Study on Modification of starch with anhydride functional polyethylene using peanut oil as compatibilizer

392 Journal of Chemistry, Vol. 43 (3), P. 392 - 396, 2005 Study on Modification of starch with anhydride functional polyethylene using peanut oil as compatibilizer (Part 1) Received 20th-Sept., 2004 Do Truong Thien, Tran Thi Y Nhi, Duong Anh Vu, Nguyen Tien An Institute of Chemistry, Vietnamese Academy of Science and Technology summary In recent years, much attention has been focused on making polyethylene degradable. The purpose of this work is to make degradable film from depolymerized tapioca starch and linear- low-density polyethylene (LLDPE) grafted with anhydride maleic (MA), using peroxide benzoyl as initiator and peanut oil as compatibilizer. Effects of MA and tapioca starch content as well as peanut oil on the film qualities were investigated through mixing torque, IR spectra, thermal analysis, scanning electron microscopy (SEM) photographs and physico-mechanical properties. I - Introduction Many solutions like recycling, incineration, landfill and using degradable plastic have been proposed for management of plastic waste. It is increasingly felt that, the best alternative would be making plastic degradable. Starch, a mixture of amylose and amylopectin, is a polymer formed in nature, therefore biodegradable. Graft polymerization of starch onto polyethylene provides another method for preparing biodegradable film. An important advantage of graft copolymerization is the fact that starch and polyethylene are held together by chemical bonding rather than existing merely as physical mixture. The two dissimilar polymers tend to be more intimately associated and separation of the two polymer phases is less likely occur [6]. In our report, in order to make polyethylene containing polar functional group, the graft polymerization of MA onto PE using peroxide benzoyl was done in Haake machine, and then resulting product was blended with tapioca starch using peanut oil as compatibilizer. II - Experimental 1. Material - Industrial grade of starch was supplied by a factory in Hoaiduc district, Hatay province, Vietnam. - Low-density-polyethylene from Hanwa Chemical Corp (Korea), its density is 0.93 g/cm3. - Anhydride maleic (MA) (analytical grade), peroxide benzoyl (PBO) from Merck Company, Germany. - Peanut oil (PO) was received from Tuongan Company, Vietnam. 2. Free-radical graft of MA onto PE The experiment carried out in Haake 393 0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 7 8 machine (Germany) with the reaction conditions were set as follows: to: 170oC; rotor speed: 150 rpm; reaction time: 7 minutes. LLDPE and PBO 0.8% (in comparison with the LLDPE content) were mixed together before their fast introduction into the preheated chamber. Within 2 minutes, MA (0.1 - 1%) was added into reaction zone. The obtained product was considered as PEM. 3. Grafting tapioca starch onto PEM The reaction condition was set as that of PE modification. After 2 minutes, the tapioca and peanut oil were added to the reaction. The obtained product was considered as PEMT and PEMT-PO (with peanut oil). 4. Measurement - Determination of mixing torque versus time (expression of relative melting viscosity) of graft copolymer was carried out by Haake software connected to an inner-mixer of Haake Polylab System with a capacity of 69 cm3. - Physico-mechanical properties were determined on a tensile tester according to ASTM D638-84 at crosshead speed of 15 mm/min from Zwick Co, Germany. - Thermo-gravimetric analysis (TGA) of graft polymer was performed in nitrogen atmosphere on TGA instrument (model –5H), Shimadzu Co., Japan. - Scanning Electron microscopy photograph with Jeon 5300, Japan. - Infrared (IR) spectra were recorded on IMPACT-410 Fourier-transformation (IR) spectrometer, Germany. III - Results and discussion 1. Free-radical graft of MA onto PE a) Rheological during grafting Torque mixing information reflects relative melt viscosity and mixing process during the course of reaction. Fig. 1 represented the mixing torque for different ratios: LLDPE/ MA/PBO: PEM1 (0.1% MA); PEM10 (1%MA); and LLDPE. The experimental results showed that the mixing torque of PEM10 is higher than that of PEM1 at the same reaction time. It could be explained that MA content is the major parameter which affects the diffusion and thus the grafting reaction. At a higher content of MA (1% compared with 0.1%) the grafting efficiency seem to be improved. The torque drops off with time because the material has become severely cross linked, it is crumblike in nature and detached from the walls leading to lower torque. Fig. 1: Plot of mixing torque versus time for grafting MA on to PE
