Polymer Process Engineering
Introduction
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Fundamental concepts + language
Nomenclature
Chemical bonding, chemical interactions, entanglements
Molecular weight
Thermal transitions
PRIMER
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Berzelius (1883) – Poly (many) + mer (unit)
Polystyrene polymerized in 1938; polyethylene glycol made in 1860s
Early polymer products were based on cellulose- gun cotton = nitrated
cellulose
WHAT IS A POLYMER?
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A polymer is…
• Long chain molecule, often based on organic
chemical building blocks (monomers)
• Long molecules (Mw ~100,000 Da) have solidlike properties
• The chain may be amorphous (no regular
structure), crystalline (a regular repeating
structure), crosslinked,…
• Dendrimers and oligomers have different
properties
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Chemical structure
Chain morphology – constitution, configuration, conformation
Degree of polymerization = number of repeating units
Building block sources – hydrocarbons, renewable materials
HOW DO YOU BUILD A MOLECULE?
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Building blocks
• 5% of petroleum goes
into polymers
• Sustainable use is
possible
• Energy recovery is
possible if solid
polymers are
combusted
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Type
C
H
O
gas
NG
3
1
0
liquid
Crude
6
1
0
solid
Coal
14
1
0
Renew- cellulose
able
6
1
5.3
Hemicellulose
6
1
8
lignin
6.8
1
3
protein
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‘Building’ methods
Chain (addition)
• Example – polyethylene (PE)
from ethylene
• Small number of reacting
chains at any one time,
which can grow into long
molecules prior to
termination
• Long reaction times needed
to achieve high conversions
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Step (condensation)
• Example – poly(ethylene
terephthalate) (PET) from
terephthalic acid and
ethylene glycol
• Endgroups react to build the
chain; long reaction times
needed to achieve high
polymer
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Multiple building blocks
• Copolymers, terpolymers, …
• Using multiple building blocks leads to
polymers with intermediate properties or
unique properties compared to the
homopolymers
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Several copolymer configurations
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Chain configurations
• Linear – repeating units are aligned
sequentially
• Branched – large segments ‘branch’ off the
main chain/carbon backbone
• Crosslinked/network – chemical crosslinks
between chains add mechanical strength
• EXAMPLES?
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Multiphase systems
• Composites
– Structural
– Random
– Other
– Nanocomposites
• Blends
– Dispersed lamellae, cylinders, spheres
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Structure – chemical, configuration
solid performance (mechanical + thermal properties)
other
HOW DO WE CLASSIFY POLYMERS?
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Mechanical + Thermal
• Thermoplastic – solidified by cooling and
reheated by melting
• Thermosets – retain their structure when
reheated after polymerization (usually
crosslinked)
• Elastomers – rubbers, deform readily with
applied force
• Thermoplastic elastomers
• other
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Very few commercial products are ‘pure’
MWD – molecular weight distribution
additives
WHAT IS IN A COMMERCIAL
PRODUCT?
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Polymers vs. metals
Why do we use
polymers?
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Polymeric materials
• Compete well on a strength/weight basis
• Easy to form into 3D shapes
• Creep under load is usually poor; this behavior
is usually corrected by adding fillers or fibers
• Low corrosion in the environment compared
to metals
• Generally good solvent resistance
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Thermoplastics
• Commodities: 75% of the polymer volume
used is with 4 polymer families, polyethylene,
polystyrene, polypropylene and poly(vinyl
chloride) [low cost]
• Intermediate: higher heat deflection
temperatures
• Engineering plastics: can be used in boiling
water
• Advanced thermoplastics: extreme properties
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Thermosets
• High moduli, high flex strengths, high heat
deflection temperatures
• Shape is retained during thermal cycling
• Often made with step/condensation
polymerization systems
• Crosslinking is usually used
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Polymerization
Formulation
Fabrication
HOW DO WE MAKE A PART?
