Thermosets_ Epoxy, Polyesters, Vinyl
esters, Polyurethanes, and Phenolics
Professor Joe Greene
CSU, CHICO
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Thermosets
Reference: Appendix E. Industrial Plastics, Modern Plastics Encyclopedia (p142)
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History
Chemistry and Chemical Structure
Applications
Mechanical Properties
Physical Properties
Processing Characteristics
Advantages/Disadvantages
Reinforced thermosets- composites
Other thermosets
Review
Questions
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Thermoset Definition
• Thermoset materials are polymers that under go a chemical
reaction to build molecular weight and viscosity.
• Thermosets are set or crosslinked with heat and can not be
reheated for forming repeated forming.
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Thermosets History
• 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.
– Others based on phenols and formaldehyde or aromatic amines and
aminophenols
– Curing can occur at room temperature with the use of 2 component
systems. Curing at elevated temperature with use of one-component.
– 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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Thermoset Chemistry
Epoxy Chemistry
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Epoxy Chemistry
• Epoxy: O
C C
H H
epoxide group
H
H
H + H2N (C) N (C) NH2
H
H
+
amines (DETA)
epoxy
• Other epoxy resins
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diglycidyl ether of bisphenol A (DGEBRA)
tetraglycidyl methylene dianiline (TGMDA
epoxy phenol cresol novolac
cycloaliphatic epoxies (CA)
• Curing agents (hardeners, catalysts, cross-linking agents)
– aliphatic or aromatic amines (DETA, TETA, hexamethylene tetramine,etc.)
– acid anhydrides (phthalic anhydride, pyromellitic dianhydride, etc.)
• Active hydrogen react with epoxide groups.
• As much as 15% hardener is needed
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Epoxy Chemistry
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Polyester Chemistry
• Unsaturated Polyesters
– Thermoset reaction between a difunctional acid (or anhydride) and a
difunctional alcohol (glycol)
– At least some of the acid (or anhydride) features double bonds
between adjacent carbon atoms for unsaturation.
– Characteristic ester linkages are formed, hence the name Polyester
O
O
C6H4(COOH)2 + (CH2)2(OH)2
terephthalic acid
+ ethylene glycol
-[(CH2)2 -O- C
- C-O]-
Polyethylene terephthalate (PET)
– Acids include: maleic, fumaric, isophthalic, terphthalic, adipic, etc.
– Anhydrides include: maleic, phthalic
– Glycols include ethylene glycol, diethylene glycol, propylene glycol
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Polyester Chemistry
• Heat or radiation can trigger the cross linking reaction
• Catalyst (or initiator) is used. Methyl ethyl ketone (MEK)
peroxide, benzoyl peroxide, and cumene hydroperoxide
• Accelerators (or promoters) speed up the reaction.
• Inhibitors extend shelf life (hydroquinone, tertiary butyl catechol)
• Condensation Reaction results in CO2 and H2O
• Monomer required to polymerize, e.g., Styrene, to react with
the unsaturations in the polyester molecules to form 3-D
network.
– Styrene at 30% to 50% in commercial polyester systems
– vinyl toluene for vinyl ester
– methyl methacrylate for methyl methacrylate ester
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Polyester Chemistry
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Sheet Molding Compound (SMC)
• SMC is the paste that is compression molded
– 33% polyester resin and stryrene, which polymerizes and crosslinks
– 33% glass fibers (1” fibers)
– 33% Calcium Carbonate
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Polyester Molding Operations
• Molding of SMC with compression molder
• Molding of BMC with compression molder
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Materials that are Compression Molded
• SMC- Sheet molding compound- Polyester, glass fiber, CaCO3
• BMC- Resin, fiber, and filler
– BMC stands for Bulk Molding Compound,
– compression molded under high temperature and pressure.
– BMC has a solid, uniform constitution. By changing the blend design,
the characteristics can be altered to meet a wide range of applications.
– We have succeeded in developing BMC as the world's first cultured
marble that has the functional specialization for home use.
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Polyester Use with RTM
• RTM: Resin Transfer Molding
– The process of injecting a liquid resin trough a glass mat while in a
heated mold.
– Materials
• Polyester
• Vinyl ester
• Epoxies
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SCRIMP Process
• Used for polyester, vinyl ester, and epoxies
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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.
• Catalyst are used to initiate reaction.
