNPs preparation. The variation of the shape and size of the LNPs derived from HWMF and SWMF after the sequential hot water extraction is shown in the TEM images in Fig. 2a. It was shown that the size of the LNPs varies with the extraction conditions. TEM images revealed that both LNPs products had spherical shapes no matter derived from HWMF or SWMF and the size of LNPs increased with increasing severity of the ASE hot water extraction stage. The smoothest surface LNPs was obtained with HWMF3/SWMF3, which was obtained from the final stage of sequential hot water extraction. This can be due to the influence of the surface energy and carbohydrate composition in the lignin-based fractions.

The size of LNPs derived from SWMF is smaller than that of HWMF can be observed clearly from TEM images as shown in Fig. 2a, which was also in line with DLS results in Fig. 2b. The SWMF gave an average particle size from 394.8 nm to 749.9 nm, while the HWMF exhibited a similar increasing trend in size but each LNPs size from HWMF were larger than these from SWMF. SWMF1 has the smallest size, while the surface of the nanoparticle is roughest. The presence of lignin-based fractions (lignin and lignin carbohydrate complex) in water reduced the surface tension at the air/water interface from 72 mN/m to around 69 mN/m for HWMF, 67 mN/m for SWMF, respectively (Fig. 2a). Both HWMF and SWMF exhibited reduced surface tension as a result of the sequential hot water extraction, suggesting that the severe ASE conditions increased the surface activity of the lignin-based fractions at the air/water interface[18].

The zeta potential and polydispersity index (PDI) are fundamental properties that determine the stability of colloidal systems of LNPs dispersed in water. The zeta potential of the LNPs ranged from − 21.5 to -29.2 mV (Fig. 2b) indicating relatively high stability in water. The lowest absolute zeta-potential value − 21.5 mV was found in SWMF1 which indicated relatively lower stability than other samples, consistent with what was observed in the TEM images that rough surfaces of LNPs relate to each other in SWMF1 (Fig. 2a). The PDI values of LNPs from both HWMF and SWMF are shown in Fig. 2b, and it provides information on the homogeneity of LNPs size distribution. The relatively high PDI values of SWMF1 (0.17) in SW and HWMF2 (0.32) in HW indicate the inhomogeneity of LNPs, which is in agreement with the TEM images (Fig. 2a).

3.2 Carbohydrate content and molar mass of lignin-based fraction (MF)

The carbohydrate composition of all MF samples was analyzed by acid methanolysis and GC is shown in Fig. 3a. In general, most abundant non-cellulosic polysaccharide (hemicellulose) in softwood is main galactoglucomanans (GGM)[40, 41]. Compared with HWMF1, the content of carbohydrates (mainly mannose, glucose, and galactose) is lower than HWMF2. The increased content of carbohydrate can be ascribed mainly to the extension of ASE extraction time. In the third stage of sequential hot water extraction, the temperature was raised from 160°C to 180°C, but only for 10 min. Thus, the carbohydrate content of HWMF3 is not higher than HWMF2. Another explanation is that with the extraction, most of the carbohydrates have been removed in the previous stage, and the lignin carbohydrate complex (LCC) linkage are easily cleaved at a higher temperature, so that the carbohydrate content of HWMF3 is lower than that of HWMF2. And a similar trend of carbohydrate content with the extraction processing was observed in SWMF samples.

The PDI values and zeta potential of the LNPs seem to correlate with the composition of the carbohydrates in the corresponding HWMF and SWMF (Fig. 2b and Fig. 3a). For HWMF, the carbohydrate content, and PDI and absolute zeta potential have the same pattern. That is, the high zeta potential and high PDI corresponding to the carbohydrate content. LNPs obtained from SWMF were smaller than the LNPs obtained from HWMF. At the same time, SWMF had a higher content of carbohydrates than HWMF (Fig. 3a) except SWMF2 had a lower content of carbohydrates than HWMF2. LNPs produced from the HWMF1 and HWMF3 fractions were larger in size than those produced from the SWMF1 and SWMF3 fractions, respectively, probably due to the higher lignin content observed in the HWMF1 and HWMF3 fractions. Nevertheless, LNPs from HWMF2 and SWMF2 fraction do not follow the above-mentioned phenomenon and the role of carbohydrates in nanoparticle formation need to be clarified in future[31].

The molar mass and molar mass dispersity (Ð_M) of HWMF and SWMF samples investigated by SEC/MALS/RI are presented in Fig. 3b. The pattern of molar mass is consistent with the patterns of carbohydrate content (Fig. 3a and b). Previous studies reported that smaller LNPs were successfully prepared with higher molar mass lignin[30, 42]. However, those statement is not consistent with the results of this study. This may be because some branched molecules as LCC exist in MF[43, 44], which influence the formation of LNPs. The size of LNPs increased with decreasing the Ð_M of the MF for both HW and SW. The SWMF1 with the highest Ð_M gave the smallest LNPs, with diameters of 394.8 nm; the lower Ð_M samples, such as SWMF2 and SWMF3, gave bigger LNPs, with diameters of 570.9 and 749.9 nm, respectively. This trend was also found for the samples from HW.

