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Preparation and Characterization of Polymeric Surfactants Based on Epoxidized Soybean Oil Grafted Hydroxyethyl Cellulose Xujuan Huang, He Liu, Shibin Shang, Xiaoping Rao, and Jie Song J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b03765 • Publication Date (Web): 29 Sep 2015 Downloaded from http://pubs.acs.org on October 3, 2015
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Journal of Agricultural and Food Chemistry
Preparation and Characterization of Polymeric Surfactants Based on Epoxidized Soybean Oil Grafted Hydroxyethyl Cellulose Xujuan Huang†, He Liu†*, Shibin Shang†‡*, Xiaoping Rao†‡and Jie Song§ †
Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry, Key
Laboratory of Biomass Energy and Material, National Engineering Laboratory for Biomass Chemical Utilization, Key and Laboratory on Forest Chemical Engineering, State Forestry Administration, Nanjing 210042, Jiangsu Province, China ‡
Institute of New Technology of Forestry, Chinese Academy of Forestry, Beijing 100091,
China §
Department of Chemistry and Biochemistry, University of Michigan-Flint, Flint,
Michigan 48502, United States AUTHOR INFORMATION *Corresponding author: He Liu & Shibin Shang Email:
[email protected] &
[email protected]. Phone: 086-25-85482452. Fax: 086-25-85482499.
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ABSTRACT: Epoxidized soybean oil (ESO) grafted hydroxyethyl cellulose (HEC)
2
was prepared via ring-opening polymerization, in which the hydroxyl groups of HEC
3
acted as initiators, and the polymeric ESO were covalently bonded to the HEC.
4
Hydrolysis of ESO grafted HEC (ESO-HEC) was performed with sodium hydroxide,
5
and the hydrolyzed ESO-HEC (H-ESO-HEC) products were characterized via Fourier
6
transform infrared (FT-IR),
7
spectroscopies, high-temperature gel permeation chromatography (HT-GPC), and
8
differential scanning calorimetry (DSC). The results indicated that ring-opening
9
polymerization of ESO occurred with the hydroxyl groups of HEC as initiators. The
10
molecular weights of the H-ESO-HEC products were varied by adjusting the mass
11
ratio of HEC and ESO. Through neutralizing the carboxylic acid of H-ESO-HEC with
12
sodium hydroxide, novel polymeric surfactants (H-ESO-HEC-Na) were obtained, and
13
the effects of polymeric surfactants on the surface tension of water were investigated
14
as a function of concentration of H-ESO-HEC-Na. The H-ESO-HEC-Na was effective
15
at lowering the surface tension of water to 26.33 mN/m, and the critical micelle
16
concentration (CMC) value decreased from 1.053 to 0.157 g/L with increases in
17
molecular weights of the polymeric surfactants. Rheological measurements indicated
18
that the H-ESO-HEC-Na solutions changed from pseudoplastic property to Newtonian
19
with increasing shear rate.
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KEYWORDS: hydroxyethyl cellulose; epoxidized soybean oil; polymeric
21
surfactants
1
H and
13
C nuclear magnetic resonance (NMR)
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INTRODUCTION
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Polymeric surfactants are important for a variety of industrial applications. The
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increasing interest in natural, renewable and biodegradable materials makes natural
26
polymers like cellulose and its derivatives attractive raw materials for the preparation
27
of bio-polymeric surfactants.1 Cellulose-based polymeric surfactants have drawn
28
much attention in the last decades because they present many novel performances
29
such as low cost, biodegradation, associative properties in water, rheological
30
properties, and surface-active properties that can control foaming or emulsion
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stability.2-7
32
Landoll did pioneering work on cellulose-based polymeric surfactants in
33
1980s.8,9 Since then, various cellulose-based polymeric surfactants have been
34
synthesized
35
Cellulose-based polymeric surfactants were generally synthesized by the modification
36
of hydrophilic cellulose backbones with hydrophobic long alkyl chains. Hydroxyl
37
groups always have chemical handles that can react with hydrophobic chains
38
containing epoxide, halide, acyl halide, isocyanate or anhydride for the preparation of
39
amphiphilic cellulose. Polymeric surfactants based on hydroxyethyl cellulose (HEC)
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were prepared by the reaction of a long-chain terminal epoxide with the hydroxyl
41
groups of HEC in an alkaline slurry.9 Partial hydrophobization of carboxymethyl
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cellulose with C12–C18 alkyl halides was carried out in the presence of sodium
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hydroxide as a catalyst in DMF/H2O (1:1).16 The HEC-based copolymer was prepared
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via ultraviolet irradiation by copolymerizing HEC with hexadecyl acrylate and
including
nonionic,
ionic,
fluorocarbon,
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amphoteric.10-15
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co-monomer styrene (St) in aqueous solution.12 The C10–C14 alkyl cellulose ester
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sulfate surfactants were prepared by hydrophilic sulfonation and hydrophobic
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esterification.17 Further attempts to substitute the environmentally dangerous
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petrochemical products as well as schemes to increase the hydrophobicity of cellulose
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derivatives with fatty acids to synthesize cellulose-based surfactants have been
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investigated.18,19 Grafting fatty acid chains to cellulose increases the hydrophobicity
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of the ester derivatives even at a low degree of esterification.
