Modification of lignin with dodecyl glycidyl ether and chlorosulfonic acid for preparation of anionic surfactant

Article abstract of DOI:10.1039/c4ra01873g

Lignin was modified through incorporation of lipophilic and hydrophilic groups for the preparation of a surfactant. In this case, alkaline lignin reacted with dodecyl glycidyl ether in the presence of dimethyl benzyl amine to incorporate lipophilic long alkyl chains, and then sulfonated with chlorosulfonic acid for the introduction of hydrophilic sulfonic acid groups. Results showed that the reaction between dodecyl glycidyl ether and carboxy group in lignin was the predominant reaction at 95-110 °C. It was found that the surface tension of the synthesized lignin surfactant solution was lower than that of commercial surfactant sodium dodecylbenzenesulphonate when the concentration was below 0.4%, indicating that the surfactant prepared from alkaline lignin had a good surface activity. A lowest critical micelle concentration of 0.50 g L^-1 and the corresponding surface tension at 29.17 mN m^-1 were achieved when the surfactant was derived from the lignin grafted with dodecyl glycidyl ether at 110 °C. The anionic lignin surfactants prepared in this study are a promising feedstock as detergents or to enhance oil recovery.

Full text of DOI:10.1039/c4ra01873g

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Modification of lignin with dodecyl glycidyl ether and chlorosulfonic acid
for preparation of anionic surfactant
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ChangꢀZhou Chen a, MingꢀFei Li a,*, YuꢀYing Wu a, RunꢀCang Sun a,b,*
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a Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083,
China;
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b State Key Laboratory of Pulp and Paper Engineering, South China University of Technology,
Guangzhou 510640, China
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*Author to whom correspondence should be addressed:
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MingꢀFei Li (Tel. +8610 62336592; Eꢀmail address: limingfei@bjfu.edu.cn)
RunꢀCang Sun (Tel. /Fax：+8610 62336972; Eꢀmail address: rcsun3@bjfu.edu.cn)
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Abstract Lignin was modified through incorporation of lipophilic and hydrophilic groups
for the preparation of surfactant. In this case, alkaline lignin reacted with dodecyl glycidyl
ether in the presence of dimethyl benzyl amine to incorporate lipophilic long alkyl chains,
and then sulfonated with chlorosulfonic acid for the introduction of hydrophilic
sulfonic acid group. Results showed that the reaction between dodecyl glycidyl ether and
carboxy group in lignin was the predominant reaction at 95 °Cꢀ110 °C. It was found that
the surface tension of the synthesized lignin surfactant solution was lower than that of
commercial surfactant sodium dodecylbenzenesulphonate when concentration was below
0.4 %, indicating that the surfactant prepared from alkaline lignin had a good surface
activity. A lowest critical micelle concentration of 0.50 g Lꢀ1 and the corresponding surface
tension at 29.17 mN/m were achieved when the surfactant was derived from the lignin
grafted with dodecyl glycidyl ether at 110 ºC. The anionic lignin surfactants prepared in
this study is a promising feedstock as detergents or to enhance oil recovery.
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1. Introduction
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The use of sustainable resources for energy and advanced ecoꢀfriendly material has
drawn much attention due to the increased consumption of fossil resources associated with
energy crisis and climate change.1, 2 Lignocellulose, mainly composed of cellulose,
hemicellulose and lignin, is a promising and renewable resource for biofuel, chemicals,
and biomaterials without competition with human’s food.3 There are some conundrums of
the development of bioꢀethanol for making biomassꢀtoꢀbiofuels economic4, but it has great
potential economic benefits to develop new materials and chemicals derived from
lignocellulose. After cellulose and hemicelluloses, lignin is the third most abundant
biopolymer from biomass and considered as the most abundant aromatic renewable
resource. Lignin mainly consists of pꢀhydroxyphenyl (H), guaiacyl (G), and syringyl (S)
units derived from three major monolignols, namely, pꢀcoumaryl alcohol, coniferyl
alcohol, and sinapyl alcohol. These units are connected by various interꢀunit linkages (e.g.,
βꢀOꢀ4', βꢀ5', βꢀβ', 5ꢀ5', 5ꢀOꢀ4', and βꢀ1', etc.) through an enzymeꢀinitiated dehydrogenative
polymerization 5, 6 Lignin can be isolated from wood, annual plants (such as wheat straw)
and agricultural residues (such as corncobs) by different processes.7, 8 However, lignin is
considered as lowꢀvalue and underutilized byꢀproduct from pulping and bioꢀrefinery
industries. Most of lignin fraction resulted from these processes is burned as fuel, and only
a small portion of lignin is converted to commercial products. The effective utilization of
lignin to produce valueꢀadded products through chemical modification will make the
biomass industry economically feasible with respect to the replacement of chemicals and
materials derived from fossil sources. Lignin is an excellent candidate for chemical
reactions due to its highly functional characteristics (rich in phenolic and aliphatic
hydroxyl groups) for the development of new chemicals.
