FARKLI BİTKİ TEMELLİ BİLEŞENLER KULLANILARAK NİŞASTA BAZLI BİYOPLASTİKLERİN SENTEZİ VE KARAKTERİZASYONU
Özet
Plastic materials, which are indispensable in daily life due to their low cost, ease of shaping, and long-term preservation in atmospheric conditions without deformation, are petroleum-based products. However, concerns about the environmental damage caused by these materials, especially throughout the process from the production of plastic materials to the disposal of their waste, have become a serious issue. The search for alternative production methods and raw material sources has accelerated in order to prevent the environmental damage that could occur with the production of over 500 million tons of toxic waste annually due to the use of 150 million tons of oil. In this context, bioplastics stand out with their biological basis, offering advantages such as high solubility and recyclability. Bioplastics can be derived from renewable plant-based raw materials, as well as sources such as cellulose, lignin, proteins, or certain animal sources. Although bioplastics are preferred for not containing toxic substances, low greenhouse gas emissions, and less energy consumption, studies have also identified disadvantages such as high cost and weaknesses in mechanical/thermal properties.
This study aimed to contribute to the expansion of the usage areas of bioplastics, which have been revealed through studies to cause less harm to the environment than plastic products, commonly used in various fields of daily life and mostly derived from petroleum and its derivatives, by developing raw materials that can be used in the preparation of biodegradable products. In this study, readily available and low-cost corn and wheat starch, which are domestically produced, were synthesized into bioplastics by polymerization in the presence of grape vinegar and deionized water using the solution casting method. During the preparation of the polymers, glycerol and sorbitol, referred to as plasticizers in the literature but used as cross-linking agents in this study, were preferred, and the effect of changes in cross-linking agent concentration on thermoplastic starch was examined. The mechanical, morphological, and thermal properties of the developed bioplastic materials were analyzed using FTIR, SEM, TGA, and Mechanical Test equipment. Additionally, the degradation process of the materials in water and soil ecosystems was simulated on a laboratory scale.
The FTIR spectra of the synthesized samples were found to be compatible with the literature, and undegraded starch granules were observed in SEM micrographs. It was determined that this situation was related to the ratio of amylose to amylopectin contained in the selected starch source, and it was found that undegraded starch granules negatively affected the tensile strength. In the mechanical tests, an average tensile strain property of 0.40-45 MPa was observed, and the sample synthesized using low-amount glycerol-containing corn starch (MG1) yielded the best result. In TGA analysis, it was determined that water in the structure evaporated between 20°C and 125°C, glycerol and sorbitol detached from the structure from 125°C onwards, and degradation occurred from 300°C onwards. When the swelling potential of the samples was examined, it was found that all samples exhibited swelling behavior, and the sample synthesized using low-amount sorbitol-containing wheat starch (BS1) showed the highest swelling behavior by swelling up to 182% until equilibrium. It was proven in the swelling test that as the ratio of the cross-linking agent increased, the swelling ratio decreased.
For environmental tests, the degradation behaviors of the samples in soil and water were monitored. Weekly weighings of the samples buried in soil and kept in water at room temperature in a closed container were conducted, and the final mass loss was calculated at the end of the fourth week. In this study, the sample with the highest mass loss in soil, with 45% mass loss, was the bioplastic sample synthesized using high-amount glycerol-containing corn starch (MG5), while the sample with the highest degradation rate in water, with a 99% degradation rate, was the bioplastic sample synthesized using high-amount glycerol-containing wheat starch (BG5). It was demonstrated in this study that an increase in the amount of glycerol led to an increase in film thickness, moisture content, and solubility in water.
