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Structure and Thermal Properties of Rice Starch-based Film Blended with Mesocarp Cellulose Fiber
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 17 (2019) 2039–2047
www.materialstoday.com/proceedings
MRS-Thailand 2017
Structure and Thermal Properties of Rice Starch-based Film Blended with Mesocarp Cellulose Fiber Sasikan Suwanprateepa,*, Chawanwit Kumsapayaa, Pornyuth Sayana a
Faculty of Science and Technology, Rajamangala University of Technology Suvarnabhumi, Nonthaburi 11000, Thailand
Abstract Mesocarp fiber is one of the wastes from palm oil mill process. It is a source of cellulose, which can be chemically treated to obtain mesocarp cellulose fiber. It can improve the properties of film and increase the value of palm oil. In this study, rice starchbased film blended with mesocarp cellulose fiber was prepared by casting method. The two-step process, the pretreatment and bleaching followed by an acid hydrolysis, provided the mesocarp cellulose fiber. The obtained rice starch-based films with 2%, 4%, 6% and 8% by weight of mesocarp cellulose fiber were characterized. It indicated that the fiber content in the composites was more than 8wt%, making the film tore easily and cannot peel the mold off. The chemical structure of rice starch-based film and its composites were studied by Fourier transform infrared spectroscopy (FTIR). The results showed the same pattern of spectra, indicating that the amount of fibers and the added chemicals cannot affect on the chemical structure of the developed film. The thermal stability was investigated by thermogravimetric/differential thermogravimetric analysis (TGA/DTG).It revealed that the thermal stability shifted towards higher temperatures with increasing amount of fiber Rice starch-based film containing 8% by weight of mesocarp cellulose fiber provided the highest thermal stability. Moreover, cellulose fiber can reduce the water absorption properties. The lowest water absorption of the composites was obtained when the films with 8% by weight of mesocarp cellulose fiber were used. This is a result of a reduction of the moisture sensitivity of starch. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The First Materials Research Society of Thailand International Conference. Keywords: Starch film; Mesocarp fiber; Cellulose; Bio-composite
* Corresponding author. Tel.: +662-968-1058; fax: +662-525-0497. E-mail address:[email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The First Materials Research Society of Thailand International Conference.
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Nomenclature St MCF St-MCF g ml o C
Starch Mesocarp cellulose fiber Rice Starch-based film blended with mesocarp cellulose fiber Gram Milliliter Degree Celsius
1. Introduction Currently, the development of bio-based products is gaining interest because it can reduce the demand for petroleum-based products that can cause global warming. Among biopolymers, starch is one of the biopolymers used in the production because of its versatility, inexpensive price, abundance and biodegradability. Normally, the starch can be used to produce thermoplastic by using heat as well as shear forces with various plasticizers such as water and glycerol together. Bioplastics derived from starch are utilized in a number of products such as food packaging films [1]. However, the properties of the biopolymer are not good enough to use, therefore the development of biopolymer properties is required for the applications, such as the mechanical and thermal properties. In previous researches, it can improve the properties of biopolymer by using several approaches, such as the blending of starch with polymers, the chemical modification of the starch and the addition of fiber or cellulose [2-6]. The fiber reinforcement is a technique commonly used of starch-based biopolymer. The cellulose were prepared to produce starch-based biopolymer with different sources, including rice husk [7], rice straw [8], luffa fiber [9], cotton stalk bark [10] and grape fruit peel [11]. Oil palm is one of the economic crops. In addition, a large crop has been cultivated in the south of Thailand with a capacity of more than one million tons per year. In the process of extracting palm oil, the waste is composed of empty bunch fiber, mesocarp fiber, shell, waste water and cake decanter. These wastes are utilized widely. The empty bunch shell and coconut fiber can be used as fuels, boiler and animal feed. The wastewater is applied to produce biogas for electricity. The sludge is also treated to produce organic fertilizer. One of the waste residues in the palm oil extraction plant is the palm oil fiber derived from mesocarp. The cellulose in the mesocarp fiber has improved the properties of the polymers because of its high crystalline nature [12]. Moreover, the hydrophilic properties of the cellulose can be incorporated with rice starch-based film as a matrix. Solution casting method was used for the preparation of composites because it consumes less energy than the hot pressing and the compression molding methods. In this research, rice starch, which is easily available in Thailand, blended with cellulose derived from mesocarp fiber was prepared to obtain the rice starch-based film composites by solution casting method. The effect of cellulose fiber contents on structure and thermal properties of composites were studied. 2. Experimental 2.1. Materials Rice starch was purchased at a local market from Cho Heng Rice Vermicelli Factory Co., Ltd. (Thailand). Mesocarp fiber was obtained from Smothong palm oil Co., Ltd. (Thailand). This fiber sample was fed to the pressing screw in order to press out excess oil and moisture. Eventually, a form of fiber was obtained. 2.2. Mesocarp cellulose fiber preparation There are two stages of mesocarp fiber extraction: the pretreatment and bleaching process followed by hydrolysis process according to the literature [13]. By following first process, pretreatment and bleaching, it can remove the impurities and waxy substances from the surface of fiber to obtain high purity of cellulose fiber. In palm oil industry, mesocarp was pressed and screwed in order to remove oil and moisture. Firstly, the fibers were dried by
