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Jun 22, 2017 - ylmethyl)phenyl)furan-2,5-dicarboxylate (EUFU-EP), was synthesized from two biobased green and low toxic compounds (2,5-...
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Bio-based Heat Resistant Epoxy Resin with Extremely High Biomass Content from 2,5-Furandicarboxylic Acid and Eugenol Jia-Tao Miao, Li Yuan, Qingbao Guan, Guozheng Liang, and Aijuan Gu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01222 • Publication Date (Web): 22 Jun 2017 Downloaded from http://pubs.acs.org on June 27, 2017

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1

Bio-based Heat Resistant Epoxy Resin with Extremely High Biomass

2

Content from 2,5-Furandicarboxylic Acid and Eugenol

3 4

Jia-Tao Miao, Li Yuan, Qingbao Guan, Guozheng Liang* and Aijuan Gu*

5

State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials,

6

Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application

7

Department of Materials Science and Engineering,

8

College of Chemistry, Chemical Engineering and Materials Science,

9

Soochow University, 199 Ren'Ai Road, Suzhou, 215123, China

10 11

Abstract

12

Preparing a bio-based (biomass-based) high performance epoxy resin with

13

extremely large biomass content is of great important for sustainable development.

14

Herein,

15

bis(2-methoxy-4-(oxiran-2-ylmethyl)phenyl)furan-2,5-dicarboxylate (EUFU-EP), was

16

synthesized

17

(2,5-furandicarboxylic acid and eugenol) and the biomass content of EUFU-EP is as

18

large as 93.3%. In addition, a new bio-based epoxy resin, EUFU-EP/MHHPA, was

19

prepared by using methyl hexahydrophthalic anhydride (MHHPA) as the curing agent

20

and 2-ethyl-4-methylimidazole as the curing accelerator. The curing reactivity and

21

integrated performances including thermal and mechanical properties as well as flame

22

retardancy of the cured resin were systematically researched, and compared with

a

new

from

epoxy

two

resin

bio-based

green

with

and

a

low

precise

toxic

structure,

compounds

* Corresponding author. Tel: +86 512 65880967. Fax: +86 512 65880089. E-mail address: E-mail address: [email protected] (Guozheng Liang), [email protected] (Aijuan Gu). . 1

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those of petrochemical resource-based epoxy resin (DGEBA/MHHPA) consisting of

24

commercial

25

2-ethyl-4-methylimidazole.

26

DGEBA/MHHPA have similar curing reactivity, but cured EUFU-EP/MHHPA resin

27

shows better thermal properties, rigidity and flame retardancy than cured

28

DGEBA/MHHPA resin. Specifically, the glass transition temperature (Tg) of

29

EUFU-EP/MHHPA resin is as high as 153.4 oC, the storage modulus at 50 oC

30

increases by 19.8%, meanwhile both peak heat release rate and total heat release

31

reduce by 19.0%. The nature behind these outstanding integrated performances is

32

attributed to the unique structure of EUFU-EP, which is not only rich in aromatic

33

structure, but also has furan ring. The especially large biomass content and

34

outstanding thermal, mechanical and flame retarding performances clearly show that

35

EUFU-EP resin has a great potential in actual applications.

diglycidyl

ether

of

Results

bisphenol

A

show

that

(DGEBA),

MHHPA

EUFU-EP/MHHPA

and and

36 37

Keywords: Biomass; Epoxy resin; Thermal property; Flame retardancy; Structure.

38 39 40

Introduction It is arguable that the petrochemical resources are indispensable; however, 1, 2

41

energy depletion becomes one of greatest challenges of the world today.

42

petrochemical resources, biomass which can translate into petrochemical resources

43

through hundreds of millions of years is characterized to be abundant, renewable, and

44

high annual output.3-7 In order to meet the challenge of energy crisis and the 2

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requirement of sustainable development, it is urgent to pay an increasing attention to

46

biomass resource.8-11

47

Thermosetting resins, strongly dependent on petroleum resources, have been key

48

and basic materials in industry since the birth of the first synthetic resin in 1872.12

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They play indispensable role from basic (chemical industry,13 coating

50

(aerospace,

51

occupies about 70% of the whole thermosetting resin market due to its outstanding

52

integrated performances.18 Note that more than 90% of epoxy resin is bisphenol A

53

epoxy resin (DGEBA),

54

epichlorohydrin in the presence of sodium hydroxide.17 Unfortunately, bisphenol A is

55

strongly dependent on petrochemical resources.

