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ARISTOTLE UNIVERSITY OF THESSALONIKI FACULTY OF ENGINEERING DEPARTMENT OF CHEMICAL ENGINEERING MASTER OF SCIENCE IN CHEMICAL ENGINEERING Master Thesis “Enzymatic and Microbial Degradation of Synthetic Polymers” Stavroula Kyriakou MARCH 2017 ARISTOTLE UNIVERSITY OF THESSALONIKI FACULTY OF ENGINEERING DEPARTMENT OF CHEMICAL ENGINEERING MASTER OF SCIENCE IN CHEMICAL ENGINEERING Master Thesis “Enzymatic and Microbial Degradation of Synthetic Polymers” Author: Stavroula Kyriakou Supervisor: Professor Emeritus Maria Liakopoulou-Kyriakides Co-supervisor: Professor Emeritus Costas Kyparissides Members of Examination Committee: Professor Angeliki Lemonidou Professor Michael Stoukides MARCH 2017 Acknowledgements I would first like to express my sincere gratitude to my supervisor Professor Emeritus Maria Liakopoulou-Kyriakides for giving me the opportunity to perform this thesis. Moreover, I would like to express my great appreciation and my special thanks to my co- supervisor Professor Emeritus Costas Kiparissides for the assignment of this interesting topic, for his valuable contribution, support and guidance throughout the process. I would also like to express my special thanks to Dr. Giannis Penloglou for his assistance and guidance in the laboratory and for the excellent cooperation. In addition, I would like to thank Dr. Olympia Kotrotsiou for her support and help in the laboratory. I would also like to acknowledge Prof. Angeliki Lemonidou and Prof. Michael Stoukides as the second readers of this thesis and I am gratefully indebted to their valuable comments. Last but not least, I would like to thank everybody in the Laboratory of Polymer Reaction Engineering at the Center for Research and Technology Hellas for the great work environment. i Abstract Polyethylene (PE) is the most widely used packaging material and considered one of the most durable plastic polymers. It is characterized by slow biodegradability and insufficient elucidation of its degradation mechanism. The aim of the study was the investigation of the biodegradability of PE powder by using different enzyme amounts of Agaricus bisporus laccase and different inoculum size values of Pseudomonas putida (DSMZ 6125). Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to measure the crystallinity of the degraded samples and double bond index, respectively. The highest decrease in the degree of crystallinity was obtained for the microbial degradation, indicating sufficient degradation and microbial attack on the crystal structure of PE. Moreover, the FTIR results verified that the DBI was higher for the enzymatically treated samples, although no significant difference was observed for the microbial treated ones, suggesting that both ways of biological degradation are effective. ii Contents 1. Polymers.............................................................................................................................. 1 1.1 Molecular and Crystal Structures of Polymers ............................................................ 1 1.1.1 Hydrocarbon molecules ....................................................................................... 2 1.1.2 Polymer Molecules ............................................................................................... 5 1.1.3 The Chemistry of Polymer Molecules .................................................................. 5 1.1.4 Molecular Weight................................................................................................. 9 1.1.5 Molecular Shape................................................................................................. 11 1.1.6 Molecular Structure ........................................................................................... 12 1.1.7 Molecular Configurations................................................................................... 15 1.1.8 Thermoplastics and Thermosetting Plastics ...................................................... 18 1.1.9 Copolymers......................................................................................................... 19 1.1.10 Diffusion in polymeric materials ........................................................................ 26 2. Polymer Classification ....................................................................................................... 29 2.1 Chemical Structure .................................................................................................... 29 2.2 Application Field ........................................................................................................ 31 2.2.1 Plastics ................................................................................................................ 31 2.2.2 Elastomers .......................................................................................................... 33 2.2.3 Coatings .............................................................................................................. 34 2.2.4 Adhesives............................................................................................................ 34 2.2.5 Films ................................................................................................................... 35 2.2.6 Foams ................................................................................................................. 35 2.3 Origin ......................................................................................................................... 35 2.4 Special Properties ...................................................................................................... 36 3. Characteristics and Processing of Polymers ..................................................................... 37 3.1 Mechanical Behavior of Polymers ............................................................................. 37 iii 3.1.1 Stress-strain Behavior ........................................................................................ 37 ........................................................................................................................................... 37 3.2 Miscellaneous Mechanical Characteristics................................................................ 39 3.2.1 Impact Strength.................................................................................................. 39 3.2.2 Fatigue ................................................................................................................ 39 3.2.3 Tear Strength and Hardness............................................................................... 39 3.3 Mechanisms of Deformation and for Strengthening of Polymers ............................ 40 3.3.1 Deformation of Semi-crystalline Polymers ........................................................ 40 3.3.2 Factors that Influence the Mechanical Properties of Semi-crystalline Materials 42 4. Degradation of Polymers .................................................................................................. 