3.3 Thermal and FTIR analysis of lignin-based fraction (MF)

In order to investigate the chemical structure of the HWMF and SWMF samples, FTIR analysis was carried out. Several absorption peaks were assigned according to the literature data[45] as shown in Fig. 4d. The strong absorption at 3430cm^− 1 corresponds to the OH group stretch which clarify that the hydroxyl groups were quite abundant in both HWMF and SWMF samples. It was also apparent that the C-H sketch in -CH₂ and -CH₃ groups (2939cm^− 1 and 2841cm^− 1, respectively) were presented in all samples[46]. The peaks around 1665 cm^− 1 and 1735 cm^− 1 in MF samples attributed to C = O stretching of conjugated and unconjugated carbonyl groups. The band at 1031 cm^− 1 can be assigned to aromatic C-H in-plane deformations of the guaiacyl (G) unit[47]. FTIR spectra of HWMFs and SWMFs show similar peak patterns and relative intensity, suggesting that no significant changes in lignin structure have occurred during the sequential hot water extraction and that there is no substantial difference between HW and SW.

The thermogravimetric curves (TG) and their derivative thermogravimetric (DTG) curves of both HWMF and SWMF samples were further studied and presented in Fig. 4a and 4c, respectively. The first stage was from room temperature to 200°C which corresponded to the evaporation of absorbed water[48]. The second stage for all samples, the stage where most of weight loss occurs between 200°C and 400°C, mainly including the degradation of lignin interunit linkages and the evaporation of some monophenols and carbohydrate decomposition[49, 50]. The degradation of hemicellulose and cellulose attached to the lignin structure is responsible for the peak of the DTG curves around 300°C[51]. After 500°C, the weight remained at the final stage which is related to non-volatile solids associated with highly condensed aromatic structures and the char of lignin[50, 52]. It was found that the final MF residue is increased with extraction processing (HWMF1༜HWMF2༜HWMF3 and SWMF1༜SWMF2༜SWMF3). The final residue of HWMF was higher than the SWMF residue which is in agreement with the size of the nanoparticles obtained from them (Fig. 2). The above results suggested that the carbohydrate content will affect the formation of LNPs, but it is not the main factor to determine the size of LNPs which need additional investigations.

3.4 NMR results of lignin-based fraction (MF)

To further investigate the role of the MF components structure on LNPs formation, 2D HSQC and ³¹P NMR were applied to both HWMF and SWMF samples (Fig. 5 and Fig. 6b). The spectra of both HWMF and SWMF samples were identical to the publication[53, 54]. In the aromatic region of the HSQC spectra of all MF samples (Fig. 5 bottom), typical signals related to G units (G₂, G₅, G₆) are identified. The condensed units G₂’ can also be found from the spectra, but there is no obvious difference between different MF samples which consider a similar aromatic structure of the lignin-based fractions. In the side-chain region of the spectra (Fig. 5 top), cross-signals of inter-unit linkages, such as β-O-4 aryl ethers (A/A’), resinols (B), and phenyl coumarans (C) are present in the HSQC spectra. The presence of signals of methoxy groups suggests these lignin-based fractions are rich in G-type units.

From Huang et al. is known that the predominant linkages of LCC are phenyl glycoside (PhGlc), benzyl ether (BE), and γ-ester (Est) [55, 56]. Although there are no obvious BE and Est signals were observed in Fig. 5, PhGlc1 linkages were observed at δ_C/δ_H = 99/4.9 ppm in all the MF samples isolated from sequential hot water extracts[57]. The presence of lignin structure and LCC in the 2D HSQC spectra further indicated that lignin-based fractions or MF is a mixture of lignin and LCC, and their structures jointly affect the formation of LNPs. The lignin-based fractions include so-called “rigid”, hydrophobic lignin units and “flexible” hydrophilic carbohydrate units resulting in good biological compatibility and strength in value-added applications[58]. It was indicated that a good knowledge of the chemical composition during the hot water extraction is both essential to assess changes during the process and to provide a deeper understanding of the factors affecting the formation of LNPs.

During sequential hot water extraction processing, the cleavage of β-O-4 aryl ether was significant and yield of degraded lignin with increased content of phenolic hydroxyl groups due to the formation of more phenolic end group[59]. This is supported by ³¹P NMR data, where the total phenolic hydroxyl group increased ((Fig. 6b), and β-O-4 linkage decreased with the extraction processing (Fig. 6a). The degree of condensation (DC) of lignin was also calculated through the region between 125 − 103 ppm by quantitative ¹³C NMR[60]. The results showed that the condensation degrees of lignin units in HWMF1, HWMF2, and HWMF3 were 37%, 47%, and 50%, respectively (Fig. 6a and (Fig. S1). The β-O-4 linkages are cleaved during sequential hot water extraction, forming lignin fragments. The DC values of lignin units increased, indicating that the sequential hot water extraction led to both depolymerization and condensation reactions, forming more carbon-carbon bonds. In addition, it was found that the “char residues” at 600°C after TG analyses were 50% for HWMF3, 48% for HWMF2, and 45% for HWMF1 in the present study (Fig. 4a). This fact suggested that the content of condensed lignin structures existed in HWMF3, which was higher than in HWMF1 and HWMF2, as revealed by the higher DC value obtained from quantitative NMR data (Fig. 6a), which is consistent with previous results[61].

