The polymerisation process

Polyvinyl chloride is made from polymerisation of vinyl chloride.

Three types of polymerisation

PVC production usually refers to the manufacture of PVC resin through the process of polymerisation which is the basis for all PVC products. Three types of PVC manufacture exist: suspension polymerisation, emulsion polymerisation and bulk (or mass) polymerisation. PVC made from suspension is by far the most common.

Suspension polymerisation, step by step

  1. The first step in the production of suspension PVC, also known as S-PVC, is to feed VCM into the polymerisation reactor alongside water and suspending agents. Through high-speed agitation, small droplets of VCM are formed.
  2. Next, an initiator or catalyst soluble in VCM is fed into the reactor. It is here, under pressure and at a temperature ranging from 40 to 60°C, that the VCM droplets are turned into PVC. The PVC obtained through this method is suspended in water and appears as particles of 50~200 μm diameter.
  3. At the final stage of the S-PVC process, the miniscule particles of PVC are discharged from the polymerisation reactor, and stripped of un-reacted VCM. Most of the water is removed, usually by centrifugation, and the solid particles are dried. The end result is PVC in the form of a white powder, or resin, which is non-toxic, odourless and inert. Importantly, all un-reacted VCM is recovered and recycled as a raw material.

Emulsion and bulk polymerisation

Emulsion polymerisation and bulk polymerisation are alternative but far less common technologies for the manufacturing of PVC. Emulsion polymerisation produces finer resin grades with much smaller particles, which are specifically required for certain applications. This type of resin is either known as E-PVC or P-PVC, since it is often used as a paste for coating surfaces.

Bulk (or mass) polymerisation yields PVC resin similar to suspension PVC. The difference is that the polymerisation occurs without water. It is primarily used for products that require high transparency and good plasticising properties.