Difference between revisions of "Plastic recycling"

Latest revision as of 20:59, 6 July 2010

Plastic recycling is the process of recovering scrap or waste plastics 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. Typically a plastic is not recycled into the same type of plastic, and products made from recycled plastics are often not recyclable.

Challenges

When compared to other materials like glass and metal materials, plastic polymers require greater processing to be recycled.^{[citation needed]} Plastics have a low entropy of mixing, which is due to the high molecular weight of their large polymer chains. A macromolecule interacts with its environment along its entire length, so its enthalpy of mixing is large compared to that of an organic molecule with a similar structure. Heating alone is not enough to dissolve such a large molecule; because of this, plastics must often be of nearly identical composition in order to mix efficiently.

When different types of plastics are melted together they tend to phase-separate, like oil and water, and set in these layers. The phase boundaries cause structural weakness in the resulting material, meaning that polymer blends are only useful in limited applications.

Another barrier to recycling is the widespread use of dyes, fillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more frequently.

The use of biodegradable plastics is increasing. If some of these get mixed in the other plastics for recycling, the reclaimed plastic is not recyclable because the variance in properties and melt temperatures.^[1] http://en.wikipedia.org/w/index.php?title=Plastic_recycling&action=edit

Processes

Before recycling, plastics are sorted according to their resin identification code, 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. They are also often separated by color. The plastic recyclables are then shredded. These shredded fragments then undergo processes to eliminate impurities like paper labels. This material is melted and often extruded into the form of pellets which are then used to manufacture other products.

Monomer recycling

Many recycling challenges can be resolved by using a more elaborate monomer recycling process, in which a condensation polymer essentially undergoes the inverse of the polymerization reaction used to manufacture it. This yields the same mix of chemicals that formed the original polymer, which can be purified and used to synthesize new polymer chains of the same type. Du Pont opened a pilot plant of this type in Cape Fear, North Carolina, USA, to recycle PET by a process of methanolysis, but it closed the plant due to economic pressures.^[2]

Thermal depolymerization

Another process involves the conversion of assorted polymers into petroleum by a much less precise thermal depolymerization process. Such a process would be able to accept almost any polymer or mix of polymers, including thermoset materials such as vulcanized rubber tires and the biopolymers in feathers and other agricultural waste. Like natural petroleum, the chemicals produced can be made into fuels as well as polymers. A pilot plant of this type exists in Carthage, Missouri, USA, using turkey waste as input material. Gasification is a similar process, but is not technically recycling since polymers are not likely to become the result.

Heat compression

Yet another process that is gaining ground with startup companies (especially in Australia, United States and Japan) is heat compression.^{[citation needed]} The heat compression process takes all unsorted, cleaned plastic in all forms, from soft plastic bags to hard industrial waste, and mixes the load in tumblers (large rotating drums resembling giant clothes dryers). The most obvious benefit to this method is the fact that all plastic is recyclable, not just matching forms. However, criticism rises from the energy costs of rotating the drums, and heating the post-melt pipes.

Other processes

A process has also been developed in which many kinds of plastic can be used as a carbon source in the recycling of scrap steel.^[3]

Applications

PET

Post-consumer polyethylene terephthalate (number 1), also known as PET, is often used as the raw material for a range of products. To obtain the pure PET, the recycled items, such as plastic bottles and containers(the main use for PET), are first inspected for any non PET materials^[4]. These materials are then removed and the PET items are sorted into different color fractions, cleaned, and prepared for processing^[5]. This sorted post-consumer PET waste is crushed, chopped into flakes, pressed into bales, and offered for sale^[6].

One use for this recycled PET that has recently started to become popular is to create fabrics to be used in the clothing industry^[7]. The fabrics are created by spinning the PET flakes into thread and yarn^[8]. This is done just as easily as creating polyester from brand new PET^[9]. The recycled PET thread or yarn can be used either alone or together with other fibers to create a very wide variety of fabrics. Traditionally these fabrics were used to create strong, durable, rough, products, such as jackets, coat, shoes, bags, hats, and accessories. However, these fabrics are usually too rough on the skin and could cause irritation. Therefore, they usually are not used on any clothing that may irritate the skin, or where comfort is required^[10]. But in today’s new eco-friendly world there has been more of a demand for “green” products. As a result, many clothing companies have started looking for ways to take advantage of this new market and new innovations in the use of recycled PET fabric are beginning to develop. These innovations included different ways to process the fabric^[11], to use the fabric, or blend the fabric with other materials^[12]. Some of the fabrics that are leading the industry in these innovations include Billabong's Eco-Supreme Suede^[13], Livity's Rip-Tide III^[14], Wellman Inc's Eco-fi(formerly known as EcoSpun)^[15], and Reware's Rewoven^[16]. Some additional companies that take pride in using recycled PET in their products are Crazy Shirts^[17] and Playback^[18].

