Why Printed and Sticky LDPE Film Needs a Complete Line, Not a Single Machine

The best LDPE film pelletizing line for printed and sticky film waste is not defined by the extruder alone. It is defined by how well nine consecutive process stages hand material to each other: pre-sorting, shredding, dry pre-cleaning, wet granulation, float-sink separation, friction washing, hot washing, mechanical and thermal drying, and finally densification followed by vented extrusion with melt filtration. Printed film and adhesive-loaded film punish every weak link in that chain, and the failure always shows up at the same place, in the pellet, as black specks, color drift, porosity or odor. Buyers who shop for a pelletizing machine in isolation almost always discover that the machine was never the constraint.

Printed and sticky film is the hardest LDPE stream in the recycling industry for three structural reasons. First, ink is not surface dirt but a bonded coating layer that represents 2 to 8 percent of film weight, and its binder chemistry decomposes into carbonized particles at melt temperatures that a poorly configured line reaches routinely. Second, the contamination is chemically diverse: agricultural film arrives with 20 to 60 percent soil and grit by weight, food packaging film carries fats and organic residue, stretch film carries pressure-sensitive adhesive, and heavy-duty sacks carry mineral or chemical powder. No single unit operation removes all four. Third, film has almost no bulk density. Loose washed film flake sits at 0.03 to 0.08 tons per cubic meter, roughly one twentieth the bulk density of rigid regrind, so conveying, feeding and metering all need dedicated engineering rather than standard components.

Polyretec, a Wanplas factory, has built plastic recycling equipment since 2010 and has operated as an independent brand since 2017, with more than 100 delivered projects, service coverage across more than 50 countries and a technical team of over 24 engineers. Printed and adhesive-contaminated LDPE film has been a repeat specialty rather than an occasional order: delivered projects include a printed bag and film pelletizing system in Turkey, a heavy-duty washing line for LDPE film with sticker labels in Mexico, and a fully automated PP and PE film washing plant in Taiwan built around the PTW1000 configuration. This article sets out the full engineering logic of that line, stage by stage, with the parameters that actually determine whether the finished pellet sells into a demanding application or a low-value one.

A film pelletizing line does not fail at the extruder. It fails three stages upstream, and the extruder is simply where the evidence becomes visible.

Grading the Difficulty of LDPE Film Waste Streams

Every line specification starts with an honest difficulty grade for the incoming material, because the same nominal throughput requires very different equipment depending on the stream. The grading below is the working scheme used to size wash tanks, blade steel, heating load and filtration on Polyretec projects. It separates four common LDPE film families by ink load, contamination type, abrasion risk and the dominant processing challenge each one creates.

Film Stream	Typical Ink Load (percent of film weight)	Dominant Contamination	Abrasion Risk	Difficulty Grade	Critical Line Stage
Post-industrial printed packaging film (converter trim, misprints)	3 to 8	Surface ink, minor dust	Low	Medium	Hot washing plus fine melt filtration
Post-consumer printed packaging film (bags, sacks, shrink hoods)	2 to 6	Ink, food residue, grease, paper labels	Medium	High	Hot washing with caustic and surfactant dosing
Agricultural film (mulch film, greenhouse film, silage film)	0 to 2	Soil, sand, stones, plant matter, moisture, 20 to 60 percent by weight	Very High	Very High	Dry pre-cleaning plus grit removal and abrasion-resistant blades
Stretch and wrapping film with adhesive	0 to 3	Pressure-sensitive adhesive, tape residue, pallet dust	Low	High	Temperature-controlled conveying and densification
Heavy-duty industrial sacks (cement, resin, fertilizer, masterbatch)	2 to 6	Mineral and chemical powder, printed liner, occasional paper ply	High	High	Bag opening, de-dusting and multi-stage rinsing
Mixed post-consumer film from municipal collection	2 to 8	All of the above plus foreign polymer and organics	Very High	Very High	The complete chain with buffered capacity at every stage

Two practical rules come out of this grading. The first is that difficulty is set by the abrasive and chemical load, not by the printing. Agricultural film with almost no ink is harder to process than a heavily printed converter trim, because sand destroys blades, pumps and screw flights while ink only degrades appearance. The second rule is that a line specified for one grade rarely upgrades cleanly to a harder grade. Adding grit removal, heating capacity and a larger water treatment loop after installation costs far more than including them in the original layout, which is why the honest answer to what will I feed this line in three years matters more than this month’s bale supply.

