Analytical Metrology and Restabilization Procedures for Post-Consumer Flake
Stabilizing post-consumer flake requires baseline infrared oxidation metrology paired with balanced phenolic-phosphite packages to prevent melt chain scission.
ASTM D5991
Meaning
Standard practice for the separation and identification of poly(vinyl chloride) (PVC) contamination in poly(ethylene terephthalate) (PET) flakes intended for recycling. Procedures defined in astm d5991 provide the basis for using thermal treatments to differentiate between these two resins based on their distinct physical responses to heat.
Separation Procedure
Placing a sample of mixed flakes in an oven at a specific temperature causes the PVC fragments to darken and shrink while the PET remains largely unchanged. This astm d5991 method relies on the dehydrochlorination of the vinyl contaminant, which results in a visible colour shift that allows for manual or optical sorting. The process involves weighing a specific quantity of flakes and spreading them in a single layer on a tray to ensure even heating.
After a duration defined by the standard, the sample is cooled and the discoloured pieces are separated for weighing to calculate the percentage of contamination.
Purity Assessment
Quantifying the level of contamination is essential for bottle-to-bottle recycling streams where even minor amounts of PVC can degrade the PET during subsequent extrusion. The results from astm d5991 determine if a batch of regrind meets the requirements for high grade applications or if it must be diverted to lower value uses.
Quality Influence
Thermal degradation of vinyl produces hydrochloric acid which damages processing equipment and reduces the molecular weight of the polyester host. Reliable application of this standard prevents the brittleness and discoloration associated with contaminated resin feeds.