Surfactants are extremely important chemicals, and numberless types of surfactants
are used for a myriad of applications, thus the development of lignin surfactant has a good
industrial prospect. Lignin itself is not very useful as a surfactant because of the nature
character of lignin, for example, the complex macromolecular structure, the large
molecular weight, the low hydrophilicity and lipophilicity.9, 10 To work effectively, most
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surfactant require water soluble and oil soluble characteristics. Lignin must be changed
into the fraction which has the hydrophilic or amphiphilic property. To date, the
introduction of hydrophilic groups into lignin by sulfonation11, 12, carboxylation13, 14, and
Mannich reaction15 has been investigated by many researchers. However, these methods
can only enhance hydrophilicity but to lipophilicity of lignin, and the surface activity of
these lignin surfactants is not satisfactory. In fact, a good lignin surfactant requires water
soluble and oil soluble characteristics by the incorporation of both lipophilic and
hydrophilic groups. Morrow et al. 16 have described a method of producing surfactants for
enhancing oil recovery from lignin by two reactions of lignin, i.e., alkylation with
different alkyl halides at phenolic sites, sufficient oxidation to break the lignin into smaller
polymeric and monomeric units, and sulfonation to increase their water solubility. Naae et
al. 17 reduced lignin in the presence of CO and H2, the resulted products were alkoxylated
with α –olefin epoxide introducing a long alkyl chian, and these compounds were changed
into oil soluble lignin surfactant by sulfonation, sulfation and alkoxysulfation. Zeng et al.
18 have reported that hydrophilic sulfonic group and lipophilic adbietic group were
introduced into the molecular structure of Kraft lignin, and the rosinꢀmodified
lignosulfonate lowed the surface tension of a 10 g Lꢀ1 aqueous solution to 49.3 mN/m.
The aim of the present study was to prepare lignin surfactant by simultaneous
incorporation of lipophilic and hydrophilic groups into lignin. Alkaline lignin was
modified with dodecyl glycidyl ether in the presence of dimethyl benzyl amine as a
catalyst, and then was converted into anionic surfantant by sulfonation with
chlorosulfonic acid. The structure of lignin after reaction with dodecyl glycidyl ether was
examined by FTꢀIR, GPC, 31PꢀNMR and 13CꢀNMR, and the surface activity of the lignin
surfactant was investigated through determining the surface tension of the aqueous
solution.
2. Experimental
2.1. Materials
Alkaline lignin (AL) from corncob was obtained from Shandong Longlive
Bioꢀtechnology Co., Ltd, China. Laurylalcohol, epichlorohydrin (ECH), tetrabutyl
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ammonium bromide (TBAB), N,Nꢀdimthylbenzylamine (BDMA), sodium dodecyl
benzene sulfonate (SDBS) and dimethyl sulfoxide (DMSO) were purchased from
Sinopharm Chemical Reagent Beijing Co., Ltd, China. Chlorosulfonic acid (99%) was
provided by Xiya reagent (Chengdu, China).
