Creep of cellulose acetate

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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
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Composites - overview
Example - carbide tools (previously discussed)
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Composites - overview
Artificial combination of matrix phase
dispersed phase
Matrix metal, alloy ceramic mat'l polymer
Dispersed phase particulate fiber
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Composites - metal matrix composites (MMCs)
Particulates ThO2-dispersed Ni (TD
Ni) sintered Al powder (SAP)
- except strengthening maintained at hi T
Improves strength creep resistance hi T
corrosion resistance
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Composites - metal matrix composites (MMCs)
Fibers Conts - C, SiC, B, Al2O3 Disconts - C,
Al2O3 , SiC whiskers
May get rxn betwn phases at hi T
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Composites - ceramic matrix composites (CMCs)
Particulates, fibers SiC, B, Al2O3 , C, SiC
Si3N4 whiskers
Improve fracture toughness
slow crack growth deflect crack
tips redistribute stresses around crack
tips bridge crack tips
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Composites - polymer matrix composites (PMCs)
Fibers mainly - glass (GFRPs), carbon (CFRPs),
aramid, others - B, SiC, Al2O3
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Composites - polymer matrix composites (PMCs)
Matrix
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Composites - polymer matrix composites (PMCs)
Very common - polyesters, vinyl esters
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Composites
Role of matrix in FR composites a. transfer
stresses betwn fibers b. provide barrier to
environment c. protect fibers
Matrix/fiber bond matrix must wet fiber
physical chemical bond desirable mechanical
interlocking
Fibers frequently coated w/ coupling agent
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Composites
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Composites
Fibers - variables amount fiber
length distribution orientation
Fiber orientation can be random aligned
intermediate