What is Polyvinyl Chloride (PVC)?

Polyvinyl chloride (PVC) holds the third place in the market for plastic production worldwide, due to the large number of compounds and derivatives that can be obtained from it.

 

PVC is structurally similar to polyethylene, except that for every two carbon atoms, one atom of hydrogen is replaced by a chlorine atom. It is produced by the free radical polymerization of vinyl chloride (chemical formula CH 2 = CHCl).

 

The resin resulting from this polymerization produces the most versatile family of plastics. It is both thermoplastic, i.e., under the action of heat it softens, and can be molded easily, and recovers its initial consistency as it cools while retaining the new shape. From this resin both flexible and rigid products can be obtained.

 

PVC is a chemical combination of carbon, hydrogen and chlorine. Its raw materials come from oil (43%) and common salt (57%), an inexhaustible resource. This type of plastic is less dependent on petroleum. Only 4% of total petroleum consumption is related to making plastics, of which only one-eighth are PVC.

 

There are two types of polyvinyl chloride, flexible and rigid. Both have high resistance to abrasion and chemicals.

 

Flexible PVC, also known as plastic, constitutes 50% of total production. In this type of PVC, a suspension or mass polymer Is used, and additives such as plasticizers make the material processable by imparting flexibility to the finished product (depending on the proportion of plasticizer used.)

 

This type of PVC is used to make tablecloths, shower curtains, furniture, electrical wires and cables, car upholstery, and more.

 

Rigid PVC uses a polymer or resin of suspension or mass PVC, that is combined with a large number of additives. These include flow modifiers, impact modifiers, stabilizers, colorings, among others. These additives do not contain plasticizers that modify the flexibility of the material. Rigid PVC is used in pipe manufactured for irrigation, joints, roofing, bottles, and also in parts of automobiles.

 

The formula of the PVC is:

 

 

Some properties of PVC occupy a privileged place within the field of plastics: they are lightweight, inert, safe, resistant to fire (i.e., do not spread flame), waterproof, insulating (i.e., thermal, electric and acoustic), highly transparent, easy to process (e.g., extrusion, injection, calendering, pressing, coating and molding pastes), plus they are recyclable. These materials can be stretched to 4.5 times their original length, and have a density of 1.3 to 1.6 g / cm 3.

 

PVC resins can be produced by four different processes: suspension, emulsion, mass and solution.

 

Suspension: This is the method most often used, and is the one by which the homopolymers and copolymers are obtained. The process is carried out in stainless steel reactors by method of loading. In the production of such resins suspending agents such as gelatin, cellulose derivatives and polyvinyl alcohol are used in an aqueous medium of purified water. Classical catalysts are organic peroxides. This type of resin has good electrical properties.

 

Emulsion: Paste or dispersion resins are obtained for the formulation of plastisols. Paste resins can be homopolymers or copolymers, and latexes are also produced. This process uses surfactants derived from fatty alcohols, in order to achieve better dispersion, and results in a smaller particle size. These surfactants have influence on the absorption properties of the plastisol. The resulting resin is not as clear or as good as the suspension stability, but neither are the uses that require such resins. The market for this type of resin is two eighths of the total world production.

 

Mass: Characterized as the "continuous process", only catalysts and water are used in the absence of suspending agents and emulsifiers. This results in a resin with good stability. Process control is very critical and therefore the quality varies. Demand for this type is increasing, and at present represents an eighth of the total world market.

 

Solution: When carried out in solution, this method produces very high quality resins for certain specialties. For this reason, the market volume is low.