Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Mar 5;5(10):4836–4843. doi: 10.1021/acsomega.9b03535

Structure–Adsorption Behavior–Dispersion Property Relationship of Alkyl Chain Cross-Linked Lignosulfonate with Different Molecular Weights

Nanlong Hong †,*, Xueqing Qiu ‡,*
PMCID: PMC7081325  PMID: 32201769

Abstract

graphic file with name ao9b03535_0010.jpg

The structure–adsorption behavior–dispersion property relationship plays a key role in designing a dispersant or surfactant, such as a coal–water dispersant and a water-reducing agent. In this work, was classified into three fractions with narrow molecular weight distributions via the ultrafiltration method. The adsorption behavior of these three fractions was tested via a quartz crystal microbalance with dissipation monitoring, which showed that the adsorption amounts of the three fractions were far higher than that of sulfomethylated lignin. Fraction-1, with the lowest molecular weight, exhibited the greatest adsorption amount on a Au surface under salt-free conditions. This result illustrates that the alkyl chain is more effective for dispersants with low molecular weight to improve its adsorption amount. Fraction-3, with the highest molecular weight, exhibited the greatest adsorption amount on a Au surface under salt-added conditions. This result further illustrates that both the alkyl chain and salt are positive factors for improving the adsorption amount of dispersants. More importantly, the dispersion stabilization of the TiO2 slurry was significantly improved using the alkAL-S fractions, especially Fraction-3. Based on these results, the alkyl chain cross-linked of lignosulfonate is a promising approach for the industrial applications of lignin as an applicable dispersant.

1. Introduction

After cellulose, lignin is the second most abundant biopolymer among all the renewable natural resources.1 In the purest sense, lignin is a three-dimensional, amorphous, and polyphenolic material that originates from three primary precursors: coniferyl, sinapyl, and p-coumaryl alcohols.2 Technical lignin, produced from soda pulping processes, is difficult to be utilized efficiently because of its low molecular weight and poor water solubility at a neutral pH.3,4 Therefore, technical lignin usually needs to be modified before use in diverse industrial applications.3,5−8

It is a known fact that the molecular weight (Mw) and the sulfonic group content are the key factors that influence the properties of technical lignin and its potential for use as an excellent dispersant in cement,9,10 coal–water slurry,11 pesticide suspension,12 and so on. To improve Mw, methods including formaldehyde condensation polymerization13,14 and graft copolymerization15−17 are commonly used. To increase the sulfonic group content, methods including sulfonation,5,6 sulfomethylation,7,8 and graft sulfonation18 are used.

The adsorption behavior is the main measurement used by researchers to investigate the dispersion mechanism of lignosulfonate in the suspension system. The conventional research methods used to study the adsorption behavior include UV spectrophotometry19,20 and electrostatic self-assembly.21,22 UV spectrophotometry is a widely applied technology that investigates the amount of dispersants adsorbed on the particle surface, but it cannot detect the conformation of the adsorbed layer. When the electrostatic self-assembly method is used, polycation electrolytes, such as poly(diallyl dimethylammonium chloride), are introduced, and it is difficult to prepare a metastable self-assembled film. Furthermore, both these methods suffer from the inability to measure the adsorption behavior in real time. Thus, finding a better way to investigate these dispersion mechanisms in real time is critical. Quartz crystal microbalance with dissipation monitoring (QCM-D) is a fundamental and efficient research method for better detecting the adsorption amount in real time and conformation of the adsorbed layer.23−25 Therefore, QCM-D was applied to test the adsorption behavior in our paper.

The results of previous studies showed that the adsorption amount of a high-Mw lignin polymer is greater than that of a low-Mw lignin polymer, and the ionic strength could enhance the adsorption amount by shielding the electrostatic repulsion between the sulfonic groups and enhancing the hydrophobic effect on the Au surface.22,26 Here, an alkyl chain was introduced to sulfomethylated lignin (AL-S) to improve the Mw of lignin via the alkyl chain cross-linked polymerization method. This method is more efficient and convenient to improve than the other reported methods for improving the Mw of lignin.13−17 Ultrafiltration (UF) of lignosulfonate is an efficient method to obtain lignin-based polymers with narrow Mw distributions.27−30 Therefore, a UF device was applied to purify and classify alkyl chain cross-linked lignosulfonate (alkAL-S) to obtain different fractions with narrow Mw distributions, denoted as Fraction-1, Fraction-2, and Fraction-3, and the adsorption behaviors of the three alkAL-S fractions on the Au surface were measured by QCM-D. Unexpectedly, the effect of the alkyl chain on the adsorption behaviors of the three fractions is distinct. The effect of ionic strength on the adsorption behavior was further investigated. Moreover, the dispersion stabilization of TiO2 was significantly improved using the three fractions. Therefore, in our study, the adsorption amount and dissipation factor could be readily improved by introducing an alkyl chain into lignosulfonate, and excellent and suitable dispersants could be designed for industrial applications.

