LDPE recycling is not difficult chemistry. Low-density polyethylene washes well, melts at a modest temperature and has established buyers. Yet film projects fail more often than rigid ones, almost always for one reason — the business case was built on the weight of the bale rather than the weight of the pellet.
This article is about that gap. Where the tonnage goes, which losses can be engineered out and which cannot, and what the three common LDPE streams do differently. It is not a walkthrough of how a film line is built or a guide to selecting one.
The same polymer arrives in three conditions that have almost nothing in common.
What LDPE Recycling Involves
LDPE recycling recovers low-density and linear low-density polyethylene film through size reduction, multi-stage washing, density separation, dewatering and drying, and then flake sale or pelletizing. The polymer stays unchanged throughout, and everything the line does is remove soil, moisture, adhesive, ink and non-target material from around it.
Two properties of film set this route apart from every rigid one, and both work against yield.
Film has an enormous surface area for its mass. Everything that attaches to a surface — soil, dust, adhesive, ink, product residue — attaches in proportion to that area. The same geometry means film carries far more water out of a wash tank than rigid flake does, and holds it in folds where centrifugal force cannot reach.
Film has almost no bulk density. Washed film flake is light and fluffy, it bridges in hoppers, and it will not fall into an extruder screw under gravity. That is why film pelletizing uses compactors and squeezers that rigid lines have no use for.
Neither problem is about polyethylene. Both are about the shape it arrives in, and they explain most of the difference between a film project and a bottle project.
Where the Tonnage Goes Between the Bale and the Pellet
A bale is weighed on arrival and a pellet is weighed on despatch, and the gap between them is the most important figure in a film recycling business case. It can only be measured by running the actual material, but where the losses sit is known in advance.
Six places the tonnage leaves. Only two of them can be reduced by buying better equipment.
| Where it leaves | What it is | Where it goes | Can equipment reduce it |
|---|---|---|---|
| Soil and grit | Field soil on mulch film, warehouse dust on stretch wrap | Pre-wash tank bottom, then water treatment sludge | No — it was never polymer |
| Water | Moisture in the bale, plus water picked up in washing | Dewatering, drying and evaporation | Partly — drying can be more efficient, but water still has to leave |
| Fines | Film cut below the screen deck of downstream equipment | Wash water, dust extraction, filter cake | Yes — screen selection and rotor condition change this |
| Non-target polymer | PP raffia, PET tape backing, laminate, rigid fragments | Float-sink discharge, sorting reject, melt filter | Partly — sorting removes it, but the tonnage is gone either way |
| Labels, tape and paper | Adhesive tape, printed labels, cardboard in bales | Friction washing, skimming, filtration | Yes — wash intensity decides how much reports to reject |
| Degraded fraction | UV-embrittled mulch film, over-sheared material | Melt filter, fines screening, off-spec pellet | Partly — gentler processing helps, but sun damage is done |
Only two of the six respond to equipment choice. The rest are properties of the bale that arrived, which is why the most valuable work a film recycler does sits upstream of the plant — specifying how bales are collected, stored and kept dry. Where post-consumer film supply aggregates is mapped by resources such as the Plastic Film Recycling directory. The first row is the one most often missed. Soil was never polymer, so it is not inefficiency; it means the bale never held as much polymer as its weight ticket implied.
Three LDPE Streams That Behave Nothing Alike
Agricultural film, stretch and shrink wrap, and post-consumer packaging film are all LDPE or LLDPE, and a specification written for one will misconfigure a line for the others. Their contamination differs in kind rather than in degree, so the wash section has to be sized against the worst of them.
| Agricultural mulch and greenhouse film | Stretch wrap and shrink film | Post-consumer packaging film | |
|---|---|---|---|
| Dominant contamination | Soil, grit, plant residue, irrigation salts | Warehouse dust, tape, label paper | Food residue, mixed polymers, ink |
| Moisture on arrival | High, variable with weather at recovery | Low, usually stored indoors | Moderate, depends on collection |
| Polymer consistency | Good — often one film specification per farm | Very good — near single-grade | Poor — LDPE, LLDPE, HDPE and PP arrive together |
| UV degradation | Significant after a season in the field | None | Minor |
| Wash intensity needed | Full — pre-wash, hot wash, chemistry, friction stages | Light — cold wash is often enough | Full, aimed at organic residue rather than soil |
| Realistic output grade | Dark pellet for non-critical film and moulding | Highest of the three, near single-grade | Grey to dark, set by ink and polymer mix |
Stretch wrap is the easiest film in the industry. Mulch film is among the hardest.