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Although fatty acid esters are found in nature as triglycerides and inexpensive as
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acylation reagents, the improvement of surface-active properties of fatty
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acid-esterified cellulose derivatives is limited.1 According to the literature, the surface
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tension of water was decreased from 72.8 mN/m to 46 - 65 mN/m by fatty
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acid-esterified cellulose derivatives.18 However, it is well known that saponified fatty
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acid esters are an important surfactant and are effective at lowering the surface tension
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of water from 20 to 40 mN/m.20,21 In addition, the surface tension of polymerized
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saponified fatty acid ester is 20.5 to 39.6 mN/m.22 This study suggests that, versus
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saponified fatty acid esters, polymerized saponified fatty acid esters have similar
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utility at lowering the surface tension of water. Saponified fatty acid-grafted cellulose
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surfactants formed via cellulose derivatives as backbones are polymerized saponified
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fatty acid surfactants. Therefore, cellulose chains grafting saponified fatty acid esters
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to form ionic surfactants—instead of fatty acid-esterified cellulose surfactants—may
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become an effective method for synthesis of cellulose-based surfactants with highly
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surface-active properties. Fortunately, the chemical reactivities of some fatty acids 4
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isolated from vegetable oils can achieve this vision.
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Soybean oil is one of the most abundant renewable vegetable oils in the world.23
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It possesses three unsaturated fatty acids, oleic (23%), linoleic (54%) and linolenic
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(8%). It contains 1, 2, and 3 double bonds, respectively.24 The double bonds can be
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used in many reactions including addition reaction25, oxidation reaction26, and
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polymerization reaction27. More significantly, the expoxidation reaction makes the
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soybean oil become epoxidized soybean oil (ESO). A ring-opening reaction of ESO
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with different alcohols was carried out in presence of Amberlyst 15 (Dry) as a
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catalyst.28 Furthermore, the ring-opening polymerization of ESO can be catalyzed by
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boron trifluoride diethyl etherate (BF3·OEt2) in liquid carbon dioxide and methylene
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chloride, respectively.26,29 The ESO-based polymeric surfactants in particular were
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prepared by hydrolysis of polymerized ESO with a base.22 These interesting works
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suggest that hydroxyl groups of cellulose can initiate ring-opening polymerization of
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ESO in the presence of catalysts. Moreover, novel saponified fatty acid-modified
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cellulose-based polymeric surfactants are obtained by saponification of the ESO
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grafted cellulose products in which fatty acid chain are combined with cellulose by an
83
ether linkage at the middle site of a fatty acid molecular chain.
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To prove this assumption, the modification of HEC by grafting ESO was
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investigated and hydrolysis of ESO grafted HEC (ESO-HEC) was performed with
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sodium hydroxide (Figure 1). The hydrolyzed ESO-HEC (H-ESO-HEC) products
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were characterized with Fourier transform infrared (FT-IR), 1H and
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magnetic resonance (NMR) spectroscopies, high-temperature gel permeation 5
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chromatography (HT-GPC), and differential scanning calorimetry (DSC). After
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neutralizing the carboxylic acid of the H-ESO-HEC with sodium hydroxide, novel
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polymeric surfactants (H-ESO-HEC-Na) were obtained and the effects of polymeric
92
surfactants on the surface tension of water were investigated as a function of
93
concentration of H-ESO-HEC-Na. In addition, the rheological behaviors of the
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H-ESO-HEC were investigated.
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MATERIALS AND METHODS
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Materials. Hydroxyethyl cellulose (HEC), epoxidized soybean oil (ESO) and
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stannic chloride (SnCl4) were purchased from Aladdin Industrial Co., Ltd. Dimethyl
98
sulfoxide (DMSO) was purchased from Sinopharm Chemical Reagent Co., Ltd.
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Sodium hydroxide (NaOH), hydrochloric acid (HCl) and ethyl acetate were obtained
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from Nanjing Chemical Reagent Co., Ltd. Deionized water was purified to a
101
conductivity of 18.3 MΩ·cm on a Hitech-Sciencetool Master-Q laboratory water
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purification system (Shanghai Hetai Reagent Co., Ltd). All chemicals were used
103
without further purification.
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Synthesis of ESO-grafted HEC Derivatives (ESO-HEC). HEC (1.0 g) was
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dissolved in 40 mL DMSO under stirring at room temperature for 2 h and then
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transferred into a three-necked round-bottomed flask. ESO (1.0 g) was added to the
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HEC solution. The mixture was stirred by mechanical agitation at room temperature.
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A mixture of 10 µL SnCl4 and 10 mL DMSO were then added dropwise into the
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reactor, and the reaction was maintained for 30 min. The resulting products were
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washed sequentially with deionized water to remove DMSO and dried under vacuum 6
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at 50 °C. Finally, the ESO-grafted HEC derivatives (ESO-HEC) were obtained.