2. Results and Discussion

2.1. Molecular Weight Distributions of the alkAL-S Fractions

The Mw distributions of the initial AL-S and alkAL-S are presented in Figure 1a. The average Mw and the polydispersity index (PDI) are also given in Table 1. The molecular weight of alkAL-S is remarkably increased via alkyl chain-bridged polymerization. The Mw of alkAL-S (61,200 Da) is approximately 11.3 times higher than that of AL-S (5400 Da). The results of the functional group content show that the phenolic group content of alkAL-S decreased remarkably (from 2.21 to 0.51 mmol/g).

Figure 1.

Figure 1

Open in a new tab

Molecular weight distributions of sulfomethylated alkaline lignin (AL-S) and alkyl chain cross-linked lignosulfonate (alkAL-S) (a), and the three different alkAL-S fractions with narrow molecular weight distributions (b).

Table 1. Molecular Weight Distribution of AL-S, alkAL-S, and Different Fractions Separated from the Three UF Membranes by GPC.

        functional group content
samples Mw (Da) Mn (Da) PDI -OH (mmol/g) SO3 (mmol/g)
AL-S 5400 2600 2.08 2.21 1.81
alkAL-S 61,200 19,800 3.09 0.51 1.62
Fraction-1 5800 3900 1.49 1.12 1.87
Fraction-2 43,600 28,800 1.51 0.62 1.72
Fraction-3 152,000 83,900 1.81 0.11 1.51
Open in a new tab

The effect of the UF method on the Mw distribution of alkAL-S is shown in Figure 1b. The value PDI of alkAL-S is wide, although the Mw increased noticeably (see Figure 1a). Based on the UF method, the Mw distribution of the fractions separated by three membranes is very narrow and symmetric (see Figure 1b). The results of the Mw distribution are also provided in Table 1. All the three fractions have a low PDI in the range of 1.49–1.81. The average Mw’s of Fraction-1, Fraction-2, and Fraction-3 are 5800, 43,600, and 152,000 Da, respectively. The results are relatively equivalent to the membrane characteristics applied to classify alkAL-S.

The functional group contents of the alkAL-S fractions were assessed, as shown in Table 1. Increasing the Mw, the functional group contents of the three fractions decreased, including −OH, −SO3H, and especially −OH. The elemental analyses of the three alkAL-S fractions were also investigated in our study (see Table 2). As expected, the content of C and H increased, and the S content decreased with the increasing Mw of fractions. The results are consistent with the results of the functional group contents.

Table 2. Elemental Analysis Results of the Three alkAL-S Fractions.

sample C % H % N % S %
Fraction-1 38.03 5.117 0.15 6.914
Fraction-2 46.34 5.893 0.11 6.142
Fraction-3 52.56 6.336 0.09 5.329
Open in a new tab

2.2. Structural Characterization

To better elucidate the structural characteristics of the three alkAL-S fractions, spectroscopic analyses, including Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR), were performed (see Figure 2). The interpretations of the FTIR spectra are shown in Figure 2a. The broad band at approximately 3450 cm–1 corresponds to O–H elongation,31 and the peaks at 2937 and 2860 cm–1 are due to the methylene stretching vibrations of the alkyl chain of C6H12Br2.13,32 As the Mw of the alkAL-S fractions increased, the intensity of A3450 decreased, whereas that of A2937 increased gradually; this result is in agreement with the functional group content results.

Figure 2.

Figure 2

Open in a new tab

Spectroscopic analysis results of the three alkAL-S fractions: (a) FTIR spectra of the fraction samples, (b) 1H NMR spectra of the fraction samples.

The 1H NMR spectra of the three fractions are presented in Figure 2b. The signals between 0.5 and 2.0 ppm are ascribed to aliphatic chain protons.33,34 The signal intensity of the aliphatic H exhibits a strong positive correlation with the increasing Mw of the alkAL-S fractions. The results are also consistent with the IR results. Therefore, through the series of characterizations of the alkAL-S fractions separated from the three membranes, the UF method is a feasible and powerful technique to obtain alkAL-S fractions with a very low polydispersity.

2.3. Film-Forming Properties and Wetting Properties on Au Surface

To investigate the effect of the alkAL-S fractions with different Mw’s on the particle distribution of aggregates, the film-forming morphology of the three fractions on a Au surface was observed by atomic force microscopy (AFM). As can be observed in Figure 3a–c, Fraction-1, with the lowest Mw, has the minimum surface roughness (root mean square, RMS), and RMS increases gradually as the Mw of the three fractions increases. Moreover, the morphology shows that the particle size gradually increases from Fraction-1 to Fraction-3. These results illustrate that the aggregation level becomes higher with the increasing Mw of the alkAL-S fractions.

