Starch Polymer ... - ACS Publications

Subscriber access provided by Gothenburg University Library

Article

Graphene Oxide Filled Lignin/Starch Polymer bionanocomposite: Structural, Physical and Mechanical studies. Meryem Aqlil, Annie Moussemba Nzenguet, Younes Essamlali, Asmae Snik, Mohamed Larzek, and Mohamed Zahouily J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04155 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 9, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40

Journal of Agricultural and Food Chemistry

1

Graphene Oxide Filled Lignin/Starch Polymer bio-

2

nanocomposite: Structural, Physical and

3

Mechanical studies

4

Meryem Aqlil1, Annie Moussemba Nzenguet1, Younes Essamlali1,2, Asmae Snik1,

5

Mohamed Larzek3 and Mohamed Zahouily1,2*

6 7 8 9 10 11 12 13

1

Laboratoire de Matériaux, Catalyse et Valorisation des Ressources Naturelles (MaCaVa), URAC 24, FST Mohammedia B. P. 146, 20650, Université Hassan II Casablanca Morocco. 2 MAScIRFoundation, Nanotechnologie, VARENA Center, Rabat Design, Rue Mohamed El Jazouli, Madinat El Irfane 10100-Rabat, Morocco ; 3 OLAC : Omnium de l’anti corrosion, ZI Tit Melil Casablanca-Morocco. * Correspondence: [email protected] ; Tel. +212661416359

14

1 ACS Paragon Plus Environment


Page 2 of 40

15

Abstract

16

In this study, graphene oxide(GO)was investigated as a potential nano-reinforcing agent in

17

starch/lignin (ST/L) biopolymer matrix. Bio-nanocomposite films based on ST/L blend matrix

18

and GO were prepared by solution casting technique of the corresponding film forming

19

solution. The structure, morphologies and properties of bio-nanocomposite films were

20

characterized by FTIR, thermal gravimetric analysis (TGA), Ultraviolet-visible (UV-Vis),

21

SEM and tensile tests. The experimental results showed that contents of GO have a significant

22

influence on the mechanical properties of the produced films. The results revealed that the

23

interfacial interaction formed in the bio-nanocomposite films improved the compatibility

24

between GO fillers and ST/L matrix. The addition of GO also reduced moisture uptake (Mu)

25

and water vapor permeability of ST/L blend films. In addition, TGA showed that the thermal

26

stability of bio-nanocomposite films was better than that of neat starch film. These findings

27

confirmed the effectiveness of the proposed approach to produce biodegradable films with

28

enhanced properties, which may be used in packaging applications.

29

Starch;

Lignin;

30

Keywords:

31

Physicochemical properties.

Graphene

oxide;

Bio-nanocomposite;

32 33 34 35


Interaction;

Page 3 of 40


36

1. Introduction

37

Due to the environmental impact caused by petrochemical-based synthetic polymers, natural

38

polymers have received tremendous attention in the last few decades because of their

39

potential to substitute the current synthetic polymers1 owing to their non-toxicity,

40

biodegradability and biocompatibility.2 Apart from their environmental benefits, bio-based

41

polymers exhibit other advantages such as low cost, non-dependence on petroleum sources

42

and availability from renewable resources. Moreover, natural bio-based polymers are easily

43

biodegradable within a short period of time and solve the waste disposal problems generated

44

by using non-biodegradable polymers.3,4 Among the many candidates of natural

45

biodegradable polymers, starch and lignin have been widely studied for the fabrication of

46

biodegradable films owing to their renewability, biodegradability and availability at low cost.

47

Starch is one of the most commonly available natural polysaccharides obtained from a great

48

variety of crops.5 It has been accepted as a good alternative for the production of

49

biodegradable plastics and has high potential for replacing current synthetic polymers.6-8

50

Starch has been widely used in several food and non-food applications, particularly in

51

agriculture, alimentary, medicine, and packaging industries.9-12 Unfortunately, thermoplastic

52

starch suffers from many drawbacks related to its water sensitivity and poor mechanical

53

properties.13,14 To overcome these limitations, many approaches were suggested in literature.

54

One of the most effective methods for the development of new and inexpensive biodegradable

55

materials with improved properties is to blend starch with either synthetic or natural

56

polymers15-18 or to incorporate a nanoscale reinforcing materials into the starch based

57

polymeric matrix.19-22 Another, approach that has been widely studied consists of the use a

58

chemically modified starch by either oxidation or carboxymethylation methods.23-25

59

Lignin, a natural biopolymer extracted from sugarcane bagasse, is the second most abundant

60

natural polymer after cellulose, it has been widely used in biodegradable polymers



61

manufacturing owing to its intrinsic properties such as high degree of crosslinking between

62

the units, hydrophobic nature, amorphous structure and three-dimensional structure.26,27 The

63

abundance of carbonyl and carboxylic groups, phenolic and aliphatic hydroxyl groups confer

64

to lignin a good ability to establish a strong interfacial interaction with other polymers making

65

this natural biopolymer a suitable candidate for blending polymers. Many researchers put

66

forward the use of lignin to blend with various synthetic polymers, either in their native state

67

or after compatibilization, such as poly(vinyl alcohol), poly(ethylene oxide) and poly(lactic

68

acid).28,29 Blending starch with lignin is an appealing approach since no compatibilization is

69

required. It is well known that the addition of lignin within starch matrix significantly

70

improves the physical and the chemical properties of starch.30-33 Baumberger et al.34-36

71

reported that blending lignin extracted either from traditional or novel pulping processes

72

within starch matrix resulted in an important improvement of the performances of starch

73

films. Besides, a significant reduction of the water solubility and water content of

74

starch/lignin film has been observed.36 Moreover, it has been previously shown that the

75

incorporation of lignin into starch can also reduce the water permeability and increases the

76

thermal stability and tensile strength of the resulted ST/L blend film.37-40 However, the

77

properties of the resulting ST/L film are highly dependent on the origin of the lignin and also

78

on the adopted extraction process. Most of the interest in developing low cost biodegradable

79

plastics is due to their wide spectrum of application which includes packaging and consumer

80

products. The major applications for starch-lignin bio-nanocomposites would be packaging

81

containers for single or short-term use, as naturally biodegradable alternatives to conventional

82

synthetic polymers, so they have great potential to be used as fresh food packaging.

83

Recently, much more attentions have been paid to the development of the new materials with

84

specific properties by incorporation of nanometric reinforcements in polymeric matrix.41,42

85

This method has been considered as an effective strategy to improve the physicochemical


Page 4 of 40

Page 5 of 40


86

properties of the polymeric matrix.43,44 The synergic effect between the nanosized filler and

87

polymer resulted in a significant improvement of properties of obtained nanocomposites.

88

Various types of nanofillers organic or inorganic are used as an effective nano-reinforcements

89

for many biopolymer matrix, like carbon nanotubes and nanofibers,45 GO,46 nanoclay47 and

90

cellulose nanocrystals,48 etc. Among the family of nanofillers, GO has attracted a great deal of

91

interest and has been widely used as a nano-reinforcement in polymer composite materials.

92

GO has been widely used in combination with different biopolymers to design new bio-

93

nanocomposites with improved mechanical, thermal, electrical, as well as, gas-, and water

94

vapor-barrier properties. In addition, high surface area, high aspect ratio, large number of

95

functional groups, and high strength of GO allow it to establish strong interfacial interactions

96

between the filler and the polymeric matrix. Moreover, the functional groups, such as

97

carboxyl, amino, or hydroxyl groups, contained in biopolymers matrix leads to a very

98

efficient interaction with the functional groups on GO.49,50 GO has the ability to form a strong

99

physical interaction within the polymeric matrix since it contains several oxygen-containing

100

functional groups, such as hydroxyl (OH) and carbonyl groups (-C=O).51,52 It has been widely

101

used to improve the thermal stability, electrical and mechanical properties of several

102

polymers.53The aim of the present work was to study the preparation of graphene oxide (GO)

103

reinforced ST/L based polymer blends. GO nanosheets were characterized using X ray

104

diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM),

105

high resolution-transmission electron microscopy (HR-TEM) and atomic force microscopy

106

(AFM). The influence of incorporation of increasing amount of GO on the structural,

107

morphological and mechanical properties as well as thermal stability of the ST/L based bio-

108

nanocomposite films was studied. Furthermore, the water swelling, hydrolytic degradation

109

and moisture absorption of the prepared bio-nanocomposites were also investigated. The



110

fundamental structure-property relationship of GO-based starch/lignin bio-nanocomposites

111

was also investigated and discussed.

