PVC is not an exception in the group of polymers when it comes to requirement of additives. Even PVC needs the use of additives. For rigid PVC mixtures, the additives include PVC stabilizers, PVC modifiers, and PVC lubricants. For flexible PVC plasticisers are used to gain flexibility.
Hydrogen and chlorine in the molecules are removed when PVC is heated to 170~180°C and release of hydrogen chloride becomes evident. Prevention of hydrogen chloride elimination due to heat and following decomposition is needed as PVC is heated to soften during the molding or extrusion procedure. The stabilizer prevents such first removal of hydrogen chloride from PVC.
Consequently, use of PVC stabilizers (metal compounds) is necessary to stop the chain reaction of decomposition. They can also impart to the PVC enhanced resistance to daylight, weathering and heat ageing and have a significant effect on the physical properties along with the price of a formula. They’re invariably provided in the type of use – unique combinations of which the main components are metal salts metal soaps and organometallic compounds. The selection of heat stabilizer depends on numerous factors including the technical demands of price, regulatory approval requirements, and the PVC product.
The primary heat stabilizers in a formulation are usually coupled with co-stabilizers which are organic substances for example epoxidised esters or polyols: an additive synergistic effect is provided by them, particularly in the case of some forms of heat stabilizer, an improvement of general stabilizer functionality. Every stabilizer has uses that are typical, although quite a few different types might be used in exactly the same program sector.
Other PVC additives may also include processing aids and pigments. These are chosen from food contact approval lists – like those regulated at national level within Europe or US Food and Drug Administration regulations – and/or in the European Pharmacopoeia Monographs.