Figure 3.

Figure 3

Open in a new tab

(a–c) Film-forming properties of the three alkAL-S fractions on a Au surface (size: 1 × 1 μm); (d–f) wetting properties of the three alkAL-S fractions on a Au surface.

The wetting properties of the three alkAL-S fractions on a Au surface were all assessed by contact angle measurements. As can be observed in Figure 3d–f, the contact angles of the alkAL-S fractions on Au gradually increase from Fraction-1 to Fraction-3. This result indicates that the affinity of Fraction-1 for the Au surface is relatively higher than that of Fraction-2 and Fraction-3 for the Au surface.

2.4. Adsorption Behavior Measurement by QCM-D

The adsorption behavior of the three alkAL-S fractions on a Au surface was investigated by QCM-D. QCM-D is an efficient tool that provides information about the adsorption amount, adsorbed layer conformation, and viscoelasticity changes.35 The adsorption amount of the alkAL-S fractions could be detected by determining the decrease in frequency (ΔF); the conformation and viscoelasticity of the adsorbed layer could also be observed by evaluating the changes in dissipation (ΔD).18 As shown in Figure 4a, we investigated the adsorption behavior of the samples at a concentration of 1 g/L under salt-free conditions; the adsorption amount of AL-S was the lowest because of its strong hydrophilicity. The results showed that the adsorption amounts of the three alkAL-S fractions increased compared with that of the straw material AL-S. As proposed in Figure 6, an alkyl chain was introduced to the AL-S molecules to improve the compatibility of the alkAL-S fractions. More importantly, Fraction-1 exhibited the highest adsorption amount and dissipation factor, which were even greater than that of lignosulfonate.23 The adsorption amount decreased with the increasing Mw of the alkAL-S fractions. This result occurred mainly because of the structural difference among the three alkAL-S fractions (see Figure 6). As seen from Figure 6, the size of the aggregates in Fraction-1 is smaller than that of the other two fractions, and therefore, the alkyl chain more effectively shields the electrostatic repulsions between the sulfonic groups in Fraction-1 than in the other fractions. The desorption of the samples is also investigated in Figure 4a, in which AL-S exhibits larger desorption amounts than the three alkAL-S fractions.

Figure 4.

Figure 4

Open in a new tab

Adsorption analysis results of the three alkAL-S fractions on a Au surface under a salt-free condition by the QCM-D method. (a) Change in frequency and dissipation (the rinsing step is also shown in the curves). (b) Changes in dissipation as a function of the change in frequency.

Figure 6.

Figure 6

Open in a new tab

Proposed adsorption mechanism of AL-S and the three alkAL-S fractions adsorbed on a Au surface under the salt-free condition.

The adsorption process of the three alkAL-S fractions was estimated by plotting the change in ΔD as a function of the changes in ΔF, and the plot was called the D–F curve (see Figure 4b). The slope of the D–F curve could be used to illustrate the conformation and viscoelasticity of the adsorbed layer and the affinity of the sample to a Au surface.36,37 As illustrated in Figure 4b, the slope of the AL-S curve is larger than that of the three alkAL-S fraction curves, and furthermore, the slopes of the alkAL-S fraction curves increased from Fraction-1 to Fraction-3. These results suggested that there was a more compact conformation and a stronger affinity between Fraction-1 and the Au surface. The conformation of the adsorbed layer of Fraction-3 is obviously looser than that of the other two fractions.

As investigated in Figure 3, the aggregation levels of the alkAL-S fractions become higher with the increasing Mw of the alkAL-S fractions, and the affinity of Fraction-1 for Au is relatively stronger than that of Fraction-2 and Fraction-3, which makes Fraction-1 preferred for adsorption on a Au surface to form a compact adsorbed conformation. The adsorption morphology of the three alkAL-S fractions adsorbed on a Au surface was also observed by AFM, as shown in Figure 5. We found that the conformation and size of the nanoaggregates were different for each of the fractions. A very compact adsorbed layer consisting of nanoaggregates was observed for Fraction-1 (see Figure 5a). The aggregate sizes of Fraction-2 and Fraction-3 were relatively larger than that of Fraction-1, and the nanoaggregates of Fraction-1 were more compact than those of the other two fractions, both of which contributed to the remarkable adsorption amount and low viscoelasticity of Fraction-1 on a Au surface.

Figure 5.

Figure 5

Open in a new tab

Adsorption morphologies of the three alkAL-S fractions on a Au surface: (a) Fraction-1, (b) Fraction-2, and (c) Fraction-3 (top image dimensions: 3 × 3 μm; bottom image dimensions: 1 × 1 μm).

