Plastic recycling: A new prospective industrial sector in Bangladesh

Bangladesh does not have any polymer industry. Despite having abundant natural gas it is deficient in raw materials for polymer production. All virgin polymers are imported. As such, there is a rapidly growing incentive to recycle plastic waste, which is vital from environmentally sustainable perspective.
Plastic recycling is the process of recovering scrap or waste plastic and reprocessing the material into useful products, sometimes completely different in form from their original state. For instance, this could mean melting down soft drink bottles and then casting them as plastic chairs and tables.
Plastic recycling is the term given to the processing of waste plastic which turns old or scrap plastic in to a useable product which can then re-enter the manufacturing chain.
Plastics are used in a wide range of products that we use on a daily basis. Up to 60% of the rubbish found in our dustbins could be recycled, and as much as 50% of waste in the average dustbin could be composted. Plastics convenience is undeniable as it is produced in vast quantities throughout the world.
Recycling plastic waste is hugely important to limit the depletion of this limited resource. Plastic waste can be found lying on roadsides, hedgerows, beaches etc., and are not bio-degradable. As they do not decompose, they are consequently harming the environment and it is our responsibility to recycle plastic waste accordingly.
Stage One - Sorting the Plastic

Before recycling, most plastics are sorted according to their resin type. In the past, plastic reclaimers used the resin identification code (RIC), a method of categorization of polymer types, which was developed by the Society of the Plastics Industry in 1988. Polyethylene terephthalate, commonly referred to as PET, for instance, has a resin code of 1. Most plastic reclaimers do not rely on the RIC now; they use automatic sort systems to identify the resin, such as near infrared (NIR) technology. Some plastic products are also separated by color before they are recycled.
Stage Two - Washing Waste Plastic
Once the waste plastic has been identified and separated in to one of its many forms the cleaning process can begin, this usually starts with washing to remove paper labels, adhesives and other impurities, all the labels on your plastic containers, bottles and even your wheelie bin need to be completely removed as these will lower the quality of the finished recycled plastic.
Stage Three- Shredding the Plastic
The shredding stage is when the waste plastic is taken and loaded on to conveyor belts or directly in to huge hoppers that funnel the clean scrap towards rotating metal teeth that rip the plastic in to small pellets which are bagged up afterwards ready for testing.
Stage Four - Identify and Classify the Plastic
Once the shredded plastic has been bagged it is then chemically tested and labelled as to its exact specification, this rGrade plastic can be used as is by adding to a mix of virgin plastic in a manufacturing run, alternatively the rGrade plastic can be further recycled.
Stage Five - Extruding
This is the final stage in recycling plastic, this involves melting the clean shredded plastic and extruding in to the form of pellets which then go on to manufacture the next lot of plastic products.
Viscosity Increasing Reactor
In the course of the extrusion process, waste plastic loses viscosity, which then may need to be increased in a subsequent process. The Austrian company Starlinger has developed a process called polycondensation. In the same process, the granulate is decontaminated so as to be suitable for direct food contact.
Following extrusion, the granulate is also amorphous. It must be thermally crystallised in order to avoid formation of lumps, then it is treated for a selected length of time in the reactor where it is subjected to heat and vacuum. The two factors temperature and time effect so-called polycondensation, a process in which H2O and glycol are released, the molecule chains lengthened and the viscosity of the granulate increased.
The writer has earned his Phd from King Fahd University of Petroleum, KSA and is now an Assistant Professor of the Dept. of Chemical Engineering at the BUET. He can be reached at: [email protected]