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Processing and Modification of Structure and Properties of Biodegradable Alloy based on Starch and Poly Lactic Acid

Esmaeili, Mohsen | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48453 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Bagheri, Reza; Pircheraghi, Gholamreza
  7. Abstract:
  8. In the recent years, the enhancing of utilization of polymeric materials, especially in packaging application, became the serious concern because of the problems of their recycling. One of efficient ways for solving this problem is usage of biodegradable polymers. Thermoplastic starch (TPS) is one the alternative materials which is produced in gelatinization process by plasticizers. However, using of TPS because of its low mechanical properties, poor processability and high water absorption is not applicable and it is necessary to improve that. One of the strategy in order to improving the TPS properties is blending with other polymers, such as polylactic acid (PLA) which the biodegradable polymer with high mechanical properties. In this study, TPS prepared in different sorbitol to glycerol ratios in order to obtain the optimized sample by mechanical, thermal and physical characterization. Finally, 58 wt.% starch, 28 wt.% sorbitol and 14wt.% glycerol were chose as optimized TPS which its elastic modulus, tensile strength and elongation to break was 62MPa, 4MPa and 96%, respectively. Calorimetry evaluation shown the glass transition temperature is 13°C which means good flexibility in room temperature. This optimized TPS resist against retrogradation after two months and Thermogravimetric analysis shown the maximum of plasticizers evaporation and thermal degradation of starch occurred in 318°C, simultaneously.
    Afterward, TPS were blended with PLA in 20 wt.%, 40wt.%, 60wt.% and 80 wt.%. In order to modify these immiscible blends, the reactive compatibilization and bulk modification were obtained. 20% of PLA was substituted by maleic anhydride grafted PLA (PLA-g-MA) as compatibilizer. Surface compatibilization increased elastic modulus and tensile strength, while, bulk modification decreased them. Elongation to break of TPS was declined from 96% to lesser than 10% by adding PLA and compatibilization caused more decreasing, whereas, elongation to break of a sample with 80% plasticized PLA increased to 143%. Both of surface compatibilization and bulk modification caused changing in morphology which changed rheological properties, calorimetric transitions, water absorption, contact angle and biodegradation rate. In all samples water absorption, contact angle and biodegradation rate were enhanced and glass transition, crystallization and melting temperature were decreased by TPS content increasing. In bulk modification, the three mentioned temperature strongly decreased and Water absorption, contact angle and biodegradation rate in bulk modified samples was more rather than compatibilized samples
  9. Keywords:
  10. Thermoplastic Starch ; Polylactic Acid ; Consistency ; Biodegradability

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