2.5. Effect of Ionic Strength on the Adsorption Behavior

In our study, we also investigated the effect of ionic strength on the adsorption behavior of the alkAL-S fractions on the Au surface. A 0.5 M NaCl salt concentration was applied in the sample solutions. As seen from Figure 7a, the adsorption amounts of all the three alkAL-S fractions increased compared with those of the salt-free solution and were even greater than those that were previously reported.24 This result occurred mainly because the salt shielded the electrostatic repulsions between the sulfonic groups.22 We also noted that the adsorption amount of Fraction-3 was the greatest, but the adsorption amount of Fraction-2 was lower than that of Fraction-1. The results may be explained as follows. First, the Mw distributions of the alkAL-S fractions are remarkably narrow and symmetric, which is conducive to preparing the uniform nanoaggregates. Second, although the particle size of Fraction-2 is larger than that of Fraction-1, the nanoaggregates formed in Fraction-1 were more compact than those in Fraction-2. Therefore, based on the above mentioned factors, the adsorption amount of Fraction-1 is greater than that of Fraction-2 but lower than that of Fraction-3. The desorption process of all the alkAL-S fractions was also investigated after the adsorption equilibrium was achieved (see Figure 7a). We found that all the alkAL-S fractions exhibited larger desorption amounts after rinsing compared with the salt-free solution. This result occurs because the density and viscosity of the solution increased after the NaCl salt was added, which makes the adsorbed layer on the Au surface more viscoelastic than that achieved under salt-free conditions.

Figure 7.

Figure 7

Open in a new tab

Adsorption analysis results of the three alkAL-S fractions on a Au surface with a 0.5 M NaCl solution by the QCM-D method. (a) Change in frequency and dissipation (the rinsing step is also shown in the curves). (b) Changes in dissipation as a function of the change in frequency.

The dissipation as a function of changes in the frequency in the adsorption processes of the three alkAL-S fractions was also estimated, as shown in Figure 7b. Unexpectedly, the slopes of the three fraction curves are very close. This result indicated that the conformation of the adsorbed layers from Fraction-2 and Fraction-3 had become more compact. We also compared the slopes of the curves obtained with the salt-free and salt-added conditions. All the slopes increased after 0.5 M NaCl was added, indicating that the conformations of the adsorbed layer became looser, and the viscoelasticity of the layer increased.

The adsorption morphology of the three alkAL-S fractions after 0.5 M NaCl was added on the Au surface was also observed by AFM, as shown in Figure 8. The aggregation levels of the three fractions improved, and the height of the adsorbed layer noticeably increased. These results further indicated that NaCl could shield the electrostatic repulsions and promote the aggregation of the alkAL-S fractions.

Figure 8.

Figure 8

Open in a new tab

Adsorption morphologies of the three alkAL-S fractions on a Au surface with a 0.5 M NaCl solution: (a) Fraction-1, (b) Fraction-2, and (c) Fraction-3 (top image dimensions: 3 × 3 μm; bottom image dimensions: 1 × 1 μm).

2.6. Dispersion Properties in TiO2 Slurry

The adsorption property plays an important role in the dispersion properties of dispersants in suspension systems, such as TiO2. TiO2 is widely applied as a mineral oxide in pigments and paints and as nanomaterials.38,39 Because of their large surface areas, TiO2 particles easily form agglomerates, which negatively affects their performance in industrial applications. Therefore, dispersants are applied to improve the dispersion stabilization of TiO2 particles, which is very important for their industrial applications.

As seen in Figure 9, the dispersion property of the TiO2 slurry was relatively improved using AL-S compared with that obtained with no additives (blank). When the three alkAL-S fractions were applied to the TiO2 suspension slurry, the dispersion stability of the TiO2 slurries containing the alkAL-S fractions improved significantly and was better than that of the TiO2 slurry containing AL-S. We found that the Mw of Fraction-1 was close to that of AL-S, but the adsorption and dispersion properties of Fraction-1 were both better than those of AL-S. This result occurred because the alkyl chain in Fraction-1 improved the affinity for the Au surface and provided steric hindrance between the TiO2 particles. On the other hand, Fraction-3 exhibited the best dispersion property in TiO2 compared with the other fractions because of its moderate sulfonic group content and high Mw, which improved the steric hindrance and electrostatic repulsion between the sample-coated TiO2 particles.

Figure 9.

Figure 9

Open in a new tab

Dispersion properties of AL-S and the three alkAL-S fractions on the TiO2 slurry.

