• A Polymer is a material that is made from many repeating molecular chains.
  • There are two main ways of forming polymers:
    • Addition polymerisation: The same monomer is linked repeatedly without changing its chemical deposition. Produces no by-products.
    • Condensation polymerisation: Different monomers react to form a polymer. Usually water is created as a by-product.
  • It is separated into three basic types:

Thermosoftening Polymers

  • These remelt after being heated.
    • This is because their molecular chains are held by weak Van der Waals forces rather than a molecular bond.
  • This also means it has directional properties
  • Their melting points are quite low: around 100 degrees
  • Common properties include: resilient, flexible and optically transparent
  • Common examples are: Polyethylene, acrylonitrile butadiene styrene (ABS), Polyvinyl Chloride (PVC) and acrylic


  • This is when the molecular structure does have crosslinking, but not complete chains
  • These tend to deform under tensile stress or heatand have high elasticity
  • The most common types of elastomers are rubbers
  • For use in high-wear conditions, it can be stiffened through a process known as vulcanisation
    • This is when an agent (usually about 4% Sulfur) is introduced to the elastomer with pressure and heat.
    • The result is a rubber that is more rigid and hard.
    • This occurs because the sulfur completes the chains and thus increases the crosslinking.
  • Vulcanised rubber is commonly used in car tyres, and can be made into a composite with steel wire and polyester for greater rigidity.

Thermosetting Polymers

  • These undergo a non-reversable change when heated and cannot be resoftened by heat.
  • Their molecular bonds have cross-linking by strong covalent bonds
  • Common properties are: tough, heat-resistant and ductile
  • Common examples are: epoxy resins, polypropylene and bakelite.
  • While thermosoftening polymers are made by additional polymerisation, thermosetting polymers are made through condensation polymerisation.

Engineering Textiles

  • These are polymers drawn into a fabric-like state


  • Strong, resilient and is resistant to water absorption (hydrophobic).
  • It is used in helium airships, some tyres, and car parts such as fan belts and radiator hoses.

Aramid Fibres

  • Aramid fibres have excellent strength qualities but tend to have poor temperature resistance.
  • They are used in aircraft manufacture and bulletproof vests.
  • Some famous examples include Nomex and Kevlar.


  • PTFE (Teflon) is fire esistant
  • It's used in dry lubrication and in filters for engines.

Methods of manufacturing Polymers

Injection moulding

  • Whenever you think polymers, you think injection moulding.
  1. Molten polymer is forced into a cavity of the desired shape through pneumatics.
  2. It's cooled to solidify
  3. Then the cavity can be taken apart and the object can be removed.
  4. If needed, the product can be machined for greater accuracy.
  • It's often used with thermosoftening polymers as they're easier to form.
  • This method is incredibly cost efficient, fast and simple for mass production
  • Most single-piece polymer equipment is made in this method.


  • Very similar to the metal forming process
  • Let this picture explain everything:
  • Also used with thermosoftening polymers.

Blow Moulding

  • Used for making plastic bottles.


  • Similar to rolling
  • This was used for making films, sheets, tiles and other flat plastics.
  • Recently, it has been used in making composite materials, replacing the coating liquid with a viscous polymer (e.g. PVC)

Rotational Moulding

  • Used to make hollow, stress free items.
  • Used with thermosoftening polymers.

Compressional moulding

  1. An unpolymerised polymer preform (powder and fillers) is compressed into a mould with applied heat
  2. The heat and pressure polymerise the it
  3. An ejector pin or separatable mould ejects the product.
  • This is used with thermosoftening polymers and elastomers
  • Can be polymerised in a different chamber to the moulding chamber in what is known as transfer moulding.
    • This allows further heating and curing to be done.

Examples and applications