15

new energy,

16

18, 19

information

17

14

) to strategic

) fields. Among them, epoxy resin

which is synthesized from bisphenol A and

56

In recent years, attempts have been made to introduce some biomass-based

57

(bio-based) units into epoxy resins instead of petroleum-based units. Various

58

biomasses have been reported (such as vegetable oil,20 itaconic acid,21, 22 cardanol,1

59

rosin,23 eugenol,

60

raw materials in synthesizing bio-based epoxy resins, of which the biomass content of

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epoxy ranges from 40.1% to 84% as summarized in Table S1 in Supporting

62

Information.

6, 24, 25

2,5-furandicarboxylic acid (FDCA),26 lignin,7, 27 etc.) to act as

63

FDCA and eugenol, both of which are common renewable resources in nature,

64

have aroused worldwide concern in recent years due to their rigid aromatic structure.

65

FDCA is classified as the top ten green chemical by US Department of Energy.28

66

Eugenol, occupying about 80% of clove oil, is a renewable biomass material with low 3

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toxicity and relatively low cost. 29 FDCA and eugenol have been used for synthesizing

68

bio-based epoxy resins, respectively. Zhang et al. reported a eugenol-based epoxy

69

resin with a biomass content of 62.7%, and the glass transition temperature (Tg) of

70

epoxy resin cured with hexahydrophthalic anhydride was only 114 °C.25 Wang et al.

71

reported two kinds of eugenol-based epoxy resins which link eugenol molecules

72

together with biomass-free α,α-dichloro-p-xylene

73

respectively. The former (melting point, 124oC) cured with 4,4’-diaminodiphenyl

74

methane has a biomass content of 70.2% and a Tg value of 114.4 °C, while the latter

75

cured with 3,3’-diaminodiphenylsulfone has a higher biomass content of 80% and

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higher Tg (207 °C). Liu’s group prepared an epoxy resin based on FDCA, the Tg of the

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epoxy resin cured with methyl hexahydrophthalic anhydride (MHHPA) was 152 oC,

78

the flexural strength was 96 MPa and the biomass content was 65.2%.26 These works

79

have significantly promoted the use of eugenol and FDCA in the field of bio-based

80

epoxy resins. However, all synthesis routes of them use dichloromethane as solvent;

81

moreover, the biomass contents and integrated performances of above bio-based

82

epoxy monomers still need increase.

24

and cyanuric chloride

6

,

83

Herein, a unique bio-based epoxy resin monomer, bis(2-methoxy-4-(oxiran-2-

84

ylmethyl) phenyl)furan-2,5-dicarboxylate (EUFU-EP), with extremely large biomass

85

content (93.3%), high thermal and mechanical properties as well as good flame

86

retardancy was designed and synthesized through building a precise structure from

87

FDCA and eugenol. The curing behavior and relationships between structure and

88

properties of EUFU-EP/MHHPA resins were intensively studied and compared with 4

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its petrochemical resource based DGEBA counterpart.

90

Experiment section

91

Raw materials

92

Eugenol, 3-chloroperoxybenzoic acid (mCPBA, 85%) and MHHPA were

93

purchased from Energy Chemical, China. FDCA was bought from Sichuan Dagaote

94

Technology

95

triethylamine, sodium sulfite, sodium carbonate, tetrahydrofuran (THF), ethyl acetate,

96

N,N-dimethylformamide (DMF) and other reagents were obtained from Sinopharm

97

Chemical Reagent Co., Ltd, China. Diglycidyl ether of bisphenol A (DGEBA) used

98

herein has an epoxy value of 0.44 mol/100 g, which was got from Nantong Xingchen

99

Synthetic Material Co., Ltd, China.

100

Co.,

Ltd,

China.

Oxalyl

chloride,

2-ethyl-4-methylimidazolet,

Synthesis of furan-2,5-dicarbonyl dichloride (FDCDCl)

101

A mixture of FDCA (15.6 g, 100 mmol), THF (100 mL) and DMF (catalyst, 0.05

102

mL) was added into a 100 mL round-bottomed flask, oxalyl chloride (19.04 g, 150

103

mmol) was added dropwise to above suspension at 0 °C. The reaction mixture was

104

slowly heated and reacted at 25 °C for 3 h until the solid was completely dissolved.

105

Then the resultant solution was rotary evaporated to obtain a white solid (19.14 g,

106

yield: 99.2%), which is FDCDCl. 1H NMR (400 MHz, DMSO-D6) δ 7.31 (s, 2H)

107

(Figure S1 in Supplementary Information).

