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PROPERTIES OF THERMOPLASTIC CASSAVA STARCH/LOW-DENS ITY POLYETHYLENE BLEND MODIFIED BY CARRAGEENAN Wanida Pomdage, Jutarat Prachayawarakorn,* Department of Chemistry, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok 10520, Thailand * e-mail: ksjutara@kmitl.ac.th Abstract: This research aimed to study the preparation and properties of polymer blend between thermoplastic cassava starch (TPCS) and low-density polyethylene (LDPE). Glycerol was used as a plasticizer at the ratio of starch: glycerol; 70:30. The compatibilizer, maleic anhydridegrafted-polyethylene (MAPE) was added into the TPCS/LDPE blend. The TPCS/LDPE blend was then, modified by different contents of carrageenan. The polymer blend was mixed using a high-speed mixer, then compounded using an internal mixer at temperature of 140 oC and the rotor speed of 40 rpm. The specimens were shaped by injection molding technique. It was found that tensile strength and Young’s modulus of the TPCS/LDPE blends significantly increased by the addition of carrageenan. For the carrageenan contents from 0 to 10%, the tensile strength increased from 8.57 to 9.29 MPa and the Young’s modulus increased from 25.0 to 134.2 MPa. Moreover, morphology of the TPCS/LDPE blends incorporated by carrageenan observed by SEM presented better phase compatibility between TPCS and LDPE. The TPCS/LDPE blends were also examined for functional group analysis, physical and morphological properties. Introduction:

Starch is produced worldwide from several crops such as rice, maize, cassava and potatoes. Starch is a blend of amylose and amylopectin macromolecules. Starch can be mixed with a plasticizer under the action of high temperature, pressure and shear. With this process a conversion of the molecular structure to thermoplastic starch (TPS) is obtained.1 TPS still has disadvantages when compared to most plastics currently in use, i.e. poor mechanical properties and sensitive to moisture. One approach to improve properties is to blend with synthetic polymers.2,3 It was reported that modulus and elongation at break of the TPS/PE blends decreased, as expected, with addition of TPS from wheat starch into the TPS/PE blends Moreover, the TPS/PE blends still showed the immiscible morphology, resulting in poor mechanical properties.4 Another approach is to use modifying agents such as agar5,6, alginate7, gelatin8, xanthan gum9 and carrageenan.10,11 Carrageenan, a linear sulfated polysaccharides extracted from red seaweeds was chosen because of its structure based on cellulose; therefore, it can be compatible with TPS. These characteristics of the carrageenan were expected to improve compatibility and the mechanical properties of the blends.

This research aimed to study on the preparation and properties of polymer blend between TPCS and LDPE with glycerol as a plasticizer. The compatibilizer; maleic anhydridegrafted-polyethylene (MAPE), was added into the TPCS/LDPE blend. The TPCS/LDPE blend was modified by different contents of carrageenan. The TPCS/LDPE blends were then examined for functional group analysis, mechanical and morphological properties. Methodology: 1. Materials

Cassava starch was purchased from Chaopraya Phuchrai 2999 (Kamphaengphet) Co., Ltd. (Kamphaengphet, Thailand). Low-density polyethylene (LDPE, DNDV-0405 R) with MFI of 32 g/10 min. was obtained from Global Connections Public Co., Ltd.

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© 38th Congress on Science and Technology of Thailand (Full paper)

(Samuthprakarn, Thailand). Glycerol (plasticizer) was purchased from Lab System Co., Ltd. (Bangkok, Thailand). MAPE (MB100D) compatibilizer was purchased from Chemical Innovation, Co.,Ltd. (Bangkok, Thailand). Carrageenan was obtained from Union Chemical 1986, Co., Ltd. (Bangkok, Thailand). 2. Sample preparation

Cassava starch and glycerol were pre-mixed in closed container and kept overnight. The weight ratio of cassava starch and glycerol was maintained at 70:30. The TPCS blend was compounded with LDPE at the ratio of 50:50 wt/wt and MAPE content was maintained at 3% by weight of LDPE. The polymer blend compounded using an internal mixer and the specimens were shaped by injection moulding technique. The property modification of the TPCS/LDPE blend was carried using different contents of carrageenan, i.e. 0%, 2%, 4%, 6%, 8% and 10% by weight of TPCS/LDPE blend. Carrageenan was added into the TPCS/LDPE blends and blended by internal mixer. 3. IR spectroscopic study

The TPCS/LDPE blends were characterized by FTIR analysis on a Spectrum 2000 GX spectrometer (PerkinElmer, USA) using KBr disk technique with a resolution of 4 cm−1 using 16 scans per sample. 4. Morphology

