High Temperature Non Aqueous Volatile Acid Titration in Recycled Polyethylene
High temperature non-aqueous titration strips volatile carboxylic acids from hot PE melt into organic media to quantify corrosion risks and thermal stability.
Die Corrosion
Meaning
Guarding metal surfaces against electrochemical or chemical degradation prevents the loss of dimensional accuracy in extrusion hardware. While die corrosion often stems from the release of acidic byproducts like hydrogen chloride during the processing of polyvinyl chloride, it also occurs when moisture reacts with flame retardant additives. The resulting pits or scale on the metal surface transfer directly to the plastic part, creating streaks or rough patches.
Chemical Attack
Corrosive agents penetrate the protective plating or base metal of the tool when temperatures exceed the stability threshold of the resin. This form of die corrosion accelerates in the presence of stagnant melt where local concentrations of volatiles increase over time.
Surface Integrity
Metal loss on the polished surfaces of a die alters the flow dynamics of the melt, leading to stagnation zones and further material breakdown. Because die corrosion is often microscopic in its early stages, it manifests first as a loss of gloss or a slight change in the color of the extrudate.
Preventive Maintenance
Specialized coatings such as chrome plating or nickel alloys provide a barrier against aggressive chemical environments. Regular cleaning and the use of purging compounds remove the acidic residues that drive die corrosion during machine downtime. Selecting stainless steel grades with high chromium content provides the primary defense when designing tools for chemically active polymers.
These material choices ensure that the precise tolerances of the flow channel remain intact over millions of cycles.