Deconvolution Protocols for Melt Crystallization Peaks in Recyclate Blends
Deconvolution of DSC melt crystallization peaks isolates PE and PP fractions in recyclates to verify composition before compounding.
Secondary Phase Contamination
Meaning
Material degradation occurring when incompatible polymers or foreign particulates are interspersed within a primary resin matrix reduces the quality of plastic parts. Moulders try to prevent secondary phase contamination to avoid structural failures and surface blemishes in their molded components. The incompatible material forms discrete droplets or flakes that do not blend with the host polymer, creating weak points.
This condition arises most frequently when regrind contains traces of other plastics from poorly sorted recycling streams.
Defect Mechanism
Stress concentrations develop at the interfaces between the host polymer and the unblended secondary material because of poor adhesion. When secondary phase contamination occurs, the part loses its impact resistance and can fail catastrophically under load. Surface defects such as delamination or peeling also occur near the gates where shear stresses are highest.
Detection Method
Microscopic inspections and thermal analysis are used to identify the presence of foreign resins in incoming material shipments. A heat flow thermogram reveals secondary phase contamination by displaying unexpected melting peaks that do not belong to the primary resin grade. This testing allows quality managers to reject bad raw materials before they enter production.
Extrusion Mitigation
Processors use fine mesh melt filters in the extruder to trap solid contaminants and unmelted foreign polymers. While secondary phase contamination cannot always be prevented at the source, effective filtering reduces the size of the foreign particles. This treatment improves the consistency of the final molded product.