PVC

PVC- or Vinyl Recycling has historically been difficult to perfect on the industrial scale.^{[citation needed]} But within the last decade several viable methods for recycling or upcycling PVC plastic have been developed.^{[citation needed]}

HDPE

The most-often recycled plastic^{[citation needed]}, HDPE or number 2, is downcycled into plastic lumber, tables, roadside curbs, benches, truck cargo liners, trash receptacles, stationery (e.g. rulers) and other durable plastic products and is usually in demand.

Other plastics

The white plastic foam peanuts used as packing material are often accepted by shipping stores for reuse.^[19]

Successful trials in Israel have shown that plastic films recovered from mixed municipal waste streams can be recycled into useful household products such as buckets.^[20]

Similarly, agricultural plastics such as mulch film, drip tape and silage bags are being diverted from the waste stream and successfully recycled ^[21] into much larger products for industrial applications such as plastic composite railroad ties.^[22] Historically, these agricultural plastics have primarily been either landfilled or burned on-site in the fields of individual farms.^[23]

CNN reports that Dr. S. Madhu of the Kerala Highway Research Institute, India has formulated a road surface that includes recycled plastic.^{[citation needed]} Aggregate, bitumen (asphalt) with plastic that has been shredded and melted at a temperature below 220 degrees C (428 °F) to avoid pollution. This road surface is claimed to be very durable and monsoon rain resistant. The plastic is sorted by hand, which is economical in India. The test road used 60 kg of plastic for an approx. 500m long, 8m wide, two-lane road.

Financial Justification

In 2008, the price of PETE dropped from $370/ton in the US to $20 in November.^{[clarification needed][24]}. PET prices had returned to their long term averages by May of 2009.^[25]

Recycling rates

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Plastic recycling rates lag far behind those of other items, such as newspaper (about 80%) and corrugated fiberboard (about 70%).^[26] All plastic bottles were recycled at a rate of 24% in 2005.^{[clarification needed]}

The quantity of post-consumer plastics recycled has increased every year since at least 1990. In 2006 the amount of plastic bottles recycled reached a record high of 2.2 trillion pounds. The amount of PET bottles recycled in 2006 increased more than 102 million pounds compared to 2005. HDPE bottle recycling increased in 2005 to 928 million pounds.

Consumer education

United States

Low national plastic recycling rates have been due to the complexity of sorting and processing, unfavorable economics, and consumer confusion about which plastics can actually be recycled.^[27] Part of the confusion has been due to the recycling symbol that is usually on all plastic items^{[citation needed]}. This symbol is called a resin identification code. It is stamped or printed on the bottom of containers and surrounded by a triangle of arrows. (See the table in Plastic.) The intent of these arrows was to make it easier to identify plastics for recycling. The recycling symbol doesn’t necessarily mean that the item will be accepted by residential recycling programs.^[28]

United Kingdom

In the UK, the amount of post-consumer plastic being recycled is relatively low^[29], due in part to a lack of recycling facilities.

The Plastics 2020 Challenge was founded in 2009 by the plastics industry with the aim of engaging the British public in a nationwide debate about the use, reuse and disposal of plastics, hosts a series of online debates on its website framed around the waste hierarchy.

Plastic identification code

Seven groups of plastic polymers,^[30] each with specific properties, are used worldwide for packaging applications (see table below). Each group of plastic polymer can be identified by its Plastic Identification code (PIC) - usually a number or a letter abbreviation. For instance, Low-Density Polyethylene can be identified by the number 4 and/or the letters "LDPE". The PIC appears inside a three-chasing arrow recycling symbol. The symbol is used to indicate whether the plastic can be recycled into new products.

