LDPE film recycling washes and pelletizes soft polyethylene — agricultural mulch and greenhouse film, silage wrap, shrink hood and packaging film. The polymer itself is straightforward. What decides whether a line works is everything that arrives with the film, because on agricultural film the contamination can weigh more than the plastic.
That is the whole difference between film and rigid recycling. A drum or a bottle is a shape problem. A roll of mulch film pulled out of a field is a loading problem: it comes in carrying soil, chemistry, water and other polymers, and each of those four has its own removal stage. Specify a line against clean packaging film and then feed it field film, and it will not simply run slower — stages that were never sized for the load will block.
Agricultural Film Is a Different Problem From Packaging Film
Post-industrial and clean packaging film is one of the easiest streams in the industry. It is dry, single-polymer, known origin, and it can often go straight into a compact granulator with no wash line at all — a low-temperature air-cooling granulator for clean PE film exists precisely for that case, and buying a full washing plant for that material is money spent on stages the material never needs.
Agricultural film is the opposite end of the same polymer. It has spent a season in contact with soil, sunlight and applied chemicals, and it was gathered by machine or by hand along with whatever it was lying on. The scale of that stream and the difficulty of handling it are documented in the FAO assessment of agricultural plastics and their sustainability, which is a useful reality check before committing to this feedstock.
The sections below are organised by the four things that arrive with agricultural film and are not film: mineral load, chemical load, water load, and foreign polymer. Each one is removed at a different place in the line, and each one is a reason for a machine that a packaging-film line does not carry.
Load 1 — Soil, Sand and Stones
Mineral contamination is the heaviest thing you will pay to transport, and the first thing you have to get rid of.
Its real cost is not the weight, it is abrasion. Sand embedded in film goes through every knife, every pump impeller and every screw flight on the line. A plant running clean film and a plant running field film can have the same machine list and completely different wear budgets, and that difference does not appear on any quotation.
Removal happens in stages rather than at one machine. Coarse material and loose soil come off in a pre-wash drum before size reduction. After the film is cut, a sink-float separation tank does the heavy lifting: polyethylene floats, and sand, stones, glass and metal fines sink out of the bottom. A high-speed friction washer then takes off what is still adhering, by mechanical action rather than chemistry.
Two practical consequences follow. First, the water circuit has to be sized for the grit, not just for the flow — sludge removal and settling capacity are what keep a film line running, and they are the stages buyers most often trim from a quote. Second, mineral load is the strongest argument for pre-washing before the cutter, because everything removed there is abrasion that never reaches the rest of the plant.
What an undersized water circuit actually does to a shift. Grit does not accumulate politely. It settles wherever the flow slows down — tank corners, pump suctions, the bottom of the friction washer — and once a settling stage is full it stops settling and starts passing solids forward. The visible symptom is not a blocked tank; it is flake that gets dirtier through the day for no apparent reason, and a friction washer that draws more current each hour. By the time anyone connects the two, the line has produced several hours of material at the wrong grade. Settling volume and sludge extraction are the cheapest stages in the quotation and the ones most often deleted from it.
Load 2 — Pesticide, Fertiliser and Odour
Chemical residue is the load that decides your washing temperature, and it is the one buyers underestimate because it is invisible.
Cold water does not remove agrochemical residue, oil or the odour that comes with it. This is the case for hot washing at 85–95 °C with 1–3% alkali, which is also the most expensive stage on the line to operate. It is worth deciding deliberately rather than by default — the article on when hot washing is necessary and when cold is enough works through the specific scenarios, and agricultural film sits firmly on the hot side of that line.
Two things follow from running a hot alkaline circuit on this material:
Wastewater becomes a real engineering item. The effluent from washing field film carries dissolved agrochemicals as well as soil. Discharge consent, treatment and sludge disposal are part of the project, and in some jurisdictions they are the part that determines whether the project is permitted at all. Establish this before ordering equipment, not after.
Odour survives into the pellet if you let it. Residual odour is a commercial problem, not a cosmetic one: film buyers reject smelly pellet because it carries into their product. Odour that survives the wash has to be pulled out in the melt, which means specifying degassing at the extruder rather than hoping the wash line was thorough.
Load 3 — Water the Film Will Not Give Up
Every washed material carries water out of the tank. Film carries far more of it, and holds onto it far harder, than anything rigid.
The reason is geometry. Film has an enormous surface area for its weight, and it folds. Water is trapped in the folds and in the film-to-film contact, where centrifugal force alone cannot reach it. A centrifugal dryer that brings rigid flake to 0.5–2% at 1500 rpm does not achieve the same result on soft film in the same pass, which is why film lines carry a drying sequence rather than a single dryer:
Mechanical squeezing first. A squeezer densifier forces water out under pressure and heat and delivers a compacted, far drier material. This is the stage that makes film drying possible at all, and it is the most common omission in an underspecified quote.
Centrifugal drying second. A centrifugal dryer at 1500 rpm removes the free water that squeezing left behind.
Hot air last. A hot-air stage finishes below 1%, which is the level a stable extrusion needs.