108

Synthesis of bis(4-allyl-2-methoxyphenyl) furan-2,5-dicarboxylate (EUFU)

109

Eugenol (16.4 g, 100 mmol) and triethylamine (16.9 mL, 120 mmol) were 5

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dissolved in ethyl acetate (200 mL) with stirring to get a solution B, into which a

111

solution of FDCDCl (50 mmol, 9.65 g) in ethyl acetate (100 mL) was added dropwise

112

at 0 °C within 20 min, followed by maintaining at 25 °C for 30 min. Then, the

113

reaction solution was filtered. After that, removing solvent through rotary evaporation,

114

washing with water and filtering to get white solid (20.5 g, yield: 91.4%), which was

115

EUFU. 1H NMR (400 MHz, CDCl3) δ 7.45 (s, 2H), 7.06 (d, J = 8.0 Hz, 2 H), 6.85 -

116

6.77 (m, 4H), 5.98 (m, 2H), 5.16 - 5.08 (m, 4H), 3.82 (s, 6H), 3.40 (d, J = 6.6 Hz, 4H).

117

13

118

122.59, 120.93, 119.98, 116.46, 113.06, 56.05, 40.30. HRMS (ESI+): m/z calcd for

119

[C26H24O7Na]+: 471.1414, found 471.1402. Anal. calcd for C26H24O7: C 69.63, H 5.39,

120

found: C 69.67, H 5.607.

121

Synthesis of EUFU-EP

C NMR (151 MHz, CDCl3) δ 156.07, 151.04, 146.82, 139.79, 137.37, 137.13,

122

mCPBA (12.2 g, 60 mmol) was slowly added into a solution consisting of EUFU

123

(8.97 g,20 mmol) and ethyl acetate (100 mL) at 0 °C, the reaction mixture was slowly

124

heated and reacted at 40 °C for 48 h. After that the resultant solution was filtered to

125

get the filtrate, which was then washed with 10% Na2SO3 solution, 5% NaHCO3

126

solution and deionized water, successively. The organic layer was dried with

127

anhydrous sodium sulfate, and ethyl acetate was rotary evaporated to give a yellow

128

solid. The solid was then washed with ethanol to give a white solid, coded as

129

EUFU-EP (6.10 g, yield: 63.5%). Melting point: 99.7 °C (differential scanning

130

calorimetry, DSC). 1H NMR (400 MHz, CDCl3) δ 7.47 (s, 2H), 7.09 (d, J = 8.0 Hz,

131

2H), 6.91 (s, 2H), 6.87 (d, J = 8.0 Hz, 2H), 3.84 (s, 6H), 3.20 – 3.14 (m, 2H), 2.88 (d, 6

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J = 5.3 Hz, 4H), 2.83 (t, J = 4.2 Hz, 2H), 2.60 – 2.54 (m, 2H). 13C NMR (151 MHz,

133

CDCl3) δ 155.97, 151.12, 146.76, 137.84, 137.05, 122.74, 121.33, 120.04, 113.51,

134

56.10, 52.46, 47.00, 38.86. HRMS (ESI+): m/z calcd for [C26H24O9Na]+: 503.1313,

135

found 503.1306. Anal. calcd for C26H24O9: C 65.00, H 5.04, found: C 64.71, H 5.176.

136

Preparation of cured resins

137

EUFU-EP and MHHPA with an equivalent molar ratio as well as

138

2-ethyl-4-methylimidazole (0.5 wt% of the total weight of EUFU-EP and MHHPA)

139

were mixed thoroughly at 80 oC for 30 min to get a clear liquid (prepolymer). The

140

prepolymer was then transferred to a preheated mold and degassed under vacuum at

141

80 oC for 30 min, followed by putting into an oven for curing using the procedure of

142

130 oC/2 h+150 oC/2 h+170 oC/2 h. After that, the mold was naturally cooled to room

143

temperature to obtain cured resin, coded as EUFU-EP/MHHPA.

144

Similarly,

EUFU-EP

145

DGEBA/MHHPA resin.

146

Characterizations

147

1

was

replaced

by

DGEBA

to

prepare

cured

H NMR spectra of FDCDCl, EUFU and EUFU-EP, 2-D HHCOSY spectra of

148

EUFU and EUFU-EP were recorded with a Bruker AVANCE III 400 MHz

149

superconducting magnetic resonance spectrometer (USA). 13C NMR spectra of EUFU

150

and EUFU-EP were recorded with an Agilent DD2-600 MHz spectrometer (USA).

151

CDCl3 and tetramethylsilane were applied as the solvent and internal standard,

152

respectively. 7

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153 154 155 156 157 158

Fourier transform infrared (FTIR) spectra were obtained using a Bruker a Vertex 70 spectrometer (USA) over the wavenumber ranging from 600 to 4000 cm-1. High-resolution mass spectra (HRMS) were tested on a Bruker UltiMate 3000 high performance liquid chromatography (HPLC) system (Germany). The elemental analysis (C and H) was performed on a Vario EL III elemental analyzer (Germany).