112

2. Materials and methods

113

2.1. Materials

114

The sugarcane bagasse (SCB) was provided from COSUMAR Group, company in south

115

Morocco. The moisture content of the sugarcane bagasse fibers was about 7%. Wheat starch

116

and graphite powder (≤ 20 µm, 99.99%)were purchased from VWR International and Sigma-

117

Aldrich, respectively. Analytical grade chemicals used for lignin extraction and graphite

118

oxidation were purchased from Sigma-Aldrich and were used as received.

119

2.2. Lignin Extraction

120

Lignin was extracted from sugarcane bagasse by alkaline hydrolysis. Firstly, the SCB fibers

121

were ground and sieved (150 µm) to remove the fine powder and the small particles. The

122

ground fibers were repeatedly washed with hot water for 2 hours at 60°C and then filtered.

123

After complete washing, the obtained residue was digested with alkali solution (15wt%

124

NaOH). The solution was then filtered and the filtrate, lignin solution, was acidified with 5N

125

H2SO4 until pH = 2 was reached. The obtained precipitate was recovered by centrifugation,

126

washed with distilled water, dried in a hot desiccator at 60°C for a complete removal of water

127

and finally ground into a uniform powder.

128

2.3. Synthesis of graphene oxide

129

Graphene oxide was prepared from natural graphite according to the Hummers method.54 In a

130

typical procedure, 1 g of graphite powder and 1g of sodium nitrate were firstly mixed together

131

until complete homogenization. Afterward, 30 ml of sulfuric acid (98%) was added and the

132

mixture was stirred for 30 minutes in an ice-bath. Next, 3 g of KMnO4 (99%) was slowly

133

added in a controlled manner to avoid the increase of the temperature (˂20°C). The flask was

134

then removed and heated in an oil bath at 40°C under constant magnetic stirring for 2hours.


Page 6 of 40

Page 7 of 40


135

Afterward, 50 ml of distilled water was slowly added, which generate an increase in the

136

temperature to 98°C. The mixture was maintained at this temperature under continuous

137

stirring for 15 minutes. Subsequently, 12 ml of H2O2 solution (30% v/v) was added to the

138

reaction mixture under vigorous stirring for 10 min. Finally, the resulting yellow cake was

139

cooled until room temperature diluted with 260 mL of distilled water and centrifuged. The

140

obtained precipitate was washed several times with distilled water and dried at 60°C during

141

72 hours. Appropriate amounts of the as-prepared graphite oxide (0.3, 0.5 and 0.7wt% with

142

respect to ST/L weight) were dispersed in 20 mL of distilled water and sonicated for

143

to make a homogeneous brown dispersion of graphene oxide nanosheets.

144

2.4. Bio-nanocomposite film processing

145

The preparation ST/L-GO bio-nanocomposites films were carried out in two consecutive

146

steps. Firstly, 0.5 g of lignin was dissolved in 50 mL of distilled water with constant stirring

147

within 12 hours at 25°C followed by sonication for 1 hour until complete dissolution.

148

Separately,

149

2.5 g of wheat starch and 0.75 g of glycerol, as a plasticizer, were dissolved in 46.25 mL of

150

distilled water at 95°C during 90 min under vigorous stirring. The starch solution was cooled

151

until room temperature while keeping a constant stirring, and then it was sonicated for

152

15 minutes to ensure the complete homogenization. The ST/L film-forming solution was

153

prepared by mixing the starch and lignin solutions under vigorous magnetic stirring for 1 h at

154

25°C until the formation of a homogeneous solution (Fig. 1). In the second step, a

155

predetermined amount of GO suspension was slowly added to the ST/L blend and the mixture

156

was sonicated during 30 minutes followed by vigorous magnetic stirring for 6 hours until the

157

formation of a homogeneous dispersion. The GO loading levels were 0.3, 0.5 and 0.7wt%

158

based on dry ST/L blend. Subsequently, the ST/L-GO film-forming solutions (Figure 1) were

159

cast onto plastic disk and left to cure at room temperature for complete water evaporation.


3 hours


160

After that, the ST/L-GO bio-nanocomposites were dried at 60°C for 6 hours to obtain dry

161

films. Pure ST/L blend and neat starch films were prepared according to the same procedure.

162

The films were coded as ST, ST/L, ST/L-0.3, ST/L-0.5 and ST/L-0.7, where the number

163

stands for the GO loadings.

164

3. Characterization techniques

165

3.1. Characterization of graphene oxide

166

X-ray diffraction (XRD) patterns were recorded at room temperature on a Bruker D8

167

Discover diffractometer using Cu-Kα radiation (λ = 1.5438 Å). The samples were finely

168

grounded before being analyzed. Fourier transform infrared spectroscopy (FTIR)

169

measurements were performed on anAffinity-1S SHIMADZU spectrometer fitted with a

170

Golden Gate single reflection ATR accessory in the range of 4000 to 400 cm−1 with a

171

resolution of 16 cm-1and an accumulation of 42 scans. Thermogravimetric analyses (TGA)

172

were conducted under air gas using a TGA-Q500 (TA Instruments) apparatus at a heating rate

173

of 10 °C/min-1 from 25 and 800°C. The Ultraviolet-visible (UV-vis) spectra were recorded on

174

the LAMBDA 1050 UV/Vis/NIR instrument in the range of 200-800 nm. Scanning electron

175

microscopy (SEM)analyses were recorded using a FEI Quanta 200 field emission. The

176

transmission electron microscopy (TEM) micrographs were obtained on a Tecnai G2

177

microscope at 120 kV. The sample used for TEM characterization were dispersed in a mixture

178

of water/ethanol (10% v/v) and then deposited on the TEM grid. The solvent was left to

179

evaporate for few minutes before analysis. High resolution transmission electron microscopy

180

(HR-TEM) analysis was carried out by a Jeol 2100F microscope, equipped with ultra-high-

181

resolution pole piece, field emission Schottky electron source and operating at 200 kV with a

182

resolution point of 0.235 nm. Atomic Force Microscopy (AFM) measurements were obtained

183

using a Veeco Dimension ICON. Before being analyzed, the samples used for AFM

184

characterizations were deposited on mica sheets.


Page 8 of 40

Page 9 of 40


185

3.2. Characterization of nanocomposite films

186

Mechanical tensile properties of the prepared bio-nanocomposite films were measured on the

187

LUDWIG mpk tensiometer upon samples with dimensions of 80 mm × 10 mm

188

(width × length), at tensile rate of 10 mm/min. Five tests were performed and the obtained

189

values are the averages of the five measurements. All film samples were preconditioned for

190

24h in a constant-temperature humidity chamber set at 40°C before testing.

191

Film thickness was measured to the nearest 0.01 mm using a hand-held micrometer (digital

192

GALIPER). Three thickness measurements were taken on each tensile testing specimen along

193

the length of the rectangular specimen, and the mean value was used in thickness calculation.

194

In order to avoid the influence of the thickness of specimens, all the samples used for the

195

measurement have a same thickness of 130 µm.

196

The moisture uptake (Mu) of the ST/L-GO bio-nanocomposites was determined according to

197

the ASTM E104 standard with slight modifications.55 Typically, rectangular specimens of the

198

prepared bio-nanocomposites (20 mm × 20 mm) were firstly dried at 105°C for 2 hours in a

199

hot desiccator and then weighted and incubated in a climatic chamber at 25°C with controlled

200

relative humidity (RH) of 75 ± 0.5%. At different intervals of time (each hour) over duration

201

of 6 hours, the films were then removed and weighted. The moisture uptake of the as-

202

prepared films was calculated according to the following equation:

Mu% =

Mf − Mi × 100 Mi

203

Where Mf and Mi are the weights of the sample after 6 hours exposure to 75 % RH and of the

204

dried sample before being incubated in the climatic chamber, respectively.