Water that reaches the extruder is not a minor inefficiency. It flashes to steam in the barrel, and the result is bubbles in the strand, unstable pressure at the die and strands that break during cutting. Most film pelletizing instability that gets blamed on the extruder is actually a drying problem three stages upstream.
The squeezer is the stage buyers delete, and the one that produces the complaint. A quotation without it looks competitive because a centrifugal dryer and a hot-air stage appear to cover drying on paper. In practice the dryer receives film that is still carrying free water in its folds, the hot-air stage cannot make up the difference within its residence time, and the plant ends up running the extruder slower to keep the strand together. The lost throughput repays the price of the squeezer quickly, but by then the machine has to be retrofitted into a line that was laid out without space for it.
Load 4 — The Plastics That Are Not LDPE
The fourth load is other polymer, and it is the one no washing stage can touch.
Agricultural film streams routinely arrive with PP baler twine, netting, tape, printed labels and multilayer barrier films. Silage wrap and some greenhouse films are multi-layer by construction. None of this is contamination that a hot alkaline wash removes, because it is not dirt — it is a different plastic bonded to or bundled with yours.
The trap is that sink-float does not catch it either. PP and PE are both lighter than water, so both float, and the density gap between them is too small for a water tank to resolve. The separation stage that removes sand, stones and PET is blind to the polymer contamination that damages your melt. Multilayer film is worse still, because the layers cannot be separated at all by mechanical recycling — barrier layers simply do not melt with the polyethylene and end up as unmelted inclusions and filter load. The Association of Plastic Recyclers design guide covers this from the design side, and its list of film constructions that cause problems is a fair description of what you will be sorting out by hand.
The practical answer is intake control rather than another machine. Know the source, refuse loads that are heavy in twine and netting, and price multilayer film as the lower-grade material it is. This is the same limitation that governs HDPE recycling, where PP caps float alongside the HDPE, and it is the reason polyolefin streams are graded by source discipline rather than by washing quality.
The Extra Stages Film Needs — Starting With Feeding
Everything above is about what comes in with the film. This section is about how film behaves once it is inside the plant, which is a separate problem and the reason a film line does not look like a rigid line.
Loose film will not feed itself. It bridges above openings, wraps around shafts and rides over screw flights instead of being drawn in. Any stage that assumes gravity feed will starve. That is why film size reduction uses a single-shaft shredder with a horizontal pusher: the ram forces material against the rotor rather than waiting for it to fall.
The same problem reappears at the extruder, in a worse form. Dried film is low in bulk density, so a conventional hopper delivers air rather than material and the output collapses. The standard answer is a pelletizing line with an integrated compactor for soft plastics, where the compactor densifies and pre-heats the film and force-feeds the screw. On soft material this is not an accessory. It is what makes stable throughput possible.
Put together, an agricultural film line carries a pre-wash drum, a ram-fed shredder, sink-float, friction washing, a hot circuit, a squeezer, a centrifugal dryer, hot air and a compactor-fed extruder — noticeably more stages than the rigid equivalent. Those stages are what a washing line for soft plastics is built around, and what each of them adds to the investment is set out in what actually adds up in plastic recycling plant cost. Power scales with throughput rather than with material: a 500 kg/h line sits around 150 kW installed and a 3000 kg/h line around 500 kW.
What a Film Line Costs to Run, and Why Scale Does Not Rescue It
Film is the cheapest feedstock on the market and the most expensive to convert. Those two facts are usually presented separately, and putting them together is what makes a film project either work or not.
| Throughput | Installed power | kWh per tonne | People per t/h | Water, m³ per tonne | Floor area |
|---|---|---|---|---|---|
| 200–300 kg/h | 110–160 kW | 440–640 | 8.0–12.0 | 16.0–20.0 | 350 m² |
| 400–600 kg/h | 160–230 kW | 320–460 | 6.0–8.0 | 16.0–20.0 | 400 m² |
| 800–1,000 kg/h | 280–500 kW | 311–555 | 4.4–6.7 | 16.7–22.2 | 750 m² |
| 1,500 kg/h | 380–600 kW | 253–400 | 4.0–5.3 | 13.3–20.0 | 1,000 m² |
Set that against a rigid line at 1,500 kg/h, which runs 128 kWh and 5.7–7.1 m³ per tonne on 600 m². Film at the same tonnage is 253–400 kWh, 13.3–20.0 m³ and 1,000 m². Two to three times the power, roughly three times the water, and two-thirds again the floor.
The reason is entirely in the extra stages this article has been describing: the pre-wash for soil, the squeezer, the hot-air dryer and the air conveying, all of which exist because film holds water and has almost no bulk density. Every one of them is a motor that a rigid line does not switch on.
Water is the number that does not improve
Energy per tonne improves with scale on a film line, from 440–640 down to 253–400 kWh. Water does not. It is 16.0–20.0 m³ per tonne at the smallest tier, actually peaks at 16.7–22.2 in the middle of the range, and is still 13.3–20.0 at full size. Going from 250 to 1,500 kg/h is five times the output for essentially the same water per tonne.