159

DSC curves were recorded on a TA instrument Q200 (USA) under a nitrogen

160

atmosphere with a flowing rate of 50 mL min-1. Each sample was weighed and sealed

161

in an aluminum crucible, and heated from room temperature to 250 oC at a heating

162

rate of 5, 10, 15 or 20 oC min-1.

163 164

Density was measured on a Shanghai Sunny Hengping FA1104J electronic balance with density device (China).

165

Dynamic mechanical analyses (DMA) were performed using TA DMA Q800

166

apparatus (USA) by multi-frequency-strain model in a single cantilever clamp at a

167

heating rate of 3 oC min-1. The tests were performed at a frequency of 1.0 Hz, a

168

deflection amplitude of oscillation of 20 µm, and a poisson’s ratio of 0.44. The

169

dimensions of specimen were (35 ± 0.02) mm× (13 ± 0.02) mm× (3 ± 0.02) mm. Tg is

170

regarded as the peak temperature of the tanδ-temperature curve.30

171

Flexural strengths were measured according to Chinese standard GB2570-95

172

using an electronic universal testing machine (SUST, Zhuhai, China) at a speed of 2

173

mm min-1.

174

Thermogravimetric (TG) analyses were performed on a TA Discovery TGA

175

Instrument (USA) under a nitrogen atmosphere (10 mL min-1) with a heating rate of 8

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10 oC min-1.

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Micro-combustion calorimetery (MCC) was performed on a Govmark MCC-2

178

microscale combustibility calorimeter (USA). 5 mg sample was heated to 700 oC at a

179

heating rate of 60 oC min-1 in a mixed stream of oxygen and nitrogen flowing at 21

180

and 79 cm3 min-1, respectively.

181

Thermogravimetric analysis infrared (TG-IR) spectra were recorded using a

182

Netzsch TGA F1 thermogravimetric analyzer (Germany) that was interfaced to a

183

Bruker

184

spectrophotometer (Germany). Ten milligrams of a sample was put in an alumina

185

crucible and heated from 30 to 800 oC with a heating rate of 10 oC min-1 under a

186

nitrogen atmosphere.

187

Results and discussion

188

Design, synthesis and characterization of EUFU-EP

189

TENSOR

27

fourier

transform

infrared

spectroscopy

It is well known that there are two methods to synthesize epoxy resin.

(FTIR)

22, 31, 32

190

Taking DGEBA as the example, the first synthesis method (Method I) is derived from

191

bisphenol A and epichlorohydrin under sodium hydroxide (Figure S2a in

192

Supplementary Information).33 Note that this method produces complex oligomers but

193

not epoxy resin monomer with precise structure. Typically DGEBA monomers are

194

marketed with average repeat unit (n) in the range of 0.03−10. 18 In addition, the

195

obtained oligomers are hardly purified and separated. Obviously, this is not conducive

196

to control structure and performances of epoxy resin. The second method (Method II)

197

for synthesizing DGEBA contains two steps. An intermediate (allyl ether compound) 9

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198

from the reaction between bisphenol A and 3-bromopropene with the aid of sodium

199

hydroxide was synthesized, and then the double bond of allyl group is oxidized by an

200

oxidizing agent to obtain an epoxy resin monomer (Figure S2b in Supplementary

201

Information).

202

monomer with precise structure. However, when Method II is used to synthesize

203

bio-based

204

petrochemical resources will reduce the biomass content of epoxy monomer to some

205

extent.

34

Different from Method I, Method II can synthesize an epoxy

epoxy

monomer,

the

reactant

(3-bromopropene)

obtained

from

206

On the other hand, there are two major problems of bisphenol A, besides its

207

dependence on the petrochemical resources, bisphenol A has similar structure with

208

estrogen, which will reduce fertility and increase the risk of developing cancers and

209

other diseases.35,

210

bisphenol A-based materials for packing infant formula,37 and the demand for

211

bisphenol A-free products is booming. Therefore, derived from less toxic raw

212

materials, a new bio-based epoxy monomer with precise structure and extremely large

213

biomass content should be designed and synthesized.

