PVC is thermally unstable. Heating results in elimination of HCl, the formation of a polyene sequence and rapid discoloration. This autocatalytic reaction begins at ca. 100°C; at 180°C a marked brown colour occurs after a few minutes.
PVC processed as pure polymer would rapidly and completely decompose at the temperature necessary for moulding or extrusion (150 - 200 C).

The necessary protection is provided by the addition of heat stabilisers. Heat stabilisers must be present in any of the PVC formulations.

Heat stabilizers retard dehydrochlorination and autooxidation and reduce fragmentation, by substitution of structural defeats for more stable groups , scavenge the evolved HCl and block the free radicals formed during the degradation process.

The main classes of PVC stabilizers are complex mixtures of metal soaps with co-stabilizers, antioxidants, solvents, lubricants, etc. The most used mixed metals are:
  • Ba/Zn
  • Ca/Zn
  • Ca/Al/Mg/Zn
Mixed Metals stabilisers can be Liquid or Solid.
A good stabilizer must have the following characteristics:
  • Does not influence the colour of the compound
  • Transparency - same refractive index as PVC resin
  • Does not impart smell or taste to the material (food packaging)
  • Has low toxicity and no migration/extraction tendency
  • Presents low water absorption and no hydrolysis
  • Imparts the desired rheological properties to the PVC melt during processing
  • Is easy to disperse and compatible with PVC and all the others major ingredients of the PVC compound
  • Has no effect on mechanical properties
  • Has good Electrical characteristics
  • Does not show plate out on processing equipments
Along with stabilizers, sold by Lagor with the commercial names of Lastab and Synpack, Lagor produces a wide range of PVC additives such as Lubricants , Antifogging, Rheology Modifiers and blowing agents.