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oven at 70 oC for 1 day. The fibers were thus shredded by a two roll mill machine, and sieved through a 40 mesh sieve. 100 g of these fibers were immersed in hot distilled water (500 ml) at 80 oC for 12 hours, and filtered in order to be water-soluble extractives. The residue was added into 1000 mL of 2.5 Mol.L-1 sodium hydroxide solution and stirred by hot plate stirrer at 120 oC for 20 min. Then it was vacuum filtered with no.1 Whatman filter paper. After that, the bleaching process was continued by using sodium hypochlorite solution with 6% active chlorine. The sodium hypochlorite solution will be separated from the fibers by filtration. Then, these fibers were washed with the distilled water. This process was repeated for three times and the white fibers will be obtained. Subsequently, the treated fibers were dried in oven at 37 oC before using them. The bleached fibers were treated by acid hydrolysis to obtain the cellulose fibers. Sulfuric acid solution (64% by weight) was added into the mesocarp fiber with the ration of 1-10 g/ml at 45 oC for 90 min. The suspension was separated by centrifugation (4,000 rpm, 10 min). The precipitates from suspension were washed repeatedly by deionized water until the pH became 5. Then, the dialysis of precipitates in water was carried out for 5 days. Subsequently, the mesocarp cellulose fibers were obtained after the suspension was homogenized at 12,000 rpm for 30 min. It was stored in a refrigerator before further using. 2.3. Preparation of rice starch-based film blended with mesocarp cellulose fiber The solution prepared by mixing 4 g of rice starch and 2.5 g of glycerol as plasticizer was blended together in 100 ml of distilled water by using magnetic stirrer. Then, the chitosan dissolved in 10% acetic acid solution was introduced into the mixture. This ratio of solution is suitable for the film formation. Mesocarp cellulose fibers were added into this solution with 2%, 4%, 6% and 8% by weight of rice starch. All formulations were mixed by using magnetic stirrer at 90 oC for 30 min. Plasticizers can improve the thermal properties of starch during the molding process. The solution was transferred to the mold then heated at 50 oC for 24 hours to obtain the rice starch-based film. The structure and thermal properties of the films were characterized. 2.4 Rice Starch-based Film Characterization 2.4.1 FTIR analysis The rice starch-based films were chemically characterized by Fourier transformed infrared spectrophotometer (FTIR) using Thermo Scientific Nicolet 6700 model. The FTIR analyses of these films were operated by attenuated total reflectance (ATR) technique. All spectra were obtained in the frequency range between 4000 and 400 cm−1 (wavenumber) at a resolution of 4 cm−1 with the average of 64 scans per sample. 2.4.2 Transparent analysis The film transparency was obtained by UV-Vis spectrometer (Model Evolution 300, Thermo). Rice starchbased films were cut to 1×3 cm and placed on the internal side of a spectrophotometer cell. Transmittance data were recorded at 480 nm because the sample was seen in yellow, which was the maximum absorption at a wavelength of 480 nm. Then the film transparency was defined as the percentage of light that allowed to be transmitted across the film. Percentage of transmittance (%T) was calculated by Beer-Lambert law as stated below, where A=absorbance at 480 nm. %T = 100 (10^-A) 2.4.2 Thermal analysis (TGA) The thermal stability of rice starch-based film was investigated through thermo-gravimetric analysis (TGA). TGA was carried out in a Mettler Toledo (Model DSC1) instrument. All experiments were performed from 50◦C to 600◦C in the nitrogen atmosphere (15 ml/min) with a heating rate of 20◦C/min.
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2.4.3 Water uptake test The water absorption ability of the film can be determined by the percentage of water uptake. In this test, a desiccator chamber was operated at 50%RH and 2.5x2.5 cm of film dimensions was prepared. The sample was dried at 50 oC for 24 hours and placed in the desiccator chamber. The weight difference was measured daily until the mass of the samples was almost constant. The water uptake of films was calculated by the following equation: Water uptake% = (Mf-Mi)/Mi x 100 when Mf is the final sample mass and Mi is the initial sample mass. 2.4.4 Film thickness Film thickness was determined by using a digital micrometre (Mitutoyo Co., Japan) with 0.001mm sensitivity. The thickness measurements were obtained from five different positions on the film for each sample. The mean value of measurements for individual sample was utilized. 3. Results and discussion 3.1 Film formation Rice starch-based films containing 0%, 2%, 4%, 6% and 8% mesocarp cellulose fiber (St-MCF) were formed. Fiber content in the composites was more than 8 wt%, making the film tore easily and cannot peel the mold off. The produced rice starch-based film was white transparent and flexible. A light brown film was obtained when the mesocarp cellulose fiber was added into the film as shown in Figure 1. The color of the film became darker when the fiber content increased. The transparency was characterized by UV-Vis spectrophotometer. The transparency was determined according to the method established by Han and Floros [14]. The films were cut into 9×45 mm dimensions and placed inside the measuring cell of the spectrophotometer. The optical absorbance was recorded at 600 nm and the percentage of transmittance was calculated. Table 1 shows the transmittance of the film at 600 nm. The films were transparent at low mesocarp cellulose fiber content but they became opaque when the fiber content increases. This is because the fiber agglomeration may also occur leading to the light scattering and subsequently the decrease of light transmittance of the film. The thickness of the films was observed in the range between 0.472 to 0.478 mm. The values obtained were not significantly different. It demonstrated that the thin film was more transparent than the thick one, which corresponding to the trend of %T. Table 1 Absorbance and transparency of the formed films. Percentage Absorbance Film of Transmittance 480nm (A ) (%T) St-MCF0% 0.487 32.58 St-MCF2% 0.575 26.60 St-MCF4% 0.582 26.18 St-MCF6% 0.586 25.94 St-MCF8% 0.611 24.49
Film thickness (mm) 0.472 0.475 0.475 0.477 0.478
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Fig.1 Rice starch-based film containing 0%, 2%, 4%, 6% and 8% of mesocarp cellulose fiber
3.2 FTIR spectroscopy Figure 2 shows FTIR spectra of raw rice starch, mesocarp fiber, rice starch-based film (St-MCF0%) and its composites (St-MCF 2-8%).
