Advanced Materials Research Vols. 123-125 (2010) pp 351-354 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.123-125.351
Preparation and Characterization of Starch/PVA Blend for Biodegradable Packaging Material Fahmida Parvin1,2, Md. Arifur Rahman2, Jahid M. M. Islam2, Dr. Mubarak A. Khan2, A. H. M. Saadat1 1
Department of Environmental Sciences, Jahangirnagar University, Savar, Dhaka.
2
Radiation & Polymer Chemistry Laboratory, Institute of Nuclear Science and Technology, Bangladesh Atomic Energy Commission, GPO Box: 3787 Dhaka 1000, Bangladesh.
[email protected],
[email protected],
[email protected],
[email protected],
[email protected]
Key words: Starch, PVA, Biodegradable.
Abstract. Polymer films of rice starch/Polyvinyl alcohol (PVA) were prepared by casting method. Different blends were made varying the concentration of rice starch and PVA. Tensile strength (TS) and elongation at break (Eb) of the prepared films were studied. Films made up of rice starch and PVA with a ratio of 2:8 showed highest TS. 10% sugar was added with highest TS giving four composition of Starch/PVA blend in order to increase TS and Eb. Films made up of rice starch and PVA and sugar with a ratio of 1:8:1 showed highest TS and Eb and the recorded value was 14.96MPa and 637% respectively. The physico-mechanical properties of the prepared sugar incorporated films were improved by grafting with acrylic monomer with the aid of UV radiation. A formulation was prepared with monomer, methylmethacrylat in methanol, and a photo initiator. The highest TS of the grafted films were recorded and the value was 16.38 MPa. The water uptake and weight loss in both soil and water of the grafted films are lower than the non-grafted films. The prepared films were further characterized with stereo micrograph and XRD. Finally, the produced film can be used as biodegradable packaging materials for shopping and garbage bags that are very popular and environment friendly. Introduction During the past twenty years, there has been an increase in the production of commodity and food packaging plastics products such as poly-olefin, accompanied by an ever-increasing amount of plastic waste. This is because such products tend to accumulate in nature due to their excellent mechanical properties, as well as chemical, weathering and biodegradable resistance [1-2]. The use of biodegradable polymers for Packaging offers an alternative and partial solution to the problem of accumulation of solid waste composed of synthetic inert polymers( Mezzanotte et al., 2005; Jayasekara et al., 2004). Starch, as an abundant and inexpensive raw material, has been applied in the field of biomaterials. However, packaging films (composed entirely of starch) lack the strength and rigidity to withstand the stresses to which many packaging materials are subjected (Parra et al., 2004). Starch-based BPs can be produced by blending or mixing them with synthetic polymers. Polyvinyl alcohol (PVA) is a biodegradable synthetic material which has the advantages of good film forming, strong conglutination, and high thermal stability. In recent years, PVA has widely used in the materials industry [3-5]. Recent preparation of starch-based polymer has been reported [6]. In this work, polymer films of rice starch/Polyvinyl alcohol (PVA) were produced and different physicomechanical and biodegradable properties were studied. The prepared films were farther grafted with acrylic monomer using UV radiation and the Physico-mechanical and biodegradable properties of the treated films were studied.
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Experimental Materials. Rice starch was collected from local rice farm (Shondhi Rice Mills, Bangladesh). The raw rice starch was further processed by grinding it to small granules. Polyvinyl alcohol, PVA (MW 15,000) was purchased from Merck Germany. The monomer Methylmethacrylate (MMA) and photo initiator Darocure-4043 were obtained from Merck Germany. Method. Starch/PVA and starch/PVA/10% sugar were blended in hot water at about 150° C for about 1 hour to form a homogeneous solution. Several formulations were prepared with this solution, varying the concentration of starch and polyvinyl alcohol (PVA). Polymer films were prepared by casting on silicon cloth. Mechanical properties; tensile strength (TS) and percent elongation at break (Eb) of the blend films were measured with Universal Testing Machine (Hounsfield Series S, UK) using DIN EN 10 002-1 method of testing polymer film. For grafting 10% sugar containing samples were chosen. A formulation was prepared with the monomer: Methylmethacrylat(MMA) in methanol, in the presence of a photo initiator, Darocure-4043and their ratio in the formulation is 5%MMA: 2%photoinitiator: 93%methanol. Prepared films were soaked in this formulation for 3 minutes and then UV irradiated under UV radiation, using a UV manicure machine (IST Technique, Germany). The intensity of the lamp was 2KW at 9.5A current and the wavelength was 254-313nm with a conveyer belt to pass under the UV lamp.Each sample was passed for 30 times under the UV lamp. After 24h, the tensile Properties of the grafted films were studied. The morphological study of the grafted film was done by Stereo Microscope. The water uptake of the sugar containing grafted and nongrafted films is monitored to find the profile of water uptake by using the following equation %water uptake = (Wa – Wo)/Wo × 100, Where Wa and Wo were the weight of the sample after and before soaking in water. The degradation in soil of the sugar containing grafted and nongrafted films is studied by determining the percentage of weight loss in soil by using this process, %weight loss = (Wo- Wa)/Wo × 100, where Wo , Wa were the weight of the sample before and after soil burial treatment. RESULT & DISCUSSIO! Mechanical Properties of Rice Starch/PVA Blend Films. Figure 1 shows the changes in tensile strength with increasing starch content in Starch/PVA blend containing no sugar. The ultimate tensile strength of the blend film containing no sugar showed a decreasing tendency with increase in percentage of starch within the range of concentration studied (Figure 1).
