How PVC is manufactured
PVC production usually refers to the manufacture of PVC resin, which is the basis for the plethora of PVC products around us. Three types of PVC manufacture exist: suspension polymerisation, emulsion polymerisation and bulk polymerisation. PVC made from suspension is by far the most common.
Vinyl chloride monomer (VCM) is the raw material for all kinds of PVC polymerisation. VCM, which is gaseous under normal conditions, is stored under pressure in order to keep it liquid
Suspension polymerisation, step by step
As a first step in the production of suspension PVC, also known as S-PVC, VCM is fed into the polymerisation reactor alongside water and suspending agents. Through high-speed agitation, small droplets of VCM are formed. It is these droplets that eventually become PVC.
As a next step in PVC manufacture, an initiator or catalyst soluble in VCM is fed into the reactor. It is here, under pressure and at 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 slurry particles of 50~200 μm diameter.
At the final stage of the S-PVC process, the slurry discharged from the polymerisation reactor is stripped of un-reacted VCM; most of the water is removed, usually by centrifugation, and the solid is 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 raw material.
Emulsion and bulk polymerisation
Emulsion polymerisation and bulk polymerisation are alternative but far less common technologies to manufacture PVC. Emulsion polymerisation produces finer resin grades with much smaller particles, which are required by certain applications. This type of resin is either known as E-PVC or P-PVC, since it is often used as paste for coating surfaces.
Bulk (or mass) polymerisation yields PVC resin similar to suspension PVC. The difference is that polymerisation occurs in the absence of water. It s primarily used for products that require high transparency and good plasticising properties.