The PIC was introduced by the Society of the Plastics Industry, Inc. which provides a uniform system for the identification of different polymer types and helps recycling companies to separate different plastics for reprocessing. Manufacturers of plastic products are required to use PIC labels in some countries/regions ^[31] and can voluntarily mark their products with the PIC where there are no requirements. Consumers can identify the plastic types based on the codes usually found at the base or at the side of the plastic products, including food/chemical packaging and containers. The PIC is usually not present on packaging films, as it is not practical to collect and recycle most of this type of waste.

See also

• Reuse of water bottles
• Bisphenol_A#Identification_in_plastics, an article on "BPA", esp. relevant to types 3 & 7 plastics.

References

External links

• West, Larry. "Recyclable Plastic: Why are So Few Food Containers Made of Recyclable Plastic?". About.com. Retrieved 2009-05-04. 
• Plastic Packaging Resin Codes data from the American Chemistry Council
• ISF's Plastics Recovery Manual
• American Chemistry Council Statement on Plastic Recycling

1. ↑ http://cygnus-group.com/use-less-stuff/Paper-and-Plastic-Grocery-Bag-LCA-Summary-3-21-08.pdf
2. ↑ http://www.allbusiness.com/chemicals/chemicals-overview/9060603-1.html
3. ↑ Steel CNN, Accessed 9.11.06
4. ↑ http://www.rewarestore.com/tech_recycled_pet.html
5. ↑ http://www.eartheasy.com/wear_ecospun.htm
6. ↑ http://www.innovations-report.com/html/reports/environment_sciences/report-7183.html
7. ↑ http://www.thisisbrandx.com/2009/11/trashy-chic-recycled-clothing-from-playback.html
8. ↑ http://www.innovations-report.com/html/reports/environment_sciences/report-7183.html
9. ↑ http://www.rewarestore.com/tech_recycled_pet.html
10. ↑ http://www.sustainableisgood.com/products/2008/04/billabong.html
11. ↑ http://www.innovations-report.com/html/reports/environment_sciences/report-7183.html
12. ↑ http://www.billabongbiz.com/bethechange/environment.php?page=sustainable
13. ↑ http://www.billabongbiz.com/bethechange/environment.php?page=sustainable
14. ↑ http://www.treehugger.com/files/2008/03/rip-tide-livity.php
15. ↑ http://www.eartheasy.com/wear_ecospun.htm
16. ↑ http://www.rewarestore.com/tech_recycled_pet.html
17. ↑ http://www.gogreenstreet.com/eco-friendly-recycled-plastic-bottle-board-shorts/
18. ↑ http://www.thisisbrandx.com/2009/11/trashy-chic-recycled-clothing-from-playback.html
19. ↑ http://www.allbusiness.com/consumer-products/office-supplies-equipment/6916130-1.html
20. ↑ Plastic trial procedure Oaktech Environmental website, accessed 9.11.06
21. ↑ Agricultural plastics recycling process Agricultural plastics recycling website, accessed 07.11.08
22. ↑ Plastic Composite Railroad Tie Facts Plastic Composite Railroad Ties website, accessed 01.21.08
23. ↑ Recycling Used Agricultural Plastics James W. Garthe, Paula D. Kowal, PennState University, Agricultural and Biological Engineering
24. ↑ Page, Candace, Waste district raises recycling fees, Burlington Free Press, November 12, 2008
25. ↑ Financial Times, May 15, 2009 (article by Max Hogg)
26. ↑ The Self-Sufficiency Handbook: A Complete Guide to Greener Living by Alan Bridgewater pg. 62--Skyhorse Publishing Inc., 2007 ISBN 1602391637, 9781602391635
27. ↑ "Where can we put all those plastics?". Seattle Times. Retrieved 2007-06-02. 
28. ↑ Where can we put all those plastics? By Tom Watson June 2, 2007 Seattle Times http://seattletimes.nwsource.com/html/homegarden/2003730398_ecoconsumer02.html
29. ↑ Plastics wasteonline.org.uk, Accessed 10.18.07
30. ↑ "Safe Use Of Plastic Food Packaging And Containers". 
31. ↑ "19". Holt Chemistry (Florida edition). Holt, Rinehart, and Winston. 2006. p. 702. ISBN 0-03-039114-8. More than hlf the states in the United States have enacted laws that require plastic products to be labeled with numerical codes that identify the type of plastic used in them.