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Tensile strength

Don't despair of standard dull textbooks. Just close the book once in a while and think what they just said in your own terms as a revelation of the spirit and wonder of nature. The books give you facts, but your imagination can supply life. 
 – Feynman. Tensile strength.

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Tensile strength

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  1. Don't despair of standard dull textbooks. Just close the book once in a while and think what they just said in your own terms as a revelation of the spirit and wonder of nature. The books give you facts, but your imagination can supply life. 
 – Feynman

  2. Tensile strength

  3. Glass transition temperature (Tg)

  4. Molecular wt. Glass transition temperature (Tg)

  5. Glass transition temperature (Tg) Chemical structure

  6. Glass transition temperature (Tg) Chain stiffness

  7. Glass transition temperature (Tg) Chain stiffness

  8. Glass transition temperature (Tg) Bulky side groups

  9. d q Describe deformation under shear by angle q d t tan q = = g x y z xy z ˙ t = h g xy xy Viscous flow Occurs only by shear

  10. Log ha (Pa) Zero Shear Rate Viscosity 5 4 3 2 1 . 0 Log g (sec-1) -3 1 -2 -1 0 2 3 4 SHEAR RATES ENCOUNTERED IN PROCESSING Compression Injection Spin Molding Extrusion Molding Drawing Calendering 102 103 104 105 100 101 Strain Rate (sec-1) Viscous flow Most polymer melts are shear-thinning (pseudoplastic) - i.e., become thinner at high shear rates

  11. Poly(di-methylsiloxane) Poly(iso-butylene) Poly(ethylene) Poly(butadiene) Log hm + constant Poly(tetra-methyl p-silphenyl siloxane) Poly(methyl methacrylate) Poly(ethylene glycol) Poly(vinyl acetate) Poly(styrene) 1 2 3 4 5 Log M + constant Viscous flow Viscosity increases with MW Plot is for zero shear rate values

  12. Creep Relaxation

  13. Creep of cellulose acetate

  14. 400C 10 600C 920C 800C 1000C 9 1100C Log E(t), (dynes/cm2) Stress relaxation of PMMA 1120C 8 1200C 1150C 1250C 7 1350C 0.001 0.01 0.1 1 10 100 1000 Time (hours) Relaxation in PMMA

  15. Creep & recovery

  16. Cl H – – Polyvinyl chloride (PVC) {-C-C-}n – – Cl H Some specific polymers Very rigid and strong, Tg = 60-80 C siding, pipe, conduit, usw. Presence of Cl gives rise to solubility in various organic solvents - allows "solvent welding"

  17. Cl H – – Polyvinyl chloride (PVC) {-C-C-}n – – Cl H Some specific polymers Presence of Cl gives rise to solubility in various organic solvents Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer" PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"!

  18. Some specific polymers Rigid PVC difficult to form by some techniques (e.g., calendaring)……so add solvent as "plasticizer" PVC sheet then roll-formed onto fabric backing and - voilá - "vinyl"! Problem: solvent slowly evaporates, exp. when (auto) vinyl seats & fascia heated by sun Soln: Armorall! Periodically put solvent back into polymer

  19. Assignment: Review today's classnotes a. tensile strength b. Tg c. viscous flow d. yielding, relaxation, crazing e. creep, relaxation, recovery f. PVC g. plasticizers

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