How to avoid polymer degradation, black spots and black specks at injection moulding, extrusion, blow moulding

What it is:

Material contamination and black spots occur when raw polymer or additives degrade at any stage in the machine. Environmental sources excluded, such a problem generates scrap parts with varying severity. Contamination can happen during both machine start-ups and the running of production.

Causes:

In a plastic processing environment, thermoplastic polymers, heat sensitive polymers, and polymers that contain additives such as a flame retardant are prone to degrade under heat, oxidation, or cross-linking. However, degradation is not limited to heat-related complications. It can also be generated by inconsistent processing temperatures. Degraded residues can take the form of crust, specks, gels, or material lumps, and the accumulation of residues creates unwanted scrap parts when processed alongside the main polymer. Material contamination can yield serious complications, and black spots are especially problematic for machine restarts.

Solutions:

The right selection of purge compound will help prevent degraded residues from accumulating in the machine. If used often enough to soften degraded residues, a purge compound can eliminate material contamination issues.

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