PP Copolymer against Homopolymer for Cold Chain Drop Impact
Polypropylene impact copolymers containing disperse ethylene propylene rubber phases maintain cold drop impact strength down to minus 40 degrees Celsius where homopolymers shatter.
Izod Impact Test
Meaning
Pendulum-based assessments of the energy required to break a plastic specimen held as a vertical cantilever provide a measure of material brittleness. The izod impact test is a staple of quality control in the polymer industry for both virgin and recycled resins. It measures the resistance of a material to a sudden, concentrated blow.
Specimen Configuration
Unlike other methods, the specimen in an izod impact test is clamped at only one end. This setup forces the material to absorb the energy through a bending motion before it snaps. The result is typically reported in units of energy per unit of thickness, allowing for comparisons across different part sizes.
Brittleness Analysis
High energy values indicate a material that can deform and resist cracking under stress. Results from the izod impact test help engineers identify if a resin has been degraded by excessive heat during the molding process. A drop in impact strength is often the first sign that the molecular weight of the polymer has decreased.
Brittle failure is characterized by a clean break with no visible deformation at the fracture site.
Notch Influence
Most specimens are prepared with a standardized notch to simulate the stress risers found in actual molded parts. The izod impact test shows how a material handles these points of weakness. Unnotched versions are also used to understand the inherent toughness of the polymer without geometric interference.