Rotation of bonds

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Rotation of bonds
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Viscous flow
Occurs only by shear
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Viscous flow
Most polymer melts are shear-thinning
(pseudoplastic) - i.e., become thinner at high
shear rates
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Viscous flow
Viscosity increases with MW Plot is for zero
shear rate values
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Creep of cellulose acetate
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Relaxation in PMMA
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Creep recovery
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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"
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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"!
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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
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Some specific polymers
silicones
Oils - Low MWliquids lubricants, hydraulic
fluids, water repellants, usw.
Elastomers - intermediate MW, crosslinked waterp
roofing, caulk, prostheses, usw.
Molding compds - high MW, crosslinked non-struct
ural parts, insulation, usw.
Crosslinking moisture reacts w/parts of chain
to crosslinkacetic acid is byproduct of rxn
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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
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Some specific polymers
Nylon cousin, but far stronger (very stiff chain)
Non-burning, very high TM, solvent resistant
When made into fibers gt Kevlar
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Some specific polymers