MFGT 104
Materials and Quality
Chap 5: Polymers and Elastomers
Professor Joe Greene
CSU, CHICO
MFGT 104
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Polymers and Elastomers
• Objectives
– Define the common terms associated with polymers and elastomers
– List the common properties of a variety of polymer and elastomer
families.
– List the various manufacturing processes associated with polymers
and elastomers.
– Describe the various properties used to designate or specify various
polymers and elastomers
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Definition of Plastics
All Materials
Simple
Liquids
Gases
Metals
Ceramics
Solids
Polymers
(polymeric molecules)
Thermoplastics
Heat Forming
Thermosets
Heat Setting
Elastomers
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Early Modified Natural Materials
• Natural Rubber (gum rubber_ natural latex)
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Little industrial significance compared to gutta percha
Melted in hot temperatures and cracked in cold temperatures
Vulcanization of rubber with sulfur (1839) by Goodyear
Small amounts of sulfur = rubber; Large amounts = ebonite (hard)
Civil War required large amounts of rubber
Today- Rubber is a multi Billion $ business
• Celluloid (substitute for horn, ivory, tortoise shell)
– Conversion of cotton into nitrocellulose (sulfuric acid and nitric acid): highly
nitrated is explosive, moderately nitrated is useful
– Pyroxylin is soluble in several solvents, used as a finish.
– Solid Pyroxylin called celluloid (powdered Pyroxylinwith pulverized gum
camphor) heated and molded for Billiard balls.
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Automotive Applications of
Plastics and Composites
n
Composite Intensive Vehicles
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Automotive Plastics and Composites Use
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Major Plastic Materials
1994
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LDPE
HDPE
PVC
PP
PS
PU
PET
Phenolic
Total
6.4 M metric tons
5.3 M metric tons
5.1 M metric tons
4.4 M metric tons
2.7 M metric tons
1.7 M metric tons
1.6 M metric tons
1.5 M metric tons
28.6 M metric tons (82% of market)
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Recycling of Plastics
• State and Federal Legislation
• PET bottle recycling
• Codes for plastics
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3
4
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PET
HDPE
Vinyl/PVC
LDPE
PP
PS
Other
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Polymer Materials
• Polymer materials are made up of “many” (poly) repeating
“units”(mers).
• Polymers are mostly based in carbon, oxygen, and
hydrogen. Some have Si, F, Cl, S
• Polymers are considered a bowl of spaghetti or a bag of
worms in constant motion.
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Polymer Materials
• Polymers are classified broadly as
– thermoplastic: form after heat. Over and over again.
– thermoset: set after heat. Only sets once. Can’t reform
• Thermoplastics
– crystalline: polymers arranged in a regular order
– amorphous: polymers arranges randomly like coil
• Thermosets
– low molecular weight monomers that crosslink and polymerize to
for polymer network
• Elastomers
– Can be either thermoplastic and thermoset
• Thermoset elastomers: natural and synthetic rubbers
• Thermoplastic elastomers: plastics that mimic rubber (EPDM, TPO, TPE)
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Macromolecules
• Simplest Plastic- Polyethylene (PE).
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Saturated Hydrocarbon
approx. 1000 Carbon atoms in backbone (chain)
Length: ~0.0025 mm (if stretched out)
Comparison: Typing paper- 0.076 mm (30 PE on end)
Repeating unit- Mer
Degree of Polymerization= n
• DP= 500 is PE (14,000amu’s)
• DP= 9 is Paraffin wax (252 amu’s)
H
H
C
C
H
H
n
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States of Thermoplastic Polymers
• Amorphous- Molecular structure is incapable of forming regular
order (crystallizing) with molecules or portions of molecules
regularly stacked in crystal-like fashion.
• A - morphous (with-out shape)
• Molecular arrangement is randomly twisted, kinked, and
coiled
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Amorphous Materials
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PVC
PS
Acrylics
ABS
Polycarbonate
Phenoxy
PPO
SAN
Polyacrylates
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
Amorphous
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States of Thermoplastic Polymers
• Crystalline- Molecular structure forms regular order (crystals) with
molecules or portions of molecules regularly stacked in crystal-like fashion.
• Very high crystallinity is rarely achieved in bulk polymers
• Most crystalline polymers are semi-crystalline because regions are
crystalline and regions are amorphous
• Molecular arrangement is arranged in a ordered state
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Crystalline polymers (PE, PP, PBT, PA,etc)
• Molecular Chains are in an order
• Crystalline structure forms from a single point,
“spherulite”. Spherulites meet to form crystal.
• Time dependent process and consumes energy.
• Most polymers are semi-crystalline with regions of
crystals surrounded by amorphous areas.
