Download - Tensile strength
Don't despair of standard dull textbooks. Just close the book once in a while and think what they just said in your own terms as a revelation of the spirit and wonder of nature. The books give you facts, but your imagination can supply life.
– Feynman
Tensile strength
Glass transition temperature (Tg)
Glass transition temperature (Tg)
Molecular wt.
Glass transition temperature (Tg)
Chemical structure
Glass transition temperature (Tg)
Chain stiffness
Glass transition temperature (Tg)
Chain stiffness
Glass transition temperature (Tg)
Bulky side groups
Viscous flow
Occurs only by shear
z
xyDescribe deformation under shear by angle
tan zxy
xy ̇ xy
Most polymer melts are shear-thinning (pseudoplastic) - i.e., become thinner at high shear rates
Zero Shear Rate Viscosity5
4
3
2
1
00 1 2 3 4-1-2-3
Log a
(Pa)
Log sec-
1).
CompressionMoldingCalenderingExtrusion
InjectionMolding
SpinDrawing
100
SHEAR RATES ENCOUNTERED IN PROCESSING
101 102 103 104 105
Strain Rate (sec-1)
Viscous flow
Viscosity increases with MW
Plot is for zero shear rate values
Viscous flow
54321
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
m + constant
Creep
Relaxation
Creep of cellulose acetate
Relaxation in PMMA
10
9
8
7
0.001 0.01 0.1 1 10 100 1000
Stress relaxationof PMMA
Time (hours)
400C
Log
E(t),
(dyn
es/c
m2 )
600C
800C920C1000C
1100C
1120C1150C1200C
1250C
1350C
Creep & recovery
Some specific polymers Polyvinyl chloride (PVC) {-C-C-}n
Cl H
Cl H – –
––
Very rigid and strong, Tg = 60-80 Csiding, pipe, conduit, usw.
Presence of Cl gives rise to solubility in various organic solvents - allows "solvent welding"
Some specific polymers Polyvinyl chloride (PVC) {-C-C-}n
Cl H
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"!
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
Assignment:
Review today's classnotesa. tensile strengthb. Tg
c. viscous flowd. yielding, relaxation, crazinge. creep, relaxation, recoveryf. PVCg. plasticizers