Ink Layers: Why Printing Governs Pellet Color and Black Speck Count

Printing ink is the single feature that decides whether a recycled LDPE pellet sells as a light gray general-purpose grade or a dark charcoal filler grade. Ink typically accounts for 2 to 8 percent of printed film weight, and its behavior in the process depends entirely on binder chemistry rather than on color.

Three binder families dominate flexible packaging. Nitrocellulose-based inks are the most common on surface-printed polyethylene bags; they are alkali-sensitive, which makes them the easiest family to remove in a caustic hot wash, but they are also thermally fragile and begin decomposing well below normal polyethylene processing temperatures. Polyurethane-based inks, used where lamination bond strength matters, resist alkali far better and often need a longer residence time, higher caustic concentration and a stronger surfactant package. Water-based inks respond well to temperature and mechanical friction but can redeposit onto flake surfaces if the wash water is not continuously cleaned, producing a gray haze that no amount of extra washing removes.

The thermal behavior matters as much as the chemistry. Ink binders that survive washing enter the extruder as an organic coating on the flake surface. Below roughly 215 degrees Celsius melt temperature they largely volatilize and leave through the vacuum vents. Above roughly 230 degrees Celsius they carbonize into hard, dark particles that the melt filter must catch. This is why black speck count is a temperature problem before it is a filtration problem: a line running a melt temperature 20 degrees too high will generate specks faster than any screen can remove them, and the operator will blame the filter.

Reverse-printed laminate is the boundary case. When ink sits between two film plies, the outer ply mechanically shields it from both chemical attack and friction, so wash efficiency drops close to zero. The realistic commercial strategy for laminate-heavy input is deliberate color homogenization: accept a stable gray or charcoal pellet, control the color difference value batch to batch through silo blending, and sell into applications where color is not a specification. Promising a natural-colored pellet from reverse-printed laminate is the most common technical overreach in this market.

Soil, Grease, Adhesive and Powder: The Four Contamination Families

Ink defines appearance, but the four contamination families below define equipment wear, water consumption, energy demand and process stability. Each family requires a different unit operation, and the reason a printed and sticky film line looks expensive on paper is that it must carry all four countermeasures simultaneously.

Mineral soil and grit. Agricultural film can arrive at 20 to 60 percent contamination by weight, mostly soil, sand and small stones, with high moisture content that inflates bale weight further. Mineral particles are harder than tool steel edges and will erode wet crusher blades, pump impellers, screw flights and even tank walls if allowed to circulate. The engineering answer is to remove as much grit as possible while it is still dry, then to design every wet stage with a sedimentation path so that the fraction which does enter the water loop settles out instead of recirculating.

Fats, oils and organic residue. Food packaging film carries grease, protein residue and sugars. These do not respond well to cold water, but they saponify readily in a caustic hot wash. Left in place, they cause three downstream problems: odor in the finished pellet, foaming in the water treatment loop, and a surface film on flake that reduces friction washer efficiency for everything else in the batch.

Pressure-sensitive adhesive. Stretch film, tape and sticker labels bring adhesive residue that behaves like a thermoplastic with an extremely low softening point. It stays manageable below roughly 40 degrees Celsius and becomes tacky between 40 and 60 degrees Celsius, which is easily reached inside a compaction screw or an agglomerator running against back pressure. Softened adhesive binds flakes into plugs that bridge above the extruder throat and stall the line. Countermeasures are mechanical and thermal rather than chemical: water-jacketed feeder housings held below 45 degrees Celsius, slightly reduced compaction ratios, and anti-bridging paddles or scrapers in hoppers.

Mineral and chemical powder. Heavy-duty sacks retain cement, fertilizer, resin dust or masterbatch pigment inside folds and seams. Powder is not abrasive in the same way as sand, but it raises ash content directly and it blinds melt filter screens quickly because the particles are fine and deformable. Bag opening followed by mechanical de-dusting before any water contact is far more effective than trying to wash powder out later, since wetted powder turns into a slurry that coats everything it touches.

Density, Thickness and Bulk Density: The Physics Behind Line Design

Three physical properties of LDPE film set hard boundaries on what the line can and cannot do, and a good specification treats them as design inputs rather than footnotes.