205

The water swelling capacity (SW) was determined as following: rectangular specimens

206

(20 mm × 20 mm) of neat ST, ST/L blend and ST/L-GO bio-nanocomposite films were firstly

207

dried in an oven at 100°C for 24h until constant weight (Wi) taken. Then, the films were



208

immersed in a glass bottle containing 20 mL of distilled water during 24 hours. After

209

immersion in water, samples were removed and weighted (Wf). The water swelling capacity

210

(SW) was calculated according to the following equation: SW % =

Wf − Wi × 100 Wi

211

The hydrolytic degradation of the prepared bio-nanocomposites was also investigated.

212

Previously dried and weighed films specimens (20 mm × 30 mm) were immersed in a glass

213

bottles containing 25 mL of distilled water and stored at room temperature. After 30 days of

214

incubation, the rectangular specimens were removed from the solution and dried at 80°C for

215

2 days. The hydrolytic degradation was estimated by weighing the films before and after

216

immersion in water.

217

The water vapor permeability (WVP) of the prepared bio-nanocomposite films was

218

determined according to the standard method E96-90 with some modifications.56 Glass bottles

219

with 20 mm diameter and of 40 mm depth were charged with 10g of distilled water and were

220

covered with the prepared bio-nanocomposite. The charged bottles were then weighted and

221

incubated in a climatic chamber at 25°C at a relative humidity of 50%. Successive weightings

222

were carried out every hour for duration of 7 hours and the changes in the bottles weight were

223

recorded function of time. The relationship between weight change and time should be

224

represented by a linear plot; the slope of this plot divided by the area of the glass bottle (m2)

225

represents the water vapor transmission rat (WVTR). The WVP (gm/m2 h Pa) was calculated

226

as follows: WVP=

WVTR WVTR X= X ΔP SR1-R2

227


Page 10 of 40

Page 11 of 40


228

Where X is the thickness of the film (m), S is the saturation vapor pressure (Pa) at the test

229

temperature (25°C), R1 and R2 are the relative humidity in the glass bottle and climatic

230

chamber, respectively.

231

4. Results and discussions

232

4.1. Characterization of GO

233

Before proceeding to the incorporation of the GO into the ST/L blend, the successfully

234

oxidation and exfoliation of GO into multilayer nanosheets was investigated by means of

235

X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force

236

microscopy (AFM) techniques. The GO nanosheets dispersion was achieved by alternating

237

vigorous magnetic stirring and intense sonication of the oxidized natural graphite. This

238

dispersion of GO was stable even after 4 weeks storage at room temperature.

239

The FTIR spectrum of GO showed many characteristics bands (Fig. 2b; right). The broad

240

band located at 3373 cm-1 was attributed to the stretching vibration of the hydroxyl groups

241

(O-H), and those observed at around 1714 and 1612 cm-1were attributed to the stretching

242

vibration of carboxylic groups and the skeletal vibrations of unoxidized graphitic domains,

243

respectively.57 In addition, other oxygen-containing functional groups such as C-OH, C-O-C

244

and C-O were clearly observed at 1363, 1148 and 1036 cm-1, respectively.58 The appearance

245

of these bands revealed the presence of numerous oxygen-containing functional groups thus

246

indicating that the graphite has been successfully oxidized into the GO nanosheets.

247

The XRD patterns of graphite and graphite oxide prepared according to the Hummer’s

248

method are shown in Figure 2 (left). The XRD pattern of the graphites how done single sharp

249

peak at 26.5° assigned to the highly organized layer structure of graphite. The interlayer

250

distance corresponding to the 002 reflections was 0.34 nm, which is in good agreement with

251

the JCPDS data N°75-2078. After oxidation of graphite, the diffraction peak observed at 2Ɵ =

252

26.5° was shifted to 2Ɵ = 10° and the d-spacing was increased from 0.34 nm to 0.88 nm (Fig. 11 ACS Paragon Plus Environment


253

2b; left). This shifting was mainly due to the formation of oxygen-containing functional

254

groups between the layers of the graphite.59 The obtained results confirmed the successful

255

oxidation of graphite into graphite oxide.

256

The scanning electron microscopy provides significant morphological information especially

257

those ascribed to the morphology and the size of the as-prepared GO. Typical SEM and TEM

258

micrographs are shown in Figure 3. SEM image in Fig. 3a showed that the as-prepared GO

259

was mainly consisting of multilayer agglomerate, which formed a three-dimensional porous

260

network. The surface morphology of GO was characterized by the presence of distinct

261

wrinkles and folding. TEM image of GO nanosheets (Fig. 3b) revealed that this sample is

262

mainly composed of assembled thin layers nanosheets with wrinkled and folded morphology.

263

These observations indicate that a high degree of exfoliation was achieved during the

264

oxidation and exfoliation processes. According to the HR-TEM micrograph of GO (Fig. 3c),

265

the value of the inter-planar distance d002 was found to be 0.75 nm. The selected area electron

266

diffraction (SAED)pattern (Fig. 3d) showed a two clear diffraction spots characteristic of

267

crystalline order, suggesting the presence of unoxidized graphitic regions within the graphene

268

oxide. This pattern is consistent with a hexagonal lattice of GO nanosheet.

269

The exfoliation level of the GO nanosheets was further investigated by AFM. As shown in

270

Fig. 3e the GO sample is mainly consisting of thin sheets irregular in sharp and adopting a

271

uniform thickness. The mean thickness of the obtained sheets was approximately 1 nm while

272

the other lateral dimensions varied from 100 to 800 nm. This relatively higher thickness,

273

which is relatively higher than that expected one for a single sheet of graphene oxide (0.34

274

nm), might be due to the presence of oxygen-containing functional groups to the surface of

275

GO nanosheets or to the existence of space between the nanosheets and the substrate due to

276

the wrinkled and folded structure of GO nanosheets that arises during solvent evaporation.60

277


Page 12 of 40

Page 13 of 40


278

4.2. Characterization of bio-nanocomposites

279

4.2.1. Fourier transform infrared spectroscopy

280

FTIR measurements provide significant information about the possible interfacial interactions

281

among starch, lignin and GO nanosheets in bio-nanocomposite films. Fig. 4 shows the typical

282

FTIR spectra of GO, neat starch and ST/L-GO bio-nanocomposite films loaded with various

283

GO amounts. It should be noted that all films were dried under vacuum at 40°C overnight

284

before being analyzed. As shown in Figure 4, neat starch exhibits typical stretching and

285

bending vibration of OH groups at 3229 and 1420 cm-1, respectively. The band observed at

286

2929 cm-1 was assigned to the C-H stretching. Besides, the bands located at 1152 cm-1 and

287

those observed at approximately 1077 and 1008 cm-1 were assigned to the stretching vibration

288

of C-O group in C-O-H and C-O-C groups of the anhydro-glucose ring of starch molecule,

289

respectively.61 The FTIR spectra of pristine lignin showed a broad peak between 3600 and

290

3200 cm-1 assigned to the alcoholic and phenolic -OH absorptions. The broad peaks at around

291

1600 and 1400 cm-1 are attributed to the aromatic structures (Fig. 4). After addition of lignin

292

biopolymer, a strong interfacial interaction between functional groups of lignin and starch

293

was occurred resulting in a better compatibility between these two biopolymers, thus

294

suggesting the formation of strong hydrogen bond between lignin and starch molecules.62,63

295

This indicated that starch and lignin achieved a high degree of compatibility. This finding was

296

further confirmed by the displacement of the carbonyl band located at around 1008 cm-1

297

towards lower wavelength numbers as shown in Fig. 4b. Compared the spectrum of ST/L

298

film to those of starch and lignin, it can be found that the spectrum of ST/L film is similar to

299

that of neat starch because the blend matrix composition is mainly based on starch

300

biopolymer.

301

The FTIR spectras of ST/L-0.3,ST/L-0.5 and ST/L-0.7 offer some important information

302

related to the interactions between oxygenated groups in GO and ST/L blend. Indeed, when



303

GO was added, the characteristic bands at 1152, 1077, 1002 cm-1 of ST/L blend shifted to

304

lower wave-numbers 1134, 1062, 999 cm-1, respectively, in ST/L blend filled by 0.7wt% of

305

GO, suggesting the occurrence of strong crosslinking reaction between the oxygen-containing

306

surface functional groups of GO (-OH, -COOH and -O-) and fuctional groups of ST/L matrix

307

(C-O and OH groups). The occurence of this interaction was further confirmed by the

308

increase in the intensity of the OH groups which indicate that additional hydrogen bondings

309

were formed (Fig. 4a). Based on the latter explanations, it seems that the ST/L-GO bio-

310

nanocomposites exhibitedan interconnected network structure linked by strong hydrogen

311

bonds either between starch and lignin biopolymers and also between ST/L blend and GO

312

nanosheets (Scheme 1).