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Hydrolysis of ESO-HEC (H-ESO-HEC). The ESO-HEC (2.0 g) was added to a
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flask with 50 mL of 0.6 M NaOH solution. The reactor was heated to 100 °C with
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agitation for 12 h under a condensing condition. After reaction, the solution was
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separated by filtration and the aqueous solution was removed by reduced pressure
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distillation. The solid product was washed with ethyl acetate three times to remove the
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glycerin. The solid product was then re-dispersed in aqueous solution and the solution
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was adjusted to pH 5~6 by 0.1 M HCl. The solution became turbid, and the product
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appeared as a floating oil. The product was extracted by ethyl acetate, and the organic
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phase was washed with hot distilled water three times. Finally, the H-ESO-HEC
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product was purified by reduced pressure distillation. The H-ESO-HEC-Na was
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obtained by neutralizing the carboxylic acid of H-ESO-HEC with sodium hydroxide.
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FT-IR. Fourier transform infrared (FT-IR) spectra was used to confirm the
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structure of the H-ESO-HEC. These spectra were obtained on the Thermo Scientific
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Nicolet IS10 spectrometer with the attenuated total reflectance (ATR) method. The
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spectra were recorded over the range 4000-500 cm-1 at 4 cm-1 resolution and averaged
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over 16 scans per sample.
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NMR. 1H NMR and 13C NMR spectra for H-ESO-HEC were recorded at 40 °C
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on a BRUKER AV400 spectrometer (Bruker, Rheinstetten, Germany) operating at a
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frequency of 400.13 and 100.61 MHz, respectively. Deuterated dimethyl sulfoxide
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(DMSO-d6) and tetramethylsilicane (TMS) were used as the solvent and the internal
132
standard, respectively. The chemical shift values were referenced to the signals of 7
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DMSO-d6 and TMS.
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HT-GPC. Molecular weight distribution curves and relative values of number
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average (Mn) and weight average (Mw) molecular weight of H-ESO-HEC were
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determined by HT-GPC (HT-GPC Module 350A, Viscotek; GPC equipped with
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I-MBHMW-3078 HT-GPC column) at 60 °C. The HT-GPC instrument was equipped
138
with refractive index detector, viscosity detector and small-angle light scattering
139
detector. The flow rate of the carrier solvent (HPLC-grade DMSO) was 1.0 mL/min.
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Samples were filtered over microfilters with a pore size of 0.2 µm (Nylon, Millex-HN
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13 mm Syringes Filters, Millipore). The results were obtained from OmniSEC
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software.
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Conductimetry. The carboxyl content of H-ESO-HEC was determined by
144
conductometric titrations.30 The H-ESO-HEC (30-40 mg) was suspended into 15 mL
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of 0.01 M hydrochloric acid solution. After 2 h of stirring, the suspensions were
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titrated with 0.01 M NaOH. The carboxyl content of the sample was determined from
147
the conductivity and VNaOH curve. The carboxyl content is calculated by the following
148
equation:
149
Carboxyl Content (mmol/g) =
c (V2 − V1 ) m
(1)
150
Here, V1 and V2 are the volumes of NaOH (mL) in the first and second inflection point
151
of titration curves, respectively. The c is the concentration of NaOH (mmol/L), and m
152
is the weight of oven-dried sample (mg). To minimize errors, titrations were
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duplicated at least three times, and the average value was retained for the discussion.
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DSC. To determine the ring-opening polymerization of ESO, the DSC 8
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measurements of the H-ESO-HEC were performed on a Diamond DSC at 40 mL/min
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dry nitrogen as the purge gas. Typically, ~4 mg of the H-ESO-HEC was accurately
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weighed in an aluminum pan and sealed with pin-perforated lids. The sample was
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cooled to -50 °C at a rate of 10 °C/min and a refrigerated cooling system was used to
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equilibrate the sample at -50 °C for 5 min. Data were recorded while the oven
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temperature was raised from -50 °C to 0 °C at 10°C /min.
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Surface Tension. The surface tension of H-ESO-HEC-Na was measured at
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25 °C using the Wilhelmy plate T107 (width: 19.44 mm; thickness: 0.1 mm; height:
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65 mm; circumference: 39.08) on a Sigma 701 Automatic Surface Tensiometer. The
164
instrument was calibrated against pure water before measurements were made. The
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concentration of H-ESO-HEC-Na surfactant was gradually increased by dispersing
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stock solution into the measurement cell. The software automatically determined the
167
surface tension as a function of the bulk concentration. The surface tension data were
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plotted against the H-ESO-HEC-Na concentration in water from 0.0003 to 2.0 g/L.
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Each concentration of aqueous H-ESO-HEC-Na solution was tested in triplicate—this
170
was done automatically by the instrument. The concentration at which the equilibrium
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surface tension of the polymeric surfactants stopped decreasing with concentration
172
and plateaued is the critical micelle concentration (CMC).22 From the inflection point
173
of the plot, the critical micelle concentration (CMC) and minimum surface tension
174
(γcmc) were derived. All data were obtained from the OneAttention software.