Density. LDPE sits at 0.915 to 0.935 grams per cubic centimeter, comfortably below water. This is the single most useful property in the whole process, because it makes float-sink separation possible: LDPE and other polyolefins float while PET, PVC, aluminum foil fragments, sand and stones sink. The margin is generous against PET at roughly 1.38 and PVC at roughly 1.40, which is why a properly operated float-sink stage removes those contaminants almost completely. The margin against PP at 0.90 to 0.91 is effectively zero, so PP film cannot be removed by density at all.

Thickness. Film in the recycling stream spans 8 to 150 micrometers, from thin shopping bags and stretch wrap to heavy-duty sack liners and greenhouse film. Thin film tears and wraps; thick film resists cutting and carries more contamination per piece. A wet crusher screen sized for one end of the range will either pass unshredded pieces or produce excessive fines at the other end, which is why blade configuration and screen aperture are chosen against the dominant thickness band, not against an average.

Bulk density. Loose film waste is between 0.03 and 0.08 tons per cubic meter. After washing and drying, the flake is still in that range. An extruder throat, by contrast, needs material approaching 0.30 tons per cubic meter or higher to feed reliably by gravity. That gap of roughly one order of magnitude is the reason film lines carry an agglomerator or a heavy compaction force feeder, and it is also the reason film conveying uses screw conveyors, blowers and mechanically assisted hoppers rather than the simple belt arrangements that work for rigid regrind.

Property	Typical Value for LDPE Film Waste	Design Consequence
Polymer density	0.915 to 0.935 grams per cubic centimeter	Float-sink separation removes PET, PVC, foil, sand and stone
PP film density (contaminant)	0.90 to 0.91 grams per cubic centimeter	Cannot be separated by density; needs near-infrared sorting or source control
Film thickness range	8 to 150 micrometers	Blade geometry and screen aperture must target the dominant band
Loose bulk density	0.03 to 0.08 tons per cubic meter	Mechanically assisted conveying and feeding throughout
Agglomerated bulk density	0.30 to 0.45 tons per cubic meter	Stable gravity feeding into the extruder throat
Melting point	105 to 115 degrees Celsius	Hot wash must stay below softening; agglomerator control is critical
Working melt temperature	195 to 215 degrees Celsius	Upper limit set by ink carbonization, not by polymer degradation

Polymer Contaminants: PP Film, Labels, Metals and Multilayer Structures

Density separation solves the easy half of the contamination problem. The remaining half consists of materials that either share LDPE density or are bonded to it, and each requires its own countermeasure.

Polypropylene film. PP is the most common polymer contaminant in polyolefin film bales and the hardest to remove, because at 0.90 to 0.91 grams per cubic centimeter it floats alongside LDPE. Modest PP content, roughly below 5 percent, is tolerable in general-purpose recycled LDPE and mostly shows as a slightly higher stiffness and a small drop in impact performance. Higher PP content produces gels, uneven melt behavior and inconsistent film blowing downstream. The two effective controls are near-infrared optical sorting on dry flake before washing, and supply-side control of what enters the bale. Optical sorting adds capital cost and only pays back when the customer specification genuinely requires it.

Paper labels and paper plies. Paper disintegrates in the wet stages and largely leaves with the water, but the fibers that remain increase ash content and produce visible brown specks. Multi-stage rinsing with fresh water on the last stage, plus a well-designed water treatment loop that removes fiber rather than recirculating it, is the practical answer.

Metals. Ferrous fragments come from staples, wire, clamps and general handling damage; non-ferrous fragments come from aluminum foil laminate and hardware. Magnetic separation over the infeed conveyor handles ferrous material cheaply and should always be installed. Eddy current separation removes non-ferrous fragments and is worth the investment whenever laminate content is significant, because aluminum flake fragments are hard, abrasive and highly visible in the finished pellet.

Multilayer and barrier structures. Laminates containing polyamide, ethylene vinyl alcohol or aluminum foil cannot be separated into their components by any mechanical washing process. They behave as infusible or partially infusible inclusions in the LDPE melt and appear as gels or specks. Their impact is controlled at the filter, not in the wash: finer melt filtration catches more of them at the cost of higher melt loss and more frequent screen changes. When laminate content is high, the honest engineering position is to target a lower-grade application for the pellet rather than to chase a filtration fineness the line cannot sustain.

