The discovery of plastics revolutionized our society by introducing an enormous and expanding range of products and have displaced many traditional materialssuch as wood, stone, horn and bone, leather, paper, metal, glass and ceramicin most of their former uses. We use plastic in an innumerable ways in our daily life such as food storage containers, water and milk bottles, packaging and carry bags, pipes, electronic items, frames, electric wiring, toys, furniture, cloths, injection syringes and other several thousands of items.
But plastic is one of the major toxic pollutants today. Plastic is a non- biodegradable substance, composed of toxic chemicals, plastic pollutes earth, air and water. Plastic causes serious damage to environment both during its production and disposal. The major chemicals that go into the making of plastic as ethylene oxide, benzene and xylenes are highly toxic and pose serious threat to living beings of all species on earth. These chemicals can cause an array of maladies ranging from birth defects to cancer, damage the nervous system and the immune system and also adversely affect the blood and the kidneys. Also many toxic gases are emitted during recycling of plastic.
More than a 100 million tones of plastic is produced world-wide each year. Disposal of plastic through recycling, burning, or land filling is a myth because it does not undergo bacterial decomposition. Once plastic is produced, the harm is done once and for all. Plastic wastes clog the drains and thus hit especially urban sewage systems. The plastic wastes being dumped into rivers, streams and seas contaminate the water, soil, marine life and also the very air we breathe. Choked drains provide excellent breeding grounds for
disease-causing mosquitoes besides causing flooding during the monsoons.
Plastics are synthetic substances produced by chemical reactions. Almost all plastics are made from carbon and petroleum, except a few experimental resins derived from corn and other organic substances.
Plastics are polymers, very long chain molecules that consist of subunits (monomers) linked together by chemical bonds. The monomers of petrochemical plastics are inorganic materials (such as styrene) and are not biodegradable.
The types of monomers and the ways that they are arranged give different chemical properties to various plastics. Plastics can be divided into two major categories:
1. Thermoset or thermosetting plastics. Once cooled and hardened, these plastics retain their shapes and cannot return to their original form.
2. Thermoplastics. Less rigid than thermosets, thermoplastics can soften upon heating and return to their original form.
To make plastics on an industrial scale the following steps are involved:
1.Raw materials and monomers are prepared: Various raw materials that make up the monomers such as Ethylene and propylene, come from crude oil, which contains the hydrocarbons. The hydrocarbon raw materials are obtained from the “cracking process” used in refining oil and natural gas
2. Carry out polymerization reactions: Various hydrocarbons obtained from cracking, are chemically processed to make hydrocarbon monomers and other carbon monomers (like styrene, vinyl chloride, acrylonitrile) used in plastics. Next, the monomers carry out polymerization reactions in large polymerization plants.
3. Process the polymers into final polymer resins: The reactions in plants produce polymer resins, which are collected and further processed. Processing can include the addition of plasticizers, dyes and flame-retardant chemicals. The final polymer resins are usually in the forms of pellets or beads.
4. Produce finished products: The polymer resins are processed into final plastic products. Generally, they are heated, molded and allowed to cool. There are several processes involved in this stage, such as Extrusion, Injection molding, Blow molding, Rotational molding, depending upon the type of product.
The first man-made plastic was created by Alexander Parkes who publicly demonstrated it at the 1862 Great International Exhibition in
After cellulose nitrate, formaldehyde was the next product to advance the technology of plastic. In 1899, Arthur Smith received British Patent 16,275, for “phenol-formaldehyde resins for use as an ebonite substitute in electrical insulation”, the first patent for processing a formaldehyde resin. However, in 1907, Leo Hendrik Baekeland improved phenol-formaldehyde reaction techniques and invented the first fully synthetic resin to become commercially successful, trade named Bakelite.
In 1926 – Vinyl or PVC – Walter Semon invented a plasticized PVC and 1927 – Cellulose Acetate was invented. In 1933 – Polyvinylidene chloride or Saran also called PVDC – accidentally discovered by Ralph Wiley, 1935 – Low-density polyethylene or LDPE by Reginald Gibson and Eric Fawcett, 1936 – Acrylic or Polymethyl Methacrylate, 1937 – Polyurethanes tradenamed Igamid for plastics materials and Perlon for fibers. by Otto Bayer and co-workers discovered and patented the chemistry of polyurethanes and in 1938 – Polystyrene made practical . In 1938 – Polytetrafluoroethylene or PTFE tradenamed Teflon by Roy Plunkett, 1939 – Nylon and Neoprene considered a replacement for silk and a synthetic rubber respectively by Wallace Hume Carothers,
1941 – Polyethylene Terephthalate or Pet by Whinfield and Dickson were invented. In 1942 – Low Density Polyethylene and Unsaturated Polyester also called PET patented by John Rex Whinfield and James Tennant Dickson. In 1951 – High-density polyethylene or HDPE tradenamed Marlex by Paul Hogan and Robert Banks, in 1951 – Polypropylene or PP by Paul Hogan and Robert Banks, in 1953 – Saran Wrap introduced by Dow Chemicals. In 1954 Styrofoam the trademarked form of polystyrene foam insulation, invented by Ray McIntire for Dow Chemicals. In 1964 – Polyimide, in 1970 – Thermoplastic Polyester this includes trademarked Dacron, Mylar, Melinex, Teijin, and Tetoron, in 1978 – Linear Low Density Polyethylene and in 1985 – Liquid Crystal Polymers were invented.
Chemicals in Plastic
The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. The backbone is that part of the chain on the main “path” linking a large number of repeat units together. To vary the properties of plastics, both the repeat unit with different molecular groups “hanging” or “pendant” from the backbone.
Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point and one or more glass transitions. Semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethane. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.
BPA (bisphenol A) is the chemical found in plastic food containers, eyeglass lenses and CDs, and researchers fear it may cause heart disease and diabetes. Some of the constituents of plastic such as
benzene and vinyl chloride are known to cause cancer. The chemical Bisphenol A, used to harden plastics in baby bottles, food containers, cling wrap, toys, CDs, sunglasses, and thousands of other products, may be harmful. Tests on animals and other research indicate that it can be toxic even at very low doses.
Past studies found that this chemical, also known as BPA, may cause a wide range of health problems, including breast and prostate cancer, infertility, diabetes, brain damage, even obesity. It is part of a class of chemicals that scientists say disrupt the hormonal system, mimicking the effects of hormones such as estrogen and testosterone.
Common plastics type are:
Polypropylene (PP) – Food containers, appliances, car fenders (bumpers).
Polystyrene (PS) – Packaging foam, food containers, disposable cups, plates, cutlery, CD boxes
High impact polystyrene (HIPS) – fridge liners, food packaging, vending cups.
Acrylonitrile butadiene styrene (ABS) – Electronic equipment cases as computer parts, drainage pipe etc
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
Poly(vinyl chloride) (PVC) – Plumbing pipes and guttering, shower curtains, window frames, flooring.
Polyurethanes (PU) – cushioning foams, thermal insulation foams, surface coatings, printing rollers.
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) – Car Interior and exterior parts