Toxicity

Due to their insolubility in water and relative chemical inertness, pure plastics generally have low toxicity in their finished state, and will pass through the digestive system with no ill effect (other than mechanical damage or obstruction). However, plastics often contain a variety of toxic additives. For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride (PVC) to make them pliable enough for use in food packaging, children's toys and teethers, tubing, shower curtains and other items. Traces of these chemicals can leach out of the plastic when it comes into contact with food. Out of these concerns, the European Union has banned the use of DEHP (di-2-ethylhexyl phthalate), the most widely used plasticizer in PVC. Some compounds leaching from polystyrene food containers have been found to interfere with hormone functions and are suspected human carcinogens.^[10]

Moreover, while the finished plastic may be non-toxic, the monomers used in its manufacture may be toxic; and small amounts of those chemical may remain trapped in the product. The World Health Organization's International Agency for Research on Cancer (IARC) has recognized the chemical used to make PVC, vinyl chloride, as a known human carcinogen.^[10] Some polymers may also decompose into the monomers or other toxic substances when heated.

The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food.^[10] Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring.^[11] A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease.^[12]

As of January 2010, the LA Times newspaper reports that the United States FDA is spending $30 million to investigate suspicious indications of BPA being linked to cancer. ^[13]

Bis(2-ethylhexyl) adipate, present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present in new car smell.

The European Union has a permanent ban on on the use of phthalates in toys. In 2009, the United States government banned certain types of phthalates commonly used in plastic.^[14]

Environmental issues

Further information: Marine debris

Plastics are durable and degrade very slowly; the molecular bonds that make plastic so durable make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of plastic has been discarded and may persist for hundreds or even thousands of years.^[15] In some cases, burning plastic can release toxic fumes. Burning the plastic polyvinyl chloride (PVC) may create dioxin.^[16] Also, the manufacturing of plastics often creates large quantities of chemical pollutants.

Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in life-critical fire suppression systems; see Montreal Protocol), the production of polystyrene contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process.

By 1995, plastic recycling programs were common in the United States and elsewhere. Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, though 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.

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 cyclic arrows, which encloses a number giving the plastic type:

Plastics type marks: the resin identification code

1. PET (PETE), polyethylene terephthalate, is commonly found in 2-liter soft drink bottles, water bottles, cooking oil bottles, peanut butter jars.
2. HDPE, high-density polyethylene, is commonly found in detergent bottles and milk jugs.
3. PVC, polyvinyl chloride, is commonly found in plastic pipes, outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.
4. LDPE, low-density polyethylene, is commonly found in dry-cleaning bags, produce bags, trash can liners, and food storage containers.
5. PP, polypropylene, is commonly found in bottle caps, drinking straws, yogurt containers.
6. PS, polystyrene, is commonly found in "packing peanuts", cups, plastic tableware, meat trays, take-away food clamshell containers.
7. There are also other types of plastics commonly found in certain kinds of food containers, Tupperware, and Nalgene bottles.

Unfortunately, recycling of plastics has proven to be a difficult process. The biggest problem is that it is difficult to automate 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. 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.

Biodegradable (compostable) plastics

Main article: Biodegradable plastic

Research has been done on biodegradable plastics that break down with exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present.^[17] The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications.

Bioplastics

Main article: Bioplastic

Some plastics can be obtained from biomass, including:

• from pea starch film with trigger biodegradation properties for agricultural applications (TRIGGER).^[18]
• from biopetroleum.^[19]

Oxo-biodegradable

Main article: Oxo Biodegradable

Oxo-biodegradable (OBD) plastic is polyolefin plastic to which has been added very small (catalytic) amounts of metal salts. As long as the plastic has access to oxygen (as in a littered state), these additives catalyze the natural degradation process to speed it up so that the OBD plastic will degrade when subject to environmental conditions. Once degraded to a small enough particle they can interact with biological processes to produce to water, carbon dioxide and biomass. The process is shortened from hundreds of years to months for degradation and thereafter biodegradation depends on the micro-organisms in the environment. Typically this process is not fast enough to meet ASTM D6400 standards for definition as compostable plastics.

Price, environment, and the future

The biggest threat to the conventional plastics industry is most likely to be environmental concerns, including the release of toxic pollutants, greenhouse gas, litter, biodegradable and non-biodegradable landfill impact as a result of the production and disposal of petroleum and petroleum-based plastics. Of particular concern has been the recent accumulation of enormous quantities of plastic trash in ocean gyres.

For decades one of the great appeals of plastics has been their low price. Yet in recent years the cost of plastics has been rising dramatically. A major cause is the sharply rising cost of petroleum, the raw material that is chemically altered to form commercial plastics.

With some observers suggesting that future oil reserves are uncertain, the price of petroleum may increase further. Therefore, alternatives are being sought. Oil shale and tar oil are alternatives for plastic production but are expensive. Scientists are seeking cheaper and better alternatives to petroleum-based plastics, and many candidates are in laboratories all over the world. One promising alternative may be fructose.^[20]

Common plastics and uses

A chair made with a polypropylene seat

Polypropylene (PP)

Food containers, appliances, car fenders (bumpers), plastic pressure pipe systems.

Polystyrene (PS)

Packaging foam, food containers, disposable cups, plates, cutlery, CD and cassette boxes.

High impact polystyrene (HIPS)

Fridge liners, food packaging, vending cups.

Acrylonitrile butadiene styrene (ABS)

Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.

Polyethylene terephthalate (PET)

Carbonated drinks bottles, jars, plastic film, microwavable packaging.

Polyester (PES)

Fibers, textiles.

Polyamides (PA) (Nylons)

Fibers, toothbrush bristles, fishing line, under-the-hood car engine mouldings.

Polyvinyl chloride (PVC)

Plumbing pipes and guttering, shower curtains, window frames, flooring.

Polyurethanes (PU)

Cushioning foams, thermal insulation foams, surface coatings, printing rollers. (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).

Polycarbonate (PC)

Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.

Polyvinylidene chloride (PVDC) (Saran)

Food packaging.

Polyethylene (PE)

Wide range of inexpensive uses including supermarket bags, plastic bottles.

Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS)

A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.

Special purpose plastics

Polymethyl methacrylate (PMMA)

Contact lenses, glazing (best known in this form by its various trade names around the world; e.g., Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for vehicles.

Polytetrafluoroethylene (PTFE)

Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly known as Teflon.

Polyetheretherketone (PEEK) (Polyetherketone)

Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace mouldings. One of the most expensive commercial polymers.

Polyetherimide (PEI) (Ultem)

A high temperature, chemically stable polymer that does not crystallize.

Phenolics (PF) or (phenol formaldehydes)

High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be moulded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam (e.g., Oasis). Problems include the probability of mouldings naturally being dark colours (red, green, brown), and as thermoset difficult to recycle.

Urea-formaldehyde (UF)

One of the aminoplasts and used as a multi-colorable alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings.

Melamine formaldehyde (MF)

One of the aminoplasts, and used as a multi-colorable alternative to phenolics, for instance in mouldings (e.g., break-resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g., Formica).

Polylactic acid (PLA)

A biodegradable, thermoplastic found converted into a variety of aliphatic polyesters derived from lactic acid which in turn can be made by fermentation of various agricultural products such as corn starch, once made from dairy products.

Plastarch material

Biodegradable and heat resistant, thermoplastic composed of modified corn starch.