The published specification for the PP PE soft film recycling washing line makes that range visible. Steam consumption is listed from 0 to 600 kg/h and chemical consumption from 0 to 12 kg/h across the SHW300 to SHW2000 models — ranges that start at zero because clean stretch wrap needs neither, while field-recovered mulch film sits at the top of both.
The consequence is direct. Specify the wash section for the dirtiest film you intend to run, not the average, because heat and chemistry can be turned down but cannot be added to a tank that was never installed.
Water Is the Consumable That Decides Whether the Line Pays
Film washing is water-intensive in a way rigid washing is not, for the same surface-area reason that makes film hard to dry. More surface means more water contact, more suspended solids in the tank, and a wash loop that loads with soil far faster than a bottle line loads with product residue.
On agricultural film the water loop is handling a soil slurry, not a rinse.
Three consequences follow, and they compound on agricultural film.
The loop has to be closed or the line will not be permitted. Discharging film wash water is not an option in most jurisdictions and would not be affordable anywhere. Closed-loop filtration is engineered into SUHUI film configurations rather than added afterwards, and the published reduction in fresh water demand on the PP PE film compacting pelletizing line is 60–80%.
Soil becomes sludge, and sludge has a disposal cost. On a mulch film line the pre-wash discharges a continuous stream of wet soil to be dewatered and hauled — a real operating line item that scales with how badly the film was recovered rather than with how good the line is.
Grit is abrasive, and it circulates. Sand in a recirculating loop wears pump impellers, tank liners and friction washer screens, which is behind most unscheduled maintenance on agricultural film lines. The pre-wash earns its place by getting grit out before the loop distributes it.
Why the Last Few Percent of Moisture Costs the Most
Water leaves film flake in two stages with very different economics. Spinning and pressing shed the free surface water for very little power, then hit a floor they cannot pass. Everything below that floor has to be boiled off, and evaporation stays expensive per kilogram however efficient the dryer is.
Mechanical removal is cheap and stops early. Everything below that floor is paid for in heat.
The published sequence puts numbers on the split. Spinning followed by pressing gets film flake to 12% and can go no further. Hot air with cyclone separation then reaches 5%, the specified condition for bagged flake. Where flake feeds a compactor and extruder directly, the compacting line takes it to 1%.
Film is the hardest form to dry and rigid flake among the easiest, for a purely geometric reason. A rigid flake is a stiff curved chip that sheds water. A film flake is limp, folds over on itself in the dryer, and traps water between the folded surfaces where centrifugal force acts on both sides equally and cancels out.
That geometry is why the plastic film squeezer granulating machine exists as a distinct machine. A high-torque screw of 300, 320 or 350 mm running at 65 to 83 rpm compresses water and trapped air out of washed film, densifies it, then melts and cuts it in the same unit across a 300–750 kg/h range, displacing part of the thermal drying load with mechanical work.
One temperature relationship matters before setting a hot wash target. LDPE melts around 105–115°C against roughly 130–135°C for HDPE and 160–165°C for polypropylene, so a hot wash at 60–80°C runs much closer to LDPE’s softening range. Film does not melt there, but it softens, and softened film is limper and harder to dewater.
What LDPE Does in the Extruder That Rigid Polyethylene Does Not
Pelletizing washed film is where low bulk density and the volatile load come due at once. A gravity hopper will not feed fluffy flake into a screw, and the moisture, ink solvent and adhesive residue that survived washing all vaporise in the barrel and need an exit before the die.
Three problems arrive together at the extruder, and each has a specific piece of hardware attached to it.
Bulk density is solved before the screw, not by it. The compacting pelletizing line puts an SHP-series compactor ahead of the extruder, where a high-speed rotor densifies flake with friction heat and feeds the screw continuously, from 150–250 kg/h on the SHP80 to 1,000–1,200 kg/h on the SHP180. Without a compactor or squeezer, feed rate on film is not stable.
Volatiles need a route out of the melt. Residual moisture, ink solvent and tape adhesive all flash off inside the barrel, and with no exit they finish up in the pellet as voids and silver streaking. Vacuum exhaust zones are the published answer — one or two of them on the compacting configuration, with an optional second extruder for heavily contaminated feed.
Melt behaviour varies more than on a rigid line. Post-consumer film is rarely one grade — LDPE, LLDPE and some HDPE arrive together, and long-chain-branched LDPE behaves quite differently in the melt from linear LLDPE. That variability is why the film pelletizing line offers three cutting configurations rather than one. Strand pelletizing is the versatile default, a water ring cutter suits soft or sticky melt, and underwater cutting gives the most uniform granule. Our article on plastic recycling pelletizing compares the single-stage and double-stage answers to that variability.
Printing Ink Sets the Colour You Can Sell
Ink is the loss that never appears in the yield ledger, because none of the tonnage leaves. It stays in the pellet and shows up in the price instead. Mechanical recycling has no deinking stage, so whatever was printed becomes part of the colour of the output.