• RIM process is used to produce fenders and bumper covers
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Polyurethane Chemistry
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Polyurethane Processing
• Polyurethane can be processed by
– Casting, painting, foaming
– Reaction Injection Molding (RIM)
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• 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
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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
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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
Non-foam cast elastomers
Coatings, binders, thermoplastic elastomers, sealants, paints
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Other Thermosets
• Phenolic
– Applications
• Pistons, Thrust pulleys
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Mechanical Properties of Thermosets
Density, g/cc
Tensile Strength, psi
Tensile Modulus, psi
Tensile Elongation, %
Impact Strength ftlb/in
CLTE
10-6 mm/mm/C
HDT
264 psi
Epoxy
1.11-1.40
Polyester
1.04 - 1.46
PET (Thermoplastic)
1.29-1.40
Polyurethane
1.03 - 1.15
4,000 – 13,000
350K
3%-6%
0.20 - 1.0
600 – 13,000
300K - 640K
2% - 6%%
0.2 - 0.4
7,000 – 10,500
400K - 600K
30% - 300%
0.25 - 0.70
175 - 10,000
10K - 100K
3% - 6%
25 to no break
45-65
55 - 100
65
100 - 200
115F-550F
140F -400F
70F -100F
70F - 150F
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Advantages of Thermosets
• Epoxy
– Excellent chemical and corrosion resistance
– Excellent thermal properties and low creep
– High stiffness and modulus properties
• Polyester
– Rigid, resilient to chemical and environmental exposures, corrosion
resistant, and flame retardant
– Easily processed in low cost equipment
• Polyurethane
– High strength to weight ratios, resistance to flame spread, excellent
thermal insulation, low cost, easily processed
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Disadvantages of Thermosets
• Epoxy
– Moisture absorption, toxicity, not recyclable
– Cost
• Polyester
– Moisture absorption, toxicity, not recyclable
– Styrene emmisions
• Polyurethane
– Moisture absorption, toxicity, not recyclable
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Additives and Reinforcements to Polyesters
• Additives– UV stabilizers, colorants, heat stabilizers, blowing agents
– Catalyst, inhibitors, promotors
• Fillers
– Talc
– Calcium carbonate
• Reinforcements
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Glass fiber- short fiber (1/8” or long fiber 1/4”)
Mineral fiber (wolastonite)
Mica
carbon fibers
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Properties of Reinforced Thermosets
Epoxy
Epoxy
With 50w% glass
Density, g/cc
Tensile Strength, psi
Tensile Modulus, psi
Tensile Elongation, %
Impact Strength ftlb/in
CLTE
10-6 mm/mm/C
HDT
264 psi
Epoxy
With 60w%
graphite
1.11-1.40
1.84
1.9
4,000 – 13,000
350K
3%-6%
0.20 - 1.0
27,000
3,000K
.5%
10
20,000
6,000K
.4%
10
45-65
2
1
115F-550F
500F
500F
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Processing of Composites
• Open Mold processes
– Hand lay-up and Spray-up
– Filament winding
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Processing of Composites
• Open Mold processes
– Vacuum bag, pressure bag, SCRIMP
– autoclave: Apply Vacuum Pressure and Heat in an oven which can be
5 feet to 300 feet long
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Thermoset Reacting Polymers
• Process Window
– Temperature and pressure must be set to produce chemical reaction
without excess flash (too low a viscosity), short shot (too high a
viscosity), degradation (too much heat)
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Processing of Composites
• Closed Mold Processes
– Compression molding [moderate pressure]
– Injection Molding [high pressure]
– Resin Transfer Molding (RTM), Structural Reaction Injection
Molding (SRIM) [low pressure]
– Pultrusion [low pressure]
Injection
Molding
Annual Part 30K – 200K
Production
Volume
Part Size
Small
< 2 lbs
Compression
Molding
30K – 200K
Structural
RIM
5K – 200 K
Medium
2 lbs – 20 lbs
Fixed
Assets
Tooling
Cost
Cycle Time
$500K-$2M
Medium
Medium to large 5 lbs
2 lbs – 20
– 50 lbs
lbs
$300K-$1M $10K - $150K
Materials
$300K -$2M
$50K -$500K
$150K-$500K $50K$300K
1 sec –
30 sec –
30 sec –
30 sec
90 sec
120 sec
Thermoplastic Thermoplastic Thermoset
Thermoset
Resin Transfer
Molding
0.5K –5 K
$20K - $300K
5 min – 30 min
Thermoset
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Injection Molding
Glass Reinforced Composites
• Plastic pellets with glass fibers are melted in screw, injected
into a cold mold, and then ejected.
Glass filled resin pellets
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Composites Have a Fiber Preform
• Fiber type
– Roving form that can be sprayed into a 3-D preform
– Roving form that is woven into a glass sheet and then formed to shape
(preform)
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Compression Molding
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Compression molding was specifically developed for replacement of metal
components with composite parts. The molding process can be carried out with
either thermosets or thermoplastics. However, most applications today use
thermoset polymers. In fact,compression molding is the most common method of
processing thermosets.
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Resin Transfer Molding
• In the RTM process, dry (i.e.,unimpregnated ) reinforcement is
pre-shaped and oriented into skeleton of the actual part known
as the preform which is inserted into a matched die mold.
• The heated mold is closed and the liquid resin is injected
• The part is cured in mold.
• The mold is opened and part is removed from mold.
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Structural RIM
• Fiber preform is placed into mold.
• Polyol and Isocyanate liquids are injected into a closed mold
and reacted to form a urethane.
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Homework Questions
1. Define PBT and PET chemical structure.
2. Why was Carothers not successful in developing polyesters?
3. Density of PET is _____ which is higher/lower than PBT and
nylon?.
4. What is the tensile strength of PET with 0%, 30% glass fibers?
What is the tensile modulus?
5. Plot tensile strength and tensile modulus of PET, PBT, Nylon 6,
PP, LDPE and HPDE to look like the following
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Tensile
Modulus,
10
Kpsi
xHDPE
xLDPE
2
5
Tensile Strength, Kpsi
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Homework Questions
6. Four typical Physical Properties of Polyester are Optical =
_______, Resistance to moisture= ______ , UV resistance=
_____, acid resistance=_______
7. The Advantages of Polyester are ________, ________,
_______, and __________.
8. The Disadvantages of Polyester are ________, ________,
_______, and __________.
9. Glass fiber affects Polyester by (strength) ________,
(modulus)________, (elongation)_______, (density)
__________, and (cost) ____________.
10. What affect does the copolymer have on the crystallinity of
polyesters and why?_________________________________
_________________________________________________.
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