PVC resin obtained from polymerization is extremely unstable due to its low thermal stability & high melt viscosity. It needs to be modified before processing into finished products. Its properties can be enhanced/modified by adding several additives, such as heat stabilizers, UV stabilizers, plasticizers, impact modifiers, fillers, flame retardants, pigments, etc.
Selection of these additives to enhance polymer’s properties is dependent on end application requirement. For example:
1.Plasticizers (Phthalates, Adipates, Trimellitate, etc.) are used as softening agents to enhance rheological as well mechanical performance (toughness, strength) of vinyl products by raising the temperature. Factors that affect the selection of plasticizers for vinyl polymer are:Polymer compatibility；low Volatility；cost.
2.PVC has a very low thermal stability and stabilizers help prevent degradation of polymer during processing or exposure to light. When subjected to heat, vinyl compounds initiate a self-accelerating dehydrochlorination reaction and these stabilizers neutralize the HCl produced enhancing the life of polymer. Factors to be considered while selecting heat stabilizer are: technical requirements；regulatory Approval；cost.
3.Fillers are added in PVC compounds for a variety of reasons. Today, a filler can be a true performance additive by delivering value in new and interesting ways at the lowest possible formulation cost. They help to: increase stiffness and strength,improve impact performance,add color, opacity and conductivity and more.
Calcium carbonate, titanium dioxide, calcined clay, glass, talc etc. are common types of fillers used in PVC.
4.External lubricants are used to assist smooth passage of PVC melt through processing equipment. while internal lubricants reduce melt viscosity, prevent overheating and ensure good color of product.
5.Other additives like processing aids, impact modifiers, are added to enhance mechanical as well as surface properties of PVC.
Post time: Dec-13-2022