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Krafft Point (KP). 20 mL 0.5 wt% surfactant aqueous solution (at least
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quintuplicate the CMC of studied surfactant) was prepared in an alkaline solution and 9
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added to a beaker. The beaker was then heated and the particular temperature was
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recorded as KP when the solution transformed from turbid to pellucid.31
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Hydrophile Lipophile Balance (HLB) Value. The emulsions were prepared
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using a mixture of the nonionic surfactants Tween 60 and Span 80 to satisfy the
181
proper HLB values for optimum emulsification conditions. The mixed HLB values
182
were calculated with the following equation:
183
HLBmix = HLBT × T % + HLBS × S %
(2)
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Here, HLBmix, HLBT and HLBS are the HLB values of the mixed surfactants, Tween 60
185
(14.9) and Span 80 (4.3), respectively. The T% and S% are the mass percentages of
186
Tween 60 and Span 80 in the mixed surfactants, respectively.32 All the HLB values
187
used were measured at 25 °C.
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Rheology. Rheological measurements were performed at a rotational rheometer
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HAAKE MARS II equipped with a measuring geometry named PP60 Ti (diameter d=
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50 mm). The H-ESO-HEC-Na-III was selected to evaluate the rheological properties.
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H-ESO-HEC-Na-III solutions at three different concentrations (0.1 g/L, 1 g/L, 5 g/L)
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were prepared to measure the shear viscosity that changed with the shear rate ranging
193
from 0.01 to 100 s-1.15 The rheological measurements were carried out at 40 °C. All
194
data were obtained using the HAKKE RheoWin data manager software.
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Statistical Method. Origin Pro 9.0 was used to calculate the standard deviation of
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carboxyl content and the surface tension of H-ESO-HEC. The standard deviation was
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calculated with the following equation:
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n
∑(X 198
S=
i
− X )2
i =1
n −1
(3)
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Here, S is the standard deviation of a sample. X i is the ith value in a sample, X is
200
the average number of a sample, n is the total number of a sample.
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RESULTS AND DISCUSSION
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Figure 1 outlines a simplified mechanism for the entire reaction. The ESO-HEC
203
was prepared via ring-opening polymerization, in which the hydroxyl groups of HEC
204
acted as initiators. In addition, the ring-opening polymerization generated new
205
hydroxyl groups that can also act as initiators via the SnCl4 catalyst. The polymeric
206
ESO were covalently bound to the HEC, and hydrolysis of ESO-HEC (H-ESO-HEC)
207
was obtained with sodium hydroxide. As shown in Table 1, H-ESO-HEC products
208
with different molecular weights were obtained by adjusting the mass ratio of HEC
209
and ESO in graft reaction. The graft reaction occurred at room temperature with a
210
short reaction time because of the high-activity of the SnCl4 catalyst. The yields of the
211
H-ESO-HEC were measured and ranged from 1.2 to 2.7 g per g HEC as the amount of
212
ESO increased in graft polymerization reaction. In addition, H-ESO-HEC-Na samples
213
with different molecular weights were obtained by neutralizing carboxylic acid of
214
H-ESO-HEC with sodium hydroxide.
215
Spectroscopic Identification of the Structures of H-ESO-HEC. In Figure 2,
216
the FT-IR spectrum of H-ESO-HEC-III attested to the presence of ESO chains onto
217
the HEC by appearance of the characteristic absorption bands assigned to the carbonyl
218
functions at 1710 cm-1 versus the HEC. The spectral peak at 2920 cm-1 was attributed 11
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to the –CH3 group of the alkane chains of ESO. Also, peaks at 716 cm-1 indicate the
220
vibration of –(CH2)n– (n ≥ 4).33 No significant change in hydroxyl group signal at
221
3360 cm-1 was noticed because the hydroxyl groups of the HEC acted as initiators and
222
were consumed in the grafting reaction. The ring-opening polymerization generated
223
new hydroxyl groups simultaneously—these are obvious from Figure 1. These results
224
indicated that the H-ESO-HEC was prepared successfully. The introduction of the ESO on HEC chains is further confirmed by the 1H and
225 226
13
C NMR spectra of the H-ESO-HEC-III in Figure 3. In 1H NMR spectrum, the
227
clusters of signal peaks ranged from δ0.8 to δ1.6. These were related to the protons of
228
the alkane chains of ESO on HEC. The peaks at δ2.1 corresponded to the side groups
229
–OH of the HEC. The alkane chains were produced by the ring-open reaction. The
230
clusters of signal peaks in the range of δ3.2 to δ5.0 were attributed to the chemical
231
shifts of anhydroglucose unit (AGU) protons. In the 13C NMR spectrum, the possible
232
assignments of the peaks were found according to the previous literature.34,35 The
233
inserted region at δ176 correspond to carbonyl signals of the carboxylate groups.36
234
The C-1 carbon resonance in AGU was poor at δ101. The clusters of signal peaks in
235
the range of δ62 to δ76 contributed to the chemical shifts of AGU carbons. Table 2
236
offers detailed information. Distinct peaks were observed at δ62. There are attributed
237
to the C-6 substituted by the hydroxyethylation and connected to the ether bond that is
238
obtained by the graft polymerization. The clusters of peaks in the range from δ10 to
239
δ35 corresponding to the carbon signals of ESO chains demonstrated that the graft
240
reaction was successful. The 1H NMR and
13
C NMR spectroscopy confirmed the
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characteristic groups of H-ESO-HEC-III.