3. Conclusions

To summarize, alkyl chain cross-linked lignosulfonate (alkAL-S) was prepared from a pulping liquor and applied to classify and obtain three different fractions with a narrow Mw distribution via a UF method. Gel permeation chromatography (GPC), FTIR, and 1H NMR measurements were performed to investigate the molecular structure of these three fractions. We found that alkAL-S with different fractions exists as nanoaggregates with different particle sizes. The adsorption properties determined via QCM-D showed that the adsorption amounts of the three fractions were far higher than that of AL-S. Fraction-1 exhibited the greatest adsorption amount on a Au surface under a salt-free condition. This result illustrates that the alkyl chain is more effective for a dispersant with a low Mw to improve the adsorption amount. Fraction-3 exhibited the greatest adsorption amount on a Au surface under a salt-added condition. This result further illustrates that both the alkyl chain and salt are positive factors to improve the adsorption amount of dispersants. More importantly, the dispersion stabilization properties of the TiO2 slurry were improved significantly using the three alkAL-S fractions, especially Fraction-3. Based on these results, the alkyl chain cross-linking of lignosulfonate is a promising approach for using lignin as an applicable dispersant in industrial applications.

4. Materials and Methods

4.1. Materials

Wheat straw alkali lignin (WAL) was supplied by Shuntai Paper Pulping Co., Ltd. (Shuntai, Hunan, China). 1,6-Dibromohexane (C6H12Br2) with a purity of 97% was supplied by Energy Chemical (Shanghai, China). All other chemicals were of analytical grade, including formaldehyde (CH2O) of 37%, sodium hydroxide (NaOH), sodium sulfite (Na2SO3), potassium iodide (KI), and hexane. Titanium dioxide (TiO2) powder was a commercial product obtained from Kermel Chemistry Co., Ltd. (Tianjin, China).

4.2. Preparation of Alkyl Chain Cross-Linked Lignosulfonate (alkAL-S)

WAL was dissolved in an alkaline NaOH solution with a pH of approximately 10. Formaldehyde was added slowly to the reaction solution at 70 °C for 20 min. Then, the temperature was heated to 95 °C, and sodium sulfite was added subsequently. Then, the reaction was maintained at 95 °C for 3 h. When the temperature was cooled to 80 °C, a C6H12Br2 reagent and a trace amount of KI were added to the reaction solution, and NaOH was used to maintain a pH of 12. The polymerization reaction was stopped after the solution was refluxed at 80 °C for 9 h. The sample was then extracted with hexane to remove the excess C6H12Br2, and the polymer in the aqueous solution was obtained.

4.3. UF of alkAL-S To Obtain Different Fractions

The UF fractions were obtained using an UF201 ultrafiltration apparatus (Wuxi Membrane Science and Technology Corp., China). UF membranes with molecular weight cutoffs of 10, 50, and 100 kDa were used in our study. Finally, alkAL-S was classified into three fractions: Fraction-1 (10–50 kDa), Fraction-2 (20–100 kDa), and Fraction-3 (>100 kDa).

4.4. Structural Property Characterization

4.4.1. Mw Measurements

The Mw distributions of the UF fractions were determined by aqueous GPC. The calibration standard was polystyrene sulfonate with a Mw ranging from 2 to 150 kDa. The eluent was a 0.10 M NaNO3 solution introduced with a flow rate of 0.50 mL/min. All the samples were dissolved and diluted to achieve a 0.3 wt % concentration using double-distilled water and filtered with a 0.22 μm filter. The UV absorption at 280 nm was monitored with a Waters 2487 UV detector (Waters Co., Milford, MA).

4.4.2. Functional Group Content and Elemental Analysis

The phenolic hydroxyl group (−OH) content of the UF fractions was detected by the Folin–Ciocalteu colorimetric method.40 The detailed procedure was described in our previous study.19 The sulfonic group (−SO3H) content of all the samples was determined by an automatic potentiometric titrator (Type 809 Titrando, Metrohm Corp., Switzerland).5 The elemental analyses of all the fraction samples were performed by an Elementar vario EL cube.

4.4.3. Infrared Spectroscopy Analysis

The FTIR spectra of the UF fractions were measured with an Autosystem XL/I-series/Spectrum2000 instrument (Thermo Nicolet Co., Madison, WI). The measurement method using the potassium bromide pressed-disk technique was followed.

4.4.4. 1H NMR Spectroscopy Analysis

The 1H NMR spectra of the three fractions were recorded with 30 mg of each sample dissolved in 0.5 mL of dimethyl sulfoxide-d6 at room temperature by a DRX-400 spectrometer (Bruker Co., Ettlingen, Germany).

4.4.5. Film-Forming Properties of the Different Fractions

The three alkAL-S fractions were spun on a Au surface with a mass concentration of 1 g/L. The film-forming properties were studied by AFM.

4.4.6. Contact Angle Measurements

The wetting properties of the alkAL-S fractions separated from the three different membranes were measured by drop shape analysis (JC2000C1)21 using a mass concentration of 1 g/L on the Au surface.