313

4.2.2. Thermogravimetric analysis

314

The thermal stability of the ST and ST/L blend films as well as the bio-nanocomposites films

315

was evaluated in order to determine if the addition of lignin and GO could produce any

316

improvement in the thermal behavior of starch. The thermogravimetric (TG)and derivative

317

thermogravimetric (DTG) curves of the starch, crosslinked ST/L and ST/L-GO bio-

318

nanocomposite are shown in Fig. 5a and Fig. 5b, respectively. Starch film exhibited tree

319

major weight losses (Fig. 5a). The first weight loss before 120°C was attributed to the

320

evaporation of water, the second one within a range of 120-330°C was due to the removal of

321

glycerol added as a plasticizer, whereas the third weight loss around 330-500°C was assigned

322

to the thermal degradation of starch. The ST/L blend showed similar thermal degradation

323

behavior as starch film (Fig. 5a). The weight losses observed at 25-150°C, 150-330°C and

324

330-490°C were due to the removal of water, thermal degradation of plasticizer and the

325

decomposition of starch and lignin, respectively. Moreover, the thermal stability of the ST/L

326

film was found to be improved after the lignin addition, since the degradation rate in the range

327

of 150-330°C was found to be decreased. This improvement in thermal stability of ST/L film


Page 14 of 40

Page 15 of 40


328

could be assigned to the high thermal stability of the lignin molecule and the formation of a

329

crosslinked ST/L network.64 For ST/L-GO bio-nanocomposites, the weight loss occurred at

330

below 100°C was related to the evaporation of the absorbed water. The water absorbency of

331

ST/L-GO bio-nanocomposites was lower than ST/L blend, suggesting that the addition of GO

332

nanosheets prevents the prepared films from the absorption of water when exposed to the

333

moisture.65 The incorporation of GO in the crosslinked ST/L matrix resulted in a slight

334

improvement of thermal stability at a loading amount of 0.3 to 0.5wt% of GO since the

335

residue increases with increasing amounts of GO. According to the DTG curve of ST/L-GO

336

films (Fig. 5b), it can be observed that the maximum degradation temperature of the ST/L-

337

0.7GO film (482°C), in the third degradation step, is slightly higher than that corresponding to

338

the ST/L blend (472°C), thus indicating that when additional amount of GO was added (up to

339

0.7wt%), the thermal stability of the resultant bio-nanocomposite was further improved.

340 341

4.2.3. Scanning electron microscopy

342

The surface morphology of the different films was examined by SEM to verify the

343

compatibility between both starch and lignin and also ST/L blend and GO. Fig.5 shows

344

typical SEM images of ST (Fig. 6a), ST/L (Fig. 6b) blend, ST/L-0.3(Fig. 6c) and ST/L-0.7

345

(Fig. 6d) films. It can be observed that all the produced films exhibited a compact and non-

346

porous structure. The ST film showed granular particles (zone marked by a yellow circle, Fig.

347

6a), which may be associated to retrograde starch. Furthermore, the ST/L blend (Fig. 6b)

348

display rod-like lignin particles embedded within the starch matrix. The presence of these

349

fiber-like lignin particles indicates that lignin acts as filler and has been successfully blended

350

within the starch matrix, which might be the reason for the strong interaction between these

351

two biopolymers. Interestingly, SEM image of ST/L blend and ST/L-GO bio-nanocomposites

352

(Fig. 6) showed that many small fibers align inside a larger single fiber of lignin.

353

Additionally,

SEM

images

of


the

ST/L-GO


354

(Fig. 6c,d) revealed that the produced films exhibited a more compact and closed

355

microstructures.

356

4.2.4. Mechanical Properties Measurement

357

The mechanical properties of polymers are of great importance especially for a versatile

358

application in food packaging. Mechanical testing provides significant information about the

359

stiffness or brittleness of the prepared bio-nanocomposites. Tensile tests were carried out to

360

investigate the effect of the addition of lignin and incorporation of GO nanosheets on the

361

mechanical properties of the resulting ST/L-GO bio-nanocomposite films. The ST/L weight

362

ratio was fixed at 50wt%. The mechanical properties of the neat starch, ST/L blend and

363

ST/L-GO bio-nanocomposites at different GO loading were measured from the stress-strain

364

curves of the corresponding bio-nanocomposites film. The tensile properties, namely Young’s

365

modulus (E, MPa), tensile strength (σ, MPa) and elongation at break (ε, %) of neat starch,

366

ST/L blend and ST/L-GO bio-nanocomposites are shown in Fig. 7. It was difficult to obtain

367

film from lignin so its mechanical properties were not mentioned. As can be seen from Fig. 7,

368

both Young’s modulus (Fig. 7a) and tensile strength (Fig. 7b) of the ST/L biofilms increased

369

and the elongation at break values decreased owing to the occurrence of strong interaction

370

between the functional groups of starch and lignin. This improvement may arise from the

371

good compatibility between the hydrophobic lignin and the hydrophilic starch moieties in the

372

presence of glycerol, which acts as a compatibilization agent and contributes to the miscibility

373

of the twophases.66 Similarly, Ҫalgeris et al.64 reported that the addition of lignin extracted

374

from hazelnut shells to plasticized starch matrix greatly improves the mechanical strength of

375

the ST/L biofilms. The evidence of the occurrence of strong interfacial interactions between

376

starch and lignin was confirmed by the FTIR spectra of the ST/L film (Fig.4). As expected,

377

both Young’s modulus and tensile strength were significantly improved after incorporation of

378

increasing amount of GO (Fig. 7a,b). The E and σ increased from 32 and 3.37 MPa to 60.23


Page 16 of 40

Page 17 of 40


379

and 5 MPa when the GO loading increased from 0 to 0.7wt%, respectively. The mechanical

380

properties enhancement was probably due to the interfacial interactions between the

381

biopolymer matrices and exfoliated GO nanosheets. These results are in good agreement with

382

the previous studies, indicating that the addition of well-dispersed GO as a reinforcement can

383

significantly enhance the resultant mechanical properties of several biopolymeric matrices

384

such as starch,67 alginate,68 polylactic acid69 and carboxymethyl cellulose.70 The elongation at

385

break (ε) does not follows the same tendency as E and σ, and decreased from 13,68 to 9.07%

386

after incorporation of increasing amount of GO from 0.3 to 0.7wt% (Fig. 7c). The significant

387

improvement in mechanical properties of ST/L-GO bio-nanocomposite films, mainly E and σ,

388

was due to the strong interaction between GO and ST/L matrix and the good dispersion of GO

389

within the ST/L matrix. The GO nanofiller, with their abundant oxygen-containing functional

390

groups, formed an interconnected network linked by strong hydrogen-bonding interaction and

391

becomes difficult to disconnect from the ST/L matrix. Moreover, the substantial enhancement

392

of the Young’s modulus (E) and tensile strength (σ) could also be due to the resistance of GO

393

to the imposed force and the applied stress. Similar results were also reported when the starch

394

was reinforced by nanofiller.71,72

395

4.2.5. UV-Vis Absorbance of the films

396

The UV-Vis spectra of pure ST, ST/L blend and ST/L-GO bio-nanocomposites films are

397

depicted in Fig. 8a. Since the ST film is transparent in the UV-Vis region, a very low

398

absorption level was obtained. Once blended with lignin, the absorption of the ST/L blend

399

was found to increase, suggesting that the transparence of the prepared film was reduced. The

400

lignin containing film was brown in color as shown in Figure 1. Additionally, when

401

increasing the amounts of GO were added to the ST/L blend, the absorption level was

402

increased gradually and follow the subsequent order: ST/L-0.3< ST/L-0.5< ST/L-0.7 (Fig.

403

8a). These results revealed that the transparency of ST/L was affected by the incorporation of



404

GO nanosheets. This behavior is expected since the color of the ST/L-GO bio-

405

nanocomposites was found to darken as the GO amount was increased (Fig.1).

