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.
Iron Contamination
Meaning
Presence of metallic iron particles in polymer resins acts as a defect source and a degradation catalyst during compounding and moulding. When iron contamination occurs, it causes dark specks in the finished plastic parts and ruins their cosmetic appearance. These metallic particles can also damage the smooth surfaces of injection moulds and extruders.
Removing these metal particles is essential for maintaining product quality.
Mechanical Failure
Sharp metallic particles embedded in a plastic part create stress concentration points. When iron contamination is present in the resin, the moulded parts are prone to cracking.
Melt Degradation
Metal surfaces and free metal ions accelerate the thermal breakdown of polymer chains at high temperatures. In the melt phase, iron contamination acts as a catalyst for oxidation reactions that scissor the polymer chains. This reaction lowers the melt viscosity of the polymer and leads to flash at the mould parting line.
It also generates volatile organic compounds that can cause odor problems in the finished product. This chemical degradation can be minimized by keeping the melt temperature as low as possible.
Magnetic Separation
Processors use heavy-duty magnets in the resin feed lines to capture metal particles before they enter the processing machinery. To eliminate iron contamination, rare-earth magnets are installed in the hopper feed throats of injection moulding machines. These magnets pull the iron particles out of the falling resin pellets.
Regular cleaning of these magnets is required to prevent them from becoming saturated and losing their efficiency. This simple step protects both the machinery and the quality of the molded parts.