(g) (f)
Transmittance
(e) (d)
2933
2850
1643 1162
(c) (b)
1034
3306 1500
(a)
3900
3400
2900
2400
Wavenumber
1900
1400
900
400
(cm-1)
Fig.2 FTIR spectra of native rice starch (a), raw mesocarp fiber (b), rice starch-based films (c) and rice starchbased film containing 2%(d) 4%(e) 6%(f) and 8%(g) of mesocarp cellulose fiber
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All spectra of St-MCF showed the same pattern of bands. These results show that the addition of various amounts of mesocarp cellulose fiber does not affect on FTIR spectra. The peak was observed at 3306 cm-1, a peak characteristic of OH stretching from St-MCF which the bandwidth was narrower than that of the raw rice starch. This is because the cellulose fiber decreased the water absorption and the presence of structure of polysaccharide in the raw starch [15]. The plasticizing process may cause the intramolecular and intermolecular hydrogen bonding between the molecules of starch due to the presence of glycerol [16-17]. All spectra exhibited the peak at 2933 cm-1 which can be assigned to CH vibrations of hydrocarbon backbone of starch and rice starch-based films. These two stretching peaks related to the aliphatic moieties in cellulose and hemicelluloses [18]. An additional peak at about 2850 cm-1 is due to CH and CH2 stretching in cellulose [19]. Moreover, the ST-MCF showed similar pattern of bands namely the peaks at 1643, 1162 and 1034 cm-1 attributed to OH deformation of H2O, C-O-C asymmetric stretching of cellulose and CO stretching of cellulose, respectively [20]. However, the peaks of St-MCF at 1346 and 1500 cm-1 indicated C=C were not appeared due to lignin removed from the treatment process but this peak is apparent in the raw mesocarp fiber [21]. Therefore, FTIR spectra can confirm that mesocarp cellulose fiber can be obtained after through two stages; the pretreatment and bleaching process and the acid hydrolysis process. 3.3 Thermo-gravimetric analysis (TGA) The thermal decomposition of the film that produced from rice starch-based film blended with mesocarp cellulose fibre was investigated. TG and first-derivative thermogravimetric (DTG) curves were obtained as shown in Figure 3. All TG curves of St-MCF show three steps of degradation as shown in Figures 3(a). Initial decomposition was observed due to the moisture removal [15,22]. The DTG curves of St-MCF show first peak at about 120oC, which are responsible to TG curves. Further, the decomposition of TG curve was obtained in range 200-350oC that DTG curve is seen in two peak at about 280oC and 350oC. The reason is the first one at 280oC is the decomposition of glycerine content and the second peak at 350oC is the decomposition of starch content [4,15]. The increasing mesocrap cellulose fibre improves thermal stability of the composites. For example, the second mass loss decreases from 73.21% of St-MCF0% to 70.86% of St-MCF8% as shown in Table2. Cellulose decomposition was occurred by depolymerisation, thermo-oxidation and dehydration, depending on the presence of type of gases in the experiment [23]. However, the decomposition was not observed at 280-500oC of lignin due to the fiber treated corresponding to the results of FTIR. Table 2 shows the onset temperature of St-MCF at 0%, 2%, 4%, 6%, and 8% of cellulose fiber. The onset temperature of St-MCF0% and St-MCF2-8% is 198oC and 225-260oC, respectively. The results showed that the onset temperature increased when mesocarp cellulose fiber was added. This may be the increased amount of fatty, wax, hemicellulose and cellulose in the composites [24-26]. Moreover, the mesocarp cellulose fiber incorporated into the rice starch-based film interacted strongly so its composites offered better thermal stability. Table 2 Thermo-gravimetric analysis data of rice starch-based films and its composites containing mesocarp cellulose fiber. Film
Onset temperature (oC)
Initial mass loss%
Second mass loss%
St-MCF 0% St-MCF 2% St-MCF 4% St-MCF 6% St-MCF 8%
198 225 249 255 260
12.70 12.71 13.79 14.54 15.99
73.21 72.23 72.07 70.87 70.86
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a 120
%Weight loss
100 80 StMCF8% StMCF6%
60
StMCF4%
40
StMCF2% StMCF0%
20 0 50
150
250
350
Temperature
450
550
(oC)
b -0.014
DTG/ug min-1)
-0.012 -0.01 -0.008 StMCF8% StMCF6% StMCF4% StMCF2% StMCF0%
-0.006 -0.004 -0.002 0 50
150
250
350
450
550
Temperature (oC) Fig.3 Thermogram (a) TG curves and (b) DTG curves of rice starch-based films and its composites containing mesocarp cellulose fiber.
3.4 Water uptake Figure 4 shows the results of the water absorption properties of film that reported the percentage of water uptake. The water uptake of rice starch-based film blended with mesocarp cellulose fiber (St-MCF) ranged about 26-53%. The film blended with 8% cellulose provided the lowest value of water uptake (26%). The results showed that the water absorption of the film decreased by increasing the mesocarp cellulose fiber contents. This may be cellulosic structure of the fiber decreased the moisture sensitivity of film, correspoding to the FTIR results [27].