Start
Intermediate
Fully Grown Spherulites
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Crystalline Materials
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LDPE
HDPE
PP
PET
PBT
Polyamides
PMO
PEEK
PPS
PTFE
LCP (Kevlar)
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
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Carbon Chain Polymers
• Homopolymers
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Simplest plastic containing one basic structure
If X = H then Polyethylene
If X = Cl the PVC
H
If X = CH3 then PP
C
If X = Benzene Ring The PS
H
H
X
C
n
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Homopolymers
• Table 3-2 Plastics Involving Single Substitutions
X Position
Material Name
Abbreviation
H
Cl
Methyl group
Benzene ring
CN
OOCCH3
OH
COOCH3
F
Polyethylene
Polyvinyl chloride
Polypropylene
Polystyrene
Polyacrylonitrile
Polyvinyl acetate
Polyvinyl alcohol
Polymethyl acrylate
Polyvinyl fluoride
PE
PVC
PP
PS
PAN
PvaC
PVA
PMA
PVF
Note:
Methyl Group is:
|
H–C–H
|
H
Benzene ring is:
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Carbon with Other Elements in Backbone
• Many backbones include O, N, S, or benzene
rings in the main chain.
• Most are homopolymers with some copolymers
and fewer terpolymers.
e.g. Polycarbonate
O
CH2
O
O
C
CH2
C
n
m
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Thermosets
• Thermosets are polymers that undergo a chemical reaction
during the polymerization.
• Thermosetting reaction is not reversible under heat.
• Epoxy
– Standard epoxy is based on bisphenol A and epichlorohydrin.
– Properties include good adhesion to many substrates, low
shrinkage, high electrical resistivity, good corrosion resistance, and
thermal.
– Processing is achieved without generation of volatiles.
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•
Polyester
and
Polyurethane
Polyester
– Thermoset reaction between a difunctional acid (or anhydride) and
a difunctional alcohol (glycol)
– Heat or radiation can trigger the cross linking reaction
– Accelerators (or promoters) speed up the reaction.
– Condensation Reaction results in CO2 and H2O.
– Monomer required to polymerize, e.g., Styrene at 30% to 50% in
commercial polyester systems
• Polurethane
– Reaction between isocyanate and alcohol (polyol). Condensation
Reaction results in CO2 and H2O.
– Crosslinking occurs between isocyanate groups (-NCO) and the
polyol’s hydroxyl end-groups (-OH)
– Thermoplastic PU (TPU) have some crosslinking, but purely by
physical means. These bonds can be broken reversibly by raising
the material’s temperature, as in molding or extrusion.
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Polyurethane Chemistry
• Reaction between isocyanate and alcohol (polyol).
• Crosslinking occurs between isocyanate groups (-NCO)
and the polyol’s hydroxyl end-groups (-OH)
• Thermoplastic PU (TPU) have some crosslinking, but
purely by physical means. These bonds can be broken
reversibly by raising the material’s temperature, as in
molding or extrusion.
• Ratio between the two give a range of properties between
a flexible foam (some crosslinking) to a rigid urethane
(high degree of crosslinking).
• In PUR foams density can range from 1 lb/ft3 to 70 lb/ft3.
• Foams are produced by chemical blowing agents.
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• Catalyst are used to initiate reaction.
• Epoxy
Applications for Thermosets
– Protective coatings: maintenance coatings for industrial and marine, tank
linings, industrial floorings, beer and beverage can coatings, food cans,
appliance primers, hospital and laboratory furniture.
– Bonding and adhesives: Automotive and aircraft industries adhesive to
metals and composites.
– Molding, casting and tooling: Molding compounds in electrical and
electronic industries, casting resins, potting resins. Prototype and master
model tools.
– Laminating and composites: Binders in fiber reinforced laminates and
composites. Laminates are used in printed wiring boards. Composite
applications include filament winding (high performance pipes in oil fields,
pressure vessels, tank and rocket motor housings), pultrusion, casting, and
molding (graphite composites for aerospace applications)
– Building and construction: Flooring (seamless, self-leveling, or epoxy
terrazzo floors), repair of bridges and roads with glass and carbon fiber
wraps, concrete crack repair, coat reinforcing bars, binders for patios,
swimming pool decks, and soil around oil-well drills.
