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.
Secondary Phosphite Hydrolysis
Meaning
Degradation reactions occur when phosphite antioxidants react with environmental moisture to form acidic compounds and lose their stabilizing activity. The occurrence of secondary phosphite hydrolysis reduces the thermal stability of the resin during subsequent melt processing steps. This breakdown can lead to black specks, odor, and polymer degradation during extrusion and injection moulding.
Moulders must protect raw materials from moisture to prevent this chemical failure.
Additive Degradation
The chemical structure of phosphite stabilizers is prone to attack by water molecules. When secondary phosphite hydrolysis occurs, it produces acidic byproducts that destroy the antioxidant.
Processing Defect
When degraded additives are processed at high temperatures, they can cause visual and structural problems in the final parts. Because secondary phosphite hydrolysis generates volatile acidic species, it can cause outgassing inside the injection mould. This gas trapped in the cavity produces splay marks and voids in the moulded parts.
It also corrodes the polished steel surfaces of the mould cavity over time. This corrosion requires frequent tool maintenance and can lead to part rejection due to poor surface appearance.
Storage Practice
Resin compounders must store additive packages in dry, climate-controlled environments to prevent moisture exposure. To prevent secondary phosphite hydrolysis, the additives are packaged in foil-lined bags with desiccant packs. These bags should only be opened immediately before the compounding step.
Once opened, the remaining material must be sealed again or stored in a nitrogen-purged hopper. This moisture management is essential for maintaining the performance of the stabilizer package.