1. Polymers aren’t very stiff

2. Stiffness dictated by structure

3. Stiffness depends on
crystallinity
crosslinking Tg

4. For fibers,
stiffness
depends on
draw ratio

5. Tensile strength

6. Glass transition temperature (Tg)

7. Glass transition temperature (Tg)
Molecular wt.

8. Glass transition temperature (Tg)
Chemical structure

9. Glass transition temperature (Tg)
Chain stiffness

10. Glass transition temperature (Tg)
Chain stiffness

11. Glass transition temperature (Tg)
Bulky side groups

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

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

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

15. Creep
Relaxation

16. Creep of cellulose acetate

17. 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

18. Creep & recovery

19. Some specific polymers
Polyvinyl chloride (PVC) {-C-C-}n
Cl 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"

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

21. 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