1. Thermosetting Polymers

2. -- Highly cross- linked (network)
THERMOSETS OR THERMOSETTING POLYMERS :
A thermoset is a type of plastic that undergoes a chemical change during production that cannot be repeated or reversed
-- Highly cross- linked (network)
-Thermosetting polymers initially begin as linear chains
-Heat or pressure – initiates the cross-linking process
-Cross-linking results in permanent chemical bonding of the individual polymer chains to one another
-Cross-linking is irreversible – thermosets can’t be recycled

4. Thermoset plastics become hard and rigid on heating- on cooling the properties are retained
By step growth mechanism(condensation polymerization), the chemical reactions are enhanced at higher temperatures and irreversible
Properties:
-- possess good strength , stiffness and hardness
- poor ductility, poor impact properties
- behavior similar to brittle metal or ceramic

5. Thermosets with fuctional units :

6. Thermoset Properties

7. PHENOLICS : Uses: - Bakelite – common phenolic thermoset
Condensation reaction between phenol and formaldehyde - initial linear phenolic resin
process continues until a linear phenol-formaldehyde chain is formed
A third location on each phenol ring provides a site for cross-linking with the adjacent chains
Uses:
Adhesives
Coatings
Moulded components for electrical or motor applications

8. AMINES :
- Produced by combining urea or melamine monomers with formaldehyde
Uses:
Adhesives
Laminates
Moulding materials for cookware
Electrical hardware like circuit breakers , switches

9. Melamine formaldehyde (MF)
COMMON NAME: Formica or Melaware
- Used in the production of plastic laminates because of its smooth surface and hygienic qualities.
PROPERTIES
waterproof
odourless
mark and scratch resistance
USES
worktops
buttons
electrical insulation

10. POLYESTERS:
- Form chains from alcohol and acid molecules by condensation reaction giving water as by-product
Uses:
Used as molding or casting materials for a variety of electrical applications
Decorative laminates
Boats and other marine equipment
As a matrix for composites such as fiberglass

11. Polyester resin COMMON NAME: Orel or Beetle PROPERTIES
Stiff, hard and brittle
Resilient as laminated GRP
USES
panels for car bodies and boat hulls

12. EPOXIES :
- Formed from molecules containing a tight C-O-C ring
- During polymerization, the C-O-C rings are opened – bonds are rearranged to join the molecules
Uses :
Adhesives
Rigid molded parts for electrical applications
Automotive components
Circuit boards
Sporting goods
Matrix for high performance fiber-reinforced composite materials for aerospace applications

14. Epoxy resin (ER) PROPERTIES Good electrical insulator hard
COMMON NAME: Araldite
Many adhesives (glues) are thermosetting plastics
It will bond most materials including woods and metals as well as some plastics
PROPERTIES
Good electrical insulator
hard
brittle unless reinforced

15. POLYIMIDES : Ring structure that contains nitrogen atom
One special group – the bismaleimides (BMI) important in aircraft and aerospace industry
Operates continuously at temperatures of 175 ˚C and do not decompose even upto 460 ˚C
INERPENETRATING POLYMER NETWORKS :
-Produced when linear thermoplastic chains are inter-twined through a thermosetting framework
Eg . Nylon, polypropylene chains can penetrate into a cross-linked silicone thermoset

16. Differences Between Thermoplastic And Thermosetting Polymers
S.No
THERMOPLASTIC
THERMOSETTING 1. 2. 3. 4. 5.
Long, straight chained carbon compounds
Formed by addition polymerization
Low strength compared to thermosets
Can be processed again and again
Eg . Polyethylene
Cross-linked compounds
Formed by condensation(step growth) polymerization
More strength compared to thermoplastics
Cannot be processed again or recycled
Eg . Bakelite, epoxy