4.5. Adsorption Behavior Measurement by QCM-D

The adsorption properties of the alkAL-S fractions on the Au surface were evaluated by QCM-D (instrument Q-Sense, Vastra Frolunda, Sweden). The sample solutions, with a mass concentration of 1 g/L under the salt-free and 0.5 M NaCl conditions, were added with a continuous flow rate of 150 μL/min into the QCM-D chamber at 25 °C.

4.6. Dispersion Properties

The dispersion stabilization properties of AL-S and the three alkAL-S fractions in TiO2 slurries were investigated using Turbiscan Lab Expert (Formulaction, L’Union, France). A 3 wt % TiO2 powder was slowly mixed with the 0.5 wt % samples in deionized water. Then, the TiO2 slurry was stirred at 1000 rpm for 10 min and measured by Turbiscan. The scan rate was one scan every 2 min, and the total scan time was 2 h.

Acknowledgments

The authors acknowledge the financial support of the Natural Science Foundation of Guangdong (2017A030308012), Doctoral Research Initiation Foundation of Dongguan University of Technology (GC300501-075), Foundation of Doctor’s Workstation of MCNAIR New Power Co., Ltd. at Dongguan University of Technology (GC200104-40, no. 186100030017), and Engineering Research Center of None-food Biomass Efficient Pyrolysis and Utilization Technology of Guangdong Higher Education Institutes (2016GCZX009).

The authors declare no competing financial interest.

