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.
Hydrochloric Acid Dehydrochlorination
Meaning
Degradation reactions in polyvinyl chloride release acid and create conjugated double bonds along the polymer chain when the material is heated. The process of hydrochloric acid dehydrochlorination causes the plastic to change color from white to yellow, then brown, and finally black. This reaction is autocatalytic because the released acid accelerates further degradation.
Preventing this breakdown is essential for processing PVC safely.
Polymer Degradation
The chemical structure of polyvinyl chloride is sensitive to high temperatures. When hydrochloric acid dehydrochlorination begins, it creates polyene sequences that make the polymer brittle.
Tool Corrosion
Acidic gases released during polymer processing attack the metal surfaces of extruders and injection moulds. While hydrochloric acid dehydrochlorination is occurring, the corrosive gas pits and degrades the steel tooling. This damage leads to rough surfaces on the moulded parts and reduces their dimensional accuracy.
To avoid this, tool steel must be protected with specialized coatings like chrome plating. Polishing and cleaning the tooling adds to the cost of the manufacturing run.
Thermal Stabilization
Additives called heat stabilizers are mixed with PVC resins to neutralize the released acid before it can propagate further reactions. To prevent hydrochloric acid dehydrochlorination, compounding facilities add calcium-zinc or tin stabilizers to the resin formulation. These additives react with the escaping chlorine atoms and keep the polymer matrix stable during melt processing.
Without these stabilizers, processing raw PVC would be impossible because the resin would decompose inside the extruder.