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 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 (T g )

Molecular wt.

Glass transition temperature (T g ) Chemical structure

Glass transition temperature (T g ) Chain stiffness

Glass transition temperature (T g ) Chain stiffness

Glass transition temperature (T g ) Bulky side groups

Viscous flow Occurs only by shear  z   xy Describe deformation under shear by angle  tan       z z     xy       ˙ ˙  

Most polymer melts are shear-thinning (pseudoplastic) - i.e., become thinner at high shear rates Zero Shear Rate Viscosity Log  a (Pa) Log  sec -1 ). Compression Molding Calendering Extrusion Injection Molding Spin Drawing 10 0 SHEAR RATES ENCOUNTERED IN PROCESSING Strain Rate (sec -1 ) Viscous flow

Viscosity increases with MW Plot is for zero shear rate values Viscosity increases with MW Plot is for zero shear rate values Viscous flow 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 Stress relaxation of PMMA Time (hours) 40 0 C Log E(t), (dynes/cm 2 ) 60 0 C 80 0 C 92 0 C C C C C C C C

Creep & recovery

Some specific polymers Polyvinyl chloride (PVC) {-C-C-} n Cl H – – – – – – – – Very rigid and strong, T g = C siding, pipe, conduit, usw. Very rigid and strong, T g = C siding, 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 – – – – – – – – 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" 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 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 classnotes a. tensile strength b. T g c. viscous flow d. yielding, relaxation, crazing e. creep, relaxation, recovery f. PVC g. plasticizers Assignment: Review today's classnotes a. tensile strength b. T g c. viscous flow d. yielding, relaxation, crazing e. creep, relaxation, recovery f. PVC g. plasticizers