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Aromatic Polyamides “Aramids”

Aromatic Polyamides “Aramids”. Beth Neilson CH 392N February 19, 2009. Definition / Invention Preparation Physical properties Fiber spinning Applications. Outline. Aramids.

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Aromatic Polyamides “Aramids”

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  1. Aromatic Polyamides“Aramids” Beth Neilson CH 392N February 19, 2009

  2. Definition / Invention Preparation Physical properties Fiber spinning Applications Outline

  3. Aramids • Federal Trade Commission definition for aramid fiber: A manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which at least 85% of the amide (-CO-NH-) linkages are attached directly between two aromatic rings • Invention • DuPont – Morgan, Kwolek et. al. • Japan, Netherlands Aromatic polyamide Amide Aromatic

  4. Chemical Structure • Homopolymer repeat units: • AB homopolymers – Type 3 • AABB homopolymers – Types 1 and 2 • Copolymers Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

  5. Chemical Structure • Aromatic units Backbone: Pendent Groups: Bridging Units: Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

  6. Preparation • AB Homopolymers • AABB Homopolymers • Polycondensation of diacid halides with diamines • Solution polycondensation • Interfacial polycondensation • Melt or vapor phase polymerization Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

  7. Solution Polycondensation • Diamine and diacid chloride – DuPont • Low temperature • Monomer purity and concentration • Amide solvent (NMP, HMPA, DMA) Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

  8. Solution Polycondensation • Poly(m-phenylene isophthalamide) Nomex® • Kwolek, S. L.; Morgan, P. W.; Sorenson, R. W. U.S. Patent 1 199 458, November 13, 1962. • DuPont, 1967

  9. Solution Polycondensation • Poly(p-phenylene terephthalamide) (PPTA) Kevlar® • DuPont – Bair, Blades, Morgan, Kwolek • AKZO – Leo Vollbracht, Twaron® Kwolek, S. L. U.S. Patent 3 819 587, 1974. Blades, H. U.S. Patent 3 869 429, 1975. Bair, T. I.; Morgan, P. W. U.S. Patent 3 673 143, 1972.

  10. Solution Polycondensation • Higashi synthesis - phosphorus-containing activating agent • Advantages: • Eliminates acid chloride starting material • Can tune reactivity by changing Ar’ Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177. Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

  11. Solution Polycondensation • Silylated diamine with diacid chloride • Increases reactivity of aromatic diamine • Faster reaction • Elimination of Me3SiCl rather than HCl • Higher molecular weight Lin, J.; Sherrington, J. C. Adv. Polym. Sci. 1994, 111, 177.

  12. Solution Polycondensation • Copolymers • Copolymerization of three or more aromatic diamines and diacid halides. • Improved solubility, thermal properties, fiber properties • Technora®

  13. Preparation of AABB homopolymers, copolymers Aromatic diamine with diacid halide High molecular weight Low temperature Monomer stoichiometry, purity, concentration Solvent Salt concentration Monomer structure (silylated amines) Reagents (triarylphosphites, pyridine) Solution Polycondensation Summary

  14. High thermal stability (Td ≥ 400°C) High tenacity (tensile strength) Chemical resistance Unique solution properties Low solubility Liquid crystallinity in p-aramids due to chain rigidity Structure dependent Meta vs. para linkages Structure of aromatic backbone Physical Properties Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989. Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

  15. Liquid crystal – substance that has properties of both a solid and a liquid Thermotropic – phase transition occurs with temperature change Lyotropic Liquid crystallinity occurs only in solution Varies as a function of polymer concentration and temperature Liquid Crystallinity Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

  16. In solution of proper concentration, liquid crystalline domains form, in which there is a high degree of order of the solute molecules. Para linkages result in rod-like extended chain structure. Hydrogen bonding Crystallization from liquid crystal solutions results in polymers with highly ordered extended-chain morphology Gives rise to polymers with higher strength and modulus Liquid Crystallinity of p-Aramids Odian, G. Principles of Polymerization, 4th Ed. Wiley: New York, 2004.

  17. Aramid Fiber Spinning Dry-jet Wet Spinning • Spinning Solution • 10-20 wt% polymer • 100% H2SO4 (H2O free) • Elongation aligns crystalline domains • Precipitates out of coagulation bath • Crystallinity of solution is translated to fiber Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

  18. Tenacity and Modulus Spinning and drawing conditions Wet vs. dry Heat treatment Polymer composition Molecular weight Properties of Aramid Fibers Yang, H. H. Aromatic High-Strength Fibers, Wiley: New York, 1989.

  19. Applications of Aramids Kevlar® http://en.wikipedia.org/wiki/Aramid#Major_industrial_uses

  20. Applications of Aramids Nomex®Technora®

  21. Applications of Aramids Hearle, J. S. High Performance Fibers, Woodhead Publishing Limited: Cambridge, 2001.

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