Polymers are macromolecular compounds made out of large number of base units. The starting units that participate in the synthesis of macromolecules are so called monomers. Monomers are linked all together by covalent bonds.
Synthetic polymers are obtained with chemical process called polymerization.
Typical synthetic polymer is polyethylene, which is obtained as a synthesis of the monomer ethylene (CH2 = CH2). Polyethylene formula can be written in the form (- CH 2 - CH 2 -) n where the number n is the degree of polymerization and represents the number of basic monomers which are bonded in the polyethylene macromolecule.
According to the physical characteristics, polymers are divided into elastomers, fibers and plastics.
Plastics structure is partially crystalline, and intermolecular forces are medium strength.
Based on physical features they structure is in between fibers and elastomers. Plastics are materials that are mainly composed out of organic macromolecular substances, with little or no additives at all. These characteristics very much dependent on pressure and temperature. The features also depend on processing which is done in a certain temperature and pressure. If processing is conducted at different temperature physical features would be also changed.
Beside polyethylene, standard polymers also include polypropylene, polyvinyl chloride, polystyrene.
Polyethylene (PE) is a macromolecular product that is obtained by polymerization of ethylene.
PE is one of the most widely used kinds of plastic.
It was discovered by chance in 1933, when chemists Eric Fawcett and Reginald Gibson in Norwich, England, in the chemical industry, Imperial (Imperial Chemistry Industries), made a white, waxy material "mother of plastic", which was eventually, because of it’s possibilities, processed and improved.
Production began in 1939. At that time polyethylene was used in military purposes, until the middle of the last century, when plastic entered into everyday life, along with global economic boom.
Polyethylene can be grouped according to the density and molecule divarication:
• High Density Polyethylene (HDPE) HDPE has a density of higher or equal than 0.941 g / cm3. HDPE is used in packaging production, like bottles for food, pharmaceutical and chemical products, crates, coverlids, water and gas pipes, shopping bags and many other consumer goods.
• Low Density Polyethylene (LDPE) LDPE has a density of 0910-0925 g / cm3. LDPE is used in the production agriculture films, in construction, greenhouses, thermo-shrinkable films, bags, water pipes, wire protectors (coats) and cables.
• Linear low density polyethylene (LLDPE) LLDPE has a density of 0915-0925 g / cm3. LLDPE has higher tensile strength as well as large impact resistance of any kind. LLDPE is used in the production of blown and cast film.
Polypropylene (PP) is a macromolecular product of propylene polymerization. It is formed as white powder or granules, and it is a hard thermoplastic polymer.
History of polypropylene began in 1954, when German and Italian chemists Karl Rehn and Giulio Natta, made the first polymerization.
Commercialization began three years later. Polypropylene represents the most versatile polymer. It is used for the production of strength, flexible, light weight and resistance to heat products. Also polypropylene can be used for fibers and in the industrial and agricultural sector.
It is used for manufacturing products like:
• Plastic parts - from toys to car industry parts
• Floor coverings - all kinds of carpets ...
• Packaging - vessels of various types, containers, bags ...
• Office Supplies
• Household appliances - majority is made out of polypropylene
• Laboratory equipment
There are three main types of polypropylene. Usage depends on features and costs:
- Homopolymer PP – indented for general use, has a wide range of usage.
- Block Copolymer PP - containing 5 - 15% of ethylene. With improved resistance to impact at temperatures below - 20°C. Their resistance can be further increased by the addition of various types of additives, usually - elastomers.
- Random Copolymer PP - containing monomer units without the typical arrangement along the polypropylene chain molecules. Such polymers typically contain 1-7% ethylene, and they are used in areas which requires a lower melting point, greater flexibility and increased transparency.
The annual global consumption of polypropylene is estimated at about 45 million tones, worth about 45 billion USD.
Polyvinyl chloride (PVC)
Polyvinyl chloride also known as PVC is a thermoplastic material derived from common salt and fossil fuels.
After polyethylene, PVC is the most important plastics. It was first discovered by Henri Victor Regnault in 1835, and after him one more time Eugen Baumann in 1872. Both times the polymer appeared as a white solid substance in the bottle vinyl chloride which are left in the sunlight.
There were a few attempts of PVC commercialization, however, the material was difficult to process. Scientists Valo Semon’s experiments have led to the creation of plasticization methods, by mixing PVC with various additives. The result was a material, which was easy to handle, and commercial use was wide.
PVC is mostly produced with method called the suspension polymerization process.
The polymerization is carried out at a low pressure of below 1 MPa, and temperature of 30 to 80 °C in the presence of an inorganic or organic peroxide activator.
Polyvinylchloride has a very wide use:
- In construction (window and doors frames, ventilation, water and sewage installations...)
- In the packaging industry - (lids for bottles, bags, packaging foils)
- In medicine - (blood bags, serum tubes, medical gloves)
- In the electro material production - (isolators for high voltage and fiber optic)
- In the car industry - (foil - isolating glass, wipers, interior, auto carpets)
- For other purposes - (toy production, sports materials, fake leather, manufacture of credit cards)
Polystyrene is a polymer which belongs to the standard plastics, and it is wide used and known as polystyrene for general purposes (GPPS). Common name is polystyrene "crystal" also polystyrene of high or high toughness (HIPS) or even more commonly name stringy polystyrene. Polystyrene is amorphous polymer, and it’s modification is possible with all types of styrene copolymers. Polystyrene are characterized by excellent dielectric and mechanical properties, and very good process ability. Polystyrene is mainly processed by molding injection and extrusion of solid and foam boards.
POLYSTYRENE FOR EXPANSION (ESA)
Polystyrene for expansion is light material of low thermal transmittance. It is shaped in the form of solid granules. Characteristics of expansion is achieved by adding a small amount of pentane in polystyrene molecules in the process of manufacturing. Under the heat influence, granules EPS expands and forms a perfect "cell" of expanded polystyrene. Expanded cells can take up to 40 times the volume of the unexpanded polystyrene beads. By molding expanded beads, desired forms are obtained.
The main usage is in the production of EPS isolation systems in construction. Today, "Styrofoam" is the main EPS isolating material.
Except isolation, EPS is also used for production of interior elements (light walls, "Ceilings", aesthetic pillars ...)
Packing usage of EPS is also great, because EPS has a major role in protection of the physical impacts on packaged products, which are mostly breakable.