LDPE (Low-Density Polyethylene)

LDPE (Low-Density Polyethylene) is produced by high-pressure free-radical polymerisation of ethylene, yielding a highly branched polymer with density 0.910–0.940 g/cm³ and melting point 98–115°C. The branching prevents tight crystalline packing, making LDPE soft, flexible, and transparent compared to HDPE. It carries Resin Identification Code 4. Major Indian applications include: retail carry bags (where not banned), agricultural mulch film (50–200 micron), greenhouse film, bubble wrap, courier bags, shrink wraps, and inner liners for corrugated boxes. India's LDPE consumption is approximately 1.2–1.5 million tonnes per year.

Recycling LDPE presents a fundamentally different logistical challenge than rigid plastics: low bulk density (15–40 kg/m³ as loose film) makes collection, transport, and storage expensive relative to material value. A cubic metre of loose LDPE film contains only 15–40 kg of material worth Rs 5–8/kg at the kabadiwala level — Rs 75–320 per cubic metre of space. Densification is a prerequisite: LDPE film is granulated or run through a densifier (friction or extruder type) to compact it to 350–500 kg/m³ before transport. Post-densification, LDPE scraps trade at Rs 12–20 per kg for clean mono-grade agricultural film, and Rs 6–10 per kg for mixed/contaminated film.

Processing at the recycling plant: LDPE film requires wet shredding or rotary shredding to avoid heat buildup (melting at 98°C, lower than other polyolefins), followed by float-sink separation (LDPE density ≤0.940 means it floats — separating it from PET, PVC, PS which sink), washing, and extrusion at 175–195°C. Key contaminants: food residue on retail bags raises BOD in washing water; agricultural film carries soil, pesticide residues, and stones (abrasive, damages extruder screws); adhesive labels cause gel specs in film output. The MFI of recycled LDPE rises with each reprocessing cycle (chain scission), eventually making it unsuitable for blown film (requires MFI 0.2–2.0 g/10 min at 190°C/2.16 kg) — degraded rLDPE is downgraded to injection moulding applications or blended with virgin.

In India, the shift away from LDPE carry bags under the single-use plastics ban (effective July 2022 under PWM Rules 2022 Amendment) for bags below 75 micron has changed the collection economics — the high-volume retail bag stream has shrunk, but demand for agricultural film recycling has grown. Recyclers building LDPE capacity should target the industrial and agricultural film segment — cleaner, less contaminated, and available in larger lot sizes from farms and greenhouses (Rs 5,000–10,000 per tonne delivered), rather than mixed post-consumer retail bags.