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Applications
for
Thermosets
Polyester
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Boat hulls, shower stalls, electrical components, appliances
Recreation vehicles, automotive body panels, floor pans; SMC
Soft tooling, patterns
Cultured marble, buttons, corrosion resistant tanks and parts,
Corrugated and flat paneling, simulated wood furniture, bowling
balls, polymer concrete, and coatings
• Polyurethane
– Rigid foams: (MDI) Laminated board stock, Moldings, Bun, Foam in place
insulation, sprayed foam, packaging
– Semi-flexible foam: (MDI and TDI) Moldings, Integral-skin moldings
– Flexible foam:(TDI) Moldings, integral skin molding, carpet
underlay
– Packaging: (TDI) Furniture cushioning
– Microcellular foam: (MDI) RIM parts, shoe soles
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Elastomers
• Elastomers are rubber like polymers that are thermoset or
thermoplastic
– butyl rubber: natural rubber
– thermoset: polyurethane, silicone
– thermoplastic: thermoplastic urethanes (TPU), thermoplastic
elastomers (TPE), thermoplastic olefins (TPO), thermoplastic
rubbers (TPR)
• Elastomers exhibit more elastic properties versus plastics
which plastically deform and have a lower elastic limit.
• Rubbers have the distiction of being strenched 200% and
returned to original shape. Elastic limit is 200%
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Rubbers
• Rubbers have the distinction of being stretched 200% and
returned to original shape. Elastic limit is 200%
• Natural rubber (isoprene) is produced from gum resin of
certain trees and plants that grow in southeast Asia, Ceylon,
Liberia, and the Congo.
– The sap is an emulsion containing 40% water & 60% rubber particles
• Vulcanization occurs with the addition of sulfur (4%).
– Sulfur produces cross-links to make the rubber stiffer and harder.
– The cross-linkages reduce the slippage between chains and results in
higher elasticity.
– Some of the double covalent bonds between molecules are broken,
allowing the sulfur atoms to form cross-links.
– Soft rubber has 4% sulfur and is 10% cross-linked.
– Hard rubber (ebonite) has 45% sulfur and is highly cross-linked.
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Rubber Additives and Modifiers
• Fillers can comprise half of the volume of the rubber
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Silica and carbon black.
Reduce cost of material.
Increase tensile strength and modulus.
Improve abrasion resistance.
Improve tear resistance.
Improve resistance to light and weathering.
Example,
• tires produced from Latex contains 30% carbon black which improves the
body and abrasion resistance in tires.
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Synthetic Rubber
• Isoprene- basic structure of rubber molecule
• Butadiene- basis for synthetic rubber (SBR) StyreneButadiene Rubber co-polymer
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Synthetic Rubber
• Polychloroprene- neoprene rubber, closest sythetic to
natural rubber. Used for fuel lines, hoses, gaskets.
• Butyl rubber- addition polymer of isobutylene.
• Thiokol- ethylene dichloride polymerized with sodium
polysulfide. Sulfur makes thiokol rubber self vulcanizing.
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Thermoplastic Elastomers
• Thermoplastic Elastomers result from copolymerization of
two or more monomers.
– One monomer is used to provide the hard, crystalline features,
whereas the other monomer produces the soft, amorphous features.
– Combined these form a thermoplastic material that exhibits
properties similar to the hard, vulcanized elastomers.
• Thermoplastic Urethanes (TPU) were the first
Thermoplastic Elastomer (TPE) used for seals gaskets, etc.
• Other TPEs
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Copolyester for hydraulic hoses, couplings, and cable insulation.
Styrene copolymers are less expensive than TPU with lower strength
Styrene-butadiene (SBR) for medical products, tubing, packaging, etc.
Olefins (TPO) for tubing, seals, gaskets, electrical, and automotive.
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Processing of Polymers
• Thermoplastics
– injection molding, extrusion, blow molding, thermoforming,
rotational molding, compression molding
• Thermosets
– compression molding, reaction injection molding, resin transfer
molding, casting, hand layup, etc.
• Elastomers
– compression molding, extrusion, injection molding, casting.
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Injection Molding Process and Cycle Time
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Extruder Equipment
• Exit zone- die
– die imparts shape on the material, e.g., rod, tube, sheet, channel
– exit material is called extrudate
– extrudate swells at end of die due to normal forces from the polymer flow,
called die swell
Die Swell
• Cooling zone
– water bath or air cooled to lower the temperature below Tg
• Auxiliary equipment
– puller
– rollers for proper thickness
– Wind-up or cut off
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Compression Molding Process
• Materials
•Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber
•Sheet Molding Compound (SMC), Bulk Molding Compound (BMC)
•Thermoplastics: Polypropylene, polyester, or others with glass fibers
•Glass Mat Thermoplastic (GMT), thermoplastic BMC
•Elastomers: Thermoplastic or Thermoset rubbers
•Thermoplastic Olefin (TPO), Thermoplastic Elastomer (TPE), Thermoplastic
Rubber (TPR)
•Thermoset Styrene Butidiene Rubber
Thermoplastic:
Heat Plastic
prior to molding
Thermosets:
Heat Mold
during molding
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Resin Transfer Molding Process
Ref: MSU Tutorial- http://islnotes.cps.msu.edu/trp/liquid/rtm/
•Materials
•Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber
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