Downloaded 195 times
Uploaded byMohamed M. Abdul-Monem
Thermal degradation of Polymers
Thermal degradation of polymers occurs when polymers are exposed to high temperatures, breaking their molecular chains. This causes changes in properties like ductility, embrittlement, and color. Degradation happens through initiation, propagation, and termination reactions that produce free radicals. Methods include depolymerization, random chain scission, and side group elimination. Thermal degradation is studied using thermogravimetric analysis and differential scanning calorimetry. Stabilizers and controlling the environment can protect polymers from thermal breakdown.
In this document
Powered by AI
Presentation by Mohamed Mahmoud Abdul-Monem on thermal degradation of polymers, focusing on the impact and mechanisms involved.
Overview of key topics in thermal degradation such as definitions, effects, mechanisms, and protection methods.
Thermal degradation defined as molecular deterioration due to overheating, affecting polymer properties.
Includes changes in chemical properties such as reduced ductility, embrittlement, and cracking in polymers.
Thermal breakdown products include compounds like carbon monoxide, ammonia, and other toxic substances.
Describes the conventional model involving initiation, propagation, and termination steps in thermal degradation.
Details the initiation process where the polymer chain loses a hydrogen atom, creating free radicals.
Explains how free radicals react with oxygen, propagating further degradation through a chain reaction.
Describes how termination occurs by combining free radicals to form inert products or using stabilizers.
Depolymerization method involves the loss of monomers as the polymer chain is heated.
Random chain scission leads to rapid decreases in molecular weight at various positions of the backbone.
Explains how side groups are removed from polymers like PVC under heat before chain breaking.
Thermogravimetric analysis (TGA) measures mass loss due to degradation, producing gaseous products.
Illustration or description of the TGA device used in thermal degradation research.
Differential Scanning Calorimetry (DSC) analyzes endothermic and exothermic reactions during thermal changes.
Methods to protect against degradation include stabilizers, radical scavengers, and using strong bond polymers.
Cites key literature on thermal degradation for further reading and research validation.
More Related Content
Similar to Thermal degradation of Polymers
More from Mohamed M. Abdul-Monem
Thermal degradation of Polymers
- 1. BY MOHAMED MAHMOUD ABDUL-MONEM DE N T A L B I O M A T E R I A L S D E P A R T M E N T F A C U L T Y O F D E N T I S T R Y A L E X A N D R I A U N I V E R S I T Y EGYPT Thermal Degradation of polymers
- 2. Contents Definition Effectof thermal degradation on polymers Thermal degradation products Mechanism of thermal degradation Methods of thermal degradation Research methods of thermal degradation Protection against thermal degradation References
- 3. Definition Thermal degradationof polymers is molecular deterioration as a result of overheating. At high temperatures the components of the long chain backbone of the polymer break and react with one another to change the properties of the polymer.
- 4. Effect of thermaldegradation on polymers The chemical reactions involved in thermal degradation lead to physical and optical property changes relative to the initially specified properties. Thermal degradation generally involves changes to the molecular weight of the polymer and typical property changes include reduced : ductility embrittlement, chalking, color changes, cracking.
- 5. Thermal degradation products Thermal breakdown products may include a complex mixture of compounds, including but not limited to: carbon monoxide, ammonia, aliphatic amines, ketones, nitriles, and hydrogen cyanide, which may be flammable, toxic and/or irritating.
- 6. Mechanism of thermaldegradation of polymers The conventional model for thermal degradation is that of an involves the major steps of : Initiation, Propagation Termination.
- 7. Initiation of thermaldegradation The initiation of thermal degradation involves the loss of a hydrogen atom from the polymer chain as a result of energy input from heat or light. This creates a highly reactive and unstable polymer ‘free radical’ (R•) and a hydrogen atom with an unpaired electron (H•).
- 8. Propagation The propagationof thermal degradation can involve a variety of reactions and one of these is where the free radical (R•) reacts with an oxygen (O2) molecule to form a peroxy radical (ROO•) which can then remove a hydrogen atom from another polymer chain to form a hydroperoxide (ROOH) and so regenerate the free radical (R•). The hydroperoxide can then split into two new free radicals, (RO•) + (•OH), which will continue to propagate the reaction to other polymer molecules. The process can therefore accelerate depending on how easy it is to remove the hydrogen from the polymer chain.
- 10. Termination The terminationof thermal degradation is achieved by ‘mopping up’ the free radicals to create inert products. This can occur naturally by combining free radicals or it can be assisted by using stabilizers in the plastic.
- 12. Methods of thermaldegradation 1.Depolymerization: Under thermal effect, the end of polymer chain departs, and forms low free radical which has low activity. Then according to the chain reaction mechanism, the polymer loses the monomer one by one.
- 14. 2.Random chain session The backbone will break down randomly, this can occur at any position of the backbone, as a result the molecular weight decreases rapidly.
- 15. 3.Side group elimination Groups that are attached to the side of the backbone are held by bonds which are weaker than the bonds connecting the chain. When the polymer is heated, the side groups are stripped off from the chain before it is broken into smaller pieces. For example the PVC eliminates HCl, under 100– 120 °C
- 17. The research methodsof thermal degradation of polymers (Thermogravimetric analysis) (TGA) refers to the techniques where a sample is heated in a controlled atmosphere at a defined heating rate whilst the sample's mass is measured. When a polymer sample degrades, its mass decreases due to the production of gaseous products like carbon monoxide, water vapour and carbon dioxide.
- 18.
- 20. (Differential scanningcalorimetry) (DSC): Analyzing the heating effect of polymer during the physical changes in terms of glass transition, melting, and so on. These techniques measure the heat flow associated with oxidation.
- 23. Protection against ThermalDegradtion Stabilizers Radical scavengers (React with free radicals) Oxidation control by inert environment Use of polymers with strong bonds like C-F in teflon.
- 24. References C.L.BeylerThermal degradationof polymers,Chapter 7 ,SPFE Handbook. C.David.Thermal degradation of polymers,Chapter 1,Comprehensive chemical kinetics.