36

The US Federal Drug Administration has banned the use of

214

Figure 1 illustrates the route to synthesize such bio-based epoxy monomer,

215

EUFU-EP, with precise structure and extremely large biomass content. Specifically,

216

eugenol with allyl group itself is taken as the reactant, so it is not necessary to use

217

bromopropene anymore, endowing EUFU-EP with very large biomass content

218

(93.3%). The specific route is composed of three steps. First, FDCDCl was obtained

219

from acylation of FDCA with oxalyl chloride in the presence of catalytic DMF; FDCA 10

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will be fully converted to FDCDCl and directly used for the next step without

221

purification. Second, triethylamine was used as base, FDCDCl and eugenol were

222

esterified to produce intermediate (EUFU) with a high yield (91.4%). Third, the target

223

product EUFU-EP was obtained by oxidizing allyl group in EUFU by mCPBA; the

224

yield of this step is 63.5%, and it was not necessary to purify EUFU-EP by column

225

chromatography, showing great potential for large-scale production. As no bisphenol

226

structure existed in the target product (EUFU-EP); moreover no bisphenol structure

227

was used and formed during the whole synthesis process, so EUFU-EP is a healthier

228

substitute compared with DGEBA.

229

230 231

Figure 1. Synthesis of EUFU-EP

232 233

Figure 2 shows 1H NMR spectra of EUFU and EUFU-EP. In the spectrum of

234

EUFU, the characteristic peaks at 5.98 ppm (Hg) and 5.08-5.16 ppm (Hh, Hi)

235

correspond to protons on double bond of allyl in EUFU, the characteristic peaks at

236

3.40 ppm (Hf), 3.82 ppm (He), and 7.45 ppm (Ha) represent protons on methylene

237

group of allyl adjacent to the double bond, methoxy group and furan ring, respectively.

238

In the spectrum of EUPU-EP, the characteristic peaks of proton on epoxy group are 11

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239

observed, such as 2.54-2.60 ppm (Hi’), 2.83 ppm (Hh’) and 3.14-3.20 ppm (Hh’), while

240

all peaks of protons (Hg, Hh and Hi) on double bond are not found. Other peaks in the

241

spectrum of EUFU-EP are similar as those of protons of EUFU, indicating that double

242

bonds of allyl groups in EUFU have been successfully oxidized to epoxy groups.

243

These assignments of protons have been also confirmed by the 2-D HHCOSY NMR

244

spectra (Figure S3 in Supplementary Information).

245

246

247

Figure 2. 1H NMR spectra of EUFU (top) and EUFU-EP (bottom)

248 249

Above statement is further confirmed by

13

C NMR spectra of EUFU and

250

EUFU-EP shown in Figure 3. The characteristic peaks at 139.79 and 116.46 ppm in

251

the spectrum of EUFU indicate C12 and C13 on allyl groups, respectively. These peaks

252

do not appear in the spectrum of EUFU-EP, instead, characteristic peaks representing

253

carbon atoms on epoxy groups appear at 52.46 ppm (C12’) and 47.00 ppm (C13’), also

254

proving that double bonds of allyl groups in EUFU have been successfully oxidized. 12

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255 256

Figure 3. 13C NMR spectra of EUFU (top) and EUFU-EP (bottom)

257 258

FTIR spectra of EUFU and EUFU-EP are shown in Figure S4 (in Supplementary

259

Information). The characteristic peak standing for C=C bonds of EUFU at 1639 cm-1

260

disappears. Instead, the characteristic peak standing for the oxirane rings of EUFU-EP

261

at 930 cm-1 appears, further proving that double bonds of allyl groups in EUFU have

262

been successfully oxidized.

263

In addition, the HRMS spectrum of EUFU-EP (Figure S5 in Supplementary

264

Information) shows that the experimental [M+Na+] is 503.1306, which is consistent

265

with the theoretical value (503.1313). The DSC curve of EUFU-EP (Figure S6 in

266

Supplementary Information) shows a clear endothermic melting peak at 99.7 oC.

267

Above characterizations fully prove that a unique bio-based epoxy resin with

268

precise structure has been facilely synthesized, its theoretical molecular weight is

269

480.47, and the epoxy value is 0.416 mol/100 g. 13

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Curing behavior and aggregation structure of EUFU-EP/MHHPA

271

Figure 4a shows DSC curves of EUFU-EP/MHHPA and DGEBA/MHHPA

272

prepolymers at different heating rates. Each curve displays a single exothermic peak

273

corresponding to the ring-opening reaction between epoxy and acid anhydride. From

274

fitting curves of heating rate vs. exothermic peak temperature of prepolymers (Figure

275

4b), the actual peak temperature (142.1 oC) of EUFU-EP/MHHPA is found to be

276

slightly higher than that of DGEBA/MHHPA (139.6 oC). At the same time, according

277

to Kissinger equation (Equation 1), dynamic curing parameters of prepolymers were

278

calculated. It is found that EUFU-EP/MHHPA has higher activation energy (71.15 kJ

279

mol-1) than DGEBA/MHHPA (61.21 kJ mol-1), so the former has lower reaction

280

activity than the latter. This is because epoxy groups of DGEBA connect with oxygen

281

atoms, increasing the polarization degree of epoxy groups due to the inductive effect,

282

and thus is more conducive to the ring opening reaction of epoxy groups.24

283

 β   AR  E ln  2  = ln  −  E  RTP  TP 

284

where Tp is the peak temperature, β is the heating rate, E is the activation energy of

285

the curing reaction, A is the pre-exponential factor, and R is the universal constant

286

(8.314 J mol-1 K-1).