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Molecular Weight and Carboxyl Content of H-ESO-HEC. The molecular
243
weight value of H-ESO-HEC was determined by HT-GPC. The HT-GPC profile
244
signals of the refractive index detector are shown in Figure 4. This shows that the
245
H-ESO-HEC with different molecular weights had a similar tendency of distribution
246
and moved towards the higher molecular weight regions as the amount of ESO
247
increased in the graft reaction. As listed in Table 1, the Mn of H-ESO-HEC (I-V)
248
ranged from 1.48 × 105 to 4.58 × 105 Da and the Mw of H-ESO-HEC (I-V) ranged
249
from 2.71 × 105 to 8.28 × 105 Da along with the mass ratio of HEC and ESO ranged
250
from 1:1 to 1:5, respectively. The conductometric titration curve to determine
251
carboxyl content of H-ESO-HEC-III was divided into three parts in Figure 5. The first
252
part showed the presence of a strong acid corresponding to excess of HCl. The second
253
part where the conductivity remains constant showed a weak acid corresponding to
254
the carboxyl content. The last part showed that strong base corresponded to an excess
255
of sodium hydroxide. The V1 and V2 are volumes of NaOH (mL) in the first and
256
second inflection points of the titration curves, respectively. Finally, the carboxyl
257
content can be calculated by the equation (1). The carboxyl contents of H-ESO-HEC
258
(I-V) were 1.89-2.80 mmol/g (Table 1). We concluded that the carboxyl content were
259
closely associated with the molecular weight. As the amount of ESO increased in
260
graft reaction, the carboxyl content increased according to the Mn of H-ESO-HEC. In
261
addition, the polydispersity indexes (PDI) of H-ESO-HEC (I-V) ranged from 1.46 to
262
2.1. This indicates that the H-ESO-HEC samples had a wide distribution (figure 4). 13
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DSC Analysis. The ring-opening polymerization of ESO grafting on HEC was
264
confirmed by DSC in which the glass transition temperature (Tg) was determined to
265
be the temperature at the inflection point. Figure 6 clearly illustrates that there was no
266
Tg in HEC and H-ESO-HEC-I because the HEC did not exhibit glass transition, and
267
there was no polymerization of ESO on HEC in H-ESO-HEC-I. Previous literature
268
reported that the products obtained by ring-opening polymerization of ESO existed
269
Tg.26
270
H-ESO-HEC-V were -25.81 oC, -23.74 oC, -22.24 oC and -21.48 oC, respectively. As
271
expected, increasing the amount of ESO in the graft reaction resulted in more ESO
272
being grafted on HEC. The ring-opening polymerization reaction took place in the
273
graft reaction—this was in consistent with the GPC results. Furthermore, the Tg of
274
H-ESO-HEC samples became higher as the molecular weights of H-ESO-HEC
275
increased.
The
Tg
of
H-ESO-HEC-II,
H-ESO-HEC-III,
H-ESO-HEC-IV
and
276
Surface Tension of Aqueous H-ESO-HEC Polymeric Surfactants. The
277
H-ESO-HEC products were added to a beaker containing the required amount of
278
NaOH to neutralize all of the acidic protons from carboxylic acid groups. This was
279
then placed in a 60oC water bath and stirred with a glass rod until the samples were
280
dissolved.28, 29 A series of aqueous solutions of the H-ESO-HEC-Na were prepared,
281
and their surface tensions were investigated at room temperature. It is well known that
282
amphiphilic polymers with a suitable hydrophilic-hydrophobic balance can form a
283
micelle structure when exposed to a selective solvent.37 As shown in Figure 7, the
284
surface tension of H-ESO-HEC-Na in water decreased markedly in the low 14
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concentration at first. When the concentration was higher, the surface tension reduced
286
slightly. Finally, the surface tension was held nearly constant because its
287
concentration was sufficiently high.
288
As shown in Table 3, the minimum surface tensions of H-ESO-HEC-Na (I-V)
289
were almost same and ranged from 26.33 mN/m to 28.88 mN/m. The
290
H-ESO-HEC-Na displayed efficient surface properties versus HEC and the
291
hydrolyzed ESO at 54.68 mN/m and 34.28 mN/m, respectively. In addition, the
292
previous studies reported that the surface tension of fatty acid-esterified cellulose
293
derivatives ranged between 46 mN/m and 65 mN/m.17, 18 Different efficiency of these
294
fatty acid modified cellulose polymeric surfactants in lowering surface tensions of
295
water was attributed to the status of fatty acid in polymeric surfactants. In our study,
296
hydroxyl groups of HEC acted as initiators for ring-opening polymerization of ESO.