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Water uptake (%)
50 40 30 StMCF0% StMCF2% StMCF4% StMCF6% StMCF8%
20 10 0 0
1
2
3
4
5
6
7
Days
Fig.4 Water uptake of films with different fiber contents
4. Conclusions Rice starch-based films blended with mesocarp cellulose fiber were prepared by solution cast method with the percentage of transmittance in range 24.49-26.60. The spectra of FTIR technique revealed that the mesocarp cellulose fiber did not affect chemical structure of the rice starch-based films. Moreover, FTIR spectra can confirm that cellulose obtained after through the two steps; the pretreatment and bleaching process and the hydrolysis process. Increasing of additions of mesocarp cellulose fiber from 2-8% to the starch matrix resulted in the enhanced thermal stability, which shown by the decrease of degradation temperature and the increase of onset temperature. The St-MCF8% gave the lowest value of water uptake (26%) because the fiber may increase the crystallinity in the structure of St-MCF, resulting in less water absorption. Acknowledgements The authors are grateful to Rajamangala University of Technology Suvarnabhumi for the financial and laboratory support. References [1] L. Averousa, N. Boquillonb, Carbohydr. Polym. 56 (2004) 111-122. [2] A.O. Ashogbon, E.T. Akintayo, Starch-St€arke 66 (2014) 41-57. [3] A. Cano, E. Fortunati, J.M. Chafer, M. Kenny, A. Chiralt, C. Gonzalez-Martínez, Food Hydrocoll. 48 (2015) 84-93. [4] H. Ibrahim, M. Farag, H. Megahed, S. Mehanny, Carbohydr. Polym. 101 (2014) 11-19. [5] M.G. Lomelí-Ramírez, S.G. Kestur, R. Manríquez-Gonzalez, S. Iwakiri, G.B. de Muniz, T.S. Flores-Sahagun, Carbohydr. Polym. 102 (2014) 576-583. [6] R. Ortega-Toro, A. Munoz, P. Talens, A. Chiralt, Food Hydrocoll. 56 (2016) 9-19. [7] A.M. Das, M.P. Hazarika, M. Goswami, A. Yadav, P. Khound, Carbohydr. Polym. 141 (2016) 20–27. [8] M. Boonterm, S. Sunyadeth, S. Dedpakdee, P. Athichalinthorn, S. Patcharaphun, R. Mungkung, R. Techapiesancharoenkij, J. Clean. Prod. 134 (2016) 592–599. [9] K. Kaewtatip, J. Thongmee, Mater. Des. 40 (2012) 314-318. [10] X. Miao, J. Lin, F. Tian, X. Li, F. Bian, J. Wang, Carbohydr. Polym. 136 (2016) 841–850. [11] M. Karatas, N. Arslan, Food Hydrocolloids 58 (2016) 235–245. [12] F. Ansari, M. Skrifvars, L. Berglund, Compos. Sci. Technol. 117 (2015) 298-306. [13] M.H. Salehudin, E. Salleh, S.N.H. Mamat, I.I. Muhamad, Proced. Chem. 9 (2014) 23-33.
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[14] J.H. Han, J. D. Floros, J. Plast. Film Sheet. 13 (1997) 287–298. [15] M.G. Lomeli-Ramirez, S.G. Kestur, R. Manriquez-Gonzalez, S. Iwakiri, G.B. de Muniz, T.S. Flores-Sahagun. Carbohyd. Polym. 102 (2014) 576-583. [16] X. Ma, P.R. Chang, J. Yu, M. Stumborg, Carbohyd. Polym. 62 (2005) 19-24. [17] R. Shi, Q. Ding, T. Han, Y. Zhang, D. Che, J. Appl. Polym. Sci. 103 (2007) 374-386. [18] B.M. Cherian, L.A. Pothan, T. Nguyen-Chung, G. Menning, M. Kottaisamy, S. Thomas, Agric. Food Chem. 56 (2008) 5617-27. [19] M.A. Tshabalala, Surface characterization. In: Rowell RM, editor. Handbook of wood chemistry and wood composites, London, 2005. [20] M.F. Rosa, E.S. Medeiros, J.A. Malmonge, K.S. Gregorski, D.F. Wood, L.H.C. Mattoso, G. Glenn, W.J. Orts, S.H. Imam, Carbohyd. Polym. 81 (2010) 83-92. [21] Y.N. Guragain, J.D. Coninck, F. Husson, A. Durand, S.K. Rakshit, Bioresour. Technol. 102 (2011) 4416-24. [22] H.Liu, F.Xie, L.Yu, L.Chen, L.Li, Prog. Polym. Sci. 34 (2009) 1348-1368. [23] B.Neher, Md.M.R. Bhuiyan, H.Kabir, Md.A.Gafur, Md.R. Qadir, F.Ahmed, J. Therm. Anal. Calorim. 124 (2016) 1281-1289. [24] Z.N. Azwa, B.F. Yousif, A.C. Manalo, W. Karunasena, Mater Des. 47 (2013) 424-442. [25] M.S. Huda, L.T. Drzal, M. Misra, A.K. Mohanty, K. Williams, D.F. Mielewski, Ind. Eng. Chem. Res. 44 (2012) 5593–601. [26] B. Wielage, T. Lampke, G. Mark, K. Nestler, D. Starke. Thermochim Acta. 337 (1999) 169–77. [27] J. Guan, M.A. Hanna, Bioresour. Technol. 97 (2006) 1716-26.
