Post Consumer Recyclate Verification Standards for High Density Polyethylene Sourcing
Post-consumer HDPE sourcing relies on batch melt testing, DSC thermal screening, and mass balance audits to prevent factory scrap and field failure.
Charpy Impact Strength
Meaning
High-rate mechanical testing quantifies the kinetic energy absorbed by a standardized notched specimen during a single pendulum fracture event. Determination of charpy impact strength establishes the energy per unit area required to break a notched polymer sample at standard temperature. Datasheet values reflect virgin resin behaviour under controlled laboratory conditions, whereas actual moulded part toughness varies with wall thickness and gate orientation.
The test stops applying to ductile materials that bend without fracturing or specimens that exceed maximum pendulum energy.
Notch Sensitivity
Local stress concentration created by sharp corners drastically reduces energy absorption under dynamic flexural loading. Sharp radii in part geometry often cause unexpected field failures despite high reported values of charpy impact strength on raw material datasheets. Molders reduce this risk through radius optimization.
Temperature Sensitivity
Polymer impact energy declines sharply below the glass transition temperature when molecular mobility becomes restricted. Ductile to brittle transitions occur at specific thermal thresholds where charpy impact strength drops to a fraction of its room temperature value. Thermal conditioning of test bars ensures consistent characterization across operating regimes.
Regrind Impact Degradation
Thermal history from multiple molding cycles degrades polymer chain length and broadens molecular weight distribution. Repeated processing steps progressively lower charpy impact strength compared to virgin resin stock. Recycled content additions must be verified through impact testing to maintain structural compliance.