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2.2. Preparation of dodecyl glycidyl ether (DGE)
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To a vigorously stirred mixture containing 37.2 g（0.2 mol）of laurylalcohol, 200 mL
of toluene, 50.0 g of 48% aqueous sodium hydroxide solution and 3.2 g (0.01 mol) of
TBAB, 37.0 g（0.4 mol）of ECH were added dropwise for 15 min at ambient temperature,
and the reaction was run for 6 h at 50 °C. When the resulting solution was cooled to room
temperature, the organic layer was separated and washed 4 times with distilled water (200
mL, 60 °C). Then the organic layer was evaporated at 60 °C under reduced pressure to
obtain DGE. The epoxy value of DGE was 0.33 mol epoxy / 100 g DGE, determined
according to the method described by Hou.19
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2.3. Reaction of AL with DGE
A 250 mL roundꢀbottom flask containing 8.0 g lignin, 1.8 g BDMA, 8.0 g DGE and
160 mL DMSO was heated for 5.0 h at various temperatures (95ꢀ110 °C). The reaction
was quenched by adding 20 mL of 2.0 M HCl under stirring for 30 min at room
temperature. The solvent was removed by rotary evaporation, and the residue was washed
with distilled water and petroleum ether for several times, and then dried overnight at
60 °C to give grafted lignin, named as DGEꢀAL.
2.4. Sulfonation of DGE-AL
The sulfonation of DGEꢀAL was conducted according to the procedure in a previous
report with minor modifications.11 A total of 2.0 g chlorosulfonic acid in 20 mL anhydrous
dichloromethane (CH2Cl2) was added dropwise into 1.0 g of DGEꢀAL in 10 mL
dichloromethane. The mixture was mechanically stirred for 2 h in an ice bath. Next, 30
mL of 2 M NaOH was added and the mixture was stirred for 1 h in an ice bath, and then it
was adjusted with 1 M HCl to pH 8.0. The resulting mixture was dialyzed with a cellulose
tube (cut off Mwꢀ3000) against water and lyophilized to yield sulfonated DGEꢀAL, named
as SDꢀAL.
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2.5. Sample characterization
FTꢀIR spectra were recorded in a Thermo Scientific Nicolet iN10 FTꢀIR Microscope
(Thermo Nicolet Corporation, Madison, WI, USA) equipped with a liquid nitrogen cooled
MCT detector. The spectra were collected in the range of 4000ꢀ650 cm−1 at 4 cm−1
resolution. NMR spectra were recorded on a Bruker AVIII 400 MHz spectrometer at 25 ºC.
For 13CꢀNMR spectra, 80 mg samples were dissolved in 1 mL of DMSOꢀd6. The sample
was modified following the procedure below for 31PꢀNMR determination. Approximate 30
mg of ovenꢀdried sample was dissolved in pyridine/chloroform (1.6:1, v/v) in a small vial
and stirred continuously. Nꢀhydroxyl naphthalimide was used as internal standard, and
chromium acetylacetonate as the relaxation reagent. Then,
2ꢀchlorlꢀ4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaꢀphosphalane (TMDP) was used for
phosphitylation of hydroxyl groups. The molecular weight of the sample was determined
by gel permeation chromatography (GPC). The lignin sample was dissolved in
tetrahydrofuran (2 mg/mL), and then the solution was analyzed on a high performance
liquid chromatography system (Agilent 1200 series, Agilent technologies, USA) with a
DAD detector. The molecular weights were calibrated via monodisperse polystyrene
standards. The sulfur content of the lignin surfactant was examined by elemental analysis
using a Vario EL III Elemental analyzer instrument (Elementar, Germany) according to a
previous report.20
2.6. Measurement of surface tension
An automatic surface tensiometer (JK99B, Shanghai Zhongchen Digital Technic
Apparatus Co., Ltd) was used to measure the surface tension of the surfactant solution at
different concentrations at room temperature (18 °C). Deionized water (surface tension
74.950 mN/m) was employed for reference, and commercial surfactant SDBS was used as
a control. Critical micelle concentration (CMC) values of lignin surfactants were
identified from the plot of the surface tension versus the surfactant concentration of water
solution.