ScienceDirect Materials Today: Proceedings 17 (2019) 2039–2047
www.materialstoday.com/proceedings
MRS-Thailand 2017
Structure and Thermal Properties of Rice Starch-based Film Blended with Mesocarp Cellulose Fiber Sasikan Suwanprateepa,*, Chawanwit Kumsapayaa, Pornyuth Sayana a
Faculty of Science and Technology, Rajamangala University of Technology Suvarnabhumi, Nonthaburi 11000, Thailand
Abstract Mesocarp fiber is one of the wastes from palm oil mill process. It is a source of cellulose, which can be chemically treated to obtain mesocarp cellulose fiber. It can improve the properties of film and increase the value of palm oil. In this study, rice starchbased film blended with mesocarp cellulose fiber was prepared by casting method. The two-step process, the pretreatment and bleaching followed by an acid hydrolysis, provided the mesocarp cellulose fiber. The obtained rice starch-based films with 2%, 4%, 6% and 8% by weight of mesocarp cellulose fiber were characterized. It indicated that the fiber content in the composites was more than 8wt%, making the film tore easily and cannot peel the mold off. The chemical structure of rice starch-based film and its composites were studied by Fourier transform infrared spectroscopy (FTIR). The results showed the same pattern of spectra, indicating that the amount of fibers and the added chemicals cannot affect on the chemical structure of the developed film. The thermal stability was investigated by thermogravimetric/differential thermogravimetric analysis (TGA/DTG).It revealed that the thermal stability shifted towards higher temperatures with increasing amount of fiber Rice starch-based film containing 8% by weight of mesocarp cellulose fiber provided the highest thermal stability. Moreover, cellulose fiber can reduce the water absorption properties. The lowest water absorption of the composites was obtained when the films with 8% by weight of mesocarp cellulose fiber were used. This is a result of a reduction of the moisture sensitivity of starch. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The First Materials Research Society of Thailand International Conference. Keywords: Starch film; Mesocarp fiber; Cellulose; Bio-composite
* Corresponding author. Tel.: +662-968-1058; fax: +662-525-0497. E-mail address:[email protected]
2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The First Materials Research Society of Thailand International Conference.
2040
S. Suwanprateep et al. / Materials Today: Proceedings 17 (2019) 2039–2047
Nomenclature St MCF St-MCF g ml o C
Starch Mesocarp cellulose fiber Rice Starch-based film blended with mesocarp cellulose fiber Gram Milliliter Degree Celsius
1. Introduction Currently, the development of bio-based products is gaining interest because it can reduce the demand for petroleum-based products that can cause global warming. Among biopolymers, starch is one of the biopolymers used in the production because of its versatility, inexpensive price, abundance and biodegradability. Normally, the starch can be used to produce thermoplastic by using heat as well as shear forces with various plasticizers such as water and glycerol together. Bioplastics derived from starch are utilized in a number of products such as food packaging films [1]. However, the properties of the biopolymer are not good enough to use, therefore the development of biopolymer properties is required for the applications, such as the mechanical and thermal properties. In previous researches, it can improve the properties of biopolymer by using several approaches, such as the blending of starch with polymers, the chemical modification of the starch and the addition of fiber or cellulose [2-6]. The fiber reinforcement is a technique commonly used of starch-based biopolymer. The cellulose were prepared to produce starch-based biopolymer with different sources, including rice husk [7], rice straw [8], luffa fiber [9], cotton stalk bark [10] and grape fruit peel [11]. Oil palm is one of the economic crops. In addition, a large crop has been cultivated in the south of Thailand with a capacity of more than one million tons per year. In the process of extracting palm oil, the waste is composed of empty bunch fiber, mesocarp fiber, shell, waste water and cake decanter. These wastes are utilized widely. The empty bunch shell and coconut fiber can be used as fuels, boiler and animal feed. The wastewater is applied to produce biogas for electricity. The sludge is also treated to produce organic fertilizer. One of the waste residues in the palm oil extraction plant is the palm oil fiber derived from mesocarp. The cellulose in the mesocarp fiber has improved the properties of the polymers because of its high crystalline nature [12]. Moreover, the hydrophilic properties of the cellulose can be incorporated with rice starch-based film as a matrix. Solution casting method was used for the preparation of composites because it consumes less energy than the hot pressing and the compression molding methods. In this research, rice starch, which is easily available in Thailand, blended with cellulose derived from mesocarp fiber was prepared to obtain the rice starch-based film composites by solution casting method. The effect of cellulose fiber contents on structure and thermal properties of composites were studied. 2. Experimental 2.1. Materials Rice starch was purchased at a local market from Cho Heng Rice Vermicelli Factory Co., Ltd. (Thailand). Mesocarp fiber was obtained from Smothong palm oil Co., Ltd. (Thailand). This fiber sample was fed to the pressing screw in order to press out excess oil and moisture. Eventually, a form of fiber was obtained. 2.2. Mesocarp cellulose fiber preparation There are two stages of mesocarp fiber extraction: the pretreatment and bleaching process followed by hydrolysis process according to the literature [13]. By following first process, pretreatment and bleaching, it can remove the impurities and waxy substances from the surface of fiber to obtain high purity of cellulose fiber. In palm oil industry, mesocarp was pressed and screwed in order to remove oil and moisture. Firstly, the fibers were dried by
