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Rotation of bonds

Rotation of bonds. 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. Log h a (Pa). Zero Shear Rate Viscosity. 5. 4. 3. 2. 1. 0. Log g ( sec -1 ). -3. 1. -2.

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Rotation of bonds

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  1. Rotation of bonds

  2. 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

  3. 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

  4. 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

  5. Creep Relaxation

  6. Creep of cellulose acetate

  7. 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

  8. Creep & recovery

  9. H 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"

  10. H 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"!

  11. 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, esp. when (auto) vinyl seats & fascia heated by sun Armorall to the rescue! Periodically put solvent back into polymer

  12. Some specific polymers silicones Oils - Low MW……liquids lubricants, hydraulic fluids, water repellants, usw. Elastomers - intermediate MW, crosslinked waterproofing, caulk, prostheses, usw. Molding compds - high MW, crosslinked non-structural parts, insulation, usw. Crosslinking – moisture reacts w/parts of chain to crosslink……acetic acid is byproduct of rxn

  13. Some specific polymers {-O-C-O- -C- -}n H O H-C-H H-C-H H polycarbonate Non-crystalline, nearly as strong as highly crystalline nylon, but tougher (stiff chain, pendant groups, H bonding betwn chains) High TM – form at elevated temps

  14. {-C- -C-N- -N-}n H H O O aramid Some specific polymers Nylon cousin, but far stronger (very stiff chain) Non-burning, very high TM, solvent resistant When made into fibers ––> Kevlar

  15. H2C-C-C{-O- -C- -O-}nC-C-CH2 H H H H-C-H H-C-H O O H H H H2N-R-NH2 hardener epoxy Prepregs Some specific polymers

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