297
The fatty acid chains were combined with HEC by ether linkage at the middle site of
298
the fatty acid molecular chain. In this structure, both the hydrophobic alkanes and the
299
hydrophilic carboxyl were introduced into HEC. The simultaneous introduction of
300
hydrophobic
301
hydrophilic-hydrophobic balance of HEC and provided an opportunity to form
302
micelles in water. The CMC values of H-ESO-HEC-Na were decreased from 1.053
303
g/L to 0.157 g/L along with the obviously increasing molecular weight of
304
H-ESO-HEC-Na. As the molecular weights increased, the H-ESO-HEC-Na displayed
305
greater propensity to form micelles because of the flexible molecular chains. This
306
indicated that the efficiency in reducing surface tension was significantly enhanced
alkanes
and
hydrophilic
carboxyl
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groups
improved
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307
when the molecular weight of H-ESO-HEC-Na increased. The KP of the
308
H-ESO-HEC-Na ranged from 39 °C to 68 °C. It increased as a function of molecular
309
weight accordingly. The HLB values of the samples ranged from 9.6 to 10.6.
310
Surface
Rheological
Properties.
The
apparent
viscosities
of
the
311
H-ESO-HEC-Na aqueous solution as a function of shear rate at different
312
concentrations were investigated. The results of H-ESO-HEC-Na-III displayed the
313
same properties as the other products (Figure 8). The curves were not smooth at the
314
low shear rate because of instrument error and the complete minor viscosity.
315
Therefore, the curve of the 0.1 g/L H-ESO-HEC-Na-III can largely be considered a
316
straight line. The curve of the 0.1 g/L H-ESO-HEC-Na-III below the CMC
317
demonstrated that the solution behaved like water due to the low number of species
318
H-ESO-HEC-Na-III in solution. The curves of the 1.0 g/L and 5.0 g/L
319
H-ESO-HEC-Na-III above the CMC that formed micelles in aqueous solution can be
320
divided into two parts. First, the viscosity of the H-ESO-HEC-Na-III solution
321
decreased as the shear rate increased, and the H-ESO-HEC-Na-III solution exhibited a
322
pseudoplastic property at the low shear rate.38 This was because micelles in aqueous
323
solution were damaged, and the macromolecules experienced conformational
324
change.39 Its winding structure was separated under the action of shearing force and
325
arranged along the flow direction along with the increasing shear rate.40 Sequentially,
326
the viscosity remained constant when the shear rate reached a certain level. It behaved
327
like a Newtonian property.41 This is because the winding structure was completely
328
destroyed, and the molecular orientation reached at limiting condition. 16
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In summary, ESO-grafted HEC were prepared via ring-opening polymerization
330
and five novel polymeric surfactants H-ESO-HEC-Na (I-V) were obtained by
331
neutralization of H-ESO-HEC with sodium hydroxide. The molecular weights of
332
H-ESO-HEC products were varied by adjusting the mass ratio of HEC and ESO in the
333
grafting reaction. The synthesized polymeric surfactants H-ESO-HEC-Na exhibited
334
higher activities in reducing water surface tension. These ranged from 26.33 mN/m to
335
28.88 mN/m in comparison to 34.28 mN/m for hydrolyzed ESO and 54.68 mN/m for
336
HEC. In addition, the efficiency in reducing water surface tension was definitely
337
enhanced when the molecular weights of H-ESO-HEC increased. Rheological
338
measurements indicated that the H-ESO-HEC-Na solutions changed from a
339
pseudoplastic state to Newtonian with increasing shear rate. This study may facilitate
340
an increase in the use of renewable and biodegradable materials with improved
341
properties as polymeric surfactants.
342 343 344
Funding
345
The authors express their gratitude for the financial support From Natural Science
346
Foundation of Jiangsu Province of China (BK2012063 and BK20140973); Special
347
Fund for Basic Scientific Research Business of Central Public Research Institutes
348
(CAFINT2012C05); National Natural Science Foundation of China (31200446).
349 350
Notes 17
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The authors declare no competing financial interest.
