Polymers are primarily made up of carbon, hydrogen and oxygen. They are the long chains which repeat themselves again and again.
Many steps are evolved in the production of plastics
Polymerization
Most common raw material required for the manufacture of plastics is oil and natural gas but they are also processed from corn and other biomass. First of all the components of these raw materials are treated in a “cracking process†which makes hydrocarbons to ethylene or propylene. If we process it further it will result in monomers like styrene, vinyl chloride etc. these monomers are now bond chemically in chains which are known as polymers. These formations and length of chains gives plastic many characteristics.
Additives
Additives are added in the plastics so as to enhance and alter their chemical, physical and mechanical properties like to give color, provide foamed structure and special characteristic of smooth surface and less friction. These articles help plastics to protect themselves from the degrading affects of bacteria micro organisms, light and heat.
Plasticizers
These are the substances to improve the workability and flexibility of plastics. These are found in the plastic film wraps which are used in packaging or processing. All these plastic containers having plasticizers and additives which are regulated by FDA (food and drug administration U.S) to say that they are completely safe.
There are different methods for processing to make the products like bottles, bags, containers etc.
Extrusion
Granules or plastic pellets are sent in the hopper. It further moves to the extruder that is a long heated chamber in which it is stirred continuously with the help of revolving screw. Here the plastic gets melted. Then this molten plastic is taken out from the die or a small opening in the shape of required product and is left for cooling. This process is used for the plastic films and bags.
Injection molding
It goes through the same process as in extrusion but when the molten plastic is taken out it is forced with high pressure in a cool and changes to solid state. The mold is opened and the required object is taken out. This is used for making butter tubs, closures, yogurt containers etc.
Blow molding
This process is used with both extrusion and injection molding. In this die makes a semi-molten tube of thermoplastic material. Cold mold is attached to the tube then compressed air is passed through interiors of mold and the tube solidifies. This process is used to make hollow products and in this process only one injection molded part is required instead of two. Another blow molding process is to inject “perform†(an intermediate shape) then it is heated and soft plastic is taken in the final shape.
Rotational molding
In this, a closed mold is placed upon a machine which can rotates on two axes at a time. Plastic pellets are put into it and heated to melt. The plastic rotation around axes which make plastic in an uniform coating in the mold. This is then cooled. This process is also used to make hollow products.
