Fabrication and Properties of Starch-Grafted Graphene Nanosheet

Article pubs.acs.org/IECR

Fabrication and Properties of Starch-Grafted Graphene Nanosheet/ Plasticized-Starch Composites Pengwu Zheng,† Tiantian Ma,‡ and Xiaofei Ma*,‡ †

School of Pharmacy, Jiangxi Science and Technology Normal University, Nanchang, Jiangxi 330013, China Chemistry Department, School of Science, Tianjin University, Tianjin 300072, China

‡

ABSTRACT: A novel method was used to prepare starch-grafted graphene nanosheets (GN-starch), in which graphene oxide was reduced with hydrazine hydrate in the presence of starch. The obtained GN-starch was characterized by electron microscopy, FTIR analysis, Raman spectra, thermogravimetric analysis, and UV−visible spectra, which confirmed that starch was effectively functionalized on the surface of graphene. Also, GN-starch exhibited high solubility and stability in water. The composites were also fabricated by using GN-starch as the filler in a plasticized-starch (PS) matrix. Because of the strong interaction between starch in GN-starch and the PS matrix, GN-starch can be well dispersed in the PS matrix and improve tensile strength to 25.4 MPa at a GN-starch content of 1.774 wt % and a moisture barrier even at a very low loading (0.248 wt %) of GN-starch fillers. PS/GN-starch composites could protect against UV light, and the conductivity of the composite could reach 9.7 × 10−4 S/cm at a GN-starch content of 1.774 wt %.

1. INTRODUCTION Graphene, a flat two-dimensional (2D) monolayer of sp2bonded carbon atoms is arranged in a hexagonal lattice, which has attracted tremendous attention in recent years due to their unique electronic, mechanical, and thermal properties.1 At present, graphene nanosheets (GNs) can mainly be prepared by three different techniques: (1) micromechanical cleavage, preparing GNs in a very limited quantity,2 (2) epitaxial growth of GN films on a substrate,3 and (3) chemical processing, including graphite oxidation or ultrasonic, microwave, or thermal exfoliation into graphene oxide (GO) and followed by the chemical reduction of GO.4 Among them, the wetchemistry approach is very suitable to preparing GN on a large scale. Since GNs had strong hydrophobic properties, they cannot be separated from each other and generally tend to form irreversible agglomerates or even restack to form graphite through strong π−π stacking interactions.5 Therefore, many protective reagents have been used to prevent the aggregation of GNs, including silicone,6 poly(sodium 4-styrenesulfonate),7 DNA,8 and so on. There is growing interest in developing biobased products and innovative processing technologies which offer sustainability and mitigation of the dependence on fossil fuel.9 Starch is a renewable carbohydrate polymer procurable at low cost from a great variety of crops. It has been investigated widely for the potential manufacture of products such as water-soluble pouches for detergents and insecticides, flushable liners and bags, and medical delivery systems and devices.10 Native starch commonly exists in a granular structure, which can be processed into plasticized starch (PS) materials.11,12 Unfortunately, PS is usually sensitive to moisture and shows low tensile strength. One significant approach is to fill a PS matrix with inorganic or organic reinforcements such as metal oxides,13 layer silicates,14 cellulose fibers,15,16 and natural polysaccharide particles.9,17,18 Recently, carbon materials have been introduced into a PS matrix. Many modifications are necessary to improve © 2013 American Chemical Society

the dispersion of carbon materials into a PS matrix. Carbon black was oxidized and added into a PS matrix to improve mechanical properties, thermal stability, and water vapor resistance of PS.19 Carbon nanotubes (CNTs) were treated with concentrated sulfuric acid and nitric acid and introduced into a PS matrix as the reinforcing fillers.20 Liu et al.21 prepared PS/carboxylate CNT composites and significantly improved the tensile strength of the PS matrix. The graphite oxide (GO) was also used as the filler in the PS matrix. The abundant oxygen-containing groups of GO could form hydrogen bond interactions with starch. These interactions and the uniform dispersion of GO in the PS matrix played important roles in improving mechanical and moisture barrier properties.22 However, the oxidation resulted in degradation of the electronic properties of graphene; therefore the reduction process was necessary. In this study, starch were grafted on the surface of graphene nanosheets (GNs) by the reduction of GO with hydrazine hydrate in the presence of starch. Starch could inhibit the occurrence of GN aggregation in the reduction process. The obtained GN-starch was explored as a promising filler to prepare PS/GN-starch composites. The starch component of GN-starch is very important in dispersing GNs. Also, the grafted starch would form the hydrogen-bond interaction with starch in a PS matrix, which could improve the dispersion of GN-starch in the matrix and the properties of the composites. Since GN has properties of UV absorbance and electric conductivity, the obtained composites could have potential applications such as ultraviolet absorbance or electrical conductivity. In addition, this novel method of fabricating Received: Revised: Accepted: Published: 14201