406

4.2.6. Moisture uptake of the films

407

The moisture uptake (Mu) of neat ST, ST/L blend and ST/L-GO bio-nanocomposites films

408

are depicted in Fig.8b. Pure starch is well known to be sensitive to water and moisture due to

409

its hydrophilic character. As shown in Fig. 8b, the Mu value of the neat ST film, after

410

exposition to an environmental relative humidity of 70% for 6h, was approximately 12.36%.

411

Moreover, it can be clearly seen that blending lignin within the starch matrix significantly

412

reduced the moisture uptake percentage of the resulting ST/L blend to 9.2%. This decrease in

413

water uptake at equilibrium can be ascribed to the partial miscibility of hydrophobic phenolic

414

compounds of lignin with the starch matrix and also to the reduction of the free hydrophilic

415

functional groups of starch witch form strong interactions within the oxygen containing

416

groups of lignin.73After the addition of an increasing amount of GO as a nanofiller, the

417

moisture uptake values were further reduced to 5.71, 5.16 and 5.15% for ST/L-GO-0.3, ST/L-

418

GO-0.5 and ST/L-GO-0.7, respectively. This decrease in the moisture uptake could be

419

assigned to the improvement of the hydrophobic nature of the ST/L-GO bio-nanocomposites

420

films and the possible occurrence of stronginterfacial interaction between the oxygen-

421

containing groups of GO and those of ST/L biopolymeric matrix, which reduce the water

422

accessibility and therfore the ability of the prepared bio-nanocomposites to absorb moisture.

423

4.2.7. Water swelling capacity of the films

424

The water swelling is one of the most significant disadvantages of a biopolymer especially for

425

packaging application. The water swelling capacity of the ST, ST/L blend and ST/L-GO bio-

426

nanocomposite films loaded with different GO contents is shown in Fig. 8c. The examination

427

of this figure revealed that the water swelling (SW) of the starch film was slightly decreased

428

after addition of lignin owing to the hydrophobic nature of lignin molecule. The SW values of


Page 18 of 40

Page 19 of 40


429

starch and lignin, after immersion in water for 24h, were 50.06 and 47.82%, respectively. At

430

GO loading of 0.3 and 0.5wt%, no significant improvement of the water uptake was observed,

431

whereas when increasing the amout of GO was used (0.7wt%) the water swelling was found

432

to decrease to 35.07%in comparison to 50 and 48% for neat ST and ST/L blend film,

433

respectively (Fig. 8c). These results suggest that theincoporation of an increasing amount of

434

GO could significantly improve the hydrophobicity of the ST/L blend films and therfore limit

435

the absorption of water by the ST/L-GO bio-nanocomposites films. Indeed, the presence of a

436

well dispersed GO nanosheets resulted in the occurence of a strong interfacial interaction

437

between the biopolymeric ST/L matrix and GO nanofiller, which resulted in the formation of

438

an interconnected network and water molecules cannot diffuse inside the bio-nanocomposite

439

film, thus preventing the absoprtion of water of the films when immersed in water and

440

decreasing the water swelling ability.72The obtained results are in good agreement with those

441

of TGA curve (Fig. 5a) since the water content, which is absorbed from the moisiture, of the

442

prepared bio-nanocomposites films decreased with an increasing amount of GO from 0.3 to

443

0.7wt%. These findings are in good argeement with those reported by Khan et al.70when

444

using GO as a nanofiller in polymeric blends.

445 446

4.2.8. Water vapor permeability of the films

447

Water vapor permeability of ST/L-GO bio-nanocomposite is one of the most important

448

features for the substitution of traditional polymers, particularly, for packaging applications.

449

Conventionally, films must limit or at least reduce moisture transfer between food and the

450

external environment. The WVP of neat ST and ST/L-GO bio-nanocomposite films at

451

different GO loading are given in Figure 8d. It was clearly observed that the values of WVP

452

for

453

ST/L-GO bio-nanocomposite were lower than that of neat ST. The WVP of the neat starch

454

was around 11.43 g m/m2 h Pa. This value was found to decrease when ST was blended with 19 ACS Paragon Plus Environment


455

lignin and filled with 0.3wt% of GO to reach 3.86 g m/m2 h Pa (Fig. 8d). After addition of

456

increasing amount of GO, the WVP of the prepared ST/L-GO films was found to decrease

457

following the loading level of GO. When GO loading was increased from 0.3 to 0.7wt%, the

458

WVP was found to decrease from 3.86 to 3.74 g m/m2 h Pa, respectively. These results could

459

be explained by the formation of a strong hydrogen bonding between GO and the blend

460

matrix which reduce the diffusion of water in the films and produce a tortuous pathway for

461

the water molecules.74,75

462

4.2.9. Hydrolytic degradation of the films

463

The hydrolytic degradation experiments were performed in water-based environment during

464

30 days in order to study the effect of blending starch with lignin biopolymer on the

465

hydrolytic degradation of ST/L blend film and also to investigate the effect of the

466

incorporation of GO as a nano-reinforcement on the long-term hydrolytic degradation of

467

ST/L-GO films. Fig.8a shows the photographs of pure ST, ST/L blend and ST/L-GO films

468

immersed in water. The digital images are taken at t = 5 min and t = 30 days in order to

469

monitor their state and check the possible visual degradation of the films.

470

It is prominent that starch is highly sensitive to water. After immersion in water for 30 days,

471

the starch film seems to keep rather good morphological dimensions, but it becomes brittle

472

and easy to break. The residual mass measured for this sample after the removal of water and

473

drying (Fig. 8b) was found to be 40.43% indicating that the major part of ST is hydrolyzed in

474

water media. This is mainly due to the presence of free hydroxyl groups, which have a high

475

affinity to water. When lignin was blended within ST matrix, the hydrolytic degradation of

476

the resulting ST/L blend was slightly reduced when compared to neat ST owing to the

477

reduction of the free hydroxyl groups of ST, which interact with those of hydrophobic lignin.

478

As shown in Fig.8b, a slight increase of the residual mass to 41.02% was observed,

479

suggesting that the starch was well blended with the lignin, which reduces the ability of water


Page 20 of 40

Page 21 of 40


480

for degradation mechanism. However, the partial degradation of ST/L blend could be ascribed

481

to the existence of free oxygen-containing functional groups remaining in the ST/L blend,

482

which favorably interact with water thus resulting in hydrolysis mechanism. In the case of

483

ST/L-GO, no visual degradation was detected since the bio-nanocomposite films still

484

maintain a good morphological aspect (Fig.8a). The remaining weight increases by increasing

485

the amount of GO (Fig. 8b). Indeed, the residual mass increased from 45.35 to 65.21wt%

486

when the GO loading was increased from 0.3 to 0.7wt%, respectively. This resistance to the

487

hydrolytic degradation might be due to the occurrence of additional interaction between the

488

free oxygen-containing functional groups of ST/L blend and the oxygenated groups of GO as

489

established by FTIR analysis (Fig. 4). Furthermore, the highly dispersed GO nanofiller in the

490

polymeric matrix resulted in the formation of a tortuous path, which limits the penetration of

491

water and therefore reduces the hydrolytic degradation of the produced bio-nanocomposites.76

492

These results are in good agreement with those reported by El achaby et al.77 when using

493

2wt% of GO filled chitosan/poly(vinylpyrrolidone) blend.

494 495

5. Conclusion

496

In this study, films based on ST/L biopolymer blend reinforced by GO were successfully

497

prepared via casting/solvent evaporation process. FTIR measurements revealed that the lignin

498

was successfully blended within the starch matrix via the occurrence of hydrogen bond

499

interactions, which resulted in the formation of a homogenous biocompatible blend matrix.

500

After the addition of GO, additional interactions were found to occur between the non-

501

interaction hydroxyls groups of starch and lignin and the oxygen containing groups of GO,

502

resulting in the formation of an interconnected network. Owing to these interactions, the

503

resulting properties of the prepared bio-nanocomposites such as water swelling, moisture

504

uptake, hydrolytic degradation, water vapor permeability, thermal stability and mechanical



Page 22 of 40

505

properties were significantly improved. As a conclusion, our findings confirmed the

506

effectiveness of the proposed approach to produce biodegradable films with enhanced

507

properties, which may be a suitable candidate for food packaging applications.