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3. Results and discussion
3.1. Synthesis and characterization of DGE-AL
Typically, Lewis bases are used to accelerate the reaction between epoxides and the
hydroxyls of phenols, alcohols and carboxyl.21 In this study, BDMA was chosen as a
catalyst of the reaction between DGE and lignin, and DGE was introduced into lignin
through lignin hydroxylꢀepoxide reaction (see Scheme 1). Because of the low
hydrophilicity and lipophilicity, lignin had a low solubility in neutral water and most of
organic solvents. For a homogeneous reaction between lignin and DGE, DMSO was
employed as a solvent for the reaction system. In order to avoid selfꢀpolymerization of
DGE in the presence of tertiary amine22, the reaction temperature was set at 95, 100 and
110 °C. After reaction, hydrochloric acid was used to deactivate the remnant DGE, and the
inactivated DGE and DGE homopolymer were washed off with petroleum ether. As seen
from Table 1, the DGEꢀAL yields were as high as 62.68ꢀ65.25%, and the molecular
weights of the products derived from the reaction conducted at 95, 100, and 110 °C were
1300, 1410, and 2050 g molꢀ1 , respectively.
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Table 1 The yields, weight average (Mw) and number average (Mn) molecular weight of
the products from the reaction of DGE with alkaline lignin
Samples a
Yield (%) b
Mw (g molꢀ1)
Mn (g molꢀ1)
Mw/Mn
DGEꢀAL 1
DGEꢀAL 2
DGEꢀAL 3
AL
65.25
64.31
62.68
ꢀ
2050
1410
1300
850
720
600
580
540
2.85
2.37
2.23
1.59
a
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AL, raw material alkaline lignin; DGEꢀAL 1, DGEꢀAL 2 and DGEꢀAL 3 were obtained
by the reaction of DGE with lignin in the presence of BDMA at 110, 100 and 95 °C for 5 h,
respectively.
b the yield of DGEꢀAL was based on the total weight of reactant.
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O
C
OH
Lignin
CH
CH
2
H C HC H C
+
3
2
OH
O
R
R
OH
OH
H
O
C
O
C
O
H3
C
HC H C
2
Lignin
H
2
C
C
C
CH
O
2
H
H
2
2
H
C
O
I
OH
R
R
H
C
H
C
OH
2
2
O
III
R=H or CH3O
=CH3(CH2)10CH2
O
II
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Scheme 1 The reaction of DGE with lignin in the presence of BDMA.
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31PꢀNMR technique has been widely applied in classification and quantitative
determination of several different classes of hydroxyl groups in the native and modified
lignin.23ꢀ25 In this study, phosphitylating agent TMDP was utilized to obtain the qualitative
and quantitative information about hydroxyl groups in lignin before and after graft. The
31PꢀNMR spectra of the samples are illustrated in Figure 1 and the contents of different
hydroxyl groups are listed in Table 2. For DGEꢀAL 1 and DGEꢀAL 3, the content of total
OH was lower than that of AL, indicating the successful introduction of DGE into lignin
in the presence of BDMA. As compared to DGEꢀAL 3, the dramatic reduction of the
carboxylic OH content in DGEꢀAL 1 suggested that the reaction between epoxide and
carboxyl was the predominant reaction when reaction temperature increased from 95 °C to
110 °C. This can be explained by the mechanism of glycidyl ether reactions with alcohols,
phenols and carboxylic acids in the presence of tertiary amine as a catalyst.
