What is PVC

What is PVC?

PVC is short for polyvinyl chloride and is referred to as a polymer with the following chemical structure.

PVC is among thermoplastic polymers that depending on the added substances, can be plasticized PVC, soft PVC, or unplasticized PVC.

Also, during the current conditions, PVC is one of the most valuable petrochemical products. Generally, more than 50% of man-made PVC is used in construction, because PVC is cheaper than other polymer materials, and different products can be made with it.

In recent years, PVC is a good alternative for building materials, and due to the durability of the product made with this material, it has become highly used, and traditional materials that can be made with PVC are gradually being eliminated.

PVC Applications:

  • Sewage Pipes
  • Profiles used in building double-pane doors and windows
  • Wallcoverings
  • Appliances
  • Wires and cable coatings
  • Medical Equipment
  • Packaging
  • Vehicle Parts
  • Electronic Parts

Furniture

PVC Production Method:

For preparing PVC polymer, different polymerization processes are used, and finally, the obtained polymer is also introduced with the same process. PVC polymerization processes are as the following:

  • Suspended Polymerization
  • Emulsion Polymerization
  • Bulk Polymerization

Different processes of PVC production cause the obtained products to be different from each other in terms of shape and granulation size, ability in absorbing conditioning oils, optical, electrical, physical, mechanical properties, and other applicational matters.

Suspended Polyvinyl chloride (PVC-S):

In this method, first, the insoluble liquid monomer is completely distributed in the water by strong mixers, and then by adding an appropriate starter that is VC-soluble, the reaction is started, and finally suspended particles of PVC as big as 20-200 micrometers are formed.

The PVC molecular chains suspended in water are easily separated from the water phase by centrifuge systems, grids, and filtration and after searching and drying, heavy and spherical PVC-S particles are obtained from them, which is appropriate polymer for making electrical products and clear artifacts through extrusion and injection processes methods. The advantage of this method is the easy transfer of heat due to the polymerization reaction that is easily done by the water environment.

Emulsion Polyvinyl Chloride (PVC-E):

In this method, first, the insoluble liquid monomers along with water-soluble emulsion substances are completely distributed in the water by appropriate mixers. By adding water-soluble starters (mostly water-soluble peroxides such as calcium sulfate) and adjusting the system’s temperature, the process is started, and then very fine PVC particles are formed. The separation of the milky color PVC solution from the unreacted monomers is done in special conditions and under vacuum pressure. The obtained substance can be directly used in coating – glazing or even it can be used as an adhesive.

The presence of emulsion substance in PVC reduces friction between the polymer and the machinery’s metal parts and leads to an ease in production. On the other hand, the presence of this same factor leads to a drop in electrical properties, inclination toward gaining electricity charge, and cloudy color in the product. The shape and size of the PVC granules in this method follow the conditions of the dryers and the separated PVC particles from the water phase, which by adjusting the dryer’s setting, the size of the particles is adjustable from 2 to 60 microns.

PVC-E is used mostly for producing artificial leather, wallpaper, and gloves.

PVC Properties:

  •  High durability
  • Resistant to unfavorable weather conditions
  •  Appropriate processability
  • Melting temperature at about 80°C
  •  Self-extinguishing
  •  Density of 8.0 to 47.1 g/cm3
  •  Resistant to U.V
  •  Continuously usable at 60°C
  •  Adaptable to additives
  •  Insoluble in alcohols, hydrocarbons, acetone
  •  Great electrical properties
  • Soluble in methyl ketone, toluene, nitrobenzene
  •  Resistant to chemical substances, oils, and weak acids
  •  Great electrical properties

K-value Concept:

Every PVC manufacturer, depending on its final use, produces a special type of polymer, which are different in terms of morphology and molecular mass. K-value or viscosity number is used as the representative of PVC’s molecular weight.

In order to measure this index, the PVC solution’s viscosity is determined. The higher this index, the higher the PVC’s molecular weight will be.

The k-value range is usually between 35 to 80.

Different uses of PVC based on K-value:

A K-value between 55 to 60 is appropriate for injection
A K-value between 66 to 68 is appropriate for the extrusion of wallcoverings, profiles, pipes, and …
A K-value between 65 to 71 is appropriate for producing flexible parts, cable coating, and …

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