(1)

287

EUFU-EP was then cured by MHHPA using the curing procedure of 130 oC/2

288

h+150 oC/2 h+170 oC/2 h. In order to make sure that the samples were fully cured

289

under this condition,

290

EUFU-EP/MHHPA resin. As shown in Figure S7 and S8 in Supplementary

291

Information, there is no exothermic peak in DSC curve, and no characteristic peak of

292

epoxy groups in FTIR spectra, verifying that EUFU-EP/MHHPA resin has been

DSC and FTIR techniques were

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used for cured

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293

completely crosslinked.

294

295 296

Figure 4. DSC thermograms (a) and fitting curves of exothermic peak temperature vs.

297

heating rate (b) of EUFU-EP/MHHPA and DGEBA/MHHPA prepolymers 15

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298

Crosslinking density is an important index for characterizing the aggregation

299

structure of thermosetting resins,38 which is often calculated according to the classical

300

rubbery elasticity theory as shown in Equation 2.26 E'=3υeRT

301

(2)

302

where E’ is the storage modulus of the thermosetting resin in the rubbery plateau

303

region, R is the universal constant, and T is the temperature at which the storage

304

modulus is minimum.30

305

Crosslinking densities of EUFU-EP/MHHPA and DGEBA/MHHPA resins are

306

found to be 1373 and 2081 mol m-3, respectively. These results are attributed to the

307

fact that EUFU-EP has higher molecular weight, smaller epoxy value and lower

308

reactivity than DGEBA.

309

310

Thermomechanical properties

311

DMA thermograms of cured EUFU-EP/MHHPA and DGEBA/MHHPA resins

312

are shown in Figure 5. It can be seen that EUFU-EP/MHHPA has higher storage

313

modulus (E’) at 50 oC (2229 MPa) than DGEBA/MHHPA, it is expected because E’

314

in the glassy state is affected synthetically by chemical structure and chain packing. It

315

is well known that the use of furan building block usually increases the stiffness of the

316

resins, 39,40 while higher density

317

packing, both of which are good for increasing E’. These two factors exist in

318

EUFU-EP/MHHPA resin. Specifically, on one hand, EUFU-EP/MHHPA resin has

319

rigid rod-like aromatic ester and furan structures. On the other hand,

27

and hydrogen bonding

27

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result in a greater chain

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320

EUFU-EP/MHHPA has higher density (1.25 g/cm3) than DGEBA/MHHPA resin (1.18

321

g/cm3) reflecting a greater chain packing; moreover, the hydrogen and oxygen atoms

322

of methoxy substituents on the aromatic rings have the ability to form hydrogen bond

323

with carbonyl of anhydride and methylene resulting from the epoxy-anhydride

324

reaction, respectively.41

325

326 327

Figure 5. DMA thermograms for storage modulus and Tan delta against temperature

328

of EUFU-EP/MHHPA and DGEBA/MHHPA resins

329 330

Generally, Tg is regarded as the peak temperature of the tanδ-temperature

331

curve.30, 42 EUFU-EP/MHHPA has higher Tg (153.4 oC) than DGEBA/MHHPA (144.1

332

o

333

Specifically, an increased crosslinking density and a structure with chemical bonds

334

that are hard to rotate can lead to a higher Tg. Compared with DGEBA/MHHPA,

335

EUFU-EP/MHHPA has lower crosslinking density, tending to get reduced Tg; while

C). Tg depends on combined effects of chemical structure and aggregation structure.

17

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336

EUFU-EP/MHHPA has rigid rod-like aromatic ester and furan structures that are very

337

difficult to rotate. The combined effect of above opposite and positive factors

338

determine the final Tg. Figure 5 suggests that the positive factor plays the domain

339

influence.

340

Note that for previously reported bio-based epoxy resins cured with MHHPA,

341

their Tg values are within 101.9-152 oC (Table S1 in Supplementary Information),

342

meaning that EUFU-EP/MHHPA reported herein shows high Tg that falls in the high

343

end range of resins reported, this is very attractive because Tg is the upper temperature

344

of service for thermosetting resins,43 that is, EUFU-EP has the biggest ability of

345

applying in strict environment requiring high temperature among all bio-based epoxy

346

resins so far.