July 12, 2013 August 29, 2013 September 6, 2013 September 6, 2013 dx.doi.org/10.1021/ie402220d | Ind. Eng. Chem. Res. 2013, 52, 14201−14207

Industrial & Engineering Chemistry Research

Article

Figure 1. TEM of GN (a) and GN-starch (b). SEM of GN (d) and GN-starch (e).

washed with diluted HCl solution and then washed with distilled water to remove the acid. 2.2.2. Preparation of GN and GN-Starch. GO was reduced to GN with hydrazine hydrate.24 A total of 0.73g GO was dispersed in 200 mL of water using ultrasonication for 5 min to obtain homogeneous dispersion. Starch (0 g or 5.84 g) was dissolved in a homogeneous GO aqueous suspension. A total of 22 mL of ammonia solution (25% w/w) was added dropwise. Then, 1.5 mL of hydrazine solution (80 wt %) was added into it. The mixture was heated in an oil bath for 4 h at 90 °C. The mixture was cooled to room temperature, centrifugated, and washed three times with N,N-dimethylacetamide/LiCl (95 wt %/5 wt %) solution to remove starch. The samples were further washed with distilled water and then dried to obtain GN or GN-starch. 2.2.3. Preparation of PS/GN-Starch Composites. GN-starch was dispersed into water (100 mL) using ultrasonication for 5 min. Glycerol (1.5 g) and starch (5 g) were added to the obtained suspensions. The loading levels (0, 0.248, 0.489, 0.945, and 1.774 wt %) of GN-starch were based on starch. The mixture was then heated at 90 °C for 0.5 h with constant stirring to plasticize starch. The mixture was cast into a film and dried in an air-circulating oven at 50 °C. The composite films,

GN-starch could also be extensively used to graft other natural polysaccharides on the surface of carbon materials.

2. EXPERIMENTAL DETAILS 2.1. Materials. Potato starch was purchased from Manitoba Starch Products (Manitoba, Canada). Natural graphite flakes were provided by Qingdao Tianhe Graphite Co., Ltd., China. The reagents (37.5% HCl, 98% H2SO4, 30% H2O2, 25% NH3, and 80% hydrazine) and the analytical grade reagents (NaNO3, KMnO4, N,N-dimethylacetamide, LiCl, and ethanol) were obtained from Tianjin Jiangtian Chemical Reagent Co., Ltd. in China. 2.2. Preparation. 2.2.1. Preparation of GO. GO was prepared using the modified Hummers’ method.23 Concentrated H2SO4 (46 mL) and NaNO3 (1 g) were added to an anhydrous beaker at 0 °C (ice bath), followed by the addition of graphite (2 g). Then KMnO4 (6 g) was added gradually with stirring while the temperature of the mixture was kept below 20 °C. The mixture was stirred for 2 h in the ice bath and the mixtures reacted for another 1 h at 35 °C. Distilled water (92 mL) was slowly added to the mixture, keeping the temperature at 98 °C for 15 min. The mixture was then further diluted to 280 mL with distilled water and treated with 30% H2O2. The mixture turned bright yellow. The product was centrifuged and 14202

dx.doi.org/10.1021/ie402220d | Ind. Eng. Chem. Res. 2013, 52, 14201−14207


Article

Figure 2. Characterization of GN-starch. (a) FTIR spectra of starch, GO, and GN-starch. (b) Raman spectra of GO and GN-starch. (c) TG of starch, GN, and GN-starch. (d) UV−visible spectra of GN-starch in water at the increasing concentrations from the bottom to top; the inset is a Lambert−Beer plot for the absorption peak.

