Melt Shear History and Contaminant Catalyzed Scission in Post Consumer Polyolefin Silo Blends
Deactivate metal catalysts and neutralize acid traces with targeted additives to stabilize viscosity drift and optimize landed cost per good recycled part.
Contaminant Catalyzed Scission
Meaning
Polymer degradation reactions occur during melt processing when foreign chemical species accelerate the breaking of polymer chains. When contaminant catalyzed scission occurs, the molecular weight of the resin drops rapidly. This change causes a spike in the melt flow index and reduces the strength of the final moulded part.
Moulders must control processing temperatures to mitigate this degradation.
Resin Damage
Trace amounts of copper or iron from recycling streams trigger polymer chain breakdown at high heat. Under these conditions, contaminant catalyzed scission lowers the melt strength of the molten plastic.
Tool Wear
Corrosive byproducts are generated when polymer chains degrade in the presence of metallic impurities and heat. While contaminant catalyzed scission takes place, acidic molecules are released that attack the highly polished surfaces of injection moulds. This chemical erosion ruins the surface finish of the tooling over time.
Repairing these moulds requires expensive and time-consuming manual polishing. Constant inspection of the mould cavities becomes necessary to prevent defective surface textures on the produced parts.
Structural Failure
The mechanical properties of a finished plastic part depend directly on the chain length of the underlying resin. When contaminant catalyzed scission is unchecked during production, the finished parts exhibit brittleness and fail under low impact loads. Such parts do not meet the load-bearing requirements of automotive or industrial applications.
Retaining long polymer chains is necessary for maintaining impact resistance.