347

348

Mechanical performance

349

Figure 6 gives flexural properties of EUFU-EP/MHHPA and DGEBA/MHHPA

350

resins. Analogical with storage modulus in the glassy state, flexural modulus reflects

351

the rigidity of resins. The flexural modulus of EUFU-EP/MHHPA is 3.33 GPa, higher

352

than that of DGEBA/MHHPA (3.05 GPa), this is consistent with the storage moduli in

353

the glassy state.

354

The flexural strength is usually used to characterize overall mechanical

355

properties of a material because the flexural loading contains multiple types of

356

loadings

357

EUFU-EP/MHHPA has slightly lower flexural strength than DGEBA/MHHPA, the

such

as

bending,

stretching,

compression,

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etc.

44

Although

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358

flexural strength of EUFU-EP/MHHPA is as high as 129.2 MPa, comparable with that

359

of reported epoxy resin with high mechanical properties,45 and is at a high level in

360

bio-based epoxy resins reported (Table S1 in Supplementary Information), so

361

EUFU-EP/MHHPA still has excellent mechanical properties.

362

363 364

Figure 6. Flexural moduli and strengths of EUFU-EP/MHHPA and DGEBA/MHHPA

365

resins

366

Flammability and mechanism of cured resins

367

Figure 7 shows curves of heat release rate (HRR) versus temperature, the

368

characteristic parameters including have longer time-to-ignition (TTI), peak heat

369

release rate (PHRR) and total heat release (THR) temperature are listed in this figure.

370

Different from about 70 s shortened TTI in eugenol-based epoxy resins

371

EUFU-EP/MHHPA resin has similar TTI as DGEBA/MHHPA; in addition,

372

EUFU-EP/MHHPA has significantly reduced PHRR and THR compared with

373

DGEBA/MHHPA,

and

the

reduction

is

about

19.0%,

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indicating

6, 24

,

that

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374

EUFU-EP/MHHPA has better flame retardancy than DGEBA/MHHPA. This

375

attractive result is attributed to the fact that the char yield (Yc) at 800 oC of

376

EUFU-EP/MHHPA resin is 10.9 wt%, about 1.7 times of that of DGEBA/MHHPA

377

(Figure 8). This is benefited from the highly compact aromatic rings of EUFU-EP,

378

which can promote carbonation,6 resulting in more residual carbon, and thus

379

displaying condensed phase mechanism of flame retardation.

380

381 382

Figure 7. Heat release rate-time curves from MCC tests for cured EUFU-EP/MHHPA

383

and DGEBA/MHHPA resins

384

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385 386

Figure 8. TGA curves of cured EUFU-EP/MHHPA and DGEBA/MHHPA resins

387 388

To further investigate the flame retarding mechanism, TG-IR technology was

389

used to directly detect components in the gas phase during degradation process.

390

Figure 9 shows three-dimensional IR spectra of pyrolysis products for

391

EUFU-EP/MHHPA and DGEBA/MHHPA resins throughout the whole thermal

392

degradation process. Since the same size, morphology and weight were taken in tests,

393

the intensity of the absorption peak in the three-dimensional spectra can reflect the

394

amounts of degradation products. Figure 9 shows that the absorption peaks of

395

EUFU-EP/MHHPA resin are much lower than those of DGEBA/MHHPA resin,

396

proving that EUFU-EP /MHHPA resin releases much less pyrolysis products than

397

DGEBA/MHHPA resin.

398

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399 400

Figure 9. Three-dimensional FTIR spectra of pyrolysis products of cured

401

EUFU-EP/MHHPA and DGEBA/MHHPA resins

402 403

Figure 10 shows FTIR spectra of pyrolysis products of EUFU-EP/MHHPA and

404

DGEBA/MHHPA at the maximum decomposition rates. It can be seen that most

405

pyrolysis products of DGEBA/MHHPA are organic combustible gases, including

406

various hydrocarbons (2968 cm-1), carbonyl compounds (1807 cm-1), aromatic

407

compounds (1604 and 1510 cm-1) and C–O–C (1221 and 1176 cm-1);46, 47 while a

408

small amount of water (3656 cm-1), CO2 (2351, 2308 and 669 cm-1) and CO (2180

409

cm-1) were also found in pyrolysis products. Differently, pyrolysis products of

410

EUFU-EP/MHHPA show less organic combustible gases (various hydrocarbons,

411

carbonyl compounds and aromatic compounds) and more none-flammable CO2, this

412

is beneficial to retard further combustion, and thus EUFU-EP/MHHPA resin has a

413

better flame retardancy.

