Meaning
Recycled thermoplastic material originates from the granulation of production waste such as sprues, runners and out of specification parts. This material is ground into small flakes that can be blended with virgin resin for reuse. Proper use of polypropylene regrind reduces the environmental impact of manufacturing while lowering the overall part cost.
Recovery Loop
Automation systems often collect runners directly from the mould and feed them into a bedside granulator. The resulting polypropylene regrind is then metered back into the main material stream at a fixed percentage. Maintaining a constant ratio of regrind to virgin material is necessary to prevent fluctuations in the moulding process.
Property Degradation
Multiple heat cycles break the long molecular chains and reduce the mechanical strength of the plastic. If the polypropylene regrind has been processed too many times, the part will become brittle and lose its impact resistance. Monitoring the yellowness index and the melt flow rate helps to identify when the material has suffered excessive thermal damage.
Oxidation can also occur if the regrind is stored in open containers where it can absorb moisture or dust from the factory floor.
Economic Balance
High percentages of recycled content can lead to visible defects like black specks or inconsistent color. While using polypropylene regrind saves money on raw materials, it can also increase the scrap rate if the quality is not controlled. A balance must be found where the cost savings of the regrind outweigh the risk of producing inferior parts.
