Bottles made of polyethylene terephthalate (PET, sometimes PETE) can be "recycled" to reuse the material out of which they are made and to reduce the amount of waste going into landfills. PET is semiporous and absorbs molecules of the food or beverage contained, and the residue is difficult to remove: Heating the plastic enough for sterilization would destroy it. Therefore, most recycled bottles are used to make lower grade products, such as carpets. To make a food grade plastic, the bottles need to be hydrolysed down to monomers, which are purified and then re-polymerised to make new PET.
In many countries, PET plastics are coded with the resin identification code number "1" inside the universal recycling symbol, usually located on the bottom of the container.
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Usage of PET
PET is used as a raw material for making packaging materials such as bottles and containers for packaging a wide range of food products and other consumer goods. Examples include soft drinks, alcoholic beverages, detergents, cosmetics, pharmaceutical products and edible oils. PET is one of the most common consumer plastics used. Polyethylene terephthalate also can be used as main material in making paper.
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Process
Post-consumer waste
The empty PET packaging is discarded by the consumer after use and becomes PET waste. In the recycling industry, this is referred to as "post-consumer PET." Many local governments and waste collection agencies have started to collect post-consumer PET separately from other household waste. Besides that there is container deposit legislation in some countries which also applies to PET bottles.
It is debatable whether exporting circulating resources that damages the domestic recycling industry is acceptable or not. In Japan, overseas market pressure led to a significant cost reduction in the domestic market. The cost of the plastics other than PET bottles remained high.
Sorting
When the PET bottles are returned to an authorized redemption center, or to the original seller in some jurisdictions, the deposit is partly or fully refunded to the redeemer. In both cases the collected post-consumer PET is taken to recycling centres known as materials recovery facilities (MRF) where it is sorted and separated from other materials such as metal, objects made out of other rigid plastics such as PVC, HDPE, polypropylene, flexible plastics such as those used for bags (generally low density polyethylene), drink cartons, glass, and anything else which is not made out of PET.
Post-consumer PET is often sorted into different colour fractions: transparent or uncoloured PET, blue and green coloured PET, and the remainder into a mixed colours fraction. The emergence of new colours (such as amber for plastic beer bottles) further complicates the sorting process for the recycling industry.
Processing for sale
The sorted post-consumer PET waste is crushed, pressed into bales and offered for sale to recycling companies. Colourless/light blue post-consumer PET attracts higher sales prices than the darker blue and green fractions. The mixed color fraction is the least valuable.
Further treatment
The further treatment process includes crushing, washing, separating and drying. Recycling companies further treat the post-consumer PET by shredding the material into small fragments. These fragments still contain residues of the original content, shredded paper labels and plastic caps. These are removed by different processes, resulting in pure PET fragments, or "PET flakes". PET flakes are used as the raw material for a range of products that would otherwise be made of polyester. Examples include polyester fibres (a base material for the production of clothing, pillows, carpets, etc.), polyester sheets, strapping, or back into PET bottles.
Melt filtration
Melt filtration is typically used to remove contaminants from polymer melts during the extrusion process. There is a mechanical separation of the contaminants within a machine called a 'screen changer'. A typical system will consist of a steel housing with the filtration medium contained in moveable pistons or slide plates that enable the processor to remove the screens from the extruder flow without stopping production. The contaminants are usually collected on woven wire screens which are supported on a stainless steel plate called a 'breaker plate' -- a strong circular piece of steel drilled with large holes to allow the flow of the polymer melt. For the recycling of polyester it is typical to integrate a screen changer into the extrusion line. This can be in a pelletizing, sheet extrusion or strapping tape extrusion line.
Drying Polyester
PET polymer is very sensitive to hydrolytic degradation, resulting in severe reduction in its molecular weight, thereby adversely affecting its subsequent melt processability. Therefore, it is essential to dry the PET flakes or granules to a very low moisture level prior to melt extrusion.
PET must be dried to <100 parts per million (ppm) moisture and maintained at this moisture level to minimize hydrolysis during melt processing.
Dehumidifying Drying - These types of dryers circulate hot and de-humidified dry air onto the resin, suck the air back, dry it and then pump again in a closed loop operation. This process reduces moisture level in the PET down to 50ppm or lower. The efficiency of moisture removal depends on the air dew point. If the air dew point is not good, then some moisture remains in the chips and cause IV loss during processing.
Infrared Drying polyester pellets and flakes - A new type of dryer has been introduced in recent years, using Infrared drying (IRD). Due to the high rate of energy transfer with IR heating in combination with the specific wavelength used, the energy costs involved with these systems can be greatly reduced, along with the size. Polyester can be dried and amorphous flake crystallized and dried within only about 15 minutes down to a moisture level of approx. 300ppm in one step, and down to <50 ppm using a buffer hopper to complete the drying in typically under 1 hour
Global statistics
Worldwide, approximately 7.5 million tons of PET were collected in 2011. This gave 5.9 million tons of flake. In 2009 3.4 million tons were used to produce fibre, 500,000 tons to produce bottles, 500,000 tons to produce APET sheet for thermoforming, 200,000 tons to produce strapping tape and 100,000 tons for miscellaneous applications. (Source: PCI, www.pcipetpackaging.co.uk )
Petcore, the European trade association that fosters the collection and recycling of PET, reported that in Europe alone, 1.6 million tonnes of PET bottles were collected in 2011 - more than 51% of all bottles. After exported bales were taken into account, 1.12 million tons of PET flake were produced. 440,000 tons were used to produce fibres, 283,000 tons to produce more bottles, 278,000 tons to produce APET sheets, 102,000 tons for strapping tape and 18,000 tons for miscellaneous applications. (Source: PCI for Petcore and EuPR)
In 2008 the amount of post-consumer PET bottles collected for recycling and sold in the United States was approx. 1.45 billion pounds.
In 2012, 81% of the PET bottles sold in Switzerland were recycled.
Increasing energy prices may increase the volume of recycling PET bottles. In Europe, the EU Waste Framework Directive mandates that by 2020 there should be 50% recycling or reuse of plastics from household streams.
In the United States the recycling rate for PET packaging was 31.2% in 2013, according to a report from The National Association for PET Container Resources (NAPCOR) and The Association of Postconsumer Plastic Recyclers (APR). A total of 1,798 million pounds was collected and 475 million pounds of recycled PET used out of a total of 5,764 million pounds of PET bottles.
Re-use of PET bottles
PET bottles are also recycled as-is (re-used) for various purposes, including for use in school projects, and for use in solar water disinfection in developing nations, in which empty PET bottles are filled with water and left in the sun to allow disinfection by ultraviolet radiation. PET is useful for this purpose because most other materials (including glass) that are transparent to visible light are opaque to ultraviolet radiation.
A novel use is as a building material in third-world countries. According to online sources, the bottles, in a labor-intensive process, are filled with sand, then stacked and either mudded or cemented together to form a wall. Some of the bottles can be filled instead with air or water, to admit light into the structure./
Source of the article : Wikipedia
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