densifier (plastic film densifier)

Densifier refers to equipment that increases the bulk density of lightweight, bulky plastic waste — primarily LDPE film, EPS foam, HDPE shrink wrap, and agricultural film — from 10–50 kg/m³ (as collected) to 250–500 kg/m³ (densified product). Two principal technologies are used in India: (1) Friction agglomerator (hot densifier) — a rotating blade in a cylindrical chamber generates friction heat (100–140°C) that softens the film surface; the material tumbles, semi-melts, and forms irregular granules (agglomerates) of 5–30 mm; output bulk density 250–400 kg/m³; throughput 100–800 kg/hr; cost Rs 4–12 lakh for Indian-made units; (2) Screw compactor / cold densifier — a screw conveyor compresses film without heating, producing a compressed 'biscuit' or 'log'; less energy-intensive but output is less flowable and slightly lower density; used for EPS foam and agricultural film in India at Rs 3–8 lakh per unit.

The economics of densification: loose LDPE film from kabadiwala collections costs Rs 50–100 per trip to transport if a full truck load (20 tonnes) requires 400–800 m³ of volume. At 15 kg/m³ bulk density, a 20-tonne LDPE load fills 1,333 m³ — impossible in a standard truck (70–80 m³ volume). After densification to 350 kg/m³, 20 tonnes occupies 57 m³ — one standard truck load. Densification is a prerequisite for any LDPE or EPS film recycling business that collects from dispersed sources: without it, transport cost exceeds material value and the business does not work. At a densification cost of Rs 0.5–1.5/kg (energy + labour + maintenance), the economics become strongly favourable.

Densifier output quality: friction agglomerators partially melt and oxidise the surface of film — this is acceptable for granulation feed (the agglomerates are re-extruded anyway) but increases MFI variability and can trap moisture in the agglomerate mass if the film was wet. Agricultural film densified directly from the field without washing often has 5–15% soil and moisture content — this must be accounted for in the effective material cost calculation. Some densifier configurations include inline washing before agglomeration (wet agglomerators), which produces cleaner output at higher energy cost (Rs 1.5–3/kg versus Rs 0.5–1.5/kg for dry densification).

For Indian recyclers building LDPE or EPS collection infrastructure, the right densifier configuration depends on collection geography and customer: aggregators in urban areas (where LDPE is collected from retailers and packaging waste generators in small lots) benefit from mobile or modular densifiers installed at collection points — Rs 3–5 lakh per unit with 200 kg/hr throughput — creating a hub-and-spoke densification network. Centrally located recyclers with their own washing lines can densify at the plant after washing, eliminating field-densification capital cost.