Plastics have become essential materials due to their numerous applications in normal life such as packaging, thermal and electric insulation, optic fibers manufacture, preserving water and foods, medical devices, etc. Therefore, a large amount of plastic products accumulate as waste in the environment. Most of the communities have chosen the option of dumping in the lands their discarded waste and must pay to ship it out of the area. In those discarded wastes approximately 20% of the volume is of plastic wastes, which is an eyesore as well as a serious problem for landfills. It is because plastics are non-biodegradable likes garden debris and paper. It remains in the land until someone picks them up. Those remaining plastic waste causes the shortage of landfill space and also causes the reduction of the petroleum reserves. Therefore it is time to recycle waste plastics.
Nowadays majority of the communities have adopted the mandatory plastic recycling system in which recyclable plastic waste are reprocessed to produce new products. Recycling and reprocessing plastic materials could save money and improve the local environment. Synthetic plastics can be recycled by melting, shredding and burning to produce similar polymers, fibrous filling as well as used in an incineration-generator to produce energy.
Four types of recycling processes like primary, secondary, tertiary and quaternary are in common practices. In case of primary plastic recycling process the products and materials of the same features like that of original products are produced. This recycling process is applicable on the semi clean industrial scrap, therefore its use is limited. By secondary recycling process these products are produced from plastic wastes which could be used to replace the use of metals, concrete and woods. However due to there low mechanical properties these products are not in common practices. In case of tertiary process the energy is o6btained from the plastic wastes by burning. This process is widely in common use because of the high heat content of plastics. But this technique adds atmospheric pollution due to toxic gas emissions.
For the sake of environment new techniques or quarternary recycling process, pyrolysis and catalytic pyrolysis have been explored. Pyrolysis of plastic waste has been proposed as a feedstock-recycling route where the plastic waste materials are processed to produce an oil feedstock for the petrochemicals industry. Catalytic pyrolysis is the main focus of research. It is expected that it could reduce the required reaction temperature, improve the yield of products, provides selectivity in the product distributions and enhance the economic potential of the process.
For the successful waste plastic recycling process five factors are necessary. First a large quantity of used plastics should be available. For getting this large quantity of used plastics, it should be collected at certain location, which is the second step. In the third step it should be separated and sorted by waste sorting machine. Few plastics are given codes to help the separating and sorting process. Reprocessing is the fourth step in the plastic recycling. This process includes melting which is applicable on those plastics which is not widely cross linked with any synthetic. If it contain so many synthetics, then it will be difficult to stretch and will be less pliable. The manufacturing of new products from melted plastics is the final step.
Plastics are divided into two ares, polymer plastics and polyethylene plastics. There are four types of polymer plastics which are recyclable like polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC). Their names and labels are very important in the recycling process. The other two types of polyethylene plastics which are recyclable are low-density polyethylene (LDPE) and high density polyethylene (HDOE).