Post-Consumer Recyclate Quality Assurance Protocol Selection
Verify post-consumer resin lot conformity by combining core lance sampling, melt flow shear sweeps, and DSC purity screens before unloading silos.
Impact Strength
Meaning
Mechanical property that measures the ability of a polymer to resist fracturing under a high-rate or shock load. Selecting a resin with sufficient impact strength is critical for protective housings, safety gear, and structural automotive parts. This property is determined by the molecular weight and the presence of impact modifiers in the compound.
Moulders must monitor this value because excessive melt temperature can degrade the polymer and reduce toughness.
Testing Method
Two standard test methods, Izod and Charpy, are used to evaluate how a polymer behaves under sudden stress. Both methods utilize a weighted pendulum that swings down to strike a notched or unnotched specimen. The energy absorbed during the fracture is calculated by measuring the height of the pendulum swing after impact.
These tests are conducted at various temperatures to determine the ductile-to-brittle transition point of the material. This characterization is essential for parts intended for cold-weather environments.
Processing Degradation
Squeezing resin through restrictive runners or using high screw speeds can shear the polymer chains, which dramatically lowers the impact strength of the molded part. This degradation occurs without any obvious change in the visual appearance of the component. The molded part may look flawless but shatter under a low load because the average molecular weight has been reduced during processing.
To avoid this, molders must maintain correct melt temperatures and optimize gate sizes to minimize shear stress.
Regrind Utilization
Incorporating recycled or reground material into the production run is a common cost-saving strategy, but it directly affects the impact strength of the finished parts. Each heat history degrade the polymer chains further, making the material more brittle with every recycle loop. High performance applications typically limit regrind content to twenty percent to preserve the required toughness.
Exceeding this limit can cause parts to fail in the field, leading to product recalls and liability claims. Moulders must perform regular mechanical testing on molded specimens to ensure that the ratio of regrind does not compromise the structural integrity of the product. This continuous verification is standard practice in demanding sectors such as electronics and defense.