Figure 1: comparison of tensile strength of the starch/PVA blend films containing sugar and without sugar
Figure 2: Comparison of TS between sugar containing MMA grafted & nongrafted starch/PVA blend films.
The tensile strength of the blend films began decreasing steadily with the increasing percentage of starch in the blend films. This must be due to the increased crystallization of the blend films. Figure 1 also shows that the TS increased initially for the blend films containing 10% starch and also 10%
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sugar as plasticizer. After the initial increase TS again start decreasing with increasing starch content. The initial increase at 10% starch content with sugar indicates the plasticizing effects on the tensile strength of the blend films. Besides this, with the acrylic monomer treatment, the TS value of the grafted starch/PVA blend film increases(Figure 2) which may be due to the crosslinking of the hydroxyl groups and branched amylopectin in starch with vinyl group forming dimensional network structure causing restricted mobility.
Figure 3: comparison of elongation at break of the starch/PVA blend films containing sugar and without sugar.
Figure 4: Comparison of TS between sugar containing MMA grafted & nongrafted starch/PVA blend films.
Figure 3 shows the changes in elongation at the break (%Eb) of the starch/PVA blend and the influence of sugar on the %Eb of the blend films. The %Eb of the blend film containing no sugar decreased with increasing starch content. But the incorporation of sugar into the blend film showed a rapid increase in the optimized compositions of the blend films. This is may be due to the plasticizing effect of the sugar on the amylose and amylopectin chain of the starch along with PVA side chain. Figure 4. shows the effect of methylmethacrylat (MMA) grafting on the sugar containing starch/PVA blend films. The maximum %Eb was found to be 347% for the MMA grafted 10% starch/PVA blend film. The grafted blend The grafted blend The grafted blend showed lower %Eb value because MMA filled up the intramolecular gaps between polysaccharide and PVA side chain. Morphological Analysis. Micrograph analysis is very important to observe the physical structure of the blend film. Figure 5 shows stereo micrographs of the MMA grafted starch/PVA blend films. Figure 5(a)-(c) shows the micrographs of 10% to 30% starch containing blend films. The blend films are seemed to be homogeneously prepared. The micrographs also reveal that the phase structures in the starch/PVA blend films with different concentrations of starch are very different. From these figure, one can see that with increasing the concentration of starch from 10 to 30%, starch micro domains reverse to be continued phase from dispersed phase, which implies that the amorphous starch is partially miscible with PVA.
(a)
(b) Figure 5: Stereo Micrographs of Starch/PVA blend Films
(c)
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Water uptake Test. Improvement in reducing water sensitivity and enhancing water resistance of thermoplastic starch materials is highly important. Water absorption of the sugar incorporated Starch/PVA blend films are shown in figure 6. Since grafting modifies the surface of a polymeric blend film, it is evident from the Figure 6 that grafting with methylmethacrylat (MMA) has lowered the water absorption of the blend films. This is may be due to the fact that polysaccharide chain of starch and OH- groups of PVA are mostly occupied with monomers (MMA). So, there is very little chance for the water molecule to be associated or absorbed with film.
Figure 6: Comparison of Water uptake between sugar containing MMA grafted & non-grafted starch/PVA blend films.
Figure 7: Comparison of Weight loss between sugar containing MMA grafted & non-grafted starch/PVA blend films in soil burial treatment.
Soil burial Test. weight losses due to soil burial treatment of the sugar incorporated Starch/PVA blend films are shown in figure 7. Since grafting modifies the surface of a polymeric blend film, it is evident from the Figure 7 that grafting with methylmethacrylat (MMA) has lowered the weight losses of the blend films compared to the nongrafted films. The weight losses are influenced by the composition of the mixture, as well as by nature of the microorganism species [7]. The highest values of weight loss were recorded for the films with a high content of starch in the mixture. Conclusion In this research a biodegradable packaging material is developed. The developed material has appropriate stability in water. It also showed mechanical properties similar to the materials made from synthetic non degradable polymers. So, prepared packaging material can be a solution of problems due to solid waste accumulation. Reference [1] I.E. Potts, R.A. Clrndinning, W.B. Ackart, W.D. Neigisch: Polymer and ecological problem, (Plenum press, Neyyork, 1973), p.61-79. [2] L.R. Kwpp, & W.J. jewel: Biodegradability of modified plastic films in controlled biological environment, Environ. Techno. 26, (1992), p.193-198. [3] N.Follain, , C.Joly, , P. Dole & C. Bliard: Properties of starch based blends. Part 2. Influence of poly vinyl alcohol addition and photocrosslinking on starch based materials mechanical properties. Carbohydrate Polymers, Vol. 60 (2005), p.185–192. [4] C. M. Xiao, & M. L. Yang: Controlled preparation of physical Cross-linked starch-g-PVA hydrogel. Carbohydrate Polymers, Vol. 64 (2006), p. 37–40. [5] M. L. Zhai, , F.Yoshii, , T. Kume, , & K. Hashim: Syntheses of PVA/starch grafted hydrogels by irradiation. Carbohydrate Polymers, Vol. 50 (2002), P. 295–303. [6] J.M.Rosiak, A. Rusinka-Rybas, W. Pekala, Method of Manufacturing Hydrogen Dressing. US Patent no 4871490. (1989) [7] N. Tudorachi , C.N. Cascaval , M. Rusu , M. Pruteanu Testing of polyvinyl alcohol and starch mixtures as biodegradable polymeric materials ,Polymer Testing, Vol.19 (2000) 785–799.