Surface-printed ink is partly removable. Hot alkaline washing combined with friction scrubbing lifts a portion of it, and the more aggressive the wash the more comes off. Reverse-printed film, where the ink sits sandwiched between layers, releases nothing at all — it is not on a surface the wash can reach.
What remains disperses through the melt during pelletizing, and colours only mix downward. Lightly printed clear stretch wrap yields a near-natural pellet. Heavily printed retail film yields grey, and grey cannot be made light again mechanically. Assess ink coverage alongside contamination, because the price gap between a natural pellet and a dark one is often larger than the gap a few points of yield creates.
Which Line Configuration Matches Your Film
Once the stream is characterised, the configuration question is narrow. Film type sets the wash intensity, moisture and bulk density set what sits between the dryer and the extruder, and the target output decides whether the line stops at flake or continues to pellet. Published SUHUI configurations map onto those three decisions directly.
Three decisions, and the film itself answers all three.
| Published configuration | Range | What it does | When it fits |
|---|---|---|---|
| Soft film washing line, SHW300 to SHW2000 | 250–2,000 kg/h, 10–20 mm flake, moisture below 5% | Anti-tangle crushing, pre-wash, friction washing, optional hot wash at 60–80°C, float-sink, two-stage dewatering, drying | Any film stream where the deliverable is washed dry flake |
| Film squeezer granulating machine, SH300 to SH350 | 300–750 kg/h, granule 12 mm and above | Squeezes water and air from washed wet film, densifies, melts and cuts in one unit | Wet film going straight to pellet, where drying load matters |
| Film compacting pelletizing line, SHP80 to SHP180 | 150–1,200 kg/h, 8–12 mm flake, drying below 1% | Compactor feeding an extruder with one to two vacuum zones, four filter options, three cutting options | Continuous film to pellet, where output grade is the priority |
Read installed power alongside capacity and the scale economy shows itself. The SHW range runs from 195 kW at 250–300 kg/h to 760 kW at 1,700–2,000 kg/h — capacity multiplies by about seven while installed power multiplies by about four. How a film line is built is covered in our guide to the plastic film recycling line, and how to compare specifications in choosing a plastic film washing line. The friction stages those lines rely on are covered in our article on the friction washer.
Frequently Asked Questions
What is LDPE recycling?
It is the recovery of low-density and linear low-density polyethylene film through size reduction, washing, density separation, dewatering and drying, then flake sale or pelletizing. The polymer is unchanged; the process removes soil, moisture, adhesive, ink residue and non-target material from around it.
Why does a tonne of baled LDPE film not produce a tonne of pellet?
Because six things leave along the way — soil and grit, water, fines cut below screen size, non-target polymer, labels and tape, and a degraded fraction. Only fines and label removal respond to equipment choice; the rest are properties of the bale.
Can agricultural mulch film and stretch wrap run on the same line?
Yes, if the line is specified for the mulch film. Heat and chemistry can be turned down for clean stretch wrap but cannot be added to a wash section that was never installed. Published steam and chemical ranges start at zero for that reason.
What moisture level does LDPE film flake need before pelletizing?
Two-stage mechanical dewatering brings washed film below 12%, and thermal drying takes it below 5% for bagged flake. Where the flake feeds a compactor and extruder directly, the published target is below 1%, because residual moisture becomes voids and streaking in the pellet.
Does washing remove printing from recycled LDPE film?
Only partly. Hot alkaline washing and friction scrubbing lift some surface-printed ink, but reverse-printed film holds ink between layers where no wash reaches. Whatever remains disperses through the melt, so heavily printed film yields a grey pellet that cannot be made light again.
Why does LDPE film need a compactor or squeezer before the extruder?
Because washed film flake has almost no bulk density. It bridges in hoppers and will not fall into a screw under gravity, so feed rate is unstable. A compactor densifies it with friction heat; a squeezer removes water and air mechanically while densifying in the same pass.
How much water does an LDPE film washing line use?
More than a rigid line, because film presents far more surface to the water, and consumption depends on soil load. Closed-loop filtration is standard rather than optional, with published reductions in fresh water demand of 60–80% on the film compacting configuration.
Comparing Film Line Quotations Against These Numbers
- Plastic Recycling Washing Line — make-up water per tonne and the 60 to 75 percent yield question
- Plastic Recycling Machine Overview — where the film line sits against shredding, pelletizing and full turnkey budgets
- Plastic Film Recycling Line — the ten stages a film line runs, and where the squeezer replaces a dryer
- Choose a Plastic Film Washing Line — comparing stage-by-stage specifications in writing, with a 20 to 30 percent capacity buffer
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