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