References

  1. Xu W.; Wang X.; Sandler N.; Willför S.; Xu C. Three-Dimensional Printing of Wood-Derived Biopolymers: A Review Focused on Biomedical Applications. ACS Sustainable Chem. Eng. 2018, 6, 5663–5680. 10.1021/acssuschemeng.7b03924. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Thakur V. K.; Thakur M. K.; Raghavan P.; Kessler M. R. Progress in Green Polymer Composites from Lignin for Multifunctional Applications: A Review. ACS Sustainable Chem. Eng. 2014, 2, 1072–1092. 10.1021/sc500087z. [DOI] [Google Scholar]
  3. Zhou H.; Chang Y.; Wu X.; Yang D.; Qiu X. Horseradish Peroxidase Modification of Sulfomethylated Wheat Straw Alkali Lignin To Improve Its Dispersion Performance. ACS Sustainable Chem. Eng. 2015, 3, 518–523. 10.1021/sc500757y. [DOI] [Google Scholar]
  4. Tejado A.; Peña C.; Labidi J.; Echeverria J. M.; Mondragon I. Physico-chemical characterization of lignins from different sources for use in phenol–formaldehyde resin synthesis. Bioresour. Technol. 2007, 98, 1655–1663. 10.1016/j.biortech.2006.05.042. [DOI] [PubMed] [Google Scholar]
  5. Bjørkmann A. Lignin sulfonation-a different approach. Cellul. Chem. Technol. 2001, 35, 113–133. [Google Scholar]
  6. Ouyang X.; Ke L.; Qiu X.; Guo Y.; Pang Y. Sulfonation of Alkali Lignin and Its Potential Use in Dispersant for Cement. J. Dispersion Sci. Technol. 2009, 30, 1–6. 10.1080/01932690802473560. [DOI] [Google Scholar]
  7. Konduri M. K. R.; Fatehi P. Production of Water-Soluble Hardwood Kraft Lignin via Sulfomethylation Using Formaldehyde and Sodium Sulfite. ACS Sustainable Chem. Eng. 2015, 3, 1172–1182. 10.1021/acssuschemeng.5b00098. [DOI] [Google Scholar]
  8. He W.; Fatehi P. Preparation of sulfomethylated softwood kraft lignin as a dispersant for cement admixture. RSC Adv. 2015, 5, 47031–47039. 10.1039/c5ra04526f. [DOI] [Google Scholar]
  9. Mollah M. Y. A.; Yu W.; Schennach R.; Cocke D. L. A Fourier transform infrared spectroscopic investigation of the early hydration of Portland cement and the influence of sodium lignosulfonate. Cem. Concr. Res. 2000, 30, 267–273. 10.1016/s0008-8846(99)00243-4. [DOI] [Google Scholar]
  10. Bishop M.; Barron A. R. Cement Hydration Inhibition with Sucrose, Tartaric Acid, and Lignosulfonate: Analytical and Spectroscopic Study. Ind. Eng. Chem. Res. 2006, 45, 7042–7049. 10.1021/ie060806t. [DOI] [Google Scholar]
  11. Hong N.; Li Y.; Zeng W.; Zhang M.; Peng X.; Qiu X. Ultrahigh molecular weight, lignosulfonate-based polymers: preparation, self-assembly behaviours and dispersion property in coal-water slurry. RSC Adv. 2015, 5, 21588–21595. 10.1039/c5ra02157j. [DOI] [Google Scholar]
  12. Qiu X.; Zeng W.; Yu W.; Xue Y.; Pang Y.; Li X.; Li Y. Alkyl Chain Cross-Linked Sulfobutylated Lignosulfonate: A Highly Efficient Dispersant for Carbendazim Suspension Concentrate. ACS Sustainable Chem. Eng. 2015, 3, 1551–1557. 10.1021/acssuschemeng.5b00252. [DOI] [Google Scholar]
  13. Tejado A.; Peña C.; Labidi J.; Echeverria J. M.; Mondragon I. Physico-chemical characterization of lignins from different sources for use in phenol-formaldehyde resin synthesis. Bioresour. Technol. 2007, 98, 1655–1663. 10.1016/j.biortech.2006.05.042. [DOI] [PubMed] [Google Scholar]
  14. Wang M.; Leitch M.; Xu C. Synthesis of phenol–formaldehyde resol resins using organosolv pine lignins. Eur. Polym. J. 2009, 45, 3380–3388. 10.1016/j.eurpolymj.2009.10.003. [DOI] [Google Scholar]
  15. Mai C.; Schormann W.; Hüttermann A.; Kappl R.; Hüttermann J. The influence of laccase on the chemo-enzymatic synthesis of lignin graft-copolymers. Enzyme Microb. Technol. 2002, 30, 66–72. 10.1016/s0141-0229(01)00457-4. [DOI] [Google Scholar]
  16. Kim Y. S.; Kadla J. F. Preparation of a Thermoresponsive Lignin-Based Biomaterial through Atom Transfer Radical Polymerization. Biomacromolecules 2010, 11, 981–988. 10.1021/bm901455p. [DOI] [PubMed] [Google Scholar]
  17. Panesar S. S.; Jacob S.; Misra M.; Mohanty A. K. Functionalization of lignin: Fundamental studies on aqueous graft copolymerization with vinyl acetate. Ind. Crops Prod. 2013, 46, 191–196. 10.1016/j.indcrop.2012.12.031. [DOI] [Google Scholar]
  18. Lou H.; Lai H.; Wang M.; Pang Y.; Yang D.; Qiu X.; Wang B.; Zhang H. Preparation of Lignin-Based Superplasticizer by Graft Sulfonation and Investigation of the Dispersive Performance and Mechanism in a Cementitious System. Ind. Eng. Chem. Res. 2013, 52, 16101–16109. 10.1021/ie402169g. [DOI] [Google Scholar]
  19. Zhou H.; Yang D.; Wu X.; Deng Y.; Qiu X. Physicochemical properties of sodium lignosulfonates (NaLS) modified by laccase. Holzforschung 2012, 66, 825–832. 10.1515/hf-2011-0189. [DOI] [Google Scholar]
  20. Li R.; Yang D.; Guo W.; Qiu X. The adsorption and dispersing mechanisms of sodium lignosulfonate on Al2O3 particles in aqueous solution. Holzforschung 2013, 67, 387–394. 10.1515/hf-2012-0108. [DOI] [Google Scholar]
