Polylife    

The campaign against the use of plastic bags has gained a lot of momentum in the country. Recently, there was pressure on the Delhi government to ban the use of plastic bags in the city. But, the government disagreed and instead, proposed to thicken the plastic bags from 20 microns to 40 microns for more durability for repeated use. It also suggested that plastic manufacturers should have state-of-the-art recycling units. But, this does not solve the problem of plastic bags choking our landfills and our lives. Here is some know-how about this trouble-maker...

    Plastic info   

Plastics are polymers – a large chain of molecules. Each individual unit is called a monomer. Most of these monomers are derived from crude oil, which contains hydrocarbons that are extracted and chemically converted to form monomers.

Some of the most common monomers are ethene, propene, styrene, and vinyl chloride. In case of plastic bags, the basic molecule or monomer is ethylene or ethene.

    Plastic Making    

• The hydrocarbons are then chemically treated to form monomers.
• The monomers are brought together to form a chain of carbon atoms – polymer resins. The process is called ‘polymerisation’. In case of polythenes, ethene monomers form a chain where each carbon atom has two hydrogen atoms attached to it. Thus, the name polythene (‘poly’ meaning many and ‘ethene’ being the basic unit).
• The polymer resins are further processed by adding plasticisers, dyes or flame-retardants depending on the requirement, and shaped into pellets or beads.
• The pellets are heated, molded (based on the type of product required) and allowed to cool. There are different methods of shaping them like extrusion, injection molding, blow molding and rotational molding.

     Plastic Recycling    

We all know that plastics are non-biodegradable. So, we recycle them. Here is how it happens:

Inspection: The plastic trash is inspected for contaminants like glass, rocks, and other types of plastic that cannot be recycled.

Chopping and washing: The selected ones are washed to remove impurities, and chopped into flakes to make recycling easier.

Flotation: The different types of plastics need to be separated. So they are put in a flotation tank where some either sink or float depending on their density.

Drying: They are dried in a drying machine.

Melting: They are put in an ‘extruder’ where there are melted by applying heat and pressure.

Filtering: The melted plastic is made to flow through a fine filter to remove any contaminant that did not get washed away. It is then moulded into strands.

Pelletising: These strands are then cooled (generally in water), and cut into same-sized pellets. Manufacturing companies can then buy these pellets to make new plastic products.