1) Catalysts or Accelerators. They are also known hardeners. They are the catalysts which are added to accelerate chemical reactions during polymerisation of plastics,
2. Fillers : These are the materials added to synthetic resins to dilute them in order to reduce their consumption. They also increase their bulk and, thus, reduce the material cost. Many of them, especially when they are finely distributed, help in increasing strength, stiffness and thermal resistance of the plastics. Materials added for this purpose include clay, talc, wood, flour, mica, quartz, alumina, carbon black, calcium carbonate, asbestos, glass fiber etc.
3. Modifiers : These are the chemicals added to plastics for changing the properties of base resin. Some of them help in improving mechanical properties as well.
4. Plasticisers: These are the chemicals added for cither softening the resins at forming temperature or to improve their toughness at the finished stage and to impart flexibility to their finished products. A plasticiser is normally a fluid of high molecular weight
5. Stabilisers : Their additions to plastics help in preventing deterioration due to the action of heat and light.
6. Initiators : They help in initiating or starting the reaction.i.e. polymerization. H202 is commonly used for this purpose.
7. Dyes and pigments: These are the colouring agents, added to impart different colours and shades to plastics.
