Plastics bags are made up of polyethylene in its low density form (LDPE). This polythene is derived from natural gas, crude oil and non-renewable sources.
Blown film extrusion or “tubular film extrusion†is one of the most common ways to make a plastic bag. The plastic resin pellets of different types are taken from storage bin and thrown in a hopper where it is melted. This melted plastic is extruded through a vertical slit die which forms a thin walled tube. Air is blown through a hole present in the centre of die into the thin walled tube. The tube expands and took the shape of bubbles. The machine used for whole of the above process is called extruder. These bubbles are made up of different widths and there it is cooled by the high speed air ring over the hot film and this film keep on moving upwards. The film then reaches to nip rolls and passed through it where it is flattened. This is called “lay-flat†tube of film.
Then this lay flat is taken back by the rollers to the extruder tower. It can be kept as it is or cut down to make more thinly flat film sheets. For the production of bags the lay flat films are left as it is. The tube of this film is sealed across the width of film and perforated. Now the end product is formed which is high density polypropylene.
Bio- degradable plastic bags are also used which are made from bio-degradable plastics that contain materials like corn starch, non-oil based materials. These plastics can be broken in the presence of sunlight.
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