Los plasticos
Enviado por Manolocamionero • 9 de Octubre de 2015 • Trabajos • 1.641 Palabras (7 Páginas) • 103 Visitas
PLASTICS UNIT
Plastics are the most common material in commercial production. Plastics are produced by the process polymerization, which occurs when monomers (chemical substances consisting of a single molecule) join together to form long chains of molecules called polymers (chemical made of many repeating units which can be a three dimensional, two-dimensional or one-dimensional network. Each repeating unit is the “-mer” or basic unit with “poly-mer. Polymers abound in nature as in DNA and RNA. Spider silk, hair, and horn are examples of protein polymers. Rubber tree latex and cellulose are used as raw material to make manufactured polymeric rubber and plastics…)
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Vulcanization is a chemical process in which the physical properties of natural or synthetic rubber are improved; resultant rubber has higher tensile strength and resistance to swelling and abrasion, and is elastic over a range of temperatures. In its simplest form, vulcanization is brought about by heating rubber with sulfur. This process was discovered in 1839 by the inventor Charles Goodyear. [pic 2] |
Plastic can be classified in either natural or synthetic:
Natural plastics, or bioplastics, are environmentally safe alternatives to conventional plastic. They are made from plant materials as vegetable fats or starches because it is composed of polymers like petroleum, the base of conventional plastic. Examples of natural plastics include amber (fossilized tree resin) and latex (form of rubber)
Synthetic plastics are the ones made by human beings and do not occur in nature. Most of the modern plastics are synthetic. The main source of synthetic plastics is crude oil, but coal and natural gas used for its production. These gases are broken down into monomers. The first synthetic manufactured plastic was Bakelite, created in 1909 for telephone casing and electrical components. The first manufactured polymeric fiber was Rayon, from cellulose, in 1910. Nylon was invented in 1935 while pursuing a synthetic spider silk.
The different types of plastics include:
Natural plastics: Plastics are organic. The raw materials used for plastic production are natural products which include cellulose, coal, natural gas, salt, crude oil... Plastics are able to balance nowadays needs with environmental concerns. Natural sources of plastics include plants (cellulose), trees (latex, amber and resin), animals (horn and milk for glue) and insects (shellac for polish)
Thermoplastics: Thermoplastics are a kind of plastics that can be heated and given shape many times without breaking the material. Some are rigid and others are extremely flexible. The molecules of thermoplastics are in long chains with very few entanglements. When heat is applied to the molecules, they move apart, increasing the distance between them, causing them to become untangled. Then, their shape can vary. Polyamide or nylon is a material used for many different things such as clothing, cupboards and gear wheels. Polypropylene is a plastic used in medical equipment, for making strings, and for making kitchen materials. Polystyrene is a type of thermoplastic used for making toys, model kits, plastic boxes and containers. Cycle of thermoplastics:[pic 3]
Thermosetting: Thermosetting or thermostable plastics are the ones which can be heated and moulded just once without breaking the material. If you heat them twice, they cannot soften as polymer chains are interlinked. Separate polymers are joined in order to form a huge polymer. The molecules of this type of plastic form rigid molecular structure. They are good electrical insulators. Epoxy resin is a type of thermosetting plastic used for adhesives, bonding and other materials. Melamine formaldehyde is used for electrical insulation, tableware… Urea formaldehyde is used for control knobs and handles, adhesives and electrical fittings. Cycle of thermosetting plastics:
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Elastomers: During processing it becomes insoluble and infusible in a permanent way. Latex, nitrile, silicone… are typical thermoset elastomers.
The differences between thermoplastics, thermosetting and elastomer:
Elastomer | Thermosetting | Thermoplastic |
Chain has a high level of dimensional stability but is still elastically malleable. Are not meltable. [pic 5] | Can no longer be shaped after hardening. Cannot be melted. [pic 6] (structure) | Molecular chains are not linked (the others are) Thermoformable (can be melted, not as the others) [pic 7] |
RECYCLING:
The process of extracting and reusing substances found in waste for avoiding too much pollution and loss of energy when building these waste products again. Every plastic container has a recycling symbol; a number from 1 to 7 inside of a triangle. This number shows information about the chemicals used in the plastic. Types include:
- PET or PETE (polyethylene terephthalate)
This plastic is usually clear and used to make bottles. Some think about it as safe, but this plastic is known to allow bacteria to accumulate. This plastic is recycled into tote bags, furniture, carpet…
2. HDPE (High Density Polyethylene)
This kind of plastic tends to be opaque and picked up by recycling programs. This plastic is one of the 3 plastics out of seven considered safe. It’s found in milk jugs, juice bottles, shampoo bottles, detergent bottles…. This plastic is recycled into pens, recycling containers, picnic tables…
V or PVC (Vinyl)
This plastic is used to make food wrap, plumbing pipes, and detergent. Although it appears to be safe, it can cause several problems (liver) It is found in shampoo bottles, clear food packaging, medical equipment… This plastic is recycled into paneling, flooring, speed bumps…
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