508 509

Acknowledgements

510

The financial assistance of the MAScIR Foundation, towards this research is hereby

511

acknowledged. We acknowledge also the financial assistance of the CNRST (Grant PPR2

512

Project, Category B).

513 514 515

6. Reference

516

1. Rodríguez-González, C.; Martínez-Hernández, A.L.; Castaño, V.M.; Kharissova,

517

O.V.; Ruoff, R.S.; Velasco-Santos, C. Polysaccharide Nanocomposites Reinforced

518

with Graphene Oxide and Keratin-Grafted Graphene Oxide. Ind. Eng. Chem. Res.

519

2012, 51, 3619-3629.

520

2. Raemdonck, K.; Martens, T.F.; Braeckmans, K.; Demeester, J.; De Smedt, S.C.

521

Polysaccharide-based systems in drug and gene delivery. Adv. Drug Deliv. Rev. 2013,

522

65, 1123-1147.

523 524 525 526 527 528

3. Bordes,

P.;

Pollet,

E.;

Avérous,

L.;

Nano-biocomposites:

Biodegradable

polyester/nanoclay systems. Prog. Polym. Sci. 2009, 34, 125-155. 4. Siracusa, V.; Rocculi, P.; Romani, S.; Rosa, M.D. Biodegradable polymers for food packaging: a review. Trends Food Sci. Technol. 2008, 19, 634-643. 5. Curvelo, A.A.S.; de Carvalho, A.J.F.; Agnelli, J.A.M.; Thermoplastic starch-cellulosic fibers composites: preliminary results. Carbohy. Polym. 2001, 45, 183-188.

529

6. Avella, M.; De Vlieger, J.J.; Errico, M.E.; Fischer, S.; Vacca, P.; Volpe, M.G.

530

Biodegradable starch/clay nanocomposite films for food packaging applications. Food

531

Chem. 2005, 93, 467-474.

532

7. Chung, Y.-L.; Ansari, S.; Estevez, L.; Hayrapetyan, S.; Giannelis, E.P.; Lai, H.-M.

533

Preparation and properties of biodegradable starch–clay nanocomposites. Carbohy.

534

Polym. 2010, 79, 391-396. 22 ACS Paragon Plus Environment

Page 23 of 40

535 536 537 538 539 540 541 542 543 544


8. Huang, M.-F.; Yu, J.-G.; Ma, X.-F. Studies on the properties of Montmorillonitereinforced thermoplastic starch composites. Polymer 2004, 45, 7017-7023. 9. Guan, J.; Eskridge, K.M.; Hanna, M.A. Acetylated starch-polylactic acid loose-fill packaging materials. Ind. Crops Prod. 2005, 22, 109-123. 10. Ou, S.; Li A.; Yang, A. A study on synthesis of starch ferulate and its biological properties. Food Chem. 2001, 74, 91-95. 11. Rehman, Z.; Shah, W.H. Thermal heat processing effects on antinutrients, protein and starch digestibility of food legumes. Food Chem. 2005, 91, 327-331. 12. Mooney, B.P. The second green revolution? Production of plant-based biodegradable plastics. Biochem. J. 2009, 418, 219-232.

545

13. Girones, J.; Lopez, J.P.; Mutje, P.; Carvalho, A.J.F.; Curvelo, A.A.S.; Vilaseca, F.

546

Natural fiber-reinforced thermoplastic starch composites obtained by melt processing.

547

Compos. Sci. Technol. 2012, 72, 858-863.

548

14. Da Róz, A.L.; Ferreira, A.M.; Yamaji, F.M.; Carvalho, A.J.F. Compatible blends of

549

thermoplastic starch and hydrolyzed ethylene-vinyl acetate copolymers. Carbohydr.

550

Polym. 2012, 90, 34-40.

551

15. Chillo, S.; Flores, S.; Mastromatteo, M.; Conte, A.; Gerschenson, L.; Del Nobile,

552

M.A. Influence of glycerol and chitosan on tapioca starch-based edible film properties.

553

J. Food Eng. 2008, 88, 159-168.

554 555 556 557 558 559

16. Kim, M., Lee, S.-J. Characteristics of crosslinked potato starch and starch-filled linear low-density polyethylene films. Carbohy. Polym. 2002, 50, 331-337. 17. Bourtoom, T.; Chinnan, M.S. Preparation and properties of rice starch-chitosan blend biodegradable film. LWT - Food Sci. Technol. 2008, 41, 1633-1641. 18. Sionkowska, A. Current research on the blends of natural and synthetic polymers as new biomaterials: Review. Prog. Polym. Sci. 2011, 36, 1254-1276.

560

19. Prachayawarakorn, J.; Sangnitidej, P.; Boonpasith, P. Properties of thermoplastic rice

561

starch composites reinforced by cotton fiber or low-density polyethylene. Carbohy.

562

Polym. 2010, 81, 425-433.

563 564 565 566

20. Kaewtatip, K.; Thongmee, J. Studies on the structure and properties of thermoplastic starch/luffa fiber composites. Mater. Des. 2012, 40, 314-318. 21. Kaewtatip, K.; Tanrattanakul, V. Structure and properties of pregelatinized cassava starch/kaolin composites. Mater. Des. 2012, 37, 423-428.



567

22. Müller, C.M.O.; Laurindo, J.B.; Yamashita, F. Effect of nanoclay incorporation

568

method on mechanical and water vapor barrier properties of starch-based films. Ind.

569

Crops Prod. 2011, 33, 605-610.

570 571

23. Hu, G., Chen, J.; Gao, J. Preparation and characteristics of oxidized potato starch films. Carbohydr. Polym. 2009, 76, 291-298.

572

24. Kim, K. W.; Ko, C.J.; Park, H.J. Mechanical Properties, Water Vapor Permeabilities

573

and Solubilities of Highly Carboxymethylated Starch-Based Edible Films. J. Food Sci.

574

2002, 67, 218-222.

575 576 577 578 579 580 581 582

25. López, O.V.; García, M.A.; Zaritzky, N.E. Film forming capacity of chemically modified corn starches. Carbohy. Polym. 2008, 73, 573-581. 26. Glasser W.G.; Northey R.A.; Schultz T.P. Lignin: Historical, biological, and materials perspectives. American Chemical Society 2000, 742. 27. Thomas Q. Hu. Q. Chemical modification, properties, and usage of lignin. Plenum Press. 2002. 28. Gordobil, O.; Egüés, I.; Llano-Ponte, R.; Labidi, J. Physicochemical properties of PLA lignin blends. Polym. Degrad. Stab. 2014, 108, 330-338.

583

29. Kadla, J.F.; Kubo, S. Lignin-based polymer blends: analysis of intermolecular

584

interactions in lignin-synthetic polymer blends. Compos. Part Appl. Sci. Manuf.

585

AIChE 2004, 35, 395-400.

586

30. Spiridon, I.; Teaca, C.-A.; Bodirlau, R. Preparation and characterization of adipic

587

acid-modified starch microparticles/plasticized starch composite films reinforced by

588

lignin. J. Mater. Sci. 2011, 46, 3241-3251.

589

31. Baumberger, S.; Lapierre, C.; Monties, B.; Lourdin, D.; Colonna, P. Preparation and

590

properties of thermally moulded and cast lignosulfonates-starch blends. Ind. Crops

591

Prod. 1997, 6, 253-258.

592

32. Vengal, J. C.; Srikumar, M. Processing and study of novellignin-starch and lignin-

593

gelatin biodegradable polymeric films. Trends Biomater. Artif. Organs. 2005, 18, 237-

594

241.

595 596

33. Stevens, E.S.; Willett, J.L.; Shogren, R.L, Thermoplastic Starch-Kraft Lignin-Glycerol Blends. J. Biobased Mater. Bioenergy 2007, 1, 351-359.

597

34. Baumberger, S.; Lapierre, C.; Monties, B.; Valle, G.D. Use of kraft lignin as filler for

598

starch films. Polym. Degrad. Stab. Biodegradable Polymers and Macromolecules

599

1998, 59, 273-277.


Page 24 of 40

Page 25 of 40


600

35. Baumberger, S.; Michon, C.; Cuvelier, G.; Lapierre, C. Lignin utilization in starch

601

thermoplastics: towards molecular origin of polymer compatibility. In Proceedings of

602

the Sixth European Workshop on Lignocellulosics and Pulps 2000, 121-124.