- PEM10 o - PEM1  - PE 394 PEM LLDPE PEM b) Infrared spectra investigation Investigation of infrared (IR) spectra were performed from 500 to 4000 wave number (cm-1) showed that the absorbance in the region 1706.20 cm-1 is due to –C=O vibration in the cyclic anhydride. It could be an evidence for the grafting of MA on to PE. Wavenumber, cm-1 Fig. 2: Infrared spectra of PEM and LLDPE c) Thermo-gravimetric (TGA) analysis TGA curves of PEM1 and PEM10 are presented in fig.3. At 163oC, weight decrease (%) for PEM10 and PEM1 are 3.075% and 0.562% respectively. At 499.94oC, weight decrease for PEM 10 is 98.036% and 96.325% for PEM1. The results demonstrated that PEM10 has lower thermal stability than that of PEM1. It is in agreement with the results observed on mixing torque investigation. 2. Grafting tapioca starch on to PEM Fig. 4 showed the relationship between torque and time of mixing of PEMT1 (PEM1/starch: 80/20) and PEMT 10 (PEM10/starch: 80/20). We can see that the torque data of PEMT10 is higher than that of PEMT1. This may be due to PEM10 containing higher MA content in comparison to MA content of PEM1. It seems to be that, PEM10 formed more ester linkages with hydroxyl group than those of PEM1, leading to higher torque data. Fig. 3: TGA curves of PEM1 and PEM10 417.14C PEMT1 PEMT10 395 0 5 10 15 20 25 30 35 40 0 1 2 3 4 5 6 7 8 Fig. 4: Plot of torque versus time of mixing for grafting MA on to PEM a) Infrared spectra investigation From infrared spectra of PEMT (Fig. 5), we could observe the absorbance peak 1711 cm–1 and 1023 cm-1 are due to ester vibration, and absorbance peak 3272 cm-1 is due to –OH vibration. This finding could demonstrate that, starch has been successfully grafted onto PEM. Fig. 5: Infrared spectra of PEMT b) Physico-mechanical properties Physico-mechanical properties of PEMT are showed in table 1. Table 1: Physico-mechanical properties of PEMT Parameter Samples E-Module, MPa Tensile strength, MPa Elongation at break, % PEMT1 (0.1% MA) 201.99 11.35 278.54 PEMT5 (0.5% MA) 194.61 14.67 286.16 PEMT10 (1% MA) 239.26 15.16 316.92 PE-T (without MA) 135.72 10.12 101.10 Experimental results showed that E-module and tensile properties (tensile strength and elongation at break) of those blend polymers follow the ranking: PEMT10 > PEMT5 > PEMT1 > PEMT (0% MA). It means that physico-mechanical properties of those polymers reduced with increasing the weight ratio of MA. This can be explained by following reasons: PE is a strong polar and brittle polymer, thus PE-T only exists as physical mixture. When MA is grafted onto PE, hydroxyl of starch reacts with anhydride to form ester
PEMT10 o: PEMT1 396 linkage so that the two polymers are held together by chemical bonding; therefore their physico-mechanical properties are improved. c) Effect of peanut oil It well established that the dispersion of one polymer in another and mutual adhesion can be promoted by adding compatibilizer as mediator molecules, which can interact equally to well with both components. These could be small molecules or even block or graft copolymer of the component polymers. The general view is that, a properly chosen compatibilizer preferentially locate itself at the interface and reduces the interfacial energy between the phases, permits finer dispersion during blending, and improves interfacial adhesion [5]. Our attempts to improve the dispersion of starch into PE matrix by adding peanut oil fall into this category. The vegetable oil also acts as an auto- oxidant to promote oxidative degradation of the polyolefin according to Griffin. Fig. 6 presented a comparative compilation of the scanning electron microscopy (SEM) photographs of the samples with and without peanut oil at the same magnification. Fig. 6: a) PEMT-3% peanut oil and b) PEMT-0% peanut oil IV - Conclusions - MA has been successfully melt grafted onto LLDPE using peroxide as initiator. - Depolymerized starch is also incorporated into anhydride functional polyethylene using peanut oil as compatibilizer in Haake machine. Peanut oil improved the dispersion of starch onto LLDPE containing anhydride group. Physical characteristics of PEMT meet packaging demand. References 1. H. P. S. Abdul Khalil, W. C. Chow, H. D. Rozman. Polym. Plast. Technol. Eng., 40 (3), P. 249 - 263 (2001). 2. E. Chiellini. ICS-UNIDO Inter. Workshop on Environ. Degrad. Plastics: Industr. Develop. and Appl., P. 7 - 24 (2000). 3. M. David Wiles, Joo Fai Tung, Gerald Scoottand Graham Swift. ICS-UNIDO Inter. Workshop on Environ. Degrad. Plastics: Industr. Develop. and Appl., P. 208 - 303 (2000). 4. Do Truong Thien, Pham The Trinh. Vietnam J. Chem., Vol. 41, P. 100 - 103 (2003). 5. P. Krishna Sastry, D. Satyanarayana, D. V. Morhan Rao. J. Polym. Sci., 70, P. 2251 - 2257 (1998). 6. G. Moad. Progress in Polym. Sci., 24, P. 81 - 142 (1999). 7. Ysükel Orhan. Inter. Bio-deterioration & Biodegradation, 45, P. 49 - 55 (2000). 8. Uipal, R Vaidya and Mirinal Bhattacharya, J. App. Polym. Sci., 52, P. 617 - 628 (1994). a b