352
REFERENCES (1) Tomanova, V.; Srokova, I.; Ebringerova, A.; Sasinkova, V., Surface-Active and Associative Properties of Ionic Polymeric Surfactants Based on Carboxymethylcellulose. Polym. Eng. Sci. 2011, 51, 1476-1483. (2) Nikfarjam, N.; Qazvini, N. T.; Deng, Y. L., Surfactant free Pickering emulsion polymerization of styrene in w/o/w system using cellulose nanofibrils. Eur. Polym. J. 2015, 64, 179-188. (3) Hu, Z.; Ballinger, S.; Pelton, R.; Cranston, E. D., Surfactant-enhanced cellulose nanocrystal Pickering emulsions. J. Colloid. Interf. Sci. 2015, 439, 139-148. (4) Khuman, P.; Singh, W. B. K.; Devi, S. D.; Naorem, H., Viscosity-Temperature Behavior of Hydroxypropyl Cellulose Solution in Presence of an Electrolyte or a Surfactant: A Convenient Method to Determine the Cloud Point of Polymer Solutions. J. Macromol. Sci. A. 2014, 51, 924-930. (5) Durand, A., Synthesis of amphiphilic polysaccharides by micellar catalysis. J. Mol. Catal. a-Chem. 2006, 256, 284-289. (6) Zhang, L. M., Cellulosic associative thickeners. Carbohyd. Polym. 2001, 45, 1-10. (7) Karlberg, M.; Thuresson, K.; Lindman, B., Hydrophobically modified ethyl (hydroxyethyl) cellulose as stabilizer and emulsifying agent in macroemulsions. Colloid. Surface. A. 2005, 262, 158-167. (8) M.L. Landoll, US Patent No. 4,228,277 (1980). (9) Landol, L. M., Nonionic polymer surfactants. J. Polym. Sci. 1982, 20, 443-455. (10) Yang F.; Liu Y.N.; Yu J.L.; Li H.P.; Gang Li, Synthesis, micellization behavior and alcohol induced amphipathic cellulose film of cellulose-based amphiphilic surfactant. Appl. Surf. Sci. 2015, 345, 187-193. (11) S. Evani, US Patent No. 4,432,881 (1984). (12) Li, Z. X.; Wang, L. G.; Huang, Y., Photoinduced graft copolymerization of polymer surfactants based on hydroxyethyl cellulose. J. Photoch. Photobio. A. 2007, 190, 9-14. (13) Sardar, N.; Ali, M. S.; Kamil, M.; Kabir-ud-Din, Phase Behavior of Nonionic Polymer Hydroxypropylmethyl Cellulose: Effect of Gemini and Single-Chain Surfactants on the Energetics at the Cloud Point. J. Chem. Eng. Data. 2010, 55, 4990-4994. (14) Thongngam, M.; McClements, D. J., Characterization of interactions between chitosan and an anionic surfactant. J. Agr. Food. Chem. 2004, 52, 987-991. (15) Wei, Y. P.; Cheng, F.; Hou, G.; Sun, S. F., Amphiphilic cellulose: Surface activity and aqueous self-assembly into nano-sized polymeric micelles. React. Funct. Polym. 2008, 68, 981-989. (16) Srokova, I.; Talaba, P.; Hodul, P.; Balazova, A., Emulsifying agents based on 18
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O-(carboxymethyl)cellulose. Tenside. Surfact. Det. 1998, 35, 342-344. (17) Yu, J. L.; Yang, F.; Liu, Z. H.; Liu, Y. N.; Li, G., Preparation and Characterization of C-10-C-14 Alkyl Cellulose Ester Sulfate Surfactant. J. Surfactants. Deterg. 2014, 17, 647-653. (18) Tomanova, V.; Pielichowski, K.; Srokova, I.; Zoldakova, A.; Sasinkova, V.; Ebringerova, A., Microwave-assisted synthesis of carboxymethylcellulose based polymeric surfactants. Polym. Bull. 2008, 60, 15-25. (19) Peydecastaing, J.; Girardeau, S.; Vaca-Garcia, C.; Borredon, M. E., Long chain cellulose esters with very low DS obtained with non-acidic catalysts. Cellulose 2006, 13, 95-103. (20) Chumpitaz, L. D. A.; Coutinho, L. F.; Meirelles, A. J. A., Surface tension of fatty acids and triglycerides. J. Am. Oi.l Chem. Soc. 1999, 76, 379-382. (21) Osipow, L.; Snell, F. D.; Marra, D.; York, W. C., Surface Activity of Monoesters - Fatty Acid Esters of Sucrose. Ind. Eng. Chem. 1956, 48, 1462-1464. (22) Liu, Z. S.; Biresaw, G., Synthesis of Soybean Oil-Based Polymeric Surfactants in Supercritical Carbon Dioxide and Investigation of Their Surface Properties. J. Agr. Food. Chem. 2011, 59, 1909-1917. (23) Meier, M. A. R.; Metzger, J. r. O.; Schäfer, H. J., Oils and Fats as Renewable Raw Materials in Chemistry. Angew. Chem. Int. Edit. 2011, 50, 3854-3871. (24) Lawate, S. S.; Lal, K.; Huang, C., Vegetable oils-structure and performance. CRC Press: New York, 1997; p 103. (25) Bantchev, G. B.; Kenar, J. A.; Biresaw, G.; Han, M. G., Free Radical Addition of Butanethiol to Vegetable Oil Double Bonds. J. Agr. Food. Chem. 2009, 57, 1282-1290. (26) Lowe, A. B., Thiol-ene "click" reactions and recent applications in polymer and materials synthesis: a first update. Polym. Chem-Uk. 2014, 5, 4820-4870. (27) Liu, Z. S.; Doll, K. M.; Holser, R. A., Boron trifluoride catalyzed ring-opening polymerization of epoxidized soybean oil in liquid carbon dioxide. Green. Chem. 2009, 11, 1774-1780. (28) Lathi, P. S.; Mattiasson, B., Green approach for the preparation of biodegradable lubricant base stock from epoxidized vegetable oil. Appl. Catal. B-Environ. 