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What is polyvinyl chloride?

The Polyvinyl chloride is a polymer whose industrial use began to develop at the beginning of the twentieth century, due among other things to its low cost, durability, resistance and its thermal and electrical insulation, among other reasons. This has allowed it to displace metals in numerous applications and use.

As its name indicates, it consists of the repetition of many vinyl chloride monomers, forming a polymer chain. Both chlorine and vinyl atoms repeat n times in the polymer, so it can also be called polyvinyl chloride ( PVC).

In addition, it is a moldable compound, so it can be used to build numerous pieces of different shapes and sizes. PVC is resistant to corrosion, mainly due to oxidation. Therefore, there is no risk in its exposure to the environment.

As a negative point, the durability of PVC can be the cause of a problem, because the accumulation of its waste can be contributors to the environmental pollution that has affected the planet so much for several years.

In 1838, the French physicist and chemist Henry V. Regnault discovered polyvinyl chloride. Later, the German scientist Eugen Baumann (1872) exposed a bottle of vinyl chloride to sunlight and observed the appearance of a solid white material: it was polyvinyl chloride.

At the beginning of the 20th century, the Russian scientist Ivan Ostromislansky and the German scientist Frank Klatte of the German Chemical Company Griesheim-Elektron tried to find commercial applications for polyvinyl chloride. They ended up frustrated, because sometimes the polymer was rigid and other times it was brittle.

In 1926 Waldo Semon, a scientist working for the BF Goodrich Company in Akron, Ohio, succeeded in creating a flexible, waterproof, fire-resistant plastic capable of bonding to metal. This was the goal sought by the company and was the first industrial use of polyvinyl chloride.

The manufacture of the polymer intensified during World War II, as it was used in the coating of the wiring of warships.

Chemical structure of polyvinyl chloride

Polyvinylchloride

The upper image illustrates the polymer chain of polyvinyl chloride. The black spheres correspond to the carbon atoms, the white ones to the hydrogen atoms and the green ones to the chlorine atoms.

Polyvinylchloride

Here, a string is made up of n units, which are enclosed in parentheses. The Cl atom points out of the plane (black wedge), although it can also point behind it, as seen with the green spheres. The H atoms are oriented downward and can be seen in the same way with the polymer structure.

Although the chain has only single bonds, these cannot rotate freely due to the steric (spatial) hindrance of the Cl atoms. 

Why? Because they are very bulky and do not have enough space to rotate in other directions. If they did, they would “hit” with neighboring H atoms.

Physical and chemical properties of polyvinyl chloride

Ability to retard fire

This property is due to the presence of chlorine. The ignition temperature of PVC is 455ºC, so the risk of burning and starting a fire is low.

In addition, the heat released by PVC when burning is less as it is produced by polystyrene and polyethylene, two of the most widely used plastic materials.

Durability

Under normal conditions, the factor that most influences the durability of a product is its resistance to oxidation.

PVC has chlorine atoms attached to the carbons in its chains, which makes it more resistant to oxidation than plastics that only have carbon and hydrogen atoms in their structure.

The examination of PVC pipes buried for 35 years, carried out by the Japan PVC Pipe & Fitting Association, showed no deterioration in these. Even its strength is comparable to new PVC pipes.

Mechanical stability

PVC is a chemically stable material that shows little change in its molecular structure and mechanical strength.

It is a long-chain viscoelastic material, susceptible to deformation by the continuous application of an external force. However, its deformation is low, since it presents a limitation in its molecular mobility.

Processing and moldability

The processing of a thermoplastic material depends on its viscosity when it is molten or melted. Under this condition, the viscosity of PVC is high, its behavior being little dependent on temperature and it is stable. For this reason, PVC can be used to make products of large size and variable shapes.

Chemical and oil resistance

PVC is resistant to acids, alkalis and almost all inorganic compounds . PVC deforms or dissolves in aromatic hydrocarbons, ketones, and cyclic ethers, but is resistant to other organic solvents such as aliphatic hydrocarbons and halogenated hydrocarbons. Also, its resistance to oils and fats is good.

Density

1.38 g / cm 3

Melting point

Between 100ºC and 260ºC.

Percentage of water absorption

0% in 24 hours

Due to its chemical composition, PVC is capable of mixing with composite numbers during its manufacture.

Then, by varying the plasticizers and additives used in this stage, different types of PVC can be obtained with a range of properties, such as flexibility, elasticity, resistance to impacts and prevention of bacterial growth, among others.

Uses / Applications of Polyvinyl Chloride

Building

PVC is an inexpensive and versatile material used in construction, healthcare, electronics, automobiles, pipes, coatings, blood bags, plastic probes, cable insulation, etc.

It is used in many aspects of construction due to its strength, resistance to oxidation, moisture and abrasion. PVC is ideal for cladding, for window frames, roofs and fences.

It has been especially useful in the construction of pipes, since this material does not undergo corrosion and its rupture rate is only 1% of that of molten metal systems.

Withstands changes in temperature and humidity, being able to be used in the wiring constituting its coating.

Packing

PVC is used in the packaging of different products, such as dragees, capsules and other items for medical use. Also, blood bank bags are made of transparent PVC.

Because PVC is affordable, durable, and waterproof, it is ideal for raincoats, boots, and shower curtains.

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