414

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415 416

Figure 10. FTIR spectra of pyrolysis products of cured EUFU-EP/MHHPA and

417

DGEBA/MHHPA resins at their maximum decomposition rates

418

419

Conclusion

420

Starting from green bio-based FDCA and eugenol, a new epoxy resin

421

(EUFU-EP), of which the biomass content is as high as 93.3%, was successively

422

synthesized using an eco-friendly route. Compared with DGEBA/MHHPA,

423

EUFU-EP/MHHPA expresses 9 °C and 19.9% enhancement in Tg and storage

424

modulus at 50 oC, respectively, as well as considerably high mechanical properties

425

and better flame retardancy. Abundant amounts of aromatic and furan structures in the

426

main chain endow cured EUFU-EP resin with much better integrated performances

427

than petrochemical resource-based DGEBA resin. Due to these attractive properties as

428

well as the advantages of non-toxic and renewably source, EUFU-EP holds a great

429

potential as a sustainable alternative for DGEBA. 23

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430

Acknowledgements

431

We thank National Natural Science Foundation of China (21274104), the Priority

432

Academic Program Development of Jiangsu Higher Education Institutions (PAPD),

433

China, and Scientific Innovation Research of College Graduate in Jiangsu Province of

434

China (KYLX16_0120), for financially supporting this project.

435 436

Supplementary data

437

Figure S1 gives 1H NMR spectra of FDCA and FDCDCl, Figure S2 shows synthesis

438

routes of commercial DGEBA, Figure S3 gives 2-D HHCOSY NMR spectra of

439

EUFU and EUFU-EP, Figure S4 gives FTIR spectra of EUFU and EUFU-EP. Figure

440

S5 gives the high-resolution mass spectrum (HRMS) of EUFU-EP, Figure S6 gives

441

DSC curve of EUFU-EP, Figure S7 gives DSC curve of cured EUFU-EP/MHHPA

442

resin, Figure S8 gives FTIR spectra of EUFU and EUFU-EP/MHHPA resin. Table S1

443

summarizes biomass contents and integrated performances of bio-based epoxy resins

444

in literature.

445 446

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447

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Ester Resin with Significantly Reduced Postcuring Temperature While Improved Toughness,

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Rigidity, Thermal and Dielectric Properties Based on Manganese-Schiff Base Hybridized

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Flame

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Graphene/Epoxy

Resin

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Behavior of Flame Retardant Unsaturated Polyester Resin Modified with A Reactive Phosphorus

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Containing Monomer. RSC Adv. 2016, 6 (55), 49633-49642. DOI: 10.1039/C6RA06544A.

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For Table of Contents Use Only

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Brief synopsis

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Novel heat-resistant epoxy resin with precise structure and extremely

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high biomass content was prepared from renewable 2,5-furandicarboxylic

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acid and eugenol.

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Figure 1. Synthesis of EUFU-EP 50x18mm (300 x 300 DPI)

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Figure 2. 1H NMR spectra of EUFU (top) and EUFU-EP (bottom) 66x55mm (300 x 300 DPI)

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Figure 3.

13

C NMR spectra of EUFU (top) and EUFU-EP (bottom) 75x71mm (300 x 300 DPI)

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Figure 4. DSC thermograms (a) and fitting curves of exothermic peak temperature vs. heating rate (b) of EUFU-EP/MHHPA and DGEBA/MHHPA prepolymers 119x176mm (300 x 300 DPI)

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Figure 5. DMA thermograms for storage modulus and Tan delta against temperature of EUFU-EP/MHHPA and DGEBA/MHHPA resins 55x37mm (300 x 300 DPI)

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Figure 6. Flexural moduli and strengths of EUFU-EP/MHHPA and DGEBA/MHHPA resins 50x31mm (300 x 300 DPI)

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Figure 7. Heat release rate-time curves from MCC tests for cured EUFU-EP/MHHPA and DGEBA/MHHPA resins 64x51mm (300 x 300 DPI)

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Figure 8. TGA curves of cured EUFU-EP/MHHPA and DGEBA/MHHPA resins 59x44mm (300 x 300 DPI)

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Figure 9. Three-dimensional FTIR spectra of pyrolysis products of cured EUFU-EP/MHHPA and DGEBA/MHHPA resins 57x22mm (300 x 300 DPI)

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Figure 10. FTIR spectra of pyrolysis products of cured EUFU-EP/MHHPA and DGEBA/MHHPA resins at their maximum decomposition rates 63x49mm (300 x 300 DPI)

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Graphic Abstract 35x14mm (300 x 300 DPI)

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