44 4.1 Abiotic Degradation................................................................................................... 44 4.1.1 Swelling and Dissolution .................................................................................... 44 4.1.2 Bond Rupture ..................................................................................................... 45 4.1.3 Thermal Degradation ......................................................................................... 49 4.2 Biological Degradation............................................................................................... 50 4.2.1 Microbial Degradation ....................................................................................... 51 4.2.2 Reasons for the Poor Biodegradability of Plastics ............................................. 53 4.2.3 Desired Characteristics of Microorganisms to degrade synthetic polymers ..... 54 4.3 Enzymatic Degradation.............................................................................................. 55 4.3.1 Enzymatic Hydrolysis .......................................................................................... 56 4.3.2 Enzymatic Oxidation........................................................................................... 56 4.4 Assimilation ............................................................................................................... 56 5. LDPE (Low-density polyethylene) ..................................................................................... 59 5.1 General Characteristics ............................................................................................. 59 5.2 LDPE Degradation ...................................................................................................... 60 iv 5.2.1 Pretreatment Effect ........................................................................................... 60 5.2.2 Polyethylene Degradation without Pretreatment ............................................. 61 5.2.3 Mechanisms of Microbial Polyethylene Degradation ........................................ 62 5.2.4 Mechanisms of Enzymatic Polyethylene Degradation....................................... 63 6. Methods ............................................................................................................................ 67 6.1 Laccase Activity Measurement.................................................................................. 67 6.2 Differential Scanning Calorimetry (DSC) ................................................................... 68 6.2.1 Power Compensation DSC Instrumentation ...................................................... 68 6.2.2 Method Characteristics ...................................................................................... 73 6.2.3 Experimental Assumption .................................................................................. 75 6.2.4 Analytical Calculations ....................................................................................... 76 6.2.5 Analytical DSC Applications ................................................................................ 77 6.2.6 Measured Properties.......................................................................................... 77 6.2.7 DSC Experimental Part ....................................................................................... 83 6.3 FTIR- Fourier Transformation Infrared Spectroscopy ............................................... 85 6.3.1 Infrared Radiation and Spectrum....................................................................... 85 6.3.2 The Michelson Interferometer........................................................................... 87 6.3.3 Instrumental Measurement ............................................................................... 93 7. Experimental Part ............................................................................................................. 95 7.1 Aim of the Study ........................................................................................................ 95 7.2 Experimental Procedure ............................................................................................ 95 7.2.1 250 mL 0.1 M Acetate Buffer pH 4.5 Preparation.............................................. 95 7.2.2 250 mL of 70% Ethanol Solution Preparation .................................................... 95 7.2.3 Enzymatic Degradation ...................................................................................... 95 7.2.4 Microbial Degradation ....................................................................................... 98 7.2.5 Differential Scanning Calorimetry Measurement Process ............................... 101 v 7.2.6 FTIR Measurement Process.............................................................................. 102 8. Results- Discussion .......................................................................................................... 104 8.1 Laccase Activity Measurement................................................................................ 104 8.2 P. putida Biomass Measurement ............................................................................ 105 8.3 Differential Scanning Calorimetry ........................................................................... 107 8.3.1 Crystallinity Changes during Enzymatic Degradation ...................................... 109 8.3.2 Crystallinity Changes during Microbial Degradation ....................................... 111 8.4 FTIR Analysis ............................................................................................................ 114 8.4.1 FTIR Enzymatic Degradation ............................................................................ 115 8.4.2 FTIR Microbial Degradation.............................................................................. 117 8.5 Double Bond Index .................................................................................................. 119 8.6 Hydrophilicity/ Hydrophobicity ............................................................................... 121 9. Conclusions ..................................................................................................................... 123 10. References ................................................................................................................... 126 vi Figures Figure 1. Classification of the characteristics of polymer molecules......................................... 2 Figure 2. Structure of ethylene. ................................................................................................. 2 Figure 3. Structure of acetylene. ................................................................................................ 3 Figure 4. Structure of butane. .................................................................................................... 4 Figure 5. Structure of isobutane. ............................................................................................... 