Types of Plastics

1. Thermoplastics

• Chemical structure remains unchanged during heating and shaping . 
• More commercially used , comprising more than 70 percent of total plastics tonnage . 
• Group of plastic that will be soften when heated and hard when cooled , regardless of the number of times the process is repeated . 
• Can be reshaped and recycled . 
• Having long chain-like molecular structure . 

2. Thermosetting Plastics

• 
  Undergo a curing process during heating and shaping , causing a permanent change ( called cross-linking ) in a molecular structure . 
• Group of plastic that will be formed permanently when cured . 
• Cannot be reshaped or recycled . 
• Having cage-like molecular structure . 
• To shape a thermoplastic polymer it must be heated so that it softens to the consistency of a liquid . 

3. Elastomers

• Are long-chain polymers in which helical or zig-zag molecular chains are free to strighten when the material is stretched , and recover when the load is removed .