The third step in the process of obtaining plastics is the synthesis of the basic polymer. There are two types of polymerization: chain-growth and step-growth. The fourth step is the incorporation of additives into the basic polymer to create useful plastics. Additives improve properties like strength, flexibility, color, and protection from degradation. Common additive types include antioxidants, ultraviolet stabilizers, plasticizers, and pigments.

1. Student 2
Explain the third and the fourth steps of the process of
obtaining plastics
3rd Synthesis of the basic polymer
Polymerization: Process in which many monomers are combined.
• Chain-growth polymerization: monomers are added to the chain one at a time only
• Step-growth polymerization: chains of monomers may combine with one another
directly

2. 4th Incorporation of additives
Additives:
• Materials mixed with polymer to make plastics.
• Additives turn basic polymers in to useful plastics
• Additives make plastics clean and healthy, safe,
work longer, look good…
Some types of additives:
• Antioxidants: to protect the polymer from degradation by ozone or oxygen
• Ultraviolet stabilizers: to protect against weathering
• Plasticizers: to increase the polymer’s flexibility
• Lubricants: to reduce friction problems
• Pigments: to give the plastic colour

3. Explain the following methods of shaping and finishing plastics.
Mention at least one object that could be made with each
technique
• Injection molding: It is the process by which a material is injected into a mould so it
takes the mould’s form.
• Foam molding: It is the process which combines plastics and gas.

4. • Vacuum forming: Sheets of plastic are heated, streched into a single-surface mold
and pressed against a mold by a vacuum.
• Calandering: This process consist of multiple hard pressure rollers used to give
form and smooth a material (plastic)

5. http://en.wikipedia.org/wiki/Polymer#Polymer_synthesis
http://www.bpf.co.uk/plastipedia/additives/default.aspx