R
CH
CH2
CH CH2
O
N
R
NR3
+
（ 1）
R
O
Z
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From Equation 1, a zwitterion (Z) was formed by the interaction between tertiary amine
and epoxide which acted as an efficient catalyst due to its high basicity.21 Because of the
relatively high acidity of carboxyl in lignin, the reaction between carboxyl and glycidyl
ether occurred first. As see from Fig. 1, the chemical shifts of 150.0ꢀ145.4 ppm,
144.5ꢀ137.0 ppm, and 136.0ꢀ133.6 ppm are assigned to aliphatic, phenolic, and carboxylic
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acid OH, respectively.26 With respect to the reaction mechanism of hydroxylꢀglycidyl
ether reactions, the following hypothesis was made: some new hydroxyl groups were
derived from the openꢀring reaction of epoxy group of DGE. Accordingly, three new kinds
of signals were assigned at the chemical shifts of aliphatic OH, derived from the reactions
of DGE with aliphatic, phenolic, and carboxylic acid OH in lignin. This was supported by
the presence of three new peaks (147.9ꢀ147.4, 147.1ꢀ146.8, and 146.6ꢀ145.8 ppm) in the
spectra of DGEꢀAL 1 and DGEꢀAL 3, which correspond to the chemical shifts of aliphatic
OH. From Fig. 1, the signals at 146.6ꢀ145.8 ppm varied more noticeably as compared to
those at 147.9ꢀ147.4 ppm and 147.1ꢀ146.8 ppm probably due to the large reduction of the
content of carboxylic OH in DGEꢀAL 1 as compared to DGEꢀAL 3 (Table 2). The signals
at 146.6ꢀ145.8 ppm were probably due to the hydroxyls derived from carboxylꢀglycidyl
ether reaction, whereas the absorptions at 147.9ꢀ147.4 ppm and 147.1ꢀ146.8 ppm probably
correspond to the hydroxyl groups derived from the alcohol and phenolꢀglycidyl ether
reactions, respectively.
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Table 2 Quantification of hydroxyl content of alkaline lignin before and after reaction with
DGE by quantitative 31PꢀNMR method
Hydroxyl content (mmol gꢀ1 of lignin)
Samples a
Aliphatic Syringyl Guaiacyl pꢀHydroxy Carbox Total
Total
OH
OH
OH
OH
phenyl OH ylic OH phenol
OH
AL
2.26
0.84
0.64
0.78
1.67
1.16
1.32
1.02
0.55
0.40
2.24
0.39
0.88
1.52
1.04
1.20
8.03
5.51
6.27
DGEꢀAL 1 2.77
DGEꢀAL 3 2.70
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a AL, DGEꢀAL 1 and DGEꢀAL 3 corresponding to the lignin samples in Table 1.
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Fig. 1 31PꢀNMR of AL, DGEꢀAL 1 and DGEꢀAL 3.
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More information of the structure of DGEꢀAL was acquired by FTꢀIR and 13CꢀNMR
spectra. Fig. 2 shows the FTꢀIR spectra of the samples. As compared to AL, the intensity
of the absorption bands at 2924 and 2853 cmꢀ1 (saturated CꢀH stretching vibration)
increased, the absorption at 1120 cmꢀ1 corresponding to CꢀOꢀC stretching vibration
became clearer, and a new peak appeared at 731 cmꢀ1 ((CH2)n ≥ 2 rocking vibration) in
DGEꢀAL spectra. The results above suggested that long alkyl chain was introduced into
lignin through the reaction between DGE and lignin in the presence of BDMA, in
accordance with the result of 31PꢀNMR analysis aforementioned.
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Fig. 2 FTꢀIR spectra of AL, DGEꢀAL and SDꢀAL samples.
Fig. 3 shows the 13CꢀNMR spectra of AL and DGEꢀAL. In the aliphatic region, five
wellꢀdefined peaks were observed at 14.0, 25.6, 28.7, 29.0 and 31.3 ppm in DGEꢀAL
spectra, and these peaks are assigned to the methyl carbon and methylene carbon of
dodecyl chains. Generally, the 13CꢀNMR chemical shift of the carbon atoms bonded to
oxygen (CH2O, CꢀOꢀC, CꢀOꢀC=O) in glycerol ether or glycerides are assigned at the
bands of 60.0ꢀ70.0 ppm.23ꢀ29 As expected, the additional peaks at 60.0ꢀ72.7 ppm attributed
to the carbon atoms in glycerol ethers crossꢀlinked structure (see Scheme 1, I, II, III) were
observed in DGEꢀAL spectra. Because of the complexity of the ringꢀopening reaction of
epoxy compound as well as the complicated structure of lignin macromolecule,30 no effort
was made to assign these peaks. It was concluded that the expected compounds were
formed in the reaction of lignin and DGE under the catalysis of dimethylbenzylamine.