The practical consequence is a planning one. If water supply, or more often effluent treatment capacity, is constrained at your site, that constraint applies at every capacity you might build. It cannot be engineered away by going bigger, and it should be checked before a bale price is negotiated rather than after. The rest of the cost layers are in what adds up in plastic recycling plant cost.
Reading a Bale Before You Buy It
Film is sold by weight and the four loads above are also weight, which is why a film bale rewards inspection more than a bale of bottles does. None of these checks needs equipment.
Weigh it against its size. Two bales of the same dimensions can differ substantially in mass, and on field film the difference is soil and water rather than polymer. A bale that is heavy for its volume is a bale where you are paying film prices for mineral load, then paying again to wash it out and dispose of it as sludge.
Wash a handful and look at what is left. Take film from inside the bale rather than the face, agitate it in a bucket of water, and let the bucket stand. The sediment at the bottom is a fair preview of what your settling stage will see every hour. Fine, gritty sediment is the abrasive kind; loose crumbly soil rinses off far more easily.
Look for what is not film. Twine, netting and tape are visible in the bale face if you look for them, and they are the one load no stage removes. Silage and manure odour is detectable by nose on a warm sample, and odour that you can smell in the bale will still be there in the pellet unless the extruder is specified with degassing.
Where Each Load Is Removed, and What Skipping It Costs
Put the four loads against the stages that handle them and the shape of a film line stops looking arbitrary. Each row is a machine that a clean-packaging-film line does not need and a field-film line cannot do without.
| Load | Removed at | What happens if that stage is missing |
|---|---|---|
| Soil, sand and stones | Pre-wash drum, sink-float, friction washer | Abrasive wear across every knife, pump and screw; ash in the pellet |
| Agrochemical residue and odour | Hot circuit at 85–95 °C with 1–3% alkali | Odour carries into the pellet and buyers reject on smell alone |
| Trapped water | Squeezer, then centrifugal dryer, then hot air | Steam in the barrel, broken strands, throughput cut to hold quality |
| PP twine, netting, multilayer film | Nowhere — intake control only | Unmelted inclusions and constant melt filter load |
The fourth row is the one that changes how a plant is run rather than how it is built. Sand can be washed out and water can be squeezed out; a different polymer cannot be removed by any stage you can buy, which is why film recyclers end up managing suppliers rather than buying more machines. What each of the other three stages adds to the capital and running cost is broken down in the machine-by-machine map of a recycling line.
Frequently Asked Questions
Can LDPE film be recycled?
Yes, with equipment built for soft material. Clean packaging film can go almost directly to a granulator. Agricultural film needs a full sequence — pre-wash, ram-fed shredding, sink-float, hot washing, squeezing, drying and compactor-fed pelletizing — because it arrives carrying soil, agrochemicals, water and other polymers.
Why is film so hard to dry?
Surface area and folding. Film traps water between layers where centrifugal force cannot reach it, so the single dryer that brings rigid flake to 0.5–2% is not enough on its own. Film needs mechanical squeezing first, then centrifugal drying, then hot air to finish below 1%.
Does agricultural film have to be hot washed?
Effectively yes. Cold water does not remove agrochemical residue, oil or the odour that comes with them, so field film generally needs 85–95 °C with 1–3% alkali. The consequence to plan for is wastewater: the effluent carries dissolved chemicals as well as soil, and treatment and discharge consent belong in the project budget from the start.
Can PP twine and netting be separated from LDPE film by washing?
No. Both PP and PE float, and the density gap is too small for a sink-float tank to resolve, so the stage that removes sand and stones passes the twine straight through. Polymer contamination has to be controlled at intake by knowing and refusing the wrong loads.
Why do film pellets sometimes smell, and does it matter?
Odour compounds absorbed during the film’s service life survive washing and are released again in the melt. It matters commercially, because film buyers reject pellet that carries odour into their product. If the feedstock has been in contact with agrochemicals or silage, specify degassing at the extruder rather than relying on the wash line.
Is a compactor really necessary for film pelletizing?
For loose film, yes. Dried film has very low bulk density, so a conventional hopper feeds air and output collapses. A compactor densifies and pre-heats the material and force-feeds the screw, which is what makes throughput stable rather than merely higher.
How can I judge how much soil a film bale is carrying?
Compare its weight against its size first — on field film, a bale that is heavy for its volume is heavy with soil and water, not polymer. Then take film from inside the bale, agitate it in a bucket of water and let it stand. The sediment shows what your settling stage will handle every hour, and fine gritty sediment is the abrasive kind that drives wear rather than the loose soil that rinses away.
What happens if a film line is built without a squeezer?
The centrifugal dryer receives film still holding free water in its folds, the hot-air stage cannot recover the difference in its residence time, and the plant compensates by running the extruder slower to stop strands breaking. The quotation looks cheaper and the line runs below its rated output permanently. Retrofitting is possible but awkward, because the layout was never given space for the machine.
If you are assessing a film stream, send us a sample description — the source of the film, how it was collected and how much soil it carries tell us more about the line you need than a tonnage figure does.