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oven at 70 oC for 1 day. The fibers were thus shredded by a two roll mill machine, and sieved through a 40 mesh sieve. 100 g of these fibers were immersed in hot distilled water (500 ml) at 80 oC for 12 hours, and filtered in order to be water-soluble extractives. The residue was added into 1000 mL of 2.5 Mol.L-1 sodium hydroxide solution and stirred by hot plate stirrer at 120 oC for 20 min. Then it was vacuum filtered with no.1 Whatman filter paper. After that, the bleaching process was continued by using sodium hypochlorite solution with 6% active chlorine. The sodium hypochlorite solution will be separated from the fibers by filtration. Then, these fibers were washed with the distilled water. This process was repeated for three times and the white fibers will be obtained. Subsequently, the treated fibers were dried in oven at 37 oC before using them. The bleached fibers were treated by acid hydrolysis to obtain the cellulose fibers. Sulfuric acid solution (64% by weight) was added into the mesocarp fiber with the ration of 1-10 g/ml at 45 oC for 90 min. The suspension was separated by centrifugation (4,000 rpm, 10 min). The precipitates from suspension were washed repeatedly by deionized water until the pH became 5. Then, the dialysis of precipitates in water was carried out for 5 days. Subsequently, the mesocarp cellulose fibers were obtained after the suspension was homogenized at 12,000 rpm for 30 min. It was stored in a refrigerator before further using. 2.3. Preparation of rice starch-based film blended with mesocarp cellulose fiber The solution prepared by mixing 4 g of rice starch and 2.5 g of glycerol as plasticizer was blended together in 100 ml of distilled water by using magnetic stirrer. Then, the chitosan dissolved in 10% acetic acid solution was introduced into the mixture. This ratio of solution is suitable for the film formation. Mesocarp cellulose fibers were added into this solution with 2%, 4%, 6% and 8% by weight of rice starch. All formulations were mixed by using magnetic stirrer at 90 oC for 30 min. Plasticizers can improve the thermal properties of starch during the molding process. The solution was transferred to the mold then heated at 50 oC for 24 hours to obtain the rice starch-based film. The structure and thermal properties of the films were characterized. 2.4 Rice Starch-based Film Characterization 2.4.1 FTIR analysis The rice starch-based films were chemically characterized by Fourier transformed infrared spectrophotometer (FTIR) using Thermo Scientific Nicolet 6700 model. The FTIR analyses of these films were operated by attenuated total reflectance (ATR) technique. All spectra were obtained in the frequency range between 4000 and 400 cm−1 (wavenumber) at a resolution of 4 cm−1 with the average of 64 scans per sample. 2.4.2 Transparent analysis The film transparency was obtained by UV-Vis spectrometer (Model Evolution 300, Thermo). Rice starchbased films were cut to 1×3 cm and placed on the internal side of a spectrophotometer cell. Transmittance data were recorded at 480 nm because the sample was seen in yellow, which was the maximum absorption at a wavelength of 480 nm. Then the film transparency was defined as the percentage of light that allowed to be transmitted across the film. Percentage of transmittance (%T) was calculated by Beer-Lambert law as stated below, where A=absorbance at 480 nm. %T = 100 (10^-A) 2.4.2 Thermal analysis (TGA) The thermal stability of rice starch-based film was investigated through thermo-gravimetric analysis (TGA). TGA was carried out in a Mettler Toledo (Model DSC1) instrument. All experiments were performed from 50◦C to 600◦C in the nitrogen atmosphere (15 ml/min) with a heating rate of 20◦C/min.
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2.4.3 Water uptake test The water absorption ability of the film can be determined by the percentage of water uptake. In this test, a desiccator chamber was operated at 50%RH and 2.5x2.5 cm of film dimensions was prepared. The sample was dried at 50 oC for 24 hours and placed in the desiccator chamber. The weight difference was measured daily until the mass of the samples was almost constant. The water uptake of films was calculated by the following equation: Water uptake% = (Mf-Mi)/Mi x 100 when Mf is the final sample mass and Mi is the initial sample mass. 2.4.4 Film thickness Film thickness was determined by using a digital micrometre (Mitutoyo Co., Japan) with 0.001mm sensitivity. The thickness measurements were obtained from five different positions on the film for each sample. The mean value of measurements for individual sample was utilized. 3. Results and discussion 3.1 Film formation Rice starch-based films containing 0%, 2%, 4%, 6% and 8% mesocarp cellulose fiber (St-MCF) were formed. Fiber content in the composites was more than 8 wt%, making the film tore easily and cannot peel the mold off. The produced rice starch-based film was white transparent and flexible. A light brown film was obtained when the mesocarp cellulose fiber was added into the film as shown in Figure 1. The color of the film became darker when the fiber content increased. The transparency was characterized by UV-Vis spectrophotometer. The transparency was determined according to the method established by Han and Floros [14]. The films were cut into 9×45 mm dimensions and placed inside the measuring cell of the spectrophotometer. The optical absorbance was recorded at 600 nm and the percentage of transmittance was calculated. Table 1 shows the transmittance of the film at 600 nm. The films were transparent at low mesocarp cellulose fiber content but they became opaque when the fiber content increases. This is because the fiber agglomeration may also occur leading to the light scattering and subsequently the decrease of light transmittance of the film. The thickness of the films was observed in the range between 0.472 to 0.478 mm. The values obtained were not significantly different. It demonstrated that the thin film was more transparent than the thick one, which corresponding to the trend of %T. Table 1 Absorbance and transparency of the formed films. Percentage Absorbance Film of Transmittance 480nm (A ) (%T) St-MCF0% 0.487 32.58 St-MCF2% 0.575 26.60 St-MCF4% 0.582 26.18 St-MCF6% 0.586 25.94 St-MCF8% 0.611 24.49
Film thickness (mm) 0.472 0.475 0.475 0.477 0.478
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Fig.1 Rice starch-based film containing 0%, 2%, 4%, 6% and 8% of mesocarp cellulose fiber
3.2 FTIR spectroscopy Figure 2 shows FTIR spectra of raw rice starch, mesocarp fiber, rice starch-based film (St-MCF0%) and its composites (St-MCF 2-8%).
