What Is Plastic?


What Is Plastic?

It is the name given to the artificial materials which can easily be formed by die casting, rolling or any other technique. The origin of the word plastic is based upon the Greek word ?plastikos? which means ?forming?. Rubbers and similar natural materials are sometimes defined under this group; however they are excluded in modern definition. Differentiating resins and plastics is difficult. In the past, the term resin was used for products that could replace natural materials in coating substances, while the term plastic was used for materials that are processed through a casting process during production.

The most important characteristics of many of the plastics is that they soften without melting when they are heated and that they can be shaped easily through mechanical means in this state and hardened when they are cooled. This characteristic comes from their molecular structures. Plastics are formed of multi-polymere molecules; polymers contain long molecule chains which separates when heated and merge back when cooled. These polymere chains are held together by weak forces such as London, Van der Waals and similar forces, or stronger forces such as hydrogen bounds and dipole-dipole interactions. When the material is heated, these forces are weakened and the interpenetrated polymere chains are separated. When the material is cooled, these chains get back together and are hardened. All plastics are obtained through a polymerization process. Plastic materials are classified under two groups: thermosets and thermoplastics. Thermoset resins do not dissolve and melt when heated. Phenolic resins, furan resins, aminoplasts, alkyds and unsaturated acidic polyesters, epoxy resins, polyurathanes and silicons are thermoset resins. Thermoplastic resins, on the other hand, can be melted and hardened back several times, in contrary with thermosets. Cellulose derivatives, addition polymers (such as polyethylene, polypropylene, vinyl acrylics, etc.) and condensation polymers (such as rubbers, polyethylene terephthalate, polycarbonates, etc.) are thermoplastic resins. While plastics are produced from natural resources such as coal and cellulose, the most important raw material for plastics is oil. Plastics can be shaped by various methods. Extrusion method in which pulverous plastic is melted, compressed and extruded inside a hot or cold chamber is the most known plastic processing technique. On the other hand, rolling, thermosetting with hydrolic presses, casting via spraying, casting via centrifuge, thermoplastic forming, vacuum casting, slabbing under pressure, moulding are the other methods for shaping plastics. Plastic materials can be shaped later as well by mechanical means, lazers, ultrasonic welding, etc. Being cheap, light and stable materials which can be easily formed, plastics have taken the place of metals in many fields. There are many plastic products used domestically or industrially.

Brief History of Plastics

The first semi-synthetic plastic was discovered by accident. In 1848, a Swedish chemist Christian Friedrich Schoenbein (1799-1869) was boiling a mixture of sulphuric acid and nitric acid in the laboratory. The mixture was poured to the ground and Schoenbein wiped the floor with his cotton-based apron. He washed it with water and hangs over the heat stove. The apron suddenly burned out once it was dry. Nitrocellulose was discovered.

The first plastic produced was "Parkesin", which was developed by British chemist and inventer Alexander Parkes in 1892, by mixing nitrocellulose with vegetable oils and a little bit of camphor. American typographer John Wesley Hyatt was granted the patent for celluloid after he discovered the plasticizing effect of camphor. Later on, many different types of plastics such as polyethylene, polyvinyl chlorür (PVC), polyurethane, etc. were developed as a result of developments in molecular physics and macro molecules.


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