4 Figure 6. Structure of typical carbon chain polymers. ............................................................... 5 Figure 7. Reaction between an initiator and the ethylene monomer. ...................................... 6 Figure 8. Active growing polyethylene chain molecule. ............................................................ 6 Figure 9. Polyethylene chain structure. ..................................................................................... 6 Figure 10. Polytetrafluoroethylene structure. ........................................................................... 6 Figure 11. Vinyl chloride polymerization. .................................................................................. 7 Figure 12. Generalized polymer structure. ................................................................................ 7 Figure 13. Hypothetical polymer molecule size distributions on the basis of number (on the left) and weight (on the right) fractions of molecules. .............................................................. 9 Figure 14. A perspective of PE molecule indicating the zigzag backbone structure. .............. 11 Figure 15. Positioning of backbone carbon atoms dependence on polymer chain shape...... 11 Figure 16. Numerous random kinks and coils on a single polymer chain by chain bond rotations. .................................................................................................................................. 12 Figure 17. Linear (a), branched (b), crosslinked (c) and network (three-dimensional) (d) molecular structures. ............................................................................................................... 13 Figure 18. Star block copolymer Vergina with 16 mixed branches [3]. ................................... 14 Figure 19. Repeated unit of a polymer. ................................................................................... 15 Figure 20. Head-to-tail configuration....................................................................................... 16 Figure 21. Head-to-head-configuration. .................................................................................. 16 Figure 22. Isotactic configuration............................................................................................. 16 Figure 23. Syndiotactic configuration. ..................................................................................... 16 Figure 24. Atactic configuration. .............................................................................................. 17 Figure 25. Cis isoprene repeat unit. ......................................................................................... 18 Figure 26. Trans isoprene repeat unit. ..................................................................................... 18 Figure 27. Random (a), alternating (b), block (c) and graft copolymers (d). ........................... 20 Figure 28. Arrangement of molecular chains in a unit cell for polyethylene. ......................... 22 vii Figure 29. Electron micrograph of a polyethylene single crystal 20,000 x. ............................. 24 Figure 30. The chain-folded structure for a plate-shaped polymer crystalline. ...................... 24 Figure 31. Transmission electron micrograph showing the spherulite structure in a natural rubber specimen (525 x). ......................................................................................................... 25 Figure 32. The detailed structure of a spherulite. ................................................................... 26 Figure 33. Transmission photomicrograph showing the spherulite structure of polyethylene. .................................................................................................................................................. 26 Figure 34. Condensation Polymerization. ................................................................................ 29 Figure 35. First manner of termination in addition polymerization. ....................................... 30 Figure 36. Second manner termination in addition polymerization........................................ 30 Figure 37. Cross-linked polymer chain molecules (a) in unstressed state (b) during elastic deformation in response to an applied tensile stress.............................................................. 32 Figure 38. Strain-stress behavior for brittle (curve A), plastic (curve B) and highly elastic (elastomeric) (curve C) polymers. ............................................................................................ 37 Figure 39. Stress-strain curve for a plastic polymer showing how yield and tensile strengths are determined......................................................................................................................... 38 Figure 40. The influence of temperature on the stress-strain characteristics of poly(methyl methacrylate). .......................................................................................................................... 38 Figure 41. Fatigue curves (stress amplitude versus the number of cycles to failure) for PET, nylon, PS, PMMA, PP, PE & PTFE.............................................................................................. 39 Figure 42. Elastic deformation of a semi-crystalline polymer. ................................................ 40 Figure 43. Plastic deformation of a semi-crystalline polymer. ................................................ 41 Figure 44. The influence of degree of crystallinity and molecular weight on the physical characteristics of PE. ................................................................................................................ 43 Figure 45. Norrish I and II reactions [18].................................................................................. 47 Figure 46. A scission reaction. .................................................................................................. 48 Figure 47. A ladder polymer structure. .................................................................................... 50 Figure 48. Polymer Biodegradation. ........................................................................................ 50 Figure 49. Relationship between T and biodegradability of polyesters by R. arrhizus lipase. m .................................................................................................................................................. 54 Figure 50. Pathways of polymer biodegradation [71]. ............................................................ 58 Figure 51. Proposed mechanism of polyethylene degradation [97, 102, 120, 141]. .............. 64 viii

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Engineering at the Center for Research and Technology Hellas for the great work environment. 3.3.2 Factors that Influence the Mechanical Properties of Semi-crystalline Materials. 42. 4. modulus and strength constitute some of the polymer properties that strongly depend on molecular weight [1].
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