Plastic

Plastic is a material consisting of any of a wide range of synthetic or semi-synthetic organics that are malleable and can be molded into solid objects of diverse shapes. Plastics are typically organic polymers of high molecular mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural. Plasticity is the general property of all materials that are able to irreversibly deform without breaking, but this occurs to such a degree with this class of moldable polymers that their name is an emphasis on this ability.

Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood, stone, horn and bone, leather, paper, metal, glass, and ceramic, in most of their former uses. In developed countries, about a third of plastic is used in packaging and another third in buildings such as piping used in plumbing or vinyl siding. Other uses include automobiles (up to 20% plastic), furniture, and toys. In the developing world, the ratios may be different - for example, reportedly 42% of India's consumption is used in packaging. Plastics have many uses in the medical field as well, to include polymer implants, however the field of plastic surgery is not named for use of plastic material, but rather the more generic meaning of the word plasticity in regards to the reshaping of flesh.

The world's first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term 'plastics'. Many chemists contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger who has been called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics". The success and dominance of plastics starting in the early 20th century led to environmental concerns regarding its slow decomposition rate after being discarded as trash due to its composition of very large molecules. Toward the end of the century, one approach to this problem was met with wide efforts toward recycling.

Environmental effects

See also: Plastic pollution, Marine debris and Great Pacific Garbage Patch

Most plastics are durable and degrade very slowly; the very chemical bonds that make them so durable tend to make them resistant to most natural processes of degradation. However, microbial species and communities capable of degrading plastics are discovered from time to time, and some show promise as being useful for bioremediating certain classes of plastic waste.

• In 1975 a team of Japanese scientists studying ponds containing waste water from a nylon factory, discovered a strain of Flavobacterium that digested certain byproducts of nylon 6 manufacture, such as the linear dimer of 6-aminohexanoate. Nylon 4 or polybutyrolactam can be degraded by the (ND-10 and ND-11) strands of Pseudomonas sp. found in sludge. This produced γ-aminobutyric acid (GABA) as a byproduct.
• Several species of soil fungi can consume polyurethane. This includes two species of the Ecuadorian fungus Pestalotiopsis that can consume polyurethane aerobically and also in anaerobic conditions such as those at the bottom of landfills.
• Methanogenic consortia degrade styrene, using it as a carbon source. Pseudomonas putida can convert styrene oil into various biodegradable polyhydroxyalkanoates.
• Microbial communities isolated from soil samples mixed with starch have been shown to capable of degrading polypropylene.
• The fungus Aspergillus fumigatus effectively degrades plasticized PVC. Phanerochaete chrysosporium was grown on PVC in a mineral salt agar. Phanerochaete chrysosporium, Lentinus tigrinus, Aspergillus niger, and Aspergillus sydowii can also effectively degrade PVC. Phanerochaete chrysosporium was grown on PVC in a mineral salt agar.
• Acinetobacter has been found to partially degrade low molecular weight polyethylene oligomers. When used in combination, Pseudomonas fluorescens and Sphingomonas can degrade over 40% of the weight of plastic bags in less than three months. The thermophilic bacterium Brevibacillus borstelensis (strain 707) was isolated from a soil sample and found capable of using low-density polyethylene as a sole carbon source when incubated at 50 degrees Celsius. Pre-exposure of the plastic to ultraviolet radiation broke chemical bonds and aided biodegradation; the longer the period of UV exposure, the greater the promotion of the degradation.
• Less desirably, hazardous molds have been found aboard space stations, molds that degrade rubber into a digestible form.
• Several species of yeasts, bacteria, algae and lichens have been found growing on synthetic polymer artifacts in museums and at archaeological sites.
• In the plastic-polluted waters of the Sargasso Sea, bacteria have been found that consume various types of plastic; however it is unknown to what extent these bacteria effectively clean up poisons rather than simply releasing them into the marine microbial ecosystem.
• Plastic eating microbes also have been found in landfills.
• Nocardia can degrade PET with an esterase enzyme.
• The fungi Geotrichum candidum, found in Belize, has been found to consume the polycarbonate plastic found in CD's.
• Phenol-formaldehyde, commonly known as bakelite, is degraded by the white rot fungus Phanerochaete chrysosporium
• The futuro house was made of fibreglass-reinforced polyesters, polyester-polyurethane, and poly(methylmethacrylate.) One such house was found to be harmfully degraded by Cyanobacteria and Archaea.

Since the 1950s, one billion tons of plastic have been discarded and some of that material might persist for centuries or much longer, as is demonstrated by the persistence of natural materials such as amber.

Serious environmental threats from plastic have been suggested in the light of the increasing presence of microplastics in the marine food chain along with many highly toxic chemical pollutants that accumulate in plastics. They also accumulate in larger fragmented pieces of plastic called nurdles. In the 1960s the latter were observed in the guts of seabirds, and since then have been found in increasing concentration. In 2009, it was estimated that 10% of modern waste was plastics, although estimates vary according to region. Meanwhile, 50-80% of debris in marine areas is plastic.

Before the ban on the use of CFCs in extrusion of polystyrene (and in general use, except in life-critical fire suppression systems; see Montreal Protocol), the production of polystyrene contributed to the depletion of the ozone layer, but current extrusion processes use non-CFCs.