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Formulation
• Additives are used to modify properties
and/or lower costs
• Additives: heat stabilizer, light stabilizer,
lubricant, colorant, flame retardant, foaming
agent, plasticizer
• Reinforcement: particulate minerals, glass
spheres, activated carbon, fibers
• Blends, alloys, laminates
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Additives can change:
•
•
•
•
Processing properties
Performance properties
Composites: polymers with fiber fillers
Packaging: multiple layers often used
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Formulation operations
• Thermoplastics: melting or solvent processing
• Thermosets: additive addition to monomers
or to prepregs
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Fabrication
• Varies by industry sector
– Adhesive
– Coating
– Elastomer
– Plastic
– fiber
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Overview of the polymer industry
Industry
General product requirements
adhesive
Strong surface forces; epoxy, superglue
coatings
Film-forming; LDPE with good impact
composites
Structural materials; epoxy + fibers
elastomers
Large deformation and recovery; rubber in tire and seals
fibers
High strength/area; polyacrylonitrile
foams
Light weight, low thermal conductivity; polyurethane
plastics
Stable deformation under static load; HDPE, PP, PVC
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Commodity plastics
Polymer
Major uses
LDPE
Packaging film, wire and cable insulation, toys, flexible bottles,
housewares, coatings
HDPE
Bottles, drums, pipe, conduit, sheet, film, wire and cable
insulation
PP
Automobile and appliance parts, rope, cordage, webbing,
carpeting, film
PVC
Construction, rigid pipe, flooring, wire and cable insulation,
film, sheet
PS
Foam and film packaging, foam insulation, appliances,
housewares, toys
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Film blowing
High strength films are achieved by
orienting the crystallites. The film is
biaxially oriented; the wind-up rolls
stretch the film in the machine direction
and the expansion of the film radially
provides a hoop stress force.
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Wire coating
Wire coating speeds can be high, and process start-up is challenging. Metal wires may need sizing,
or wetting agents in the polymer melt for good adhesion.
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Calendaring
Thin and thick section calendaring is used to make wide sheets (8-12 ft).
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Bottle blowing
The parison is inflated,
developing biaxially
orientation similar to that of
blown film. The sides of the
mold provide cooling, quickly
‘freezing’ in the orientation
developed during the
blowing process. When this
process is used to make soda
bottles of PET, the
orientation is critical to
achieving low carbon dioxide
permeation rates (and long
bottle shelf life).
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Compression molding
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Thermoset applications
Polymer
Major uses
PhenolElectrical equipment, automobile parts, utensil handles,
formaldehyde resins plywood adhesives, particleboard binder
(PF)
Urea-formaldehyde
resins (UF)
Similar to the above; textile coatings and sizings
Unsaturated
polyester (UP)
Construction, vehicle parts, boat hulls, marine accessories,
corrosion-resistant ducts, pipes and tanks, business equipment
Epoxy (EP)
Protective coatings, adhesives, electrical parts, industrial
flooring, highway paving materials, composites
MelamineSimilar to UF resins; decorative panels, counter and table tops,
formaldehyde resins dinnerware
(MF)
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Elastomers
• The polymers used for elastomers usually have
very low heat deflection and melt temperatures
• Solids with good mechanical properties are made
by crosslinking polymer chains together
• The “molecular weight” of elastomer parts is the
size of the object
• Vulcanization of rubber uses sulfur to provide
crosslinks between the C=C bonds of natural
rubber.
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Fibers
• Fibers are based on highly crystalline polymers
that can be oriented axially to have great
strength. Orientation (cold drawing) develops
crystal structure in the solid.
• Most natural fibers from biomass are based
on cellulose; spider silk has different
compositions and is based on a set of
copolymers
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Elastomer polymers
Polymer family
description
Styrene-butadiene
Copolymers with a range of constitutions; SBR – styrenebutadiene rubber
Polybutadiene
Cis-1,4-polymer
Ethylene-propylene
EPD – ethylene-propylene-diene monomer; the small amounts
of diene provide unsaturation
Polychloroprene
Poly(2-chloro-1,3-butadiene); this polar elastomer has excellent
resistance to non-polar organic solvents (gasoline, diesel)
Polyisoprene
Poly(cis-1,4-isoprene); synthetic natural rubber
Nitrile rubber
Copolymer of acrylonitrile and butadiene
Butyl rubber
Copolymer of isobutylene and isoprene
Silicon rubber
Rubber based on polysiloxanes
Urethane rubber
Elastomer with polyethers linked via urethane groups
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Synthetic fibers
Fiber type
description
Cellulosic
acetate rayon
Cellulose acetate
viscose rayon
regenerated cellulose
Non-cellulosic
Polyester
Mostly poly(ethylene terephthalate)
Nylon
Nylon 6,6; nylon 6, nylon 10; other aliphatic, aromatic
polyamides
Olefin
Polypropylene; copolymers of vinyl chloride + acrylonitrile, vinyl
acetate, vinylidene chloride
Acrylic
> 80% acrylonitrile; modacrylic = acrylonitrile + vinyl chloride or
vinylidene chloride
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Coatings
• Coatings. Major area for expansion; solar cells,
windows, … Supplier base is highly
fragmented.
