Thermoset Materials

MFG 355

Introduction

• Thermoplastics vs Thermosets– Thermal properties– Strength– Uses– Processing

Viscosity and Thermal Control during Crosslinking

General Properties of Thermosets

• Strength

• Flexibility

• Thermal

• Creep

• Ability to reinforce

• Ability to cure at room temperature

Formaldehyde Resins

• Phenolic

• Urea formaldehyde

• Melamine formaldehyde

Crosslinking

• Reactive Groups—Phenolics

C

C

C

C

C

C

O

HH

HH

H

H

PhenolC

O

H H

FormaldehydePlus

Thermoset Types

• Phenolics

Crosslinking

• Reactive Groups—Amino plastics

N

H

H

R

N

H

H

Amine PlusC

O

H H

Formaldehyde

Amine plastics – clear adhesive

Chipboard

Melamine

C

NC

N

CNN

N

N

H

H

HH

H

H

Crosslinking as Polymers are Formed

Three active sites

Formaldehyde

C

O

H H

Plus

Crosslinking as Polymers are Formed

Melamine Formaldehyde Water

Thermoset Types

• Melamine Plastics

Crosslinking as Polymers are Formed

Melamine Formaldehyde

OHH

Water

Polyester Thermosets (TS) or Unsaturated Polyesters (UP)

• Largest group of thermosets

• Most like to be reinforced with fiberglass

O

O

R1

R

Initiator(usually peroxide)

C

C

R1

R

H

H

Carbon-carbonDouble bond

Crosslinking

• Reactive Groups—Unsaturated polyesters

Plus

Thermoset Types

• Unsaturated Polyesters

Crosslinking Mechanism for Thermoset Polyesters

C C C C O

OO

OH H

H

H

C C C C O

OO

OH H

H

H

O

O

R1

R

Polyester

Peroxide

Styrene(large quantities)

C

C

C

CH

CH

CH

CH

CH

H

H H

Crosslinking – Heat

C

C

C

CH

CH

CH

CH

CH

H

H H

C C C C O

OO

OH H

H

H

C C C C O

OO

OH H

H

H

Peroxidebreaks apart

Crosslinking – Approach of styrene

C

C

C

CH

CH

CH

CH

CH

H

H H

C C C C O

OO

OH H

H

H

C C C C O

OO

OH H

H

H

Crosslinking – bond to styrene

C C C C O

OO

OH H

H

H

C C C C O

OO

OH H

H

H

Half of peroxide bonds with other end of broken styrene molecule

When styrene's double bond breaks, one end forms a free radical

Crosslinking – approach to polymer

C C C C O

OO

OH H

H

H

Styrene free radical causes the polymer's double bond to break and allows it to accept a new pi bond

Crosslinking– bonding to polymer

C C C C O

OO

OH H

H

H

Problems: Polymers not lined up, steric interference

Solution: Styrene

C

C

C

CH

CH

CH

CH

CH

H

H H

New bond

New free radical

Crosslinking– approach of styrene

C C C C O

OO

OH H

H

H

C

C

C

CH

CH

CH

CH

CH

H

H H

Crosslinking– activation of styrene

C C C C O

OO

OH H

H

H

Styrene's double bond opens, allowing two new free radical sites

Crosslinking – bonding of styrene

Problems: Polymers still not lined up, steric interference

C

C

C

CH

CH

CH

CH

CH

H

H H

Solution: Still more styrene

New bond Double bond opens but can't create a bond with any other open bond because of steric effects

Crosslinking – bonding of 2nd styrene

New bond

Free radical

Crosslinking– bonding with 2nd polymer

Up to 8 styrenes might be needed in the bridge

New bond

Crosslinking– bonding with 2nd polymer

Etc.

Crosslinking– more styrene

Crosslinking– more styrene

Crosslinking–bonding to 3rd polymer

Laminating Resins

Additives to Thermoset Polyesters

Fillers like Calcium Carbonate

Tougheners like rubbers

Antioxidants and UV stabilizers

Reinforcements

Molding Compounds

Molding Compounds

R

N N

H

H

H

H

Hardener(amine shown)

Epoxy Rings

Crosslinking

• Reactive Groups—Epoxies

Plus

Thermoset Types

• Epoxies

Vinyl Esters (VE)

Polyimides

NN

C

C

C

C

C

C

C

C

C

C

O O

OO

R R1

H

H

Condensation Imide

N

C

C

C

C

O

O

RN

CC

C

C

O

O

H

H H

H

Carbon-carbonDouble bond Imide

React with addition reaction

Thermoset Types

• Imides

Crosslinking

• Reactive Groups—Polyurethanes

PlusOO

R HH

Polyols

CN

RN

CO O

H

H H

H

Diisocyanates

Thermoset Types

• Polyurethanes

Crosslinking Between two Existing Polymer Chains

C CO O

H H

H

H

H

H

C C C C O

OO

OH H

H

H

PolymerizationActive Sites

CrosslinkingActive Site

Thank You