04 epoxies

8/8/2019 04 Epoxies

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Epoxies

A. Brent Strong

8/8/2019 04 Epoxies


Epoxies

Second most widely used family of thermosets(after polyesters)

Large portion of uses are non-reinforced

(adhesives, paints, etc.) Circuit boards are the largest reinforced

application (low conductivity, low volatiles)

Advanced composites use epoxies because of

± Thermal stability ± Adhesion

± Mechanical properties

8/8/2019 04 Epoxies


Epoxy Structure

C C

Epoxy ring

OC C

O( )n

Polymer portion

Epoxy ring

Number of repeat units

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Epoxy í specific molecules

CCC

O

CCC

O

NC C C

O

C C C

O

N C

C

C

C

C

O

C

C

C

C

C

O

C

C

C

C

O

C

a) Diglycidyl Ether of Bisphenol A (DGEBPA)

b) Tetraglycidylmethylenedianiline

(TGMDA)

c) Epoxidized phenolic resin

(Epoxy Novalac)

CO C

O

C

C

C

OCCCO

OH

COCCC

O c

cn

( )n

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Properties í chain length (n)

Number of repeat

units (n)

Heat Distortion Temperature

(HDT) (°F/°C)

Physical state

2 105/40 Semi-solid

4 160/70 Solid

9 265/130 Solid

12 300/150 Solid

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Epoxy í specialty molecules

O

O

CCOCCOCCC

OH

C O C C C

OH

O C C O C C C

OH

NC

C

C

NH2

C C C

OH

O C C O C C C

O

Toughened Epoxy Resin

O

CC

ON

C

O

O

CCCOC

C C C

O

OC

O

CC

ON

C

O

O

C C C O C

CCC

O

O C

C

High Temperature Epoxy Resins

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Epoxies í HDT and structure

Resin Type

(predominate)

Heat Distortion Temp (HDT)

(°F/°C)

Aliphatic

(straight chain)

255-270/125-132

Aliphatic

(cyclical)

230-300/110-150

Aromatic(cyclical)

290-350/145-175

Aromatic

(straight chain)

265-290/130-145

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Curing Epoxies

Epoxies use hardeners instead of initiators

for curing

Hardeners can be almost any moleculethat will react with (open) the epoxy ring

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Epoxy Crosslink Mechanism

H

HN

C

C...

C

O

C C...

N

C

C...

C C C...

O

C C

H H

Hardener

Epoxy

The other end can also react.

Cured Polymer

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Curing

C C

Epoxy ring

OC

O

()n

Epoxy ring

N

N

HH

HH

N

N

HH

HH

C

Hardener molecules have two

reactive ends, so they can each

react with two epoxy molecules.

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Effects of various hardenersHardeners Advantages Disadvantages

Aliphatic amines Convenience, low cost, roomtemp cure, low viscosity

Skin irritant, critical mixratios, blushes

Aromatic amines Moderate heat resistance,

chemical resistance

Solids at room temp,

long and elevated cures

Polyamides Room temp cure, flexibility,

toughness, low toxicity

High cost, high

viscosity, low HDT

Amidoamines Toughness Poor HDT

Dicyandiamide Good HDT, good electrical Long, elevated cures

Anhydrides Heat and chem resistance Long, elevated cures

Polysulfide Moisture insensitive, quick set Odor, poor HDT

Catalytic Long pot life, high HDT Long, elevated cures,poor moisture

Melamine/form. Hardness, flexibility Elevated temp cure

Urea/form. Adhesion, stability, color Elevated temp cure

Phenol/form. HDT, chem resistance,

hardness

Solid, weatherability

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Epoxy and Polyester ComparisonComparisons Polyester Epoxy

Active site C=C

Crosslinking reaction Addition/free radical Ring opening

Crosslinking agent Initiator (peroxide) Hardener

Amount of x-link agent 1-2% of resin 1:1 with resin

Solvent/viscosity Styrene (active)/low Infrequent/high

Volatiles High Low

Inhibitors, accelerators Frequent Infrequent

Reactant toxicity Low Moderate

Cure conditions Room temp or heated Heated (some room)

Shrinkage High Low

Post cure Rare Common

O

C C

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Polyester and Epoxy í Properties

Property Polyester EpoxyAdhesion Good Excellent

Shear strength Good Excellent

Fatigue resistance Moderate Excellent

Strength/stiffness Good Excellent

Creep resistance Moderate Moderate to good

Toughness Poor Poor to good

Thermal stability Moderate Good

Electrical resistance Moderate Excellent

Water absorption resist Poor to moderate Moderate

Solvent resistance Poor to moderate Good

UV resistance Poor to moderate Poor to moderate

Flammability resistance Poor to moderate Poor to moderate

Smoke Moderately dense Moderately dense

Cost Low Moderate

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Epoxy

8/8/2019 04 Epoxies


Thank you

Brent Strong

04 epoxies

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