tometer, Hitachi Company. The UV−vis spectra of PS/GNstarch composites were recorded using a blank cuvette as a reference. The fracture surfaces of PS/GN-starch composites were tested with a Nanosem 430 Scanning Electron Microscope. The composites were cooled in liquid nitrogen and then broken. The fracture faces were vacuum coated with gold for SEM. A Testometric AX M350-10KN was operated to test the mechanical properties at a crosshead speed of 50 mm/min for tensile testing (ISO 1184−1983 standard). PS/GN-starch composites were conditioned at 25 °C and 50% RH for 48 h before testing. The data were averaged over 6−8 specimens. Water vapor permeability (WVP) tests were carried out using ASTM method E96 (1996) with some modifications.13 The films were cut into circles, sealed over with melted paraffin, and stored in a desiccator at 25 °C. a RH of 0% was maintained using anhydrous calcium chloride in the cell. Each cell was placed in a desiccator containing saturated sodium chloride to provide a constant RH of 75%. Water vapor transport was determined by the weight gain of the permeation cell. Slopes were calculated by linear regression (weight change vs time). The water vapor transmission rate (WVTR) was defined as the slope (g/s) divided by the transfer area (m2). After the

about 0.2-mm-thick, were preconditioned in a climate chamber at 25 °C and 50% RH for at least 48 h prior to testing. 2.3. Characterization Techniques. For transmission electron microscopy (TEM) testing, the suspension of GN and GN-starch was dropped onto a copper grid, which was coated with a carbon film, air-dried, and then examined using a Tecnai G2 F20 TEM. Then, GN and GN-starch were viewed using a Hitachi S-4800 scanning electron microscope. FTIR analysis of GO, starch, and GN-starch were performed on a BIO-RAD FTS3000 IR Spectrum Scanner. The sample powders were evenly dispersed in KBr and pressed into transparent sheets for testing. Raman spectra of GO and GN-starch were recorded from 800 to 2000 cm−1 on a Renishaw inVia reflex Raman microprobe (Renishaw Instruments) using a 532 nm argon ion laser. Thermal properties of starch, GN, and GN-starch were measured with a STA 409 PC thermal analyzer, NETZSCH, Germany. The weights of the samples were about 10−15 mg, and they were heated from room temperature to 600 °C at a heating rate of 15 °C/min in a nitrogen atmosphere. The UV−visible (UV−vis) spectra of the aqueous solutions with different concentrations of GN-starch were recorded from 200 to 800 nm using a model U-1800 UV−vis spectropho14203



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Figure 3. SEM micrograph of the fragile fractured surface of PS/GN-starch composites with different contents of GN-starch. (a) 0.248 wt %, (b) 0. 489 wt %, (c) 0.945 wt %, and (d) 1.774 wt %.

permeation tests, film thickness was measured and WVP (g m−1 s−1 Pa−1) was calculated as WVP =

O− stretching. The peak at 1156 cm−1 was ascribed to C−O bond stretching of the C−O−H group, and the two peaks at 1080 and 980 cm−1 were attributed to C−O bond stretching of the C−O−C group.25 These main characteristic peaks appeared in FTIR spectrum of GN-starch. It illustrated that there were starch components in GN-starch. When GO is reduced to GN, most of the oxygen-containing (epoxide, hydroxyl, and carboxyl) groups are removed, and the sp3 carbon bonds of GO are converted into sp2 carbon bonds of GN.24 In the presence of starch, the parts of the sp3 carbon bonds were kept, and the removed oxygen containing groups were replaced with oxygen atoms of hydroxyl groups in starch. The ether bonds could form between GN and starch. As shown in Figure 2a, the intensity ratio of the peaks at 980 (the C−O− C group) and 1160 cm−1 (the C−O−H group) decreased much, when starch was grafted onto GN. The more C−O−C groups in GN-starch than starch indicated the formation of C− O−C bonds in GN-starch. The Raman spectra of GO and GN-starch are shown in Figure 2b. The peaks are observed at about 1350 cm−1 for the disordered structure of CNT (D mode) and at about 1590 cm−1 for the graphite structure of CNTs (G mode). The G band is usually related to the E2g phonon of sp2 atoms, and the D band is a breathing mode of k-point phonons of A1g symmetry.26 The intensity ratio (ID/IG) of the D band to G band in graphitic materials has been used to determine the size of sp2 domains.27 The ID/IG ratios were 0.88 for GO and 1.19 for GN-starch. The increased ID/IG ratios for GN-starch suggested the decrease in size of sp2 domains. It revealed that the disorder degree of GN-starch increased. It could be well explained by the creation of numerous new graphitic domains in GN-starch that are smaller in size than the ones presented in