The lignin contains abundant hydroxyl groups, including hydroxyl of phenolic, aliphatic, and carboxylic groups, leading to lignin with different reactivities[62]. The hydroxyl group contents of both HWMF and SWMF samples, a probably critical factor for the formation of LNPs, were determined by ³¹P NMR (Fig. 6b). The increased phenolic hydroxyl contents have a positive effect on LNPs size, from 394.8 nm to 749.9 nm for SWMF samples and from 616.3 nm to 892.8 nm for HWMF samples, respectively. These results are consistent with the contents of phenolic hydroxyl groups of the corresponding HWMF and SWMF samples. Yan et al. reported similar phenomena that LNPs with low phenolic hydroxyl content showed relatively smaller particle sizes. This is probably because low phenolic hydroxyl contents mean stronger π − π interactions resulting in a smaller size of LNPs[63]. However, the effect of phenolic hydroxyl content on the size of LNPs is only applicable to the comparison between the same raw materials, and other factors need to be considered in the variation of the size of LNPs between different lignin sources. For example, compared to HWMF, SWMF has higher phenolic hydroxyl content but smaller particle[64].

In addition to phenolic hydroxyl groups, aliphatic hydroxyl groups in lignin also play an important role in the size of LNPs due to ability of these groups form intermolecular hydrogen bonds that hold lignin subunits together to form LNPs[30, 65]. As shown in Fig. 6b, the aliphatic hydroxyl groups of LNPs derived from SWMF are higher than HWMF. Interestingly, it was reported that aliphatic hydroxyl groups form stronger hydrogen bonds than phenolic hydroxyl groups in FTIR observations of lignin model compounds [66]. Based on solubility studies in organic solvents, the lignin samples with the highest aliphatic hydroxyl groups content had the lowest solubility [67]. This agrees with the LNPs size of the SWMF being smaller than the HWMF.

In summary, a comprehensive understanding of the relation between lignocellulosic biomass extraction and LNPs formation would be beneficial for the valorization of lignin-based fractions and the biorefinery process. Lignin-based fractions (methanol fraction, MF) were obtained after sequential hot water extraction and XAD 8 separation from different parts of the Norway spruce (HW and SW). The acetonitrile-water system is also suitable for lignin-based fractions obtained after hot water extraction, and LNPs were directly prepared from both HWMF and SWMF using the acetonitrile-water system in ultrasonic bath only 1 min. LNPs prepared from HWMF or SWMF exhibit different nanosizing behaviors that size increased with extraction processing. The low β-O-4 linkage, high phenolic group, and low aliphatic groups of MF at the third stage of sequential hot water extraction promote the formation of large-sized LNPs with regularly shaped and homogenous surface morphology features. Even HWMF2 and SWMF2 with relatively high carbohydrate content can still form LNPs with smooth and regular surfaces using an acetonitrile-water system, which provides a way for high-value utilization of lignin-based fraction (lignin and lignin-carbohydrate complex mixture) and further facilitates integration into nanocomposites.

Funding

This work was supported by the National Natural Science Foundation of China (No. 32171717, 32071720, 32271814), Natural Science Foundation of Tianjin (No. 22JCYBJC01560), the financial support from the China Scholarship Council (No. 202008120139) and the Walter Ahlström Foundation.

Conflict of interest

The authors declare no competing interests.

Authorship contribution statement

Chunlin Xu supervised the project. Jiayun Xu and Andrey Pranovich designed the experiments. Jiayun Xu performed the experiments, data analysis, and wrote the original draft. Andrey Pranovich, Rui Liu, and Luyao Wang assisted in the experiments and data analysis. Jarl Hemming assisted in SEC/MALS/RI analysis. All authors discussed experiments and results. Chuanling Si co-supervised the work and Lin Dai reviewed & edited, guiding the manuscript. All authors have given approval for the final version of the manuscript.

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Towards a deep understanding of the biomass fractionation in respect of lignin nanoparticles formation

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Journal Publication

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Abstract

Figures

1. Introduction

2. Materials and methods

2.1 Materials

2.2 Methanol fraction (MF) isolation

2.3 Lignin nanoparticles (LNPs) preparation

2.4 Analytical methods

3. Results and discussions

3.1 The morphology and properties of LNPs prepared from lignin-based fractions (MF)

3.2 Carbohydrate content and molar mass of lignin-based fraction (MF)

3.3 Thermal and FTIR analysis of lignin-based fraction (MF)

3.4 NMR results of lignin-based fraction (MF)

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Journal Publication

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