Polypropylene Heterophasic Copolymer Selection Guidelines for Frozen Packaging Containers
Polypropylene impact copolymers for frozen containers balance rubber content and viscosity matching to prevent cold brittle failure at minus twenty degrees.
Ductile Brittle Transition Temperature
Meaning
A physical property of polymers represents the temperature threshold at which a plastic material shifts its fracture behavior from a tough, energy-absorbing state to a fragile, easily cracked state. Below the ductile brittle transition temperature, a polymer loses its ability to yield plastically under stress and instead fails through rapid crack propagation. Moulders and product designers use this metric to determine the lower temperature limit for safe mechanical performance of plastic components.
Material Chemistry
Amorphous and semi-crystalline resins behave differently when subjected to sub-zero temperatures. Polypropylene exhibits a relatively high ductile brittle transition temperature near zero degrees Celsius, which restricts its use in cold-weather outdoor applications. Polyethylene remains tough at much lower temperatures due to its specific molecular structure and lower glass transition point.
Molding Influence
Injection molding parameters directly influence how a part responds to mechanical impact at various temperatures. High residual stresses or severe molecular orientation from fast cooling rates can elevate the ductile brittle transition temperature of the molded part compared to the raw resin. Minimizing these molded-in stresses through optimized packing pressure and mold temperature yields a more durable part.
Product Application
Parts that encounter sudden impact, like automotive bumpers or industrial storage crates, require a transition temperature well below the expected service environment. If the transition temperature rises too high, unexpected failure occurs. This property therefore dictates resin selection for cold-service conditions.