(g) (f)
Transmittance
(e) (d)
2933
2850
1643 1162
(c) (b)
1034
3306 1500
(a)
3900
3400
2900
2400
Wavenumber
1900
1400
900
400
(cm-1)
Fig.2 FTIR spectra of native rice starch (a), raw mesocarp fiber (b), rice starch-based films (c) and rice starchbased film containing 2%(d) 4%(e) 6%(f) and 8%(g) of mesocarp cellulose fiber
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All spectra of St-MCF showed the same pattern of bands. These results show that the addition of various amounts of mesocarp cellulose fiber does not affect on FTIR spectra. The peak was observed at 3306 cm-1, a peak characteristic of OH stretching from St-MCF which the bandwidth was narrower than that of the raw rice starch. This is because the cellulose fiber decreased the water absorption and the presence of structure of polysaccharide in the raw starch [15]. The plasticizing process may cause the intramolecular and intermolecular hydrogen bonding between the molecules of starch due to the presence of glycerol [16-17]. All spectra exhibited the peak at 2933 cm-1 which can be assigned to CH vibrations of hydrocarbon backbone of starch and rice starch-based films. These two stretching peaks related to the aliphatic moieties in cellulose and hemicelluloses [18]. An additional peak at about 2850 cm-1 is due to CH and CH2 stretching in cellulose [19]. Moreover, the ST-MCF showed similar pattern of bands namely the peaks at 1643, 1162 and 1034 cm-1 attributed to OH deformation of H2O, C-O-C asymmetric stretching of cellulose and CO stretching of cellulose, respectively [20]. However, the peaks of St-MCF at 1346 and 1500 cm-1 indicated C=C were not appeared due to lignin removed from the treatment process but this peak is apparent in the raw mesocarp fiber [21]. Therefore, FTIR spectra can confirm that mesocarp cellulose fiber can be obtained after through two stages; the pretreatment and bleaching process and the acid hydrolysis process. 3.3 Thermo-gravimetric analysis (TGA) The thermal decomposition of the film that produced from rice starch-based film blended with mesocarp cellulose fibre was investigated. TG and first-derivative thermogravimetric (DTG) curves were obtained as shown in Figure 3. All TG curves of St-MCF show three steps of degradation as shown in Figures 3(a). Initial decomposition was observed due to the moisture removal [15,22]. The DTG curves of St-MCF show first peak at about 120oC, which are responsible to TG curves. Further, the decomposition of TG curve was obtained in range 200-350oC that DTG curve is seen in two peak at about 280oC and 350oC. The reason is the first one at 280oC is the decomposition of glycerine content and the second peak at 350oC is the decomposition of starch content [4,15]. The increasing mesocrap cellulose fibre improves thermal stability of the composites. For example, the second mass loss decreases from 73.21% of St-MCF0% to 70.86% of St-MCF8% as shown in Table2. Cellulose decomposition was occurred by depolymerisation, thermo-oxidation and dehydration, depending on the presence of type of gases in the experiment [23]. However, the decomposition was not observed at 280-500oC of lignin due to the fiber treated corresponding to the results of FTIR. Table 2 shows the onset temperature of St-MCF at 0%, 2%, 4%, 6%, and 8% of cellulose fiber. The onset temperature of St-MCF0% and St-MCF2-8% is 198oC and 225-260oC, respectively. The results showed that the onset temperature increased when mesocarp cellulose fiber was added. This may be the increased amount of fatty, wax, hemicellulose and cellulose in the composites [24-26]. Moreover, the mesocarp cellulose fiber incorporated into the rice starch-based film interacted strongly so its composites offered better thermal stability. Table 2 Thermo-gravimetric analysis data of rice starch-based films and its composites containing mesocarp cellulose fiber. Film
Onset temperature (oC)
Initial mass loss%
Second mass loss%
St-MCF 0% St-MCF 2% St-MCF 4% St-MCF 6% St-MCF 8%
198 225 249 255 260
12.70 12.71 13.79 14.54 15.99
73.21 72.23 72.07 70.87 70.86
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a 120
%Weight loss
100 80 StMCF8% StMCF6%
60
StMCF4%
40
StMCF2% StMCF0%
20 0 50
150
250
350
Temperature
450
550
(oC)
b -0.014
DTG/ug min-1)
-0.012 -0.01 -0.008 StMCF8% StMCF6% StMCF4% StMCF2% StMCF0%
-0.006 -0.004 -0.002 0 50
150
250
350
450
550
Temperature (oC) Fig.3 Thermogram (a) TG curves and (b) DTG curves of rice starch-based films and its composites containing mesocarp cellulose fiber.
3.4 Water uptake Figure 4 shows the results of the water absorption properties of film that reported the percentage of water uptake. The water uptake of rice starch-based film blended with mesocarp cellulose fiber (St-MCF) ranged about 26-53%. The film blended with 8% cellulose provided the lowest value of water uptake (26%). The results showed that the water absorption of the film decreased by increasing the mesocarp cellulose fiber contents. This may be cellulosic structure of the fiber decreased the moisture sensitivity of film, correspoding to the FTIR results [27].
