Improving the impact strength of compounds is the role of an important group of additives. Impact modifiers compensate for inherent brittleness, or embrittlement occurring at sub-zero temperatures, notch-sensitivity and crack propagation. The mechanism normally involves introducing a component that is elastomeric or rubbery in nature, which can absorb the energy of an impact or dissipate it. Jennifer Markarian looks at some of the options for the compounder wanting to improve toughness.
Impact modifiers are key additives for increasing flexibility and impact strength to meet physical property requirements of rigid parts. Some unmodified polymers such as rigid polyvinyl chloride (PVC), polystyrene (PS) or styrene acrylonitrile (SAN) are brittle at ambient temperatures. Others such as polyamides or polyolefins are ductile at ambient temperature but become brittle at low temperatures. Some, such as polycarbonate (PC), may have good dart impact but poor notch impact resistance. An impact modifier is needed whenever the polymer system does not meet the impact requirements for a particular application.