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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
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