Polyvinyl Chloride (PVC)
What is Polyvinyl Chloride (PVC)?
PVC is Polyvinyl Chloride. This is a plastic that has the following chemical formula: CH2=CHCl (see picture on the right).
Plastic covers a wide rage of synthetic or semi-synthetic polymerization products (i.e. long-chain carbon-based "organic" molecules) which name refers to the fact that in their semi-liquid state they are malleable, or have the property of plasticity.
After the First World War, there were a boom in new forms of plastics due to the improvements in the chemical technology sector, including "polystyrene (PS)" and "polyvinyl chloride (PVC)", developed by the I.G. Farben company of Germany.
Nowadays, PVC is commonly used in the construction sector, for example in window frames and shutters, pipe cabling and coating, etc.. Vinyl is also used in gramophone records, and that is why we use the term vinyl records to refer to them. PVC can be used for tons of other applications from industrial ware and widely used in the healthcare sector, to car spare parts, toys factory, food packaging, raingear, etc. (This is described below).
PVC can be clear or colored, rigid or flexible, depending on the added compounds and final application that needs to be achieved; For example there exists different PVC grades such as coast or blow film, high impact, wire and cable grade, thermoforming, injection molding, rotational molding, etc.
How is it produced
The basic raw materials for PVC are derived from salt and oil.
The electrolysis of salt water produces chlorine. The chlorine is then combined with ethylene that has been obtained from oil. The resulting element is ethylene dichloride, which is converted at very high temperatures to vinyl chloride monomer. These monomer molecules are polymerized forming polyvinyl chloride resin.
For example rigid PVC like the one which is used in windows frames is normally PVCU ("unplasticized"). On the other hand flexible PVC is achieved by adding plasticizers such as phthalates.
Furthermore, pure poly-chloroethene is unstable when exposed to visible light or UV. In order to modify this disadvantage and make it suitable for different applications antioxidants are added. Some other additives comprise:
Characteristics of Polyvinyl Chloride
|Tensile strength||2.60 N/mm²|
Notched Impact Strength
|2.0 - 45 Kj/m²|
Thermal Coefficient of expansion
|80 x 10-6|
|Max Cont Use Temp||60 oC|
|RESISTANCE TO CHEMICALS|
|Dilute Acid||Very good|
|Dilute Alkalis||Very good|
|Oils and greases||Good (variable)|
|Aliphatic Hydrocarbons||Very good|
|Halogenated Hydrocarbons||Moderate (variable)|