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The Environmental Behaviour Of Polymers


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How environmental factors affect the structure of polymers

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The Environmental Behaviour Of Polymers

  1. 1. ENVIRONMENTAL BEHAVIOUR OF POLYMERS HNC/D Applied Chemistry Polymer Chemistry By Sabrina Lee
  2. 2. DEGRADATION WHAT IS DEGRADATION? Degradation is a type of organic chemical reaction in which a compound is converted into a simpler compound. [1] EXAMPLES OF DEGRADATION? Examples of degradation include environmental degradation e.g. the hole in the o-zone layer caused by car emissions and pollution (physical) and chemical degradation.
  3. 3. DEGRADATION IN POLYMERS POLYMER DEGRADATION Degradation in polymers refers to a change in the properties of a polymer under the influence of one or more environmental factors FACTORS  Heat  Light  Chemicals – Acids, Alkalis and some salts
  4. 4. IS DEGRADATION DESIRED OR UNDESIRED? Are the changes in the properties of a polymer due to degradation desired or undesired? UNDESIRABLE CHANGES X Cracking X Chemical disintegration of products DESIRABLE CHANGES  Biodegradation – deliberately lowering the molecular weight of a polymer for recycling, often termed “aging”.
  5. 5. TYPES OF DEGRADATION IN POLYMERS PHOTOINDUCED DEGRADATION Degraded by photolysis to give a lower molecular weight – often via visible light or UV, X-rays or gamma rays. THERMAL DEGRADATION Degraded by thermolysis at high temperatures to give monomers, oils, gases and water. Includes: Pyrolysis, Hydrogenation and Gasification CHEMICAL DEGRADATION Degraded by solvolysis and mainly hydrolysis to lower molecular weight
  6. 6. ANTI-DEGRADANTS WHAT ARE ANTI-DEGRADANTS? Deterioration inhibitor in rubber compounds to deter the aging of rubber products HOW DO THEY WORK? Anti-degradants cover the surface of the rubber product to prevent direct contact between rubber and oxygen, thus preventing the degradation, or “aging” of the product i.e. wax products
  7. 7. EXAMPLES OF WAXES ANIMAL WAXES Beeswax Chinese wax Lanolin (wool wax) Shellac wax VEGETABLE WAXES Bayberry wax Carnauba wax Castor wax Jojoba oil Soy wax MINERAL WAXES Ceresin waxes Montan wax Ozocerite Peat waxes PETROLEUM WAXES Paraffin wax Microcrystalline wax Petroleum jelly SYNTHETIC WAXES Polyethylene waxes Chemically modified waxes Substituted amide waxes Polymerised α-olefins
  8. 8. ENVIRONMENTAL DEGRADATION WHAT IS ENVIRONMENTAL DEGRADATION? • The deterioration of the environment through depletion of resources, such as air, water and soil. • The destruction of ecosystems and the extinction of wildlife • When natural habitats are destroyed or natural resources are depleted, the environment is degraded.
  9. 9. FACTORS OF ENVIRONMENTAL DEGRADATION NATURAL FACTORS • Droughts • Storms – e.g. hurricanes, tornadoes, volcanic eruptions These factors lead to land degradation caused by erosion. HUMAN FACTORS • Deforestation • Industrialisation • Urbanisation These factors lead to water, air and land pollution. [3]
  10. 10. ENVIRONMENTAL STRESS CRACKING (ESC) [2] WHAT IS ESC? • Unexpected brittle failure of thermoplastic polymers • Accounts for 15-30% of all plastic component failures in service • Caused by exposure to liquid chemicals • Occurs mostly in amorphous, brittle polymers like polystyrene and polycarbonate
  11. 11. ESC AND POLYMER DEGRADATION ESC and polymer degradation are not the same thing. Polymer degradation involves breaking polymer bonds, whereas ESC does not. ESC breaks the secondary linkages between polymers instead.
  12. 12. EXAMPLES OF ESC ESC is seen in various polymers from plastic drinking glasses to the automotive industry. The need to resist ESC in the automotive industry is high as a number of different polymers are subjected to a number of fluids. Examples: • Petrol • Brake fluid • Windscreen cleaning solution
  13. 13. HOW DOES STRUCTURE AFFECT REACTIVITY? The structure of a polymer depends upon various factors: • Number of branches (methyl groups) • Type of branching – long or short branched polymers • Number of cross links within a polymer All of these factors contribute to physical and mechanical properties of a polymer.
  14. 14. HOW DOES STRUCTURE AFFECT REACTIVITY? (Cont.) BRANCHING • Branching makes a polymer less dense resulting in low tensile strength and low melting points. • Branching also reduces the free volume of a polymer, resulting in a higher glass-transition temperature, Tg.
  15. 15. HOW DOES STRUCTURE AFFECT REACTIVITY? (Cont.) CROSS LINKING Cross linkage is described as a short side chain of atoms linking two longer chains in a polymeric material [1]. Cross links can either be covalent or ionic bonds. Polymers with a high enough degree of cross-linking have "memory." When the polymer is stretched, the cross-links prevent the individual chains from sliding past each other. The chains may straighten out, but once the stress is removed they return to their original position and the object returns to its original shape.
  16. 16. HOW DOES STRUCTURE AFFECT REACTIVITY? (Cont.) FUNCTIONAL GROUPS Different functional groups can affect a polymers properties by • Different groups lending the polymer to ionic or hydrogen bonding, depending upon where the bond is formed, resulting in higher tensile strength and crystalline melting points. • Amides or carbonyl groups form hydrogen bonds between adjacent chains while polymers such as Ethene have no permanent dipole, resulting in VDW forces which are much weaker. Hydrogen bonding is stronger than VDW, resulting in higher MP & tensile strengths.
  17. 17. REFERENCES [1] Oxford Dictionary of Chemistry Sixth Edition Published 2008 Edited by John Daintith [2] 17px-Crazes1.jpg [3]