WVTR ·x P(R1 − R 2)

where P is the saturation vapor pressure of water (Pa) at the test temperature (25 °C), R1 is the RH in the desiccator, R2 is the RH in the permeation cell, and x is the film thickness (m). Under these conditions, the driving force [P(R1 − R2)] is 1753.55 Pa. The electrical conductivities of composite films were stored at 75% RH in closed chambers. Volume resistivity measurements were performed on the composite films. The films with dimensions of 30 mm × 5 mm and 0.5 mm thickness were measured using a model ZL7 electrometer (SPSIC Huguang Instruments & Power Supply Branch, China) using a four-point test fixture.

3. RESULTS AND DISCUSSION 3.1. Characterization of GN-Starch. Raw graphite consisted of randomly aggregated, thin sheets. After being oxidized and reduced, the GN sheets (Figure 1a) appeared flat and transparent, with a few wrinkles and folding on the surface. Compared to GN, GN-starch (Figure 1b) became dark. It could be related to starch, which covered GN. TEM images clearly exhibited the ultrathin and homogeneous graphene sheets. Further, SEM images revealed that the surface of GN (Figure 1c) was obviously covered with polymer components, i.e., starch (Figure 1d). In Figure 2a, the FTIR spectrum of starch shows a broad band at 2920 cm−1, related to the C−H stretching vibration of methylene groups. In the fingerprint region of the starch spectrum, there are three peaks that are characteristic of −C− 14204



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GO.28 This was similar to cyclodextrin-functionalized graphene nanosheets.5 The thermogravimetric (TG) and derivative thermogravimetric (DTG) curves of starch, GN, and GN-starch are shown in Figure 2c. The thermal decomposition temperature is the temperature at the maximum rate of mass loss, which appeared at 280−320 °C for starch thermal degradation. The GN-starch exhibited a weight loss of about 50 wt % at the starch thermal decomposition temperature. The quantity of starch was calculated by matching the percentage weight loss of GNstarch to the percentage of weight loss of starch at the decomposition temperature (about 64 wt %). The starch content of GN-starch was estimated to be about 80 wt %. It revealed that a large number of starch components were functionalized on GN. Figure 2d exhibits the UV−vis spectra of GN-starch with different concentrations in distilled water. The absorption peak at about 270 nm was attributed to the characteristic absorption of graphene. The straight line passing through the origin describes the relationship of the observed absorption peak and the GN-starch concentrations. It indicated that aggregation (or precipitation) of GN-starch sheets did not occur in the tested concentration range.29 GN-starch exhibited good stability in water because of the hydrophilic starch and the thin layers of the GN sheet. The good stability of the GN-starch suspension in water was very important for the preparation of starch-based composites using the casting process. In addition, the UV−vis spectra of GO and GN (not show here) respectively had absorption peaks at 226 and 268 nm. The red shift was previously reported when GO was being reduced30 and used as a monitoring tool for the reduction of GO.31 Therefore, the absorption peaks at 270 nm for GNstarch revealed that GN in GN-starch had been reduced. 3.2. Morphology of the Composites. The SEM images of the fracture surfaces of the PS/GN-starch composites are shown in Figure 3. GN-starch sheets were found to be uniformly dispersed in the PS matrix with the different GNstarch contents from 0.248 to 1.774 wt %. It was similar to the earlier report.22 In addition, GN-starch appeared to be covered by the PS matrix, which was related to the strong interfacial interactions between starch in GN-starch and the matrix. 3.3. Mechanical Properties of the Composites. Figure 4 reveals the effect of GN-starch content on the mechanical

properties of the composites. GN-starch had an obvious reinforcing effect on the PS matrix. The tensile strength of PS was only 8.2 MPa. For the composites, the tensile strength reached 25.4 MPa at a loading level of 1.774 wt % GN-starch. The improvement in tensile strength was related to good interfacial interaction, which may have led to a higher efficiency of stress transfer from the PS matrix to the GN-starch fillers.32 In Figure 4, the changes of the elongation at the break of the composites exhibited the contrary tendency as tensile strength when GN-starch fillers were added into the PS matrix. The elongation at the break decreased from about 25% to 4% when the GN-starch loading level increased from 0 to 1.774 wt %. Generally, the well-dispersed fillers could constrain the surrounding polymers, decrease the mobility of matrix chains, and further result in the higher tensile strength and lower elongation at the break. 3.4. WVP of the Composites. Figure 5 exhibited the moisture transport through the composite films with different

Figure 5. The effect of GN-starch content on water vapor permeability of PS/GN-starch composites.