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Fig. 3 13CꢀNMR of AL, DGEꢀAL 1 and DGEꢀAL 3.
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3.2. Preparation and characterization of SD-AL
Surfactants are amphiphilic materials containing both a polar longꢀchain hydrocarbon
“tail” and polar, usually ionic, “head” groups. Because of the lack of hydrophilic groups,
only the introduction of long alkyl chain into lignin cannot make lignin became a good
surfactant. In this case, lignin achieved both hydrophilic and hydrophobic characteristics
which were different from those of commercial surfactants. AL grafted with DGE under
different temperatures were sulfonated with chlorosulfonic acid, and then neutralized with
sodium hydroxide, yielding anionic surfactant SDꢀAL. The FTꢀIR spectra of SDꢀAL are
shown in Fig. 2. For the spectra of SDꢀAL, the intensity of the bands at 2924 and 2853
cmꢀ1 correspond to methyl and methylene vibration, respectively. The new absorptions at
1073 and 1040 cmꢀ1 correspond to the symmetric and asymmetric stretching vibrations of
S–O bond, respectively.31 The appearance of a strong peak at 1217 cmꢀ1 is indicative of
the S=O stretch of the sulfatesalt as well as the sulfonic acid,32 indicating the existence of
SO3 groups in SDꢀAL. As compared to DGEꢀAL, the intensity of the peak at 1120 cmꢀ1
corresponding to CꢀOꢀC stretching vibration in SDꢀAL became weak, indicating the
partial hydrolysis of ester groups during the preparation of SDꢀAL.
The effect of hydrolysis of ester groups during the preparation of SDꢀAL was
investigated through examining the content of the dichloromethaneꢀinsoluble components
of DGEꢀAL after treatment with 2 M NaOH for 1 h in an ice bath. Briefly, 1g of DGEꢀAL
was added to 30 mL of 2 M NaOH and the solution was stirred for 1h in an ice bath. After
the reaction, DGEꢀAL was regenerated by precipitation through adjusting the resulting
solution to pH=2 with 30% acetic acid. The result showed that the contents of
dichloromethaneꢀinsoluble components were 29.71%, 27.72 % and 26.43% of the weight
of regenerated DGEꢀAL 1, DGEꢀAL 2 and DGEꢀAL 3, respectively. This indicated that
some deꢀalkylation of DGEꢀAL occurred during the preparation of SDꢀAL. The
generation of dichloromethaneꢀinsoluble components should be due to the hydrolysis of
the ester groups in DGEꢀAL. Thus, optimization of the neutral condition for sulfonic acid
group should be conducted in a future study.
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Table 3 Elemental analysis, yield, CMC and surface tension of water at CMC of all
surfactant samples
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Yield
(%) b
CMC
(g Lꢀ1)
Surface tension of CMC
(mN/m)
Samples a
Elemental analysis (%)
S
C
H
AL
ꢀ
63.00
45.00
5.60
5.21
ꢀ
ꢀ
ꢀ
SDꢀAL 1
78.2
0.50
29.17
7.14
SDꢀAL 2
SDꢀAL 3
SDBS
7.27
7.81
ꢀ
46.15
46.23
ꢀ
5.96
5.91
ꢀ
77.8
78.5
ꢀ
0.55
0.58
0.97
29.65
30.21
30.50
a
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SDBS, commercial surfactant sodium dodecyl benzene sulfonate; SDꢀAL 1, SDꢀAL 2
and SDꢀAL 3 derived from the sulfonation of DGEꢀAL 1 DGEꢀAL 2, and DGEꢀAL 3 at
the same condition, respectively.
b the yield of SDꢀAL was based on the weight of DGEꢀAL.
ꢀ, no measurement.
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3.3. Characteristics of SD-AL as a surfactant
Fig. 4 shows the isotherms of the surface tension of aqueous solution plotted against
concentrations of SDꢀAL as compared to commercial surfactant SDBS. By the addition of
lignin surfactant, the surface tension of water decreased with the increase of the
concentration. For SDꢀAL 1, SDꢀAL 2, and SDꢀAL 3, the surface tension was lower than
that of SDBS when the concentration of aqueous surfactant solution was below 0.4 %.
