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Presentation on photo degradation and photo stabilization of polymers

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Presentation made by Joel Lalucherian, Prof R.N.Desai & Prof Bhakti D Patel at All India Seminar on Polymer Processing, reclamation and its end-of-life impact on environment at Gujarat State Center of The Institution of Engineers (India)

Published in: Engineering
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Presentation on photo degradation and photo stabilization of polymers

  1. 1. PRESENTED BY- Joel Lalucherian Rubber Technology B.E. 5th semester L.D College Of Engineering Guided by- Prof. R.N Desai Prof. B.D.Patel
  2. 2. Photodegradation
  3. 3. Different Types of Degradation Chemical Degradation Thermal Degradation Biodegradation Radiolytic Degradation Mechanical Degradation Photodegradation
  4. 4. Photodegradation Photodegradation is degradation of a photodegradable molecule caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light, and ultraviolet light.
  5. 5. Factors Causing Photodegradation INTERNAL IMPURITIES Hydroperoxide Carbonyl Unsaturated bonds Catalyst residue Change transfer (CT) complexes with oxygen EXTERNAL IMPURITIES Traces of solvent, catalyst,etc. Compounds from a polluted urban atmosphere and smog Additives Traces of metal & metal oxides from processing equipments & containers, such as Fe, Ni or Cr.
  6. 6. Photo-initiation . . RH R H→ + . . ROOH RO OH→ +
  7. 7. Propagation . . 2R O ROO+ → . . ROO R'H ROOH R'+ → + . . RO R'H ROH R'+ → + . . 22ROOH RO ROO H O→ + + . . RO R'H ROH R'+ → +
  8. 8. Reaction Cycle
  9. 9. Termination . . 2ROO ROO ROOR O+ → + . . ROO R ROOR+ → . . R R R R+ → −
  10. 10. Effects of Photodegradation & Need for Photostabilization Loss in physical properties Discolouration Hence in order to avoid such problems in the service life of any product we give photostabilization effect to the polymer.
  11. 11. Photostabilization
  12. 12. Photostabilization Photostabilization is the retardation or elimination of the photodegradation of any polymer. Stablizers are classified as: Light screeners UV absorbers Excited state quenchers Peroxide decomposers Radical scavengers
  13. 13. Factors affecting thickness of absorber coating The amount of the absorber required to provide economical protection in a polymer depends on: Thickness of the polymer product Tolerance of colour Effect of high concentration of absorbers on it Compatibility of the absorber with it
  14. 14. Mode of action of UV absorbers It interacts with the first step of the photo-oxidation process. It absorbs the harmful UV radiation before it reaches to the photo active chromophoric species in the polymer molecule (300-400nm). Hence, energy dissipates in the manner that does not lead to photosensitization. A UV absorber should be light stable.
  15. 15. Light Screeners Application of a coat of material on the polymer to screen it from photodegradation. Some examples are pigments, carbon black, etc. The energy that attacks the chromophoric group is absorbed and dissipated in a manner that it does not affect the polymer.
  16. 16. Pigments Pigments are insoluble inorganic or mineral and organic compounds of complex structure. Powdered metal Aluminium is an excellent reflector to UV light. Fe2O3, Fe3O4, ZnO, TiO2 are inorganic pigment excellent UV screener. Organic pigments such as azo and anthraquenone display good UV light absorption.
  17. 17. Benefits of using Pigments Cost reduction Reinforcement Hardening Improving slip and skid resistance Colour effect Storage stability
  18. 18. Pigment as a Light Screener Pigment as a light screener should be: Light stable for long term performance without fading. Heat stable to withstand polymer processing conditions. Migration resistant. Low cost. Non-toxic.
  19. 19. Radical Scavengers The radical scavengers operate by interfering with the propagating step in the oxidative chain and this can be achieved by two routes: Reaction with propagating radicals (R. , RO. , ROO. ). Reaction with resulting hydroperoxides which are the source of chain branching through the propagating process. Quinones react with alkyl radicals to form radicals that do not initiate polymer oxidation.
  20. 20. Quenchers Quenchers deactivate excited states of chromophoric groups in polymers before bond scission can occur by two mechanisms:  Energy Transfer Process Intermolecular Energy Transfer Intramolecular Energy Transfer Chemical and / or Physical Deactivation
  21. 21. Quenching Mechanism There are two mechanisms: Long range Energy Transfer Contact (Collisional) Energy Transfer Ch - Chromophoric group Q - Quencher
  22. 22. Carbon Black Acts as an UV absorber as well as a radical scavenger. Carbon black absorbs UV radiation more efficiently than conventional coloured pigments. Carbon black consists of functional groups such as carbonyl, hydroxyl, quinone, ether, etc. that as a radical scavenger.
  23. 23. Conclusion Complete stabilization of polymers against photodegradatoin is not possible, hence the additives must decompose –OOH, and acts as quenchers of some excited state in the early stages of photodegradation. The “hydroperoxide” (POOH) is the most important initiator in the photooxidative process. Hence it must be quenched.
  24. 24. Innovative Stabilizations Use of PTFE (teflon) as a light screener due to its high bond dissociation enthalpy. Application of coatings with high refractive index difference with air will lead to better stabilizing effect. (Concept of Rubber paints).

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