2007, 69, 207-212. (29) Biresaw, G.; Liu, Z. S.; Erhan, S. Z., Investigation of the surface properties of polymeric soaps obtained by ring-opening polymerization of epoxidized soybean oil. J. Appl. Polym. Sci. 2008, 108, 1976-1985. (30) Perez, D. D.; Montanari, S.; Vignon, M. R., TEMPO-mediated oxidation of cellulose III. Biomacromolecules 2003, 4, 1417-1425. (31) Wang, X. G.; Yan, F.; Li, Z. Q.; Zhang, L.; Zhao, S.; An, J. Y.; Yu, J. Y., Synthesis and surface properties of several nonionic-anionic surfactants with straight chain alkyl-benzyl hydrophobic group. Colloid. Surface. A. 2007, 302, 532-539. (32) Liu, W. R.; Sun, D. J.; Li, C. F.; Liu, Q.; Xu, H., Formation and stability of paraffin oil-in-water nano-emulsions prepared by the emulsion inversion point method. J. Colloid. Interf. Sci. 2006, 303, 557-563. (33) Wei, Y. P.; Cheng, F.; Zheng, H., Synthesis and flocculating properties of 19
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Figure captions Figure 1. Synthetic route of H-ESO-HEC polymeric surfactants Figure 2. FT-IR spectra of HEC and H-ESO-HEC-III Figure 3. 1H NMR and 13C NMR spectrum of H-ESO-HEC-III sample in DMSO-d6 Figure 4. GPC profile signal of the refractive index of H-ESO-HEC samples Figure 5. Conductometric titration curve of H-ESO-HEC-III Figure 6. The DSC curves of HEC and H-ESO-HEC samples Figure 7. Effect of H-ESO-HEC-Na concentration in water on equilibrium surface tension of water Figure 8. Apparent viscosity of the H-ESO-HEC-Na-III solution as a function of shear rate
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Tables Table 1. Effect of reaction condition on yield and carboxyl content and the HT-GPC data of H-ESO-HEC HEC:ESO
Samples
Yielda
Carboxyl Content
(mass ratio)
(g/g)
(mmol/g)
—
—
0
HEC
b
HT-GPC data Mn×10 (Daltons)
Mw×105(Daltons)
PDIc
0.7
2.28
3.20
5
H-ESO-HEC-I
1:1
1.2
1.89±0.13
1.48
2.71
1.80
H-ESO-HEC-II
1:2
1.6
2.12±0.06
1.55
3.31
2.10
H-ESO-HEC-III
1:3
1.9
2.35±0.10
3.77
5.50
1.46
H-ESO-HEC-IV
1:4
2.1
2.72±0.03
4.19
6.61
1.57
H-ESO-HEC-V
1:5
2.7
2.80±0.11
4.58
8.28
1.80
a
Expressed as g of the H-ESO-HEC per g HEC (on dry mass basis)
b
Expressed as mmol of carboxyl per g H-ESO-HEC (on dry mass basis)
c
Determined by Mw/Mn
Table 2. 1H and 13C NMR signals of H-ESO-HEC 1
13
H NMR
Signal
C NMR
δ (ppm)
Signal
δ (ppm)
-OH
2.10
-COOH
176
-(CH2)n-CH3
0.90
-CH3
15
-(CH2)n-CH3
1.30-1.50
-CH2-
27-35
CH2-O-CH2
2.80
CH2-O-CH2
83
CH-OH
3.20
CH-OH
80
AGU-H1
4.75
AGU-C1
101
AGU-H2
3.50
AGU-C2
74
AGU-H3
3.55
AGU-C3
70
AGU-H4
3.30
AGU-C4
76
AGU-H5
3.65
AGU-C5
73
AGU-H6
3.45
AGU-C6
62
Table 3. CMC, γcmc, KP and HLB value of samples Samples
CMC (g/L)
γcmc (mN/m)
KP (oC)
HLB value
HEC
—
54.68±1.20
—
—
H-ESO-Na
1.105
34.28±0.93
18
9.6-10.6
H-ESO-HEC-Na-I
1.053
26.33±0.56
39
9.6-10.6
H-ESO-HEC-Na-II
0.702
28.88±0.99
42
9.6-10.6
H-ESO-HEC-Na-III
0.514
27.83±0.61
45
9.6-10.6
H-ESO-HEC-Na-IV
0.402
26.37±0.50
52
9.6-10.6
H-ESO-HEC-Na-V
0.157
26.94±1.26
68
9.6-10.6
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Figure graphics Figure 1.
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Figure 2.
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Figure 3.
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Figure 4.
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Figure 5.
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Figure 6.
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Figure 7.
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Figure 8.
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Table of Contents Graphics (For Table of Contents only)
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