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Odian Book 2-12

Odian Book 2-12. Common Engineering Thermosets (Not elastomers). Bismaleimides Epoxies Phenol / Formaldehyde Sheet Molding Compound Polyurethanes** **Also thermoplastics. Step & Chain Growth. Step & Chain Growth. Step Growth. Chain Growth. Step Growth. Epoxy Systems.

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Odian Book 2-12

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  1. Odian Book 2-12

  2. Common Engineering Thermosets(Not elastomers) • Bismaleimides • Epoxies • Phenol / Formaldehyde • Sheet Molding Compound • Polyurethanes** **Also thermoplastics Step & Chain Growth Step & Chain Growth Step Growth Chain Growth Step Growth

  3. Epoxy Systems f = 2 “Tube A” f = 4 “Tube B” Mechanism Network

  4. Advantageous Properties of epoxies High chemical and solvent resistance Outstanding adhesion to many substrates Good impact resistance Good electrical properties Epoxy Systems

  5. Epoxy Systems f = 2 “Tube A” f = 4 “Tube B” Network

  6. Epoxy Systems Diglycidal Ether of Bisphenol-A (DGEBA)

  7. Epichlorohydrin: Background Chlorine intensive - 4 atoms of chlorine/epi Yields: - chlorination: 82% - HOCl and closure: 92% Byproducts: - chlorinated organics Hydraulic load: - 47 lbs water/lb of epi

  8. Epoxy Systems <Mn> ≈ 15,000 – 20,000 g/mol Viscous liquid to solid

  9. Polyurethanes and Polyureas • Thermoplastics • Thermosets

  10. Important Starting Materials for Polyurethanes Relative rates 30,000x • Diisocyantes • Polymeric Glycols (aka polyols) • MW < 3,000 g/mol • Chain extenders • Catalysts • Trialkyl tin acetate • Dialkyl tin diacetate

  11. Diisocyanates • Diphenylmethane diisocyanate (MDI) • Toluene diisocyanate (TDI) • Dicyclohexylmethane diisocyanate (H-MDI) • Hexamethylene diisocyanate (HDI) • Cycloaliphatics

  12. Diisocyanates • Phosgenation

  13. Chain Extenders • For urethanes • For ureas

  14. Polyurethane Fibers Excess Pre-polymer Chain extenders

  15. Sheet Molding Compound

  16. Sheet Molding Compound

  17. Phenol Formaldehyde Resins • 1872 – Invented by Bayer • 1907 – First patent and commercial process by Baekeland • Success: First wholly synthetic polymer used commercially

  18. Phenol Formaldehyde Resins • Excellent thermal stability • High char yield • Low smoke generation • Low smoke toxicity

  19. Base-Catalyzed Phenol-Formaldehyde Resins (Resols) • Base catalyzed • Excess formaldehyde • Resols cure with heat alone

  20. Base-Catalyzed Phenol-Formaldehyde Resins (Resols)

  21. Base-Catalyzed Phenol-Formaldehyde Resins (Resols) • Excess formaldehyde • Resols cure with heat alone

  22. Base-Catalyzed Phenol-Formaldehyde Resins (Resols) • Cure of resole prepolymer proceeds under neutral or acidic conditions and at elevated temperature. • Crosslinking occurs via the continued formation of methylene links and the formation of dibenzyl ether linkages. • Higher temperatures favor the formation of methylene bridges • Both are condensation reactions and produce water

  23. Acid-Catalyzed Phenol-Formaldehyde Resins (Novolacs)

  24. Acid-Catalyzed Phenol-Formaldehyde Resins (Novolacs) • Acid Catalyzed • Excess phenol • No hydroxy methyl groups • Tg = 40 C • MW = 1 – 3000 g/mol • Require second additive for cure • Hexamethylene tetraamine

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