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Fabrication, Characterization and Microstructure Optimization of PLA/ TPS/ Gelatin Ternary Alloy for the Production of Biodegradable Film

Afzali, Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57261 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza
  7. Abstract:
  8. Using bio-based and biodegradable polymers is one of the main ways to minimize environmental concerns by lowering reliance on oil reserves and solving disposal problems. Among the different types of these polymers, polylactic acid (PLA) has attracted a lot of attention for polymer film applications due to its adequate tensile strength and appropriate elastic modulus. However, drawbacks such as low flexibility and a prolonged rate of biodegradation prevent its use in pure form. Blending PLA with thermoplastic starch (TPS) is one strategy to solve the mentioned problems. On the other hand, because of the higher biodegradation rate of gelatin than TPS, adding gelatin to the PLA/ TPS blend can improve the biodegradation rate even further. The current study aims to improve the biodegradation rate of PLA and develop a biobased and biodegradable polymer blend with acceptable properties. In this regard, after finding a suitable method for producing PLA/ TPS/ Gelatin in a significant range of gelatin concentration, in samples containing PLA with a fixed concentration of 50 wt%, the concentration of gelatinized gelatin (GG) was changed from 0 to 15%. In order to characterize the samples, imaging by scanning electron microscopy and rheology, differential scanning calorimetry and tensile tests were used. To assess hydrophilicity and biodegradability, solubility in water, as well as weight loss in the soil, were determined. The results show that by replacing TPS with GG, the microstructure has changed from a co-continuous phase to a polylactic acid matrix phase and dispersed starch/ gelatin particles, and the smallest size of dispersed particles corresponds to the microstructure of the sample with 5 wt% GG. In the mentioned sample, along with the insignificant increase in tensile strength and elastic modulus to the values of 28.8 and 1730 MPa, respectively, the strain at the break has reached 14.5%, representing an 80% improvement over the gelatin-free sample. The biodegradability test findings demonstrate that the sample containing 5 wt% GG lost more than 45% of its weight within 30 days, whereas the pure PLA and PLA/ TPS blend lost less than 1 and 40% of their weight during this period, respectively. In the following of the research, to improve the compatibility, the effect of adding 1 phr of Epoxidized soybean oil (ESO) on the ternary blends was explored. ESO has increased complex viscosity and storage modulus by improving compatibility. By adding ESO to the sample composition containing 5 wt% GG, the values of tensile strength and elastic modulus have decreased by 22% and 9%, respectively. While the strain at the break has increased by 18% to 17.06%. ESO’s influence on soil weight loss varies depending on the concentration of GG in the blend. At low concentrations of GG (0 and 5 wt%), biodegradability is reduced with the addition of the oil; while this value is increased for samples containing 10 and 15 wt% GG. The findings of this study indicate that 50 wt% of PLA, 45 wt% of TPS, and 5 wt% of GG is an optimal composition for developing a biodegradable and bio-based polymer whose flexibility and rheological properties can be improved by adding 1 phr of ESO
  9. Keywords:
  10. Polylactic Acid ; Starches ; Gelatin ; Biodegradability ; Polyethylene/Thermoplastic Starch Blend ; Biodegradable Polymer

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