mechanical recycling (physical recycling)

Mechanical recycling refers to the collection of post-consumer or post-industrial plastic waste followed by a physical processing sequence — sorting, washing, size reduction, drying, and melt extrusion or direct compounding — that converts waste plastic into recycled pellets, granules, or flake for use as secondary raw material. The polymer's chemical structure is retained (though some chain scission and degradation occur with each thermal processing cycle). Mechanical recycling is contrasted with chemical recycling, which breaks the polymer into monomers or fuels, and with pyrolysis, which thermally decomposes the polymer to oil and gas.

The typical mechanical recycling process line for post-consumer rigid plastics (HDPE, PP, PET) in India: incoming bales → bale breaking → pre-sort (manual, remove non-plastic) → shredding (2–4 stage, to 10–30 mm flake) → float-sink water tank (separates polyolefins from PET/PVC by density) → friction washer (hot water 50–80°C, caustic 0.5–2%) → rinsing → centrifugal dryer → thermal dryer (moisture ≤0.1%) → extrusion (single or twin-screw, 180–240°C depending on polymer) → pelletising → sieving → packaging. Line throughput: 200–2,000 kg/hr depending on equipment scale. A complete 500 kg/hr line costs Rs 1.5–4 crore for locally manufactured equipment; imported European lines (Erema, Starlinger) cost Rs 6–20 crore for equivalent throughput.

The key quality limitation of mechanical recycling is degradation accumulation over cycles: each melt-extrusion cycle causes chain scission (reducing molecular weight) and thermal oxidation, which lowers impact strength, tensile modulus, and colour. Virgin PET has an intrinsic viscosity (IV) of 0.76–0.84 dL/g; mechanically recycled rPET drops to 0.65–0.75 dL/g after one cycle and may require SSP (Solid-State Polycondensation) to restore IV for bottle or food-contact use. HDPE shows yellowing and MFI increase after 3–5 cycles. PP shows embrittlement from thermal oxidation. Contamination management is more critical than equipment specification: a Rs 20-crore Erema line processing contaminated feedstock will produce worse pellets than a Rs 2-crore local line processing clean, sorted streams.

Under India's Plastic Waste Management Rules 2016 and EPR framework, mechanical recycling is the primary qualifying activity for PWP (Plastic Waste Processor) registration and EPR credit generation for Categories I and II plastics (rigid and flexible plastic packaging). As of FY2023-24, approximately 3.5–4 million TPA of plastic waste is mechanically recycled in India across an estimated 4,000–7,000 recycling units, predominantly in clusters in Delhi-NCR, Mumbai, Surat, Chennai, and Hyderabad. The sector is fragmented — 80%+ of operators are informal micro-units with no EPR registration — creating consolidation opportunities for formal recyclers with PWP status.