GN-starch contents. Water vapor easily went through PS film with the highest WVP values of 1.5 × 10−10 g m−1 s−1 Pa−1. With the increasing of GN-starch contents, WVP values decreased obviously. The addition of GN-starch probably introduced a tortuous path for a water molecule to pass through.17 Since GN-starch could disperse well in the matrix, there were few paths for the water molecule to pass through with the higher loading of GN-starch. Generally, the composites exhibited a moisture barrier in comparison to the pure PS film. 3.5. Functional Properties of the Composites. Figure 6a shows the ultraviolet−visible absorbance of PS/GN-starch composites with different GN-starch contents. The absorbance was remarkably enhanced by the addition of GN-starch sheets compared to the absorbance of pure PS. In the near-ultraviolet range (200−400 nm), PS exhibited low absorbance. With increasing GN-starch content, the UV absorbance and the peak intensity of the composites increased. The absorbance value peaked at 2.875 for the composite with 0.489 wt % GN-starch, meaning that the transmittance of UV light was only 0.13%, and most of the UV light was shielded. PS/GN-starch composites could effectively protect against UV light and potentially be applied to UV-shielding materials.33

Figure 4. The effect of GN-starch content on tensile strength (a) and elongation at break (b) of PS/GN-starch composites. 14205



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composites containing 1.774 wt % GN-starch, the tensile strength reached 25.4 MPa, while the tensile strength of PS was only 8.2 MPa. WVP values decreased from 1.5 × 10−10 to 1.1 × 10−10 g m−1 s−1 Pa−1 when the loading of GN-starch increased from 0 to 0.248 wt %. GN-starch also endowed the PS matrix with UV absorbance and electrical conductivity. Most of the UV light could be shielded by PS/GN-starch composites, and the conductivity of the composite could reach 9.7 × 10−4 S/cm at a GN-starch content of 1.774 wt %.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 22 27406144. Fax: +86 22 27403475. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Science and Technology Project of Jiangxi Provincial Office of Education (KJLD12082, GJJ12590, and Innovation Platform “project 311”) and Nature Science Foundation of Jiangxi Province (20132BAB 206006) and the National Nature Science Foundation of China (51162011).

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REFERENCES

(1) Wang, X.; Yang, H. Y.; Song, L.; Hu, Y.; Xing, W. Y.; Lu, H. D. Morphology, Mechanical and Thermal Properties of GrapheneReinforced Poly(butylene succinate) Nanocomposites. Compos. Sci. Technol. 2011, 72, 1−6. (2) Feng, Y. Y.; Zhang, X. Q.; Shen, Y. T.; Yoshino, K.; Feng, W. A mechanically strong, flexible and conductive film based on bacterial cellulose/graphene nanocomposite. Carbohydr. Polym. 2012, 87, 644− 649. (3) Wang, L.; Tian, L. H.; Wei, G. D.; Gao, F. M; Zheng, J. J.; Yang, W. Y. Epitaxial Growth of Graphene and their Applications in Devices. J. Inorg. Mater. 2011, 26, 1009−1019. (4) Wang, K.; Feng, T.; Qian, M.; Ding, H.; Chen, Y. W.; Sun, Z. The Field Emission of Vacuum Filtered Graphene Films Reduced by Microwave. Appl. Surf. Sci. 2011, 257, 5808−5812. (5) Guo, Y. J.; Guo, S. J.; Ren, J. T.; Zhai, Y. M.; Dong, S. J.; Wang, E. Cyclodextrin Functionalized Graphene Nanosheets with High Supramolecular Recognition Capability: Synthesis and Host-Guest Inclusion for Enhanced Electrochemical Performance. ACS Nano 2009, 7, 4001−4010. (6) Verdejo, R.; Barroso-Bujans, F.; Rodriguez-Perez, M. A.; Saja, J. A. D.; Lopez- Manchado, M. A.. Functionalized Graphene Sheet Filled Silicone Foam Nanocomposites. J. Mater. Chem. 2008, 18, 2221−2226. (7) Stankovich, S.; Piner, R. D.; Chen, X.; Wu, N.; Nguyen, S. T.; Ruoff, R. S. Stable Aqueous Dispersions of Graphitic Nanoplatelets via the Reduction of Exfoliated Graphite Oxide in the Presence of Poly(sodium 4-styrenesulfonate). J. Mater. Chem. 2006, 16, 155−158. (8) Patil, A. J.; Vickery, J. L.; Scott, T. B.; Mann, S. Aqueous Stabilization and Self-Assembly of Graphene Sheets into Layered Bionanocomposites Using DNA. Adv. Mater. 2009, 21, 3159−3164. (9) Liu, D. G.; Zhong, T. H.; Chang, P. R.; Li, K. F.; Wu, Q. L. Starch Composites Reinforced by Bamboo Cellulosic Crystals. Bioresour. Technol. 2001, 101, 2529−2536. (10) Ma, X. F.; Jian, R. J.; Chang, P. R.; Yu, J. G. Fabrication and Characterization of Citric Acid-Modified Starch Nanoparticies/ Plasticized-Starch Composites. Biomacromolecules 2008, 9, 3314− 3320. (11) Chang, P. R.; Wu, D. L.; Anderson, D. P.; Ma, X. F. Nanocomposites Based on Plasticized Starch and Rectorite Clay: Structure and Properties. Carbohydr. Polym. 2012, 89, 687−693.

