Meaning
Reactive chemical additives designed to link low molecular weight polymer chains during melt processing provide a means of restoring degraded plastics. Applying a chain extender is common when processing recycled polyesters or polyamides that have suffered hydrolytic cleavage. These multi-functional molecules bond with terminal groups of the polymer chains to reconstruct the molecular weight.
This action preserves the mechanical properties of the recycled resin.
Chemistry Type
Bifunctional or multifunctional monomers represent the primary classes of these additives. Epoxy-functional compounds react efficiently with the end groups of condensation polymers. Each chain extender molecule holds multiple reactive sites to bridge polymer fragments.
Viscosity Enhancement
Adding these agents directly raises the melt viscosity of the polymer. The molecular weight recovery achieved by a chain extender prevents parison sag during blow molding and bubble collapse during film extrusion. Processing speeds can be maintained at levels comparable to virgin resins.
Regrind plastics show measurable improvements in melt strength after reactive compounding.
Processing Impact
Dosage must be controlled to prevent excessive gelation or high motor torque in the extruder. When the chain extender concentration is too high, crosslinking occurs and yields hard gel particles that ruin the surface finish of molded parts. This degradation of processing stability limits the maximum percentage of regrind that can be reclaimed.
Optimizing the feeding rate ensures a consistent viscosity profile, reducing downtime caused by screen pack blinding.
