Plastics derive from organic materials. They can be moulded into any required shape and consistency. This characteristic allows plastics to be implemented into a great variety of products.
Most plastics are derived from organic materials, that is, substances made from things that have lived, including oil, cotton, sugar cane, coal, corn and many others. There are however exceptions such as silicone which is derived from sand.
At the point of processing plastics consist of granules, pre-formed tablets, powders, syrups or pastes.
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Plastics are classified as:
- Natural, a material that can be moulded in its natural form. Examples are amber, gutta percha, horn, rubber, and tortoiseshell.
- Semi-synthetic, that means, made of a chemically altered natural material. Examples are casein, cellulosic plastics and rubber.
- Synthetic, that is entirely laboratory made, as for example is the case with phenol formaldehyde and the many poly-plastics.
Plastics are based on polymers. That is a material made up of many smaller base units. The simplest plastic is polythene consisting of base units of carbon atoms with two hydrogen atoms to each carbon.
The base unit is referred to as a monomer. Many monomer units linked together create a polymer, through a chemical process known as polymerization. Polymerization can be demonstrated by hooking together hundreds of paper clips (base units) to form chains.
Chains in different configurations make plastics with different properties.
Plastics are divided into two distinct groups:
- thermosets, plastics that on being heated and moulded set permanently, and thus cannot be re-melted and re-formed.
- thermoplastics, plastics that can be re-melted after moulding again and again, and thus can be recycled by melting and reforming.
They owe their name to their most important property, the ability to be shaped to almost any form to produce articles of practical value.
Plastics can be stiff and hard or flexible and soft. Because of their light weight, low cost, and desirable properties, their use has rapidly increased and they have replaced other materials such as metals and glass. They are used in millions of items, including cars, bullet-proof vests, toys, hospital equipment, and food containers.
More than a hundred billion pounds of plastic were produced in 2000. Their increased use has resulted in concern with:
- the consumption of natural resources such as oil;
- the toxicity associated with their manufacture and use;
- the environmental impact arising from discarded plastics.
In many plastic products, the polymer is only one constituent. In order to arrive at a set of properties appropriate to the product, the polymer is almost always combined with other ingredients, or additives, which are mixed in during processing and fabrication. Among these additives are:
- Plasticizers: Plasticizers are used to change the Glass Transition Temperature of a polymer. The plasticizer may also change the flammability, odour, biodegradability, and cost of the finished product.
- Colorants: The ease with which colour is incorporated throughout a molded article is an advantage of plastics over metals and ceramics, which depend on coatings for colour. Organic compounds can be used to add colour either as pigments (insoluble) or as dyes (soluble).
- Reinforcements: Reinforcements are used to enhance the mechanical properties of a plastic. Finely divided, can be incorporated as particulate fillers. Incorporating large amounts of particulate filler during the making of plastics can increase their stiffness.
- Stabilizers: In order for a plastic to have a long and useful life in any application, the properties of that plastic should change as little as possible with time. they are added, usually in small quantities, to counter the effects of aging.
Because all carbon-based polymers are subject to oxidation, the most common stabilizers are antioxidants. Other stabilizers are designed specifically to reduce degradation by sunlight, ozone, and biological agents.
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Industrial practices in plastic manufacture can lead to polluting effluents and the use of toxic intermediates, the exposure to which can be hazardous. Better industrial practices have led to minimizing exposure of plant workers to harmful fumes. Much progress has been made in developing “green processes” that avoid the use of detrimental substances.
In addition, efforts are ongoing to employ “friendly” processes involving enzyme-catalyzed low-temperature methods akin to biological reactions to replace more polluting high-temperature processes involving operations like distillation.
Spillage of plastic pellets that find their way into sewage systems, and eventually to the sea, has hurt wildlife that may mistake the pellets for food. Better “housekeeping” of plastic molding facilities is being enforced in an attempt to address this problem.
Plastics may also result in problems resulting from their improper use, and there is need of better education concerning limitations of use, for example, precautions that should be taken with items such as frying pan coatings and microwavable containers.
When exposed to high temperatures, some plastics decompose or oxidize and produce low molecular weight products that may be toxic.
Reduced Use and Recycling
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The use of plastics can be reduced through a better choice of container sizes and through the distribution of liquid products in more concentrated form.
