CHM 585 /490

1. CHM 585 /490 Chapter 12 Additives

2. Chapter 12Additives • Antioxidants • UV stabilizers • Antistatic Agents • Peroxides • Lubricants • FR • Heat stabilizers

3. Antioxidants • Antioxidants retard the oxidative degradation of plastics which is initiated when free radicals are created in the polymer by heat, UV, mechanical shear, or metallic impurities

4. Antioxidants • $160 million in U.S. • Hindered phenols • Phosphites • Thioesters

5. Hindered Phenols • BHT has FDA approval and is relatively inexpensive • But volatile and may cause discoloration

6. Less Volatile Hindered Phenols

7. Phosphites • Often used as costabilizers with hindered phenols

8. Thioesters • S(CH2CH2CO2R)2 • Often used with hindered phenols

9. UV Stabilizers • $130 Million in U.S. • Preferential UV absorbers • Absorb preferentially to the polymer and dissipate the absorbed energy without harm to the polymer • Quenching Agents • Metal chelates that convert the excess energy absorbed to heat

10. UV Stabilizers • Free Radical Terminators • Radical scavengers that both inhibit the propagation of free radicals and act as a scavenger • Hydroperoxide Decomposers • Metal chelates and hindered amines that prevent the formation of free radicals by stabilizing hydroperoxides

11. Preferential UV absorbers

12. Hindered Amine Light StabilizersHALS

13. Antistatic Agents • Static electricity can build up on the surface of polymers and needs to be dispersed to avoid the possibility of sparking, the accumulation of dust and other complications

14. Antistatic Agents • Typically hygroscopic chemicals such as ethoxylated amines

15. Peroxides • For polymerization of • PVC • LDPE • ABS For crosslinking resins As hardeners for unsaturated polyester resins(thermoset polyester)

16. Lubricants • Internal lubricants to improve flow • External to enhance mold release • Typically long hydrocarbon chain with a polar end

17. Lubricants • Fatty acid amides • Fatty acid esters • Fatty acids • Fatty acid salts • Waxes

18. FR

21. Flame Retardants • Chemicals used to retard ignition and burning of plastics • Worldwide market $2.5 Billion • FR additives enable plastics to meet various fire safety and performance standards imposed upon them. • UL

22. FR Mechanisms • Absorbing heat by the release of water • Forming an insulating char on the substrate which starves the fire • Interfering with the chemical reactions that maintain the fire and promote the spread of flame

23. Absorbing heat by the release of water • Alumina Trihydrate Al2O3.3H20 • Largest volume FR in the U.S. • 240,000 metric tons • ATH used in polyacrylates ( e.g. Dupont’s Corian), thermoset polyester resins, polyolefins and PVC

24. Forming an insulating char on the substrate which starves the fire • Phosphorous flame retardants • Phosphate esters (RO)3PO • PVC, Polyurethanes, PPO

25. Interfering with the chemical reactions that maintain the fire and promote the spread of flame • Halogenated compounds • Brominated aromatics most common • Nylons, polyesters, styrenics, polyolefins

26. Halogenated FR • “Free radical capture" process - takes place in the vapor phase. On combustion at a temperature of over 600° F, the halogen forms hydrochloric or hydrobromic acid that reacts with the antimony oxide to form antimony trihalide or antimony oxyhalide. • The flame retarding action takes place in the vapor stage above the burning material. It is thought that "free radicals propagate" the flame. • Antimony trihalides or antimony oxyhalides act as "free radical traps", and take up free radicals.

27. 1 + 1 = 3 ! Synergy

28. Heat Stabilizers • Used for PVC • > $200 M business in U.S. • Various barium, cadmium, tin compounds that scavenge reactive organic chlorine bonds thereby preventing catastrophic dehydrochlorination

29. Fillers • Glass fibers • Nickel • Clay • Prevent shrinkage • Mica • Pigments

30. Other Additives • Nucleating agents • Clarifiers • Impact Modifiers • Antimicrobial agents