After sulfurization under the same conditions, the lignin surfactant derived from the
reaction of lignin with DGE at a high temperature had a low surface tension at equivalent
concentration of aqueous solution. It was consistent with the result reported by Košıková
et al., in which the higher amount of alkylhalide was used to modify the prehydrolysis
lignin, the lower surface tension was observed.33
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55
50
45
40
35
30
SD-AL 1
SD-AL 2
SD-AL 3
SDBS
0.0
0.2
0.4
0.6
0.8
1.0
Concentration (%)
293
294
Fig. 4 Isotherms of surface tension of water plotted against concentration of SDꢀAL
surfactant and SDBS.
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Generally, the concentration of surfactant influences the physical and chemical
properties of surfactant solution. CMC is considered to be a fundamental property of
surfactants. A number of interfacial phenomena such as detergency can take place due to
the presence of micelles in solutions. In addition, other phenomena such as the surface
tension reduction is not directly influenced by the formation of micelles.34 Therefore,
CMC and the corresponding surface tension are important indicators to measure the
surface activity of surfactants SDꢀAL. As seen from the data listed in Table 3, the CMC of
SDꢀAL decreased with the increase of reaction temperature between DGE and lignin, a
lowest CMC (0.50 g Lꢀ1) and the corresponding surface tension (29.17 mN/m) were
achieved when the surfactant derived from the lignin grafted with DGE under 110 ºC. This
was because under a similar content of sulfur, surfactant derived from the lignin grafted
with DGE under high temperature has a high lipophilicity than that prepared under low
temperature. The CMC and surface tension at the corresponding CMC of all surfactants
derived from lignin were lower than the CMC (0.97 g Lꢀ1) and the corresponding surface
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tension (30.50 mN/m) of the commercial surfactant SDBS, indicating that SDꢀAL
surfactants had a good surface activity. Furthermore, the lignin surfactant prepared showed
a good ability to reduce the surface tension of aqueous solution, comparable to those of
the products prepared previously. In Košıková B’s work,33 a series of ligninꢀbased surface
active agents derived from alkylation of beechwood prehydrolysis lignin with
laurybromide decreased the surface tension of aqueous solution to 30ꢀ40 mN/m at the
concentration of 1 g Lꢀ1. Homma et al.35 reported that nonionic polymeric surfactants
derived from the modification of acetic acid lignin with polyethylene glycol
diglycidylethers lowed the surface tension of aqueous solution to 36 mN/m at the
corresponding CMC (50g Lꢀ1). The results of the present study suggested that lignin
surfactants with high surface activity was prepared by modification of lignin with DGE
and chlorosulfonic acid.
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4. Conclusion
A long alkyl chain was successfully introduced into lignin by the reaction between
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lignin and DGE in the presence of BDMA as a catalyst. The reaction between DGE and
carboxy group was the predominant reaction at 95 °Cꢀ110 °C. The surface tension of the
lignin surfactant solution was lower than that of commercial surfactant sodium
dodecylbenzenesulphonate when the concentration of surfactant solution was below 0.4 %,
indicating that the surfactants prepared from modified alkaline lignin had a good surface
activity. A lowest CMC (0.50 g Lꢀ1) and the corresponding surface tension (29.17 mN/m)
were achieved when the surfactant was derived from the lignin grafted with DGE at 110
ºC. The anionic lignin surfactants prepared in this study could be utilized as detergents or
to enhance oil recovery.
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Acknowledgements
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We express our gratitude for the financial support from Beijing Forestry University Young
Scientist Fund (BLX2012025), the National Natural Science Foundation of China
(3110103902), the Major State Basic Research Projects of China (973ꢀ2010CB732204),
and the Open Foundation of the State Key Laboratory of Pulp and Paper Engineering
(201261).
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Improving the surface activity of lignin through chemical modification for preparation
of anionic surfactant.