Recycling of plastics is desirable because it avoids their accumulation in landfills. While plastics constitute only about 8 percent by weight or 20 percent by volume of municipal solid waste, their low density and slowness to decompose makes them a visible pollutant of public concern.
Labeling plastic items with symbols has been employed, which enables consumers to identify them easily for placement in separate containers for curbside pickup. However, success depends on how conscientious consumers are in employing such standards and the ability of collectors to keep various types of plastic separate.
To separate plastics, it is first necessary to identify the different types as indicated in the table. One must also distinguish between thermoplastics and thermosets.
The capacity to recycle bottles appreciably exceeds their supply by about 40 percent, so local governments and environmental groups need to encourage greater participation in this practice among consumers.
Increasing amounts of plastic components appear in automobiles, and their recovery from junked cars is a possibility. Its success depends on the ability of a prospective “junker” to identify and separate the plastic items.
The effort continues to use fewer different kinds of plastics and to adopt designs that allow for easier recycling bot still retain desirable properties.
There are, however, some worthwhile products that can be produced from mixed plastic, but the market for such a product is limited, so efforts to obtain separated plastics are preferred.
Discarded plastics are hard to eliminate from the environment because they do not degrade and have been designed to last a long time. It is possible to design polymers containing monomer species that may be attacked by chemical, biological, or photochemical action so that degradation by such means will occur over a predetermined period of time.
A problem with the degradation of plastics is that it is probably undesirable in landfills because of the leachants produced that may contaminate water supplies. It is better in these instances to ship the plastics to composting facilities. This requires the separation of degradable plastics from other materials and the availability of such facilities.
Degradable polymers may have limited use in the reduction of litter and production of flushable plastics, but it seems unlikely that the use of such materials will be a viable means of disposal for large amounts of plastic products. Degradation leads to the loss of most of the potential energy content of plastics that might be recovered by trash-to-energy procedures.
Trash to Energy
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A method of plastic disposal with more positive environmental implications is burning and recovering the energy for power generation or heating.
Plastics contain much of the energy potential of the petroleum from which they are made, and they, in a sense, are just borrowing this energy that may be recovered when the plastic is burned. Environmentalists and the public have objected to this procedure, leading to legislative restrictions.
However, it is possible to construct a “high-tech” incinerator designed to operate at appropriate temperatures and with sufficient air supply that these problems are minimized. Remaining toxic substances in fumes may be removed by scrubbing.
Toxic ash, for the most part, does not arise from the polymer components of the feedstock, but rather from other materials mixed with the polymers as well as from fillers, catalyst content, and pigments associated with the polymers. Proper design of the polymers and crude separation of the incinerator feedstock can reduce this problem.
Also, it’s possible to insolublize the ash by converting it into a cementlike material that will not readily dissolve.
Facilities for converting trash to energy in an environmentally acceptable way are expensive and at present not cost-effective when considering short-range funding. However, in the long run, they are environmentally desirable and reduce the need for alternative means for plastic waste disposal. It’s imperative that legislators and taxpayers soon adopt this long-range perspective.
5 Cool Things You Never Knew About Plastic Materials
1) The roots of plastic materials actually date back to the 1600s, when synthetic materials were made from bio-derived items such as eggs and blood protein. The first man-made plastic came over 200 years later, when Alexander Parkes developed parkesine, a material made from cellulose and treated with nitric acid. The first fully synthetic plastic, bakelite, was developed in 1907 New York. Scientists have developed a wide array of plastics with many special properties in only 100 years.
2) A species of fungus has been discovered in the Amazon which feeds on plastic and can do so without oxygen. While this might not seem like a big deal, researchers are currently studying the fungus – and plastic – to see if advances can be made in bio-remediation technology.
3) It’s estimated that energy saved from recycling one plastic bottle is enough to power a 100 watt light bulb for an hour. According to the Environmental Protection Agency, recycling one ton of plastic is good enough to conserve 3.8 barrels of crude oil.
4) Plastics play an increasingly important role in aviation and aerospace. Aerospace companies use plastic materials to make lighter planes. Some plastics, like PEEK, do well in the air because they are chemical resistant, lightweight, and relatively strong.
5) Plastic has played a central role in the development of the medical industry over the past 60 years. Swiss researchers recently developed a polymer that can be ingested in pill form and deliver dosage to the appropriate parts of the body that need treating. Plastics have also had a huge impact on the development of high quality prosthetics. 3D printing is on the verge of making custom prosthetics cheaper than ever before.
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