1. Most of the important things in the world have been accomplished by people who have kept on trying when there seemed to be no hope at all

 – Dale Carnegie

2. Another lesson for life –
silicon vs. silicone

3. Creep
Relaxation

4. Creep of cellulose acetate

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

6. Creep & recovery

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

8. Some specific polymers
Polyvinyl chloride (PVC) {-C-C-}n
Cl H
H H –
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"!

9. 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

10. silicones Some specific polymers 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

11. Rotation of bonds

12. 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

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

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

15. Assignment:
Review today's classnotes
a. creep, relaxation, recovery
b. PVC
c. plasticizers
d. polycarbonates
e. aramids, Kevlar
f. epoxies, prepregs