• Paints. Major area for expansion; vehicles,…
Materials supplier base is clustered; painting
systems base is clustered; user base is
fragmented
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Adhesives
• Highly fragmented market.
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Foams
• Major area: insulation
for housing, sound
control,…
• Materials:
polystyrene,
polyurethanes, …
• Reaction injection
molding example
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Composites
• Thermosets and thermoplastics
• Sheet molding compounds
• Filament winding
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Polymer nomenclature is widely varied.
Trademarks and common names may be industry-sector specific.
Nomenclature: Polymer Handbook. Chapter 1.
HOW DO WE NAME POLYMERS?
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Source-based names
• Source-based name when the polymer is derived
from a single (original or hypothetical) monomer;
or random co-/ter-polymers
–
–
–
–
Poly(vinyl alcohola)
Poly(styrene-co-butadiene)
Polyformaldehyde (not polyoxymethylene)b
Poly(ethylene oxide) (not poly(ethylene glycol)b
a–
when the name is long, parentheses are used to
separate the name from ‘poly’
b - actually the second name is quite common
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Structure-based names
• Structure-based name when the
constitutional repeating unit (CRU) has several
components
• The CRU is independent of the monomers and
polymerization methods
– Poly(hexamethylene adipamide)
– Poly(ethylene terephthalate)
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copolymers
Type
Connective
Example
unspecified
-co-
Poly(A-co-B)
statistical
-stat-
Poly(A-stat-B)
random
-ran-
Poly(A-ran-B)
alternating
-alt-
Poly(A-alt-B)
periodic
-per-
Poly(A-per-B-per-C)
block
-block- (-b-)
Poly(A-b-B) or Poly A-block-poly B
graft
-graft- (-g-)
Poly(A-g-B) or Poly A-graft-poly B
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Source-based name
Structure-based name
Trade name, abbreviation
polyethylene
polymethylene
PE, LDPE, HDPE, LLDPE
polypropylene
Poly(propylene)
PP
polyisobutylene
Poly(1,1-dmethylethylene)
PIB
polystyrene
Poly(1-phenylethylene)
Styron, Styrofoam
Poly(vinyl chloride)
Poly(1-chloroethylene)
PVC
Poly(vinylidene chloride)
Poly(1,1-dichlorethylene)
Saran
polytetrafluoroethylene
Poly(difluoromethylene)
Teflon
Poly(vinyl acetate)
Poly(1-acetoxyethylene)
PVAC
Poly(vinyl alcohol)
Poly(1-hydroxyethylene)
PVAL
Poly(methyl methacrylate)
Poly(1-methoxycarbonyl-1methylethylene)
PMMA; Lucite, Plexiglass
polyacrylonitrile
Poly(1-cyanoethylene)
PAN; Orlon, Acrilan fibers
polybutadiene
Poly(1-butenylene)
BR rubber
polyisoprene
Poly(1-methyl-1-butenylene)
NR rubber
polychloroprene
Poly(1-chloro-butenylene)
Neoprene
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Polymers with other backbones
Source-based name
Structure-based name
Trade name, abbreviation
polyformaldehyde
Poly(oxymethylene)
POM
Poly(ethylene oxide)
Poly(oxyethylene)
PEO
Poly(ethylene glycol adipate)
Poly(oxyethylene oxyadipoyl)
Polyester 2,6
Poly(ethylene terephthalate)
Poly(oxyethylene oxy-terephthaloyl)
PET; Dacron
Poly(hexamethylene
adipamide)
Poly(iminoadipoyl imino-hexamethylene) Nylon 6,6
Poly(e-caprolactam)
Poly(imino[1-oxohexamethylene])
Nylon 6
polyglycine
Poly(imino[1-oxoethylene])
Nylon 2
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Bonding along the backbone is not extraordinary.
With long chains, secondary valence forces, integrated over the entire
chain, provide considerable ‘bonding’ forces.
Chain entanglements provide physical linkages.
WHY ARE LONG CHAIN MOLECULES
SOLIDS?