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Water uptake (%)
50 40 30 StMCF0% StMCF2% StMCF4% StMCF6% StMCF8%
20 10 0 0
1
2
3
4
5
6
7
Days
Fig.4 Water uptake of films with different fiber contents
4. Conclusions Rice starch-based films blended with mesocarp cellulose fiber were prepared by solution cast method with the percentage of transmittance in range 24.49-26.60. The spectra of FTIR technique revealed that the mesocarp cellulose fiber did not affect chemical structure of the rice starch-based films. Moreover, FTIR spectra can confirm that cellulose obtained after through the two steps; the pretreatment and bleaching process and the hydrolysis process. Increasing of additions of mesocarp cellulose fiber from 2-8% to the starch matrix resulted in the enhanced thermal stability, which shown by the decrease of degradation temperature and the increase of onset temperature. The St-MCF8% gave the lowest value of water uptake (26%) because the fiber may increase the crystallinity in the structure of St-MCF, resulting in less water absorption. Acknowledgements The authors are grateful to Rajamangala University of Technology Suvarnabhumi for the financial and laboratory support. References [1] L. Averousa, N. Boquillonb, Carbohydr. Polym. 56 (2004) 111-122. [2] A.O. Ashogbon, E.T. Akintayo, Starch-St€arke 66 (2014) 41-57. [3] A. Cano, E. Fortunati, J.M. Chafer, M. Kenny, A. Chiralt, C. Gonzalez-Martínez, Food Hydrocoll. 48 (2015) 84-93. [4] H. Ibrahim, M. Farag, H. Megahed, S. Mehanny, Carbohydr. Polym. 101 (2014) 11-19. [5] M.G. Lomelí-Ramírez, S.G. Kestur, R. Manríquez-Gonzalez, S. Iwakiri, G.B. de Muniz, T.S. Flores-Sahagun, Carbohydr. Polym. 102 (2014) 576-583. [6] R. Ortega-Toro, A. Munoz, P. Talens, A. Chiralt, Food Hydrocoll. 56 (2016) 9-19. [7] A.M. Das, M.P. Hazarika, M. Goswami, A. Yadav, P. Khound, Carbohydr. Polym. 141 (2016) 20–27. [8] M. Boonterm, S. Sunyadeth, S. Dedpakdee, P. Athichalinthorn, S. Patcharaphun, R. Mungkung, R. Techapiesancharoenkij, J. Clean. Prod. 134 (2016) 592–599. [9] K. Kaewtatip, J. Thongmee, Mater. Des. 40 (2012) 314-318. [10] X. Miao, J. Lin, F. Tian, X. Li, F. Bian, J. Wang, Carbohydr. Polym. 136 (2016) 841–850. [11] M. Karatas, N. Arslan, Food Hydrocolloids 58 (2016) 235–245. [12] F. Ansari, M. Skrifvars, L. Berglund, Compos. Sci. Technol. 117 (2015) 298-306. [13] M.H. Salehudin, E. Salleh, S.N.H. Mamat, I.I. Muhamad, Proced. Chem. 9 (2014) 23-33.
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[14] J.H. Han, J. D. Floros, J. Plast. Film Sheet. 13 (1997) 287–298. [15] M.G. Lomeli-Ramirez, S.G. Kestur, R. Manriquez-Gonzalez, S. Iwakiri, G.B. de Muniz, T.S. Flores-Sahagun. Carbohyd. Polym. 102 (2014) 576-583. [16] X. Ma, P.R. Chang, J. Yu, M. Stumborg, Carbohyd. Polym. 62 (2005) 19-24. [17] R. Shi, Q. Ding, T. Han, Y. Zhang, D. Che, J. Appl. Polym. Sci. 103 (2007) 374-386. [18] B.M. Cherian, L.A. Pothan, T. Nguyen-Chung, G. Menning, M. Kottaisamy, S. Thomas, Agric. Food Chem. 56 (2008) 5617-27. [19] M.A. Tshabalala, Surface characterization. In: Rowell RM, editor. Handbook of wood chemistry and wood composites, London, 2005. [20] M.F. Rosa, E.S. Medeiros, J.A. Malmonge, K.S. Gregorski, D.F. Wood, L.H.C. Mattoso, G. Glenn, W.J. Orts, S.H. Imam, Carbohyd. Polym. 81 (2010) 83-92. [21] Y.N. Guragain, J.D. Coninck, F. Husson, A. Durand, S.K. Rakshit, Bioresour. Technol. 102 (2011) 4416-24. [22] H.Liu, F.Xie, L.Yu, L.Chen, L.Li, Prog. Polym. Sci. 34 (2009) 1348-1368. [23] B.Neher, Md.M.R. Bhuiyan, H.Kabir, Md.A.Gafur, Md.R. Qadir, F.Ahmed, J. Therm. Anal. Calorim. 124 (2016) 1281-1289. [24] Z.N. Azwa, B.F. Yousif, A.C. Manalo, W. Karunasena, Mater Des. 47 (2013) 424-442. [25] M.S. Huda, L.T. Drzal, M. Misra, A.K. Mohanty, K. Williams, D.F. Mielewski, Ind. Eng. Chem. Res. 44 (2012) 5593–601. [26] B. Wielage, T. Lampke, G. Mark, K. Nestler, D. Starke. Thermochim Acta. 337 (1999) 169–77. [27] J. Guan, M.A. Hanna, Bioresour. Technol. 97 (2006) 1716-26.