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ISSUES TO ADDRESS... What are the basic microstructural features ? 1 How do these features dictate room T tensile response ? Hardening, anisotropy, and.

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Presentation on theme: "ISSUES TO ADDRESS... What are the basic microstructural features ? 1 How do these features dictate room T tensile response ? Hardening, anisotropy, and."— Presentation transcript:

1 ISSUES TO ADDRESS... What are the basic microstructural features ? 1 How do these features dictate room T tensile response ? Hardening, anisotropy, and annealing in polymers. CHAPTER 4: POLYMER STRUCTURES

2 2 Polymer = many mers Covalent chain configurations and strength: Direction of increasing strength Adapted from Fig. 14.2, Callister 6e. Adapted from Fig. 14.7, Callister 6e. POLMER MICROSTRUCTURE

3 3 Thermoplastics: --little cross linking --ductile --soften w/heating --polyethylene (#2) polypropylene (#5) polycarbonate polystyrene (#6) Thermosets: --large cross linking (10 to 50% of mers) --hard and brittle --do NOT soften w/heating --vulcanized rubber, epoxies, polyester resin, phenolic resin Adapted from Fig , Callister 6e. (Fig is from F.W. Billmeyer, Jr., Textbook of Polymer Science, 3rd ed., John Wiley and Sons, Inc., 1984.) THERMOPLASTICS VS THERMOSETS

4 Molecular weight, M w : Mass of a mole of chains. 4 Tensile strength (TS): --often increases with M w. --Why? Longer chains are entangled (anchored) better. % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases. Adapted from Fig , Callister 6e. (Fig is from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.) MOLECULAR WEIGHT & CRYSTALLINITY

5 At right, the common mer elements. Mer weights are calculated by the number of each element times its molecular weight. For example, polytetrafluoroethylene is: 2(carbon)*12.011g/mol * 4(flourine)*19.00 g/mol = g/mol

6 Number average and weight average molecular weight, M n and M w Number average and weight average degree of polymerization, n n and n w

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