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Chemical bonding in polymers
•
•
Most primary bonds along the
backbone are covalent
Secondary valence bonds
–
–
–
–
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Much smaller forces than the
covalent bonds, but become
significant when integrated over the
entire chain
Consider the forces acting on this
macromolecule as it is ‘pulled’
through the tube surrounding its
structure in three dimensional space
As each chain segment moves, it
must overcome the local
interactions at the tube surface
Longer chains will have more
resistance to motion
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Secondary valence forces
• Secondary valence forces affect the glass transition, the
melting temperature, crystallinity, melt flow,…
• They include: nonpolar dispersion, polar dipoles, polar
induction, and hydrogen bonds
Secondary bond
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Bond energy,
kcal/mol
Range of action,
Angstrom
Dispersion
0.1-5.0
3-5 (r-6)
Dipole-dipole
0.5-5.0
1-2 (r-3)
Dipole-induced
dipole
0.05-0.5
1-2 (r-6)
Hydrogen bond
1.0-12
2-3 (r-2)
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Few synthetic polymers are monodisperse, i.e., have one chain length.
Many biological polymers do have specific molecular weights, e.g., proteins,
DNA, …
The molecular weight distribution has critical effects on polymer properties
in the melt and solid states.
WHAT ARE TYPICAL CHAIN LENGTH
DISTRIBUTIONS?
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Typical effects of molecular weight
distributions
• Homopolymers with different molecular weight distributions may be
insoluble in each other
# carbon atoms
State
Use
1-4
Gas
Gaseous fuel
5-11
Low viscosity liquid
gasoline
9-16
Medium viscosity
liquid
kerosene
16-25
High viscosity liquid
Oil, grease
25-50
Crystalline solid
Paraffin wax
1000-3000
Plastic solid
(crystalline +
amorphous)
polyethylene
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Linear
alkane
properties
51
MWD - oligomer
• Poly(a-olefin); PAO6
• Synthetic base oil –
vehicle use
• Trimer, tetramer,
pentamer, hexamer,
heptamer
• Based on 1-decene
• Ionic polymerization
• Differential distribution
by size exclusion
chromatography
• PeakFit™ used for curve
deconvolution
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Two polyethylenes
•
•
•
•
•
•
Weight frequency, differential
distributions
Number-average molecular
weights are the same
Weight-average molecular
weights are different

Narrow MWD – PD ~ 5.7
Broad MWD – PD ~ 15
Differences in flow, tensile and
appearance properties 
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n  M

n
i
Mn
i
i
i
PD 
w  M n  M


w

n  M
i
i
Mw
i
i
2
i
i
i
i
i
i
i
i
Mw

Mn
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In-class exercise
HOW DOES CHAIN LENGTH AFFECT
PROCESSING?
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In-class exercise
HOW DOES CHAIN LENGTH AFFECT
PERFORMANCE?
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Thermal properties are often key criteria used to select polymers for specific
applications.
Five regions of viscoelastic behavior (many polymers have all five): < glass
transition, power law region, rubbery plateau, rubbery flow, fluid flow
Other – crystalline solids, crosslinked elastomers
WHAT ARE IMPORTANT THERMAL
TRANSITIONS?
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Five regions of viscoelasticity
•
•
•
•
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Use amorphous polymers below Tg
Use crystalline polymers below Tm
Crosslinked elastomers at G
Melt processing between B and C
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Typical G vs T plots
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regions
• Viscoelasticity: most polymers creep(slow flow) under long-term stress.
Creep may not be recoverable, i.e., the sample may not recoil to its
original dimensions. Over short periods of time, polymers are elastic.
• Solid yield and fracture: elasticity for e < 0.1%; PS is brittle and fails at low
elongations. PE yields, and then undergoes cold drawing to > 300%
elongation.
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BUILDING A GLOSSARY
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Medical applications are a
rich applications area for
polymers.
Local variations in surface
roughness at the nanoscale
can induce strains in cell
membranes, leading to the
growth of F-actin stress
fibers that span the length
of the cell.
W.E. Thomas, D. E. Discher, V. P. Shastri,
Mechanical regulation of cells by materials
and tissues, MRS Bulletin, 35 (2010), 578583.
POLYMER SCIENCE DIRECTIONS
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Cells feel their environment
• Tissues are hydrated natural polymers with controlled
elasticity
• Most animals cells require adhesion to a solid to be
viable
• Tissue elasticity (~ kPa’s) is important for regulating cell
growth, maturation and differentiation. Brain – 0.2 < E <
1 kPa; fat – 2 < E < 4 kPa; muscle – 9 < E < 15 kPa;
cartilage – 20 < E < 25; bone – 30 < E < 40 kPa
• Nanoroughness seems to affect a number of cell
processes
• 3D scaffolding is important
• Mechanotransduction: cells adhere to surfaces via
adhesive proteins attached to adaptor proteins, to the
actomyosin cytoskeleton.
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