Impact Strength

Also called: Izod impact, Charpy impact, notched impact strength

Impact strength measures how much energy a plastic absorbs before breaking under a sudden blow, commonly tested by Izod or Charpy methods.

Impact strength describes a plastic ability to absorb energy from a sudden blow without breaking. It is commonly tested on notched bars with the Izod method (ASTM D256, ISO 180) or Charpy method (ISO 179). Results are reported in J/m or kJ/m2, and the method and notch type must be stated for results to be comparable.

Why it matters when buying recycled plastic

• Impact strength often falls with repeated processing and contamination, so it is a good indicator of recycled material quality.
• Mixing incompatible plastics, such as PP with PE, or ABS with HIPS, can reduce impact strength sharply.
• Fillers raise stiffness but usually reduce impact; check ash content alongside.
• For crates, buckets, helmets and housings, ask for impact test data or test moulded samples yourself.

Typical behaviour

PP copolymer, HIPS, ABS and PC are chosen for toughness, while GPPS and PMMA are relatively brittle. Impact strength also drops at low temperature, so specify the test temperature if the part will be used in the cold.