  21. Deng Y.; Zhang W.; Wu Y.; Yu H.; Qiu X. Effect of Molecular Weight on the Adsorption Characteristics of Lignosulfonates. J. Phys. Chem. B 2011, 115, 14866–14873. 10.1021/jp208312a. [DOI] [PubMed] [Google Scholar]
  22. Ouyang X.; Deng Y.; Qian Y.; Zhang P.; Qiu X. Adsorption Characteristics of Lignosulfonates in Salt-Free and Salt-Added Aqueous Solutions. Biomacromolecules 2011, 12, 3313–3320. 10.1021/bm200808p. [DOI] [PubMed] [Google Scholar]
  23. Palmqvist L.; Holmberg K. Dispersant Adsorption and Viscoelasticity of Alumina Suspensions Measured by Quartz Crystal Microbalance with Dissipation Monitoring and in Situ Dynamic Rheology. Langmuir 2008, 24, 9989–9996. 10.1021/la800719u. [DOI] [PubMed] [Google Scholar]
  24. Gan L.; Zhou M.; Yang D.; Qiu X. Aggregation and adsorption behaviors of carboxymethylated lignin (CML) in aqueous solution. Holzforschung 2013, 67, 379–385. 10.1515/hf-2012-0119. [DOI] [Google Scholar]
  25. Hong N.; Yu W.; Xue Y.; Zeng W.; Huang J.; Xie W.; Qiu X.; Li Y. A novel and highly efficient polymerization of sulfomethylated alkaline lignins via alkyl chain cross-linking method. Holzforschung 2016, 70, 297–304. 10.1515/hf-2015-0043. [DOI] [Google Scholar]
  26. Qin Y.; Qiu X.; Liang W.; Yang D. Investigation of Adsorption Characteristics of Sodium Lignosulfonate on the Surface of Disperse Dye Using a Quartz Crystal Microbalance with Dissipation. Ind. Eng. Chem. Res. 2015, 54, 12313–12319. 10.1021/acs.iecr.5b03582. [DOI] [Google Scholar]
  27. Toledano A.; García A.; Mondragon I.; Labidi J. Lignin separation and fractionation by ultrafiltration. Sep. Purif. Technol. 2010, 71, 38–43. 10.1016/j.seppur.2009.10.024. [DOI] [Google Scholar]
  28. Duval A.; Molina-Boisseau S.; Chirat C. Fractionation of lignosulfonates: comparison of ultrafiltration and ethanol solubility to obtain a set of fractions with distinct properties. Holzforschung 2015, 69, 127–134. 10.1515/hf-2014-0082. [DOI] [Google Scholar]
  29. Li Y.; Qi B.; Luo J.; Wan Y. Effect of alkali lignins with different molecular weights from alkali pretreated rice straw hydrolyzate on enzymatic hydrolysis. Bioresour. Technol. 2016, 200, 272–278. 10.1016/j.biortech.2015.10.038. [DOI] [PubMed] [Google Scholar]
  30. Delgado N.; Ysambertt F.; Chávez G.; Bravo B.; García D. E.; Santos J. Valorization of Kraft Lignin of Different Molecular Weights as Surfactant Agent for the Oil Industry. Waste Biomass Valorization 2019, 10, 3383–3395. 10.1007/s12649-018-0352-4. [DOI] [Google Scholar]
  31. Cao J.; Xiao G.; Xu X.; Shen D.; Jin B. Study on carbonization of lignin by TG-FTIR and high-temperature carbonization reactor. Fuel Process. Technol. 2013, 106, 41–47. 10.1016/j.fuproc.2012.06.016. [DOI] [Google Scholar]
  32. Boeriu C. G.; Bravo D.; Gosselink R. J. A.; van Dam J. E. G. Characterisation of structure-dependent functional properties of lignin with infrared spectroscopy. Ind. Crops Prod. 2004, 20, 205–218. 10.1016/j.indcrop.2004.04.022. [DOI] [Google Scholar]
  33. Toledano A.; Serrano L.; Garcia A.; Mondragon I.; Labidi J. Comparative study of lignin fractionation by ultrafiltration and selective precipitation. Chem. Eng. J. 2010, 157, 93–99. 10.1016/j.cej.2009.10.056. [DOI] [Google Scholar]
  34. Joffres B.; Lorentz C.; Vidalie M.; Laurenti D.; Quoineaud A.-A.; Charon N.; Daudin A.; Quignard A.; Geantet C. Catalytic hydroconversion of a wheat straw soda lignin: Characterization of the products and the lignin residue. Appl. Catal., B 2014, 145, 167–176. 10.1016/j.apcatb.2013.01.039. [DOI] [Google Scholar]
  35. Hu Y.; Jin J.; Han Y.; Yin J.; Jiang W.; Liang H. Study of fibrinogen adsorption on poly(ethylene glycol)-modified surfaces using a quartz crystal microbalance with dissipation and a dual polarization interferometry. RSC Adv. 2014, 4, 7716–7724. 10.1039/c3ra46934d. [DOI] [Google Scholar]
  36. Saarinen T.; Orelma H.; Grönqvist S.; Andberg M.; Holappa S.; Laine J. Adsorption of different laccases on cellulose and lignin surfaces. BioResources 2009, 4, 94–110. [Google Scholar]
  37. Virtanen H.; Orelma H.; Erho T.; Smolander M. Development of printable bioactive paper containing laccase. Process Biochem. 2012, 47, 1496–1502. 10.1016/j.procbio.2012.06.001. [DOI] [Google Scholar]
  38. Liu C.; Yang S. Synthesis of Angstrom-Scale Anatase Titania Atomic Wires. ACS Nano 2009, 3, 1025–1031. 10.1021/nn900157r. [DOI] [PubMed] [Google Scholar]
  39. Chen X.; Mao S. S. Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications. Chem. Rev. 2007, 107, 2891–2959. 10.1021/cr0500535. [DOI] [PubMed] [Google Scholar]
  40. de Sousa F.; Reimann A.; Björklund Jansson M.; Nilberbrant N. O.. Estimating the amount of phenolic hydroxyl groups in lignins. 11th International Symposium on Wood and Pulping Chemistry: Nice, France, 2001; Vol. 3, pp 649–653.

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES