Leading granule manufacturers admit that they cannot produce granules without black specks. In the complex manufacturing process, flow dead zones cannot be avoided. In these zones with little to almost no melt flow, the plastic burns due to excessive thermal stress. This is how the black specks are developed in the granules. This is particularly visible in transparent plastics (see photo). If granules cannot be supplied without black specks, the manufacturer cannot produce molded parts / extrudates without black specks.
Black specks can mostly be avoided if the flow dead zones are regularly cleaned of combustion residues. This is only possible with chemical, foaming cleaning agents. The foaming effect brings the cleaning chemicals into the flow dead zones. This allows the chemicals to reach the residues and loosen them from the metal surfaces. The dissolved combustion residues are then flushed out of the system. Conventional non-foaming cleaning granules do not reach and clean these flow dead zones.