Figure 6. Functional properties of PS/GN-starch composites. (a) ultraviolet−visible absorbance, (b) electrical conductivity.

The conductivity of PS/GN-starch composite films with different GN-starch contents is shown in Figure 6b. After reduction, the sp2 hybridized structure of graphites was partly restored, and the conductivity of the composite was enhanced by the increasing GN-starch content. By increasing the GNstarch content from 0 to 0.248 wt %, the conductivity of the composites increased by 5−6 orders of magnitude in contrast with PS. The uniform dispersion of GN-starch improved the conductivity of the PS matrix, probably due to the formation of conductive networks throughout the insulating PS matrix.34 With a higher GN-starch content (>0.248 wt %), the enhancement of the conductivity was not obvious.

4. CONCLUSIONS A method was successfully developed to fabricate starch-grafted graphene nanosheets. This method would be applied to the function of other natural polysaccharides at the surface of carbon materials to overcome the aggregation of CNT or graphene. The obtained GN-starch exhibited good stability in water, ascribed to the hydrophilic starch and the thin sheets of graphene. The grafted starch in GN-starch could form hydrogen bond interactions with a PS matrix. These interactions and the uniform dispersion of GN-starch sheets in the PS matrix could improve mechanical and moisture barrier properties of PS/GN-starch composites. For the 14206



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polypropylene composites reinforced with recycled fibers. Chem. Eng. J. 2011, 166, 1170−1178. (33) Ma, X. F.; Chang, P. R.; Yang, J. W.; Yu, J. G. Preparation and Properties of Glycerol Plasticized-Pea Starch/Zinc Oxide-Starch Bionanocomposites. Carbohydr. Polym. 2009, 75, 472−478. (34) Feng, Y.; Huang, S. H.; Kang, K.; Duan, X. X. Preparation and characterization of graphene and few-layer grapheme. New Carbon Mater. 2011, 26, 26−30.