Climate change

The effect of plastics on global warming is mixed. Plastics are generally made from petroleum. If the plastic is incinerated, it increases carbon emissions; if it is placed in a landfill, it becomes a carbon sink although biodegradable plastics have caused methane emissions. Due to the lightness of plastic versus glass or metal, plastic may reduce energy consumption. For example, packaging beverages in PET plastic rather than glass or metal is estimated to save 52% in transportation energy.

Production of plastics

Production of plastics from crude oil requires 62 to 108 MJ of energy per kilogram (taking into account the average efficiency of US utility stations of 35%). Producing silicon and semiconductors for modern electronic equipment is even more energy consuming: 230 to 235 MJ per 1 kilogram of Si, and about 3,000 MJ per kilogram of semiconductors. This is much higher, compared to many other materials, e.g. production of iron from iron ore requires 20-25 MJ of energy, glass (from sand, etc.) - 18-35 MJ, steel (from Fe) - 20-50 MJ, paper (from timber) - 25-50 MJ per kilogram.

Incineration of plastics

Controlled high-temperature incineration, above 850C for two seconds, performed with selective additional heating, breaks down toxic dioxins and furans from burning plastic, and is widely used in municipal solid waste incineration. Municipal solid waste incinerators also normally include flue gas treatments to reduce pollutants further. This is needed because uncontrolled incineration of plastic produces polychlorinated dibenzo-p-dioxins, a carcinogen (cancer causing chemical). The problem occurs as the heat content of the waste stream varies. Open-air burning of plastic occurs at lower temperatures, and normally releases such toxic fumes.

Pyrolytic disposal

Plastics can be pyrolyzed into hydrocarbon fuels, since plastics have H and C. One kilogram of waste plastic produces roughly a liter of hydrocarbon.

Recycling

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, although the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken back down to a feedstock state.

The greatest challenge to the recycling of plastics is the difficulty of automating the sorting of plastic wastes, making it labor-intensive. Typically, workers sort the plastic by looking at the resin identification code, although common containers like soda bottles can be sorted from memory. Typically, the caps for PETE bottles are made from a different kind of plastic which is not recyclable, which presents additional problems to the automated sorting process. Other recyclable materials such as metals are easier to process mechanically. However, new processes of mechanical sorting are being developed to increase capacity and efficiency of plastic recycling.

While containers are usually made from a single type and color of plastic, making them relatively easy to be sorted, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types and colors of plastics. In such cases, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field of active disassembly, which may result in more consumer product components being re-used or recycled. Recycling certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.

A first success in recycling of plastics is Vinyloop, a recycling process and an approach of the industry to separate PVC from other materials through a process of dissolution, filtration and separation of contaminations. A solvent is used in a closed loop to elute PVC from the waste. This makes it possible to recycle composite structure PVC waste which normally is being incinerated or put in a landfill. Vinyloop-based recycled PVC's primary energy demand is 46 percent lower than conventional produced PVC. The global warming potential is 39 percent lower. This is why the use of recycled material leads to a significant better ecological footprint. This process was used after the Olympic Games in London 2012. Parts of temporary Buildings like the Water Polo Arena or the Royal Artillery Barracks were recycled. This way, the PVC Policy could be fulfilled which says that no PVC waste should be left after the games.

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows", which encloses a number giving the plastic type:

1-PETE 2–HDPE 3-PVC 4-LDPE 5-PP 6-PS 7-Other

Plastics type marks: the resin identification code

1. PET (PETE), polyethylene terephthalate
2. HDPE, high-density polyethylene
3. PVC, polyvinyl chloride
4. LDPE, low-density polyethylene,
5. PP, polypropylene
6. PS, polystyrene
7. Other types of plastics (see list, below)

recycling one ton of plastic can save 5,774 Kwh of energy, 16.3 barrels of oil, 98,000,000 Btu's of energy, and 30 cubic yards of landfill space, 48,000 gallons of  H₂O, 3/2 tons of CO₂ a year, 245/594 tons of AlO₂, 2,887/1,600,000 tons of Au, 2,887/25,000 tons of S, gain almost 65/8 tons of O per year

See also

• Conductive polymer
• Corn construction
• Molding (process)
  • Flexible mold
  • Injection molding
• Films
• Light activated resin
• Nurdle
• Organic light emitting diode
• Plastics engineering
• Plastics extrusion
• Plastic film
• Plastic recycling
• Plasticulture
• Progressive bag alliance
• Roll-to-roll processing
• Self-healing plastic
• Thermoforming
• Timeline of materials technology

References

• Substantial parts of this text originated from An Introduction To Plastics v1.0 / 1 March 2001 / greg goebel / public domain.

External links

• J. Harry Dubois Collection on the History of Plastics, ca. 1900–1975 Archives Center, National Museum of American History, Smithsonian Institution.
• Material Properties of Plastics – Mechanical, Thermal & Electrical Properties
• List of over 600 plastics
• Plastics Historical Society
• History of plastics, Society of the Plastics Industry
• What Are Plastics Made Of? January 1943 Popular Science
• "A brief history of plastics, natural and synthetic", from BBC Magazine
• Scientists have announced a new rock type: plastiglomerate