Impact Modifier

The polymeric additives incorporated in PVC compositions are broadly classified into two groups based on the function they perform, viz. processing aids and impact modifiers. A processing aid improves the melt-processing characteristics of PVC compositions and the melt properties e.g. increase in melt strength, cohesion and elongation and in many cases reduction in melt modulus. It may increase the melt viscosity and also have an external lubricant effect. At their usual levels of incorporation of 1-6phr, processing aids do not significantly affect the end-use properties of the composition. An impact modifier, as the name suggests improves the toughness of rigid PVC compositions, in which they are usually incorporated in proportions of 5 -15 phr.However, there is some overlap in the types of polymer used for the two respective purposes. i.e. many impact modifiers have some processing-aid action and some processing aids can affect product properties even at their relatively low level of addition.