Impact modifier - Thermoplastic polymers, elastomers and additives

Impact modifiers are used to improve impact resistance, especially at low temperatures. This is generally achieved by blends of polymers, a rigid thermoplastic and an elastomer, so that plastics with a broad spectrum of well-balanced properties are obtained. Impact modifiers work by absorbing impact energy and dissipating it nondestructively. Impact modifiers are typically elastomeric materials and are added to a wide range of thermoplastic materials at levels up to 20%.

The main types of impact modifiers are acrylics, styrenics including methacrylate-butadiene-styrene (MBS) and copolymers of acrylonitrile butadiene-styrene (ABS), chlorinated polyethylene (CPE), ethylene-vinylacetate (EVA) copolymers, ethylene copolymers and acrylate (EMA, EBA) and ethylene-propylene copolymers and terpolymers. The main market for impact modifiers is PVC, PE and PP, although they are used in a wide range of other recycled polymers and engineering. The EPDM (ethylene propylene diene monomer rubber) and the EPR (ethylene rubber) propylene) are used to modify polyolefins, mainly in the automotive industry. Although rubber is being replaced by impact resistant polymers such as metallocenes and ethylene copolymers, it offers better performance and cost.

An essential morphological characteristic in polymers modified to increase the impact resistance is that there is a multiphase structure, as a consequence of a certain incompatibility between the rigid thermoplastic phase and the elastic component, that is, the elastomeric phase.