603 604 605 606 607 608

36. Baumberger, S. Chemical Modification, Properties, and Usage of Lignin. Kluwer Academic, Plenum Publishers 2002, 1-20. 37. Bodirlau, R.; Teaca, C.-A.; Spiridon, I. Influence of natural fillers on the properties of starch-based biocomposite films. Compos. Part B Eng. 2013, 44, 575-583. 38. Kaewtatip, K.; Thongmee, J. Effect of kraft lignin and esterified lignin on the properties of thermoplastic starch. Mater. Des. 2013, 49, 701-704.

609

39. Miranda, C.S.; Ferreira, M.S.; Magalhães, M.T.; Santos, W.J.; Oliveira, J.C.; Silva,

610

J.B.A.; José, N.M. Mechanical, Thermal and Barrier Properties of Starch-based Films

611

Plasticized with Glycerol and Lignin and Reinforced with Cellulose Nanocrystals.

612

Mater. Today Proc., ANM 2014: 5th International conference on Advanced

613

Nanomaterials 2015, 2, 63-69.

614

40. Miranda, C.S.; Ferreira, M.S.; Magalhães, M.T.; Bispo, A.P.G.; Oliveira, J.C.; Silva,

615

J.B.A.; José, N.M. Starch-based Films Plasticized with Glycerol and Lignin from

616

Piassava Fiber Reinforced with Nanocrystals from Eucalyptus. Mater. Today Proc.,

617

ANM 2014: 5th International conference on Advanced Nanomaterials 2015, 2, 134-

618

140.

619 620 621 622

41. Chivrac, F.; Pollet, E.; Avérous, L. Progress in nano-biocomposites based on polysaccharides and nanoclays. Mater. Sci. Eng. Rep. 2009, 67, 1-17. 42. Paul, D.R.; Robeson, L.M. Polymer nanotechnology: Nanocomposites. Polymer 2008, 49, 3187-3204.

623

43. Avella, M.; Vlieger, J. J. D.; Errico, M. E.; Fischer, S.; Vacca, P.; Volpe, M. G.

624

Biodegradable starch/clay nanocomposite films for food packaging applications. Food

625

Chemistry 2005, 93, 467-474.

626


627


628

Polym. 2010, 79, 391-396.

629

45. Sanchez-Garcia, M.D.; Lagaron, J.M.; Hoa, S.V. Effect of addition of carbon

630

nanofibers and carbon nanotubes on properties of thermoplastic biopolymers.

631

Compos. Sci. Technol., Special issue on Chiral Smart Honeycombs 2010, 70, 1095-

632

1105.



Page 26 of 40

633

46. Rodríguez-González, C.; Martínez-Hernández, A.L.; Castaño, V.M.; Kharissova,

634

O.V.; Ruoff, R.S.; Velasco-Santos, C. Polysaccharide Nanocomposites Reinforced

635

with Graphene Oxide and Keratin-Grafted Graphene Oxide. Ind. Eng. Chem. Res.

636

2012, 51, 3619-3629.

637


638


639

Polym. 2010, 79, 391-396.

640

48. Goffin, A.-L.; Raquez, J.-M.; Duquesne, E.; Siqueira, G.; Habibi, Y.; Dufresne, A.;

641

Dubois, P.From Interfacial Ring-Opening Polymerization to Melt Processing of

642

Cellulose

643

Biomacromolecules 2011, 12, 2456-2465.

644 645 646 647

Nanowhisker-Filled

Polylactide-Based

Nanocomposites.

49. Rouf, T. B.; Kokini, J. L. Biodegradable biopolymer–graphene nanocomposites. Journal of Materials Science 2016, 51, 9915-9945. 50. Kim, H.; Abdala, A. A.; Macosko, C. W. Graphene/Polymer Nanocomposites. Macromolecules 2010, 43, 6515-6530.

648

51. Jiang, L.; Shen, X.-P.; Wu, J.-L.; Shen, K.-C. Preparation and characterization of

649

graphene/poly(vinyl alcohol) nanocomposites. J. Appl. Polym. Sci.2010, 118, 275-

650

279.

651

52. Wei, T.; Luo, G.; Fan, Z. J.; Zheng, C.; Yan, J.; Yao, C. Z. Preparation of graphene

652

nanosheet/polymer composites using in situ reduction-extractive dispersion. Carbon

653

2009, 47, 2296-2299.

654

53. Kai, W.; Hirota, Y.; Hua, L.; Inoue, Y. Thermal and mechanical properties of a

655

poly(ϵ-caprolactone)/graphite oxide composite. J. Appl. Polym. Sci. 2008, 107, 1395-

656

1400.

657 658

54. Hummers, W.S.; Offeman, R.E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339-1339.

659

55. Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous

660

Solutions, ASTM Standard E104-51 (reapproved 1971), American society for testing

661

and materials, Philadelphia, PA (1986)

662 663

56. Standard Test Methods for Water Vapor Transmission of Materials, ASTM Standard E96-90, procedure D.

664

57. Wang, G., Wang, B., Park, J., Yang, J., Shen, X., Yao, J., Synthesis of enhanced

665

hydrophilic and hydrophobic graphene oxide nanosheets by a solvothermal method.

666

Carbon 2009, 47, 68-72. 26 ACS Paragon Plus Environment

Page 27 of 40

667 668


58. Chandra, S.; Sahu, S.; Pramanik, P.A novel synthesis of graphene by dichromate oxidation. Materials Science and Engineering B 2010, 167, 133-136.

669

59. Paredes, J.I.; Villar-Rodil, S.; Martínez-Alonso, A.; Tascón, J.M.D. Graphene oxide

670

dispersions in organic solvents. Langmuir ACS J. Surf. Colloids 2008, 24, 10560-

671

10564.

672

60. Stankovich, S.; Dikin, D.A.; Piner, R.D.; Kohlhaas, K.A.; Kleinhammes, A.; Jia, Y.;

673

Wu, Y.; Nguyen, S.T.; Ruoff, R.S. Synthesis of graphene-based nanosheets via

674

chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558-1565.

675

61. Prachayawarakorn, J.; Sangnitidej, P.; Boonpasith, P. Properties of thermoplastic rice

676

starch composites reinforced by cotton fiber or low-density polyethylene. Carbohydr.

677

Polym. 2010, 81, 425-433.

678 679

62. Kaewtatip, K.; Thongmee, J. Studies on the structure and properties of thermoplastic starch/luffa fiber composites. Mater. Des. 2012, 40, 314-318.

680

63. Prachayawarakorn, J.; Ruttanabus, P.; Boonsom, P. Effect of Cotton Fiber Contents

681

and Lengths on Properties of Thermoplastic Starch Composites Prepared from Rice

682

and Waxy Rice Starches. J. Polym. Environ. 2011, 19, 274-282.

683

64. Çalgeris, Đ.; Çakmakçı, E.; Ogan, A.; Kahraman, M.V.; Kayaman-Apohan, N.

684

Preparation and drug release properties of lignin–starch biodegradable films. Starch-

685

Stärke 2012, 64, 399-407.

686

65. El Achaby, M.; El Miri, N.; Snik, A.; Zahouily, M.; Abdelouahdi, K.; Fihri, A.;

687

Barakat, A.; Solhy, A. Mechanically strong nanocomposite films based on highly

688

filled carboxymethyl cellulose with graphene oxide. J. Appl. Polym. Sci. 2016, 133,

689

42356.

690

66. Vengal, J. C.; Srikumar, M. Processing and study of novel lignin-starch and lignin-

691

gelatin biodegradable polymeric films. Trends Biomater. Artif. Organs. 2005, 18, 237-

692

241.

693 694

67. Li, R.; Liu, C.; Ma, J. Studies on the properties of graphene oxide-reinforced starch biocomposites. Carbohydr. Polym. 2011, 84, 631-637.

695

68. Ionita, M.; Pandele, M.A.; Iovu, H. Sodium alginate/graphene oxide composite films

696

with enhanced thermal and mechanical properties. Carbohydr. Polym. 2013, 94, 339-

697

344.

