Thermosets_ Epoxy, Polyesters, Vinyl esters, Polyurethanes, and Phenolics

billowycookieΠολεοδομικά Έργα

29 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

520 εμφανίσεις

1

Thermosets_ Epoxy, Polyesters, Vinyl
esters, Polyurethanes, and Phenolics

Professor Joe Greene

CSU, CHICO

2

Thermosets

Reference: Appendix E.
Industrial Plastics, Modern Plastics Encyclopedia

(p142)


History


Chemistry and Chemical Structure


Applications


Mechanical Properties


Physical Properties


Processing Characteristics


Advantages/Disadvantages


Reinforced thermosets
-

composites


Other thermosets


Review


Questions


3

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.

4

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.









5

Epoxy Chemistry

Thermoset Chemistry

6

Epoxy Chemistry


Epoxy: O H H


C C H + H
2
N (C) N (C) NH
2


H H H H


epoxide group + amines (DETA) epoxy



Other epoxy resins


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





















7

Epoxy Chemistry

8

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


C
6
H
4
(COOH)
2
+ (CH
2
)
2
(OH)
2
-
[(CH
2
)
2

-
O
-

C
-

C
-
O]
-

terephthalic acid + ethylene glycol


Polyethylene terephthalate (PET)



Acids include: maleic, fumaric, isophthalic, terphthalic, adipic, etc.


Anhydrides include: maleic, phthalic


Glycols include ethylene glycol, diethylene glycol, propylene glycol












O

O

9

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 CO
2

and H
2
O


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

10

Polyester Chemistry

11

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

12

Polyester Molding Operations


Molding of SMC with compression molder


Molding of BMC with compression molder

13

Materials that are Compression Molded


SMC
-

Sheet molding compound
-

Polyester, glass fiber, CaCO
3


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.

14

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

15

SCRIMP Process


Used for polyester, vinyl ester, and epoxies

16

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/ft
3

to 70 lb/ft
3
.


Foams are produced by chemical blowing agents.


Catalyst are used to initiate reaction.


RIM process is used to produce fenders and bumper covers


17

Polyurethane Chemistry

18

Polyurethane Processing


Polyurethane can be processed by


Casting, painting, foaming


Reaction Injection Molding (RIM)

19

Applications for Thermosets


Epoxy


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.












20

Applications for Thermosets


Polyester


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


Non
-
foam cast elastomers


Coatings, binders, thermoplastic elastomers, sealants, paints













21

Other Thermosets


Phenolic


Applications


Pistons, Thrust pulleys









22

Mechanical Properties of Thermosets



Epoxy
Polyester
PET (Thermoplastic)
Polyurethane
Density, g/cc
1.11-1.40
1.04 - 1.46
1.29-1.40
1.03 - 1.15
Tensile Strength,
psi
4,000 – 13,000
600 – 13,000
7,000 – 10,500
175 - 10,000
Tensile Modulus,
psi
350K
300K - 640K
400K - 600K
10K - 100K
Tensile Elongation, %
3%-6%
2% - 6%%
30% - 300%
3% - 6%
Impact Strength ft-
lb/in
0.20 - 1.0
0.2 - 0.4
0.25 - 0.70
25 to no break
CLTE
10-6 mm/mm/C
45-65
55 - 100
65
100 - 200
HDT 264 psi
115F-550F
140F -400F
70F -100F
70F - 150F
23

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

24

Disadvantages of Thermosets


Epoxy


Moisture absorption, toxicity, not recyclable


Cost


Polyester


Moisture absorption, toxicity, not recyclable


Styrene emmisions



Polyurethane


Moisture absorption, toxicity, not recyclable


25

Additives and Reinforcements to Polyesters


Additives
-



UV stabilizers, colorants, heat stabilizers, blowing agents


Catalyst, inhibitors, promotors



Fillers


Talc


Calcium carbonate


Reinforcements


Glass fiber
-

short fiber (1/8” or long fiber 1/4”)


Mineral fiber (wolastonite)


Mica


carbon fibers


26

Properties of Reinforced Thermosets



Epoxy
Epoxy
With 50w% glass
Epoxy
With 60w%
graphite
Density, g/cc
1.11-1.40
1.84
1.9
Tensile Strength,
psi
4,000 – 13,000
27,000
20,000
Tensile Modulus,
psi
350K
3,000K
6,000K
Tensile Elongation, %
3%-6%
.5%
.4%
Impact Strength ft-
lb/in
0.20 - 1.0
10
10
CLTE
10-6 mm/mm/C
45-65
2
1
HDT 264
psi
115F-550F
500F
500F
27

Processing of Composites


Open Mold processes


Hand lay
-
up and Spray
-
up










Filament winding


28

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












29

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)

30

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
Compression
Molding
Structural
RIM
Resin Transfer
Molding
Annual Part
Production
Volume
30K – 200K
30K – 200K
5K – 200 K
0.5K –5 K
Part Size
Small
< 2 lbs
Medium
2 lbs – 20 lbs
Medium
2 lbs – 20
lbs
Medium to large 5 lbs
– 50 lbs
Fixed
Assets
$300K -$2M
$500K-$2M
$300K-$1M
$10K - $150K
Tooling
Cost
$50K -$500K
$150K-$500K
$50K-
$300K
$20K - $300K
Cycle Time
1 sec –
30 sec
30 sec –
90 sec
30 sec –
120 sec
5 min – 30 min
Materials
Thermoplastic
Thermoplastic
Thermoset
Thermoset
Thermoset
31

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

32

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)

33

Compression Molding


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.

34

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.

35

Structural RIM


Fiber preform is placed into mold.


Polyol and Isocyanate liquids are injected into a closed mold
and reacted to form a urethane.


36

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



Tensile

Modulus,

Kpsi

Tensile Strength, Kpsi

2

5

10

50

xLDPE

xHDPE

37

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?_________________________________
_________________________________________________.