Saturday, January 5, 2013

Plastic Recycling

Closed Loop Recycling take discarded soft drinks and water bottles made from polyethylene terephthalate (PET) and milk bottles made from high density polyethylene (HDPE) and recycle them back into food-grade plastic. The resulting rPET and rHDPE is then used to make new bottles and food packaging.

The plant in Dagenham is the first to use state of the art technology to sort, wash and super clean both types of plastic meeting EU and US FDA standards.

The facility is capable of recycling 35,000 tonnes of bottles each year. 875 million bottles that would otherwise have been exported for recycling, or sent to landfill, will now be processed and remain in the UK. This represents nearly 20% of the plastic bottles that are currently collected for recycling in the UK, saving approximately 52,500 tonnes of carbon dioxide per year.

The mixed PET and HDPE bottles arrive at the plant squashed together into square bales which typically contain around 12,500 bottles. The bottle bales are placed on a conveyor belt which feeds the bale breaker - six large rotating "cork screws" that loosen and open up the bale.

Once the bottles are loose, they pass through the trommel, a perforated, rotating drum much like a washing machine where small bits of rubbish, such as stones and dirt, as well as any lids and caps that have come off the bottles. These lids and caps are often not the same type of plastic as the bottles and are often made from coloured plastics, so they need to be discarded. Metal contaminants such as food and drink cans, screws and wire are removed. A powerful electromagnet extracts steel objects and then a device is used to remove any aluminium objects. Paper, carrier bags and films are then separated from the bottles by a row of air jets.

Three optical sorting machines that are capable of recognising, separating and ejecting selected bottles from a mixed batch are utilised. Each machine is programmed to detect a different type of plastic or colour and when this passes under its sensors, a jet of air is fired to remove it from the rest. The result of this sorting process is the separation of the plastic into five storage bunkers:

Onward reprocessing at Closed Loop
Clear PET bottles
Light blue PET bottles
HDPE bottles

Bottles Recycled at other facilities
Coloured PET
Other plastics

From the storage bunkers the clear and light blue PET bottles go through a final manual sorting process to remove any contaminants prior to granulating and washing. This involves hand-picking anything which is not clear or light blue PET which may have made it through the previous sorting equipment.

The HDPE bottles are also manually sorted, but before this is done, they are sent through a fourth sorting machine which separates them into natural HDPE, which is what milk bottles are made from, and coloured HDPE which is typically used for cleaning products. It is very important that any bottles that have been in contact with cleaning products or other liquids are removed from the process. The coloured HDPE bottles are separated and sold to manufacturers of drainage pipes, wheelie bins, garden furniture and many other items.

Granulating and Washing
After manual sorting, the vast majority of contaminants will have been removed, leaving mainly clear and light blue PET bottles and natural HDPE bottles, which are now ready to be granulated. The granulators cut and chop the bottles into small flakes. For the rest of the process, the flakes of PET and HDPE are moved around the plant using pipes and blowers instead of conveyor belts. Prior to washing, the flakes are put through a dry cleaner to remove anything lighter than the flakes themselves. Any loose labels, fines and small contaminants are removed by a zig-zag classifier, a device which uses an upward thrust of air to blow any labels, paper, or other light material higher than the heavier flake. To clean the flake of label residue, glues and ink, a hot wash is used. The flakes are washed for 15 minutes at 80°C using a weak solution of caustic soda so that the detached glues and label fragments sink to the bottom where they are removed. The flakes and any plastic labels detached are then rinsed and dried. The flakes of lids and caps, which are mainly made from coloured HDPE, will still be present and must be removed from the PET flakes prior to decontamination. This is achieved as PET sinks in water while HDPE floats.

To return the PET flakes back into a food-grade product, a process is used to super-clean the plastic and remove all traces of contaminants. The surface layer of the PET flake is removed using a solution of caustic soda. For HDPE bottles, they pass through a colour sorter to remove any coloured flakes and the natural HDPE is ready to be processed back into food-grade standard material.

M&S are now using this process to include 10% recycled material in their milk bottles.

For more details see:

1 comment:

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