(12) Pushpadass, H. A.; Hanna, M. A. Age-Induced Changes in the Microstructure and Selected Properties of Extruded Starch Films Plasticized with Glycerol and Stearic Acid. Ind. Eng. Chem. Res. 2009, 48, 8457−8463. (13) Yu, J. G.; Yang, J. W.; Liu, B. X.; Ma, X. F. Preparation and Characterization of Glycerol Plasticized-Pea Starch/ZnO-Carboxymethyl-Cellulose Sodium Nano- composites. Bioresour. Technol. 2009, 100, 2832−2841. (14) Ma, X. F.; Yu, J. G.; Wang, N. Production of Thermoplastic Starch/ MMT-Sorbitol Nanocomposites by Dual-Melt Extrusion Processing. Macromol. Mater. Eng. 2007, 292, 723−728. (15) Gironès, J.; López, J. P.; Mutjé, P .; Carvalho, A. J. F.; Curvelo, A. A. S.; Vilaseca, F. Natural fiber-reinforced thermoplastic starch composites obtained by melt processing. Compos. Sci. Technol. 2012, 72, 858−863. (16) Kumar, A. P.; Singh, R. P. Biocomposites of Cellulose Reinforced Starch: Improvement of Properties by Photo-induced Crosslinking. Bioresour. Technol. 2008, 99, 8803−8809. (17) Chang, P. R.; Jian, R. J.; Zheng, P. W.; Yu, J. G.; Ma, X. F. Preparation and Properties of Glycerol Plasticized-starch (GPS)/ Cellulose Nanoparticle (CN) Composites. Carbohydr. Polym. 2010, 79, 301−305. (18) Chang, P. R.; Jian, R. J.; Yu, J. G.; Ma, X. F. Fabrication and Characterization of Chitosan Nanoparticles/Plasticized-starch Composites. Food Chem. 2010, 120, 736−740. (19) Qian, D. Y.; Chang, P. R.; Zheng, P. W.; Ma, X. F. Preparation and Characterization of Plasticized Starch/Carbon Black-Oxide Nanocomposites. Ind. Eng. Chem. Res. 2012, 51, 7941−7947. (20) Cao, X. D.; Chen, Y.; Chang, P. R.; Huneault, M. A. Preparation and Properties of Plasticized Starch/Multiwalled Carbon Nanotubes Composites. J. Appl. Polym. Sci. 2007, 106, 1431−1437. (21) Liu, Z. J.; Zhao, L.; Chen, M. N.; Yu, J. G. Effect of Carboxylate Multi-walled Carbon Nanotubes on the Performance of Thermoplastic Starch Nanocomposites. Carbohydr. Polym. 2012, 83, 447−451. (22) Ma, T. T.; Chang, P. R.; Zheng, P. W.; Ma, X. F. The Composites Based on Plasticized Starch and Graphene Oxide/ Reduced Graphene Oxide. Carbohydr. Polym. 2013, 94, 63−70. (23) Hummers, W. S.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339−1339. (24) Luo, D. C.; Zhang, G. X.; Liu, J. F.; Sun, X. M. Evaluation Criteria for Reduced Graphene Oxide. J. Phys. Chem. C 2011, 115, 11327−11335. (25) Chang, P. R.; Zheng, P. W.; Liu, B. X.; Anderson, D. P.; Yu, J. G.; Ma, X. F. Characterization of Magnetic Soluble Starch-functionalized Carbon Nanotubes and its Application for the Adsorption of the Dyes. J. Hazard. Mater. 2011, 186, 2144−2150. (26) Haubner, K.; Murawski, J.; Olk, P.; Eng, L. M.; Ziegler, C.; Adolphi, B.; Jaehne, E. The route to functional graphene oxide. Chemphyschem 2010, 11, 2031−2139. (27) Dong, H. Q.; Li, Y. Y.; Yu, J. H.; Song, Y. Y.; Cai, X. J.; Liu, J. Q.; Zhang, J. M.; Ewing, R. C.; Shi, D. L. A Versatile Multicomponent Assembly via β-cyclodextrin Host-Guest Chemistry on Graphene for Biomedical Applications. Small 2013, 9, 446−456. (28) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of Graphene-Based Nanosheets via Chemical Reduction of Exfoliated Graphite Oxide. Carbon 2007, 45, 1558−1565. (29) Wu, Z. G.; Feng, W.; Feng, Y. Y.; Liu, Q.; Xu, X. H.; Sekino, T.; Fujii, A.; Ozaki, M. Preparation and Characterization of ChitosanGrafted Multiwalled Carbon Nanotubes and their Electrochemical Properties. Carbon 2007, 45, 1212−1218. (30) Kim, T.; Lee, H.; Kim, J.; Suh, K. S. Synthesis of Phase Transferable Graphene Sheets Using Ionic Liquid Polymers. ACS Nano 2010, 4, 1612−1618. (31) Li, D.; Mueller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable aqueous dispersions of graphene nanosheets. Nature Nanotechnol. 2008, 3, 101−105. (32) Franco-Marquès, E.; Méndez, J. A.; Pèlach, M. A.; Vilaseca, F.; Bayer, J.; Mutjé, P. Influence of coupling agents in the preparation of 14207


Fabrication and Properties of Starch-Grafted Graphene Nanosheet

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