How are PP granules made from post-consumer scrap?

Polypropylene is the second most commonly recycled polymer in India after HDPE. PP is everywhere: woven sacks that carry grain and fertiliser, injection-moulded crates and containers, automotive interiors, caps and closures, furniture, and packaging. When that material reaches end-of-life, it becomes a valuable feedstock for recycled PP granule production.

Step 1: Scrap collection and sourcing

Post-consumer PP scrap comes from several streams: used woven sacks from agriculture, cement, and chemical packaging; injection-moulded containers, crates, and bins; caps and closures; automotive dashboard and door panel scrap; and furniture.

Post-industrial PP scrap is often cleaner and more consistent: injection-moulding sprue and runner waste, edge trimmings, and manufacturing rejects. Post-industrial material is preferred by granule producers who need tighter MFI control.

Step 2: Sorting by type and colour

PP comes in two major structural variants: homo-polymer (PPH) and co-polymer (PPCP). These have meaningfully different properties — homo-polymer is stiffer and more heat-resistant; co-polymer has better impact resistance and flexibility. Mixing them produces an inconsistent blend that performs poorly in either application.

Step 3: Size reduction

Bulk PP scrap — bales of woven sacks, crates, lumps — is shredded into coarse pieces (50–100 mm) by a primary shredder. This increases surface area for effective washing and reduces the load on the downstream extruder.

Step 4: Washing

The wash process typically involves a pre-wash (cold water, removing loose soil and dust), followed by a hot wash with caustic soda or detergent (removing oils, adhesives, and surface films), then friction washing (high-speed mechanical scrubbing while wet), and finally a rinse and hydro-cyclone separation to remove dense contaminants.

PP floats in water (density ~0.90 g/cm³) — this makes it easy to separate from denser contaminants using sink-float tanks. A well-run washing line is the difference between granules that run clean and granules full of carbonised inclusions.

Step 5: Drying

After washing, the PP flake carries surface moisture. This must be removed before extrusion — moisture in the extruder causes steam pockets in the melt, leading to voids in the strand and surface defects. Drying to below 0.1% moisture content is essential for consistent extrusion.

Step 6: Extrusion and pelletisation

The dried PP flake is fed into a single or twin-screw extruder. Temperature zones progressively melt the material (PP melts at approximately 160–170°C). The molten PP is pushed through a die plate, and the strands are cooled in a water bath before being chopped into granules — typically 3–5 mm.

Step 7: Quality testing

Quality recycled PP granule producers test MFI on every batch (230°C, 2.16 kg per ISO 1133 / ASTM D1238). Additional tests include density measurement, contamination check, and colour consistency assessment. Suppliers who test every batch and provide documentation have nothing to hide.

PP granule grades from OPAC POLYMERS

We supply PP homo-polymer and co-polymer in natural, black, and mixed colour grades. MFI range: 4 to 30 g/10min @ 230°C / 2.16 kg, available in multiple sub-ranges matched to injection moulding, packaging film, and other applications. All material is washed, dried, extruded, and batch-tested before dispatch.