Morphology of the blends was observed by Scanning Electron Microscope (LEO 1450 VP). The samples were immersed in a nitrogen liquid before fractured. After that the samples were sputter-coated with a thin layer of gold to prevent electrical charging during the observation. 5. Tensile properties The tensile testing was carried out using Universal Testing Machine (LLOYD Instrument, LR 5K, UK) with 5 kN load cell and a rate of 100 mm/min according to ASTM D638. The samples were injection molded Standard type I dumbbell-shaped samples. These were conditioned at the temperature of 23±1 �C and relative humidity of 60±5% before testing samples. 6. Water absorption The blended samples were immersed in distilled water. The amount of water absorbed by the samples was measured for a month and was recorded every day. The percentage water absorption was calculated as followed :(Eq. 1). Water absorption (%) = (W2 – W1)/ W1 × 100 (1) where W1 and W2 were the initial weight and wet weights of the samples, respectively. Results, Discussion: 1. IR spectroscopic study

Figure 1. IR spectra of LDPE blends modified by different contents of carrageenan

(A) 0% (B) 6% and (C) 10%

(C)

(A)

(B)

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© 38th Congress on Science and Technology of Thailand (Full paper)

FTIR spectra of the TPCS/LPPE blends with difference contents of carrageenan are shown in Figure 1. The TPCS/LDPE blends showed main peaks at 3500-3250 cm-1 (O-H stretching), 3000-2800 cm-1 (C–H asymmetric stretching of –CH2–, –CH2– deformation), 1650 cm-1 (O-H bending of bounded water), 1460 cm-1 (C-H bending of –CH2–), 1300-1000 cm-1 (C-O-C stretching) and 1200-1000 cm-1 (C-O-H bending). IR peak shift of O-H stretching and the decrease of the peak intensity was also found for the TPCS/LDPE blends added by carrageenan. It may be due to the interaction between hydroxyl groups of starch and carrageenan. Furthermore, the addition of carrageenan into the TPCS/LPPE blend caused a new peak 1260 cm-1, assigned to –OSO3 stretching of carrageenan.12 2. Morphology

Figure 2. SEM micrographs of different TPCS/LDPE blends modified by different contents of carrageenan (A) 0% (B) 6% and (C) 10%

SEM micrographs of TCPS/LDPE blends are shown in Figure 2. It was observed that

the TCPS/LDPE blend showed phase incompatibility with the presence of voids (Figure 2(A)). However, when carrageenan added into the blends (Figure 2(B) and Figure 2(C)), the TPCS and LDPE component showed better phase compatibility and more homogeneous phase, indicating by the reduction of voids in the modified blend.

(A) (B)

(C)

300X 300X

300X

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3. Tensile properties

Figure 3. Mechanical properties of TCPS/LDPE blends. (A) Stress at max load (B) Young’s modulus (%) and (C) Strain at max load

(B)

(C)

(A)

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© 38th Congress on Science and Technology of Thailand (Full paper)

The mechanical properties of the TPCS/LDPE blends with different contents of carrageenan are shown in Figure 3. For increasing carrageenan contents, the stress at max load and Young’s modulus of the TPCS/LDPE blends significantly increased from 8.57 to 9.29 MPa and 25.0 to 134.2 MPa respectively, while the elongation decreased from 126 to 23%. This could be due to the similar chemical structures and interaction between hydroxyl group of starch and carrageenan as observed by IR peak shift (Figure 1) and morphology (Figure 2). 4. Water absorption

Figure 4. Percentage water absorption of different TPCS/LDPE blends.

Water sensitivity is another important criterion for many practical applications of

starch products. Figure 4 showed the relationship between water absorption and immersion time of different TPCS/LDPE blends. It was found that water absorption of the TPCS/LDPE blends slighty increased with the addition of carrageenan. This is because of the hydrophilic character of carrageenan in comparison to starch hydrophilic property. Conclusions: The biodegradable TPCS and LDPE blend were prepared using the internal mixer and injection molding machine. The TPCS/LDPE blend was modified using different contents of carrageenan. It was found that the introduction of carrageenan could effectively improve the tensile strength, Young’s modulus and morphology of TPCS/LDPE blend because of its structural compatibility between starch and carrageenan. In addition, water absorption slightly increased and IR peak of O-H stretching shifted with the addition of carrageenan. References:

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4. N. St-Pierre, B. D. Favis, B. A. Ramsay, J. A. Ramsayt and H. Verhoogt. Polymer 1997;38: 647-655.

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5. Y. Wu, F. Geng, P. R. Chang, J. Yu and X. Ma. Carbohydrate Polymers 2009;76:299–304

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Polymers,2012;87:1810-1816. Keywords: Thermoplastic starch, Polymer blend, Carrageenan, Injection molding, Mechanical properties