698

69. Li, W.; Xu, Z.; Chen, L.; Shan, M.; Tian, X.; Yang, C.; Lv, H.; Qian, X. A facile

699

method to produce graphene oxide-g-poly(L-lactic acid) as an promising

700

reinforcement for PLLA nanocomposites. Chem. Eng. J. 2014, 237, 291-299. 27 ACS Paragon Plus Environment


Page 28 of 40

701

70. Wang, J.; Feng, M.; Zhan, H. Preparation, characterization, and nonlinear optical

702

properties of graphene oxide-carboxymethyl cellulose composite films. Opt. Laser

703

Technol. 2014, 57, 84-89.

704 705 706 707

71. Ma, X.; Yu, J.; Wang, N. Glycerol plasticized-starch/multiwall carbon nanotube composites for electroactive polymers. Compos. Sci. Technol. 2008, 68, 268-273. 72. Li, R.; Liu, C.; Ma, J. Studies on the properties of graphene oxide-reinforced starch biocomposites. Carbohydr. Polym. 2011, 84, 631-637.

708

73. Lepifre, S.; Baumberger, S.; Pollet, B.; Cazaux, F.; Coqueret, X.; Lapierre, C.

709

Reactivity of sulphur-free alkali lignins within starch films. Ind. Crops Prod., 6th

710

International Lignin Institute conference 2004, 20, 219-230.

711

74. Bai, H.; Sun, Y.; Xu, J.; Dong, W.; Liu, X. Rheological and structural characterization

712

of HA/PVA-SbQ composites film-forming solutions and resulting films as affected by

713

UV irradiation time. Carbohydrate Polymers 2015, 115, 422-431.

714

75. Yadollahi, M.; Namazi, H.; Barkhordari, S. Preparation and properties of

715

carboxymethyl

cellulose/layered

double

716

Carbohydrate Polymers 2014, 108, 83-90.

hydroxide

bionanocomposite

films.

717

76. Han, D.; Yan, L.; Chen, W.; Li, W. Preparation of chitosan/graphene oxide composite

718

film with enhanced mechanical strength in the wet state. Carbohydr. Polym. 2011, 83,

719

653-658.

720

77. El Achaby, M.; Essamlali, Y.; El Miri, N.; Snik, A.; Abdelouahdi, K.; Fihri, A.;

721

Zahouily, M.; Solhy, A. Graphene oxide reinforced chitosan/polyvinylpyrrolidone

722

polymer bio-nanocomposites. J. Appl. Polym. Sci. 2014, 41042, 1-11.


Page 29 of 40


723

Figure captions:

724

Figure 1. Digital images of ST, ST/L blend and ST/L-GO films forming solutions and the

725

corresponding isolated solid films.

726

Figure 2. XRD patterns (left)and FTIR spectra (right) of (a) graphite and (b)graphite oxide

727

Figure 3. (a) SEM micrograph of graphene oxide nanosheets, (b) TEM micrograph of

728

graphene oxide nanosheets, (c) HR-TEM image of graphene oxide, (d) Electron diffraction

729

pattern from SAED measurements for graphene oxide sample and (e) AFM image and the

730

corresponding line profiles of the GO nanosheets.

731

Figure 4. FTIR spectra of ST, lignin, ST/L blend, ST/L-0.3, ST/L-0.5and ST/L-0.7 bio-

732

nanocomposites films and GO powder in the region of (a) 600-4000 cm-1 and (b)

733

1600-600 cm-1.

734

Figure 5. (a) TGA and (b) DTG curves of neat ST, ST/L blend, ST/L-0.3, ST/L-0.5 and

735

ST/L-0.7 bio-nanocomposite films. Inset in figure 5a TGA curve in temperature range of 250-

736

500°C.

737

Figure 6. SEM micrographs of (a) neat starch, (b) ST/L blend, (c) ST/L-0.3 and (d) ST/L-0.7

738

films. Regions surrounded by yellow circle indicate granular particles.

739

Figure 7. Mechanical properties of ST, ST/L blend and ST/L-0.3, ST/L-0.5 and ST/L-0.7: (a)

740

Young’s modulus, (b) Tensile strength hand (c)Elongation at break.

741

Figure 8. (a)UV-Vis spectra, (b) Moisture uptake, (c) Water swelling and (d) Water vapor

742

permeability of neat ST, ST/L blend and ST/L-GO bio-nanocomposite films loaded with

743

different GO loading (0.3, 0.5 and 0.7wt%).

744

Figure 9. (a)Photographs of neat ST, ST/L blend and ST/L-GO bio-nanocomposites

745

immersed in water for 5 min and 30 days, (b) Residual mass of neat ST, ST/L blend and

746

ST/L-GO bio-nanocomposite loaded with different GO amount after a degradation period of

747

30 days 29 ACS Paragon Plus Environment


748

Figure graphics:

749

Figure 1.

750 751


Page 30 of 40

Page 31 of 40

752


Figure 2.

Transmittance (%)

Intensity (a.u)

d002 = 0.336 nm d002 = 0.88 nm

(b)

(b) C-O-C

(a)

(a) C-C

OH

5

10

15

20

25

30

35

40

C-O

4000 3500 3000 2500 2000 1500 1000 -1

2θ (°)

Wavenumber (cm )

753



754

Figure 3.

755 756


Page 32 of 40

Page 33 of 40

757


Figure 4. (a)

ST

(b) ST -1

1152 cm

% Transmitance (a.u)

% Transmitance (a.u)

Lignin ST/L ST/L-0.3 ST/L-0.5 ST/L-0.7 C-H

GO

C-H

1159 cm

4000

1714 cm -1 1612 cm

OH

3500

3000

2500

2000

1500

1152 cm

ST/L-0.3

-1

1002 cm

-1

1152 cm

ST/L-0.5

-1

1002 cm

-1

1148 cm

ST/L-0.7

-1

999 cm -1

1134 cm C-O

-1

989 cm

1000

1500

-1

758

ST/L

-1

1036 cm -1

-1

OH

Lignin

-1

1008 cm -1

1250

1000

750 -1

Wavenumbers (cm )

Wavenumbers (cm )

759



Figure 5.

Weight (%)

Weight loss (%)

80

2 1,6

60

40

1,4

5

20

60

1 0 250

300

350

400

450

500

Temperature (°C)

40

1: ST 2: ST/L 3: ST/L-0.3 4: ST/L-0.5 5: ST/L-0.7

20

0

(b) (b)

1,8

(a)

80

100

Deriv. Weight (%/°C)

760

Page 34 of 40

5 1

1,2 1,0

3

0,8 0,6 0,4

3

5

100

200

0,2 0,0

-20

-0,2 0

100

200

300

400

500

600

700

800

0

Temperature (°C)

300

400

500

Temperature (°C)

761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 34 ACS Paragon Plus Environment

600

700

800

Page 35 of 40

784


Figure 6.

785

786 787 788



789

Figure 7. 70

Young's modulus (MPa)

(a) 60 50 40 30 ST

Tensile strength (MPa)

5,4 4,8

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

(b)

4,2 3,6 3,0 2,4 1,8 1,2 ST

Elongation at break (%)

24

790 791

(c)

20 16 12 8 ST


Page 36 of 40

Page 37 of 40

Figure 8. 3,0

14

5

1. ST 2. ST/L blend 3. ST/L-0.3 4. ST/L-0.5 5. ST/L-0.7 6. GO

Absorbance (a.u)

2,5 2,0 1,5 1,0

4 3

(a)

6 2

0,5

1

(b)

12

Moisiture uptake (%)

792 793


0,0

10 8 6 4 2 0

400

500

600

700

800

ST

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

Wavelenght (nm) 60

12 10

WVP (g m/m h Pa)

40

8

2

Swelling (%)

50

30 20 10 0

6 4 2 0

ST

794 795

(d)

(c)

ST/L

ST/L-0.3 ST/L-0.5 ST/L-0.7

ST

A

796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 37 ACS Paragon Plus Environment

ST/L-0.3

ST/L-0.5

ST/L-0.7


817 818

Figure 9.

819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 38 ACS Paragon Plus Environment

Page 38 of 40

Page 39 of 40


843

Scheme

844

Scheme 1. Schematic representation of the structure of the ST/L-GO bio-nanocomposite film

845

and the possible interactions between starch, lignin and GO nanosheets.

846

847 848



849

TOC Graphic:

850 851

852 853


Page 40 of 40

Starch Polymer ... - ACS Publications

Recommend Documents