Complete Line Architecture: Material Flow From Bale to Big Bag

A complete LDPE film washing and pelletizing plant is a sequence of buffered unit operations, each with its own throughput curve, and the art of line engineering is matching those curves so no stage starves or floods the next one. The table below is the full stage list for a printed and sticky film line, with the equipment parameters that a buyer should see on a technical offer. Throughput figures assume a nominal 1000 kilograms per hour of finished pellet; a 500 kilograms per hour line scales the same architecture down rather than deleting stages.

Stage	Equipment	Key Parameters	Function	Removal or Effect
1. Infeed	Chain plate conveyor with sorting platform	Belt width 1000 to 1500 millimeters, speed 3 to 12 meters per minute, variable frequency drive	Bale feeding and manual removal of oversize foreign objects	Removes rope, wood, rigid parts, textiles
2. Ferrous removal	Overband or drum magnetic separator	Magnetic field strength 8000 to 12000 gauss at the working gap	Continuous ferrous extraction	Removes 95 percent or more of loose ferrous fragments
3. Non-ferrous removal	Eddy current separator	Rotor speed 1500 to 3000 revolutions per minute, belt width 1000 to 1200 millimeters	Aluminum and non-ferrous metal ejection	Protects blades and reduces visible metallic specks
4. Shredding	Single-shaft or double-shaft shredder	Rotor diameter 400 to 800 millimeters, blades in D2 or SKD-11 tool steel, screen 60 to 150 millimeters, drive 55 to 160 kilowatts	Size reduction of bales and large sheets	Produces conveyable, meterable fragments
5. Dry pre-washing	Friction bag opener plus de-dusting and grit removal drum	Rotor speed 300 to 600 revolutions per minute, perforated screen 8 to 20 millimeters	Mechanical release of dry soil and powder	Removes 40 to 60 percent of dry soil before any water contact
6. Wet granulation	Wet crusher with water injection	Knife gap 0.3 to 0.8 millimeters, screen aperture 30 to 60 millimeters, rotor 400 to 900 revolutions per minute, drive 55 to 132 kilowatts	Final size reduction under water spray	Detaches soil, prevents dust, cools the cut
7. Float-sink separation	Two or three float wash tanks in series with screw discharge	Tank length 3 to 6 meters each, paddle agitation, inclined discharge screw at 25 to 35 degrees	Density-based sorting	Removes PET, PVC, foil, sand, stone; each additional tank raises purity
8. Friction washing	High-speed friction washer, counter-current	Rotor speed 700 to 1200 revolutions per minute, screen 3 to 8 millimeters, drive 30 to 55 kilowatts	Mechanical scrubbing of flake surfaces	Removes over 90 percent of loosely bound surface contamination
9. Hot washing	Heated wash reactor with agitator	75 to 95 degrees Celsius, caustic soda 0.5 to 2.0 percent plus surfactant, residence 10 to 20 minutes, steam or thermal oil heating	Chemical attack on ink binders, grease and adhesive	Removes 70 to 90 percent of surface ink and most saponifiable residue
10. Rinsing	Rinsing tank plus second friction washer	Counter-current fresh water on the final stage	Chemical carry-over removal	Neutralizes flake surface, prevents redeposition
11. Mechanical dewatering	Horizontal centrifugal dryer	Rotor 700 to 1000 revolutions per minute, screen 0.5 to 1.5 millimeters, drive 22 to 45 kilowatts	Bulk water removal	Outlet moisture 3 to 8 percent
12. Thermal drying	Hot air pipe dryer plus vertical drying silo	Air temperature 80 to 120 degrees Celsius, silo residence 15 to 40 minutes	Residual moisture removal and buffering	Outlet moisture below 1 percent
13. Agglomeration	Agglomerator or high-compaction force feeder	Rotor 700 to 1000 revolutions per minute, water-cooled housing, drive 90 to 250 kilowatts	Densification of dried film flake	Bulk density raised to 0.30 to 0.45 tons per cubic meter
14. Extrusion	Single-screw extruder with double-stage venting, or two-stage extrusion system	L/D 30 to 36 to 1, vacuum minus 0.08 to minus 0.095 megapascals, barrel zones 160 to 200 degrees Celsius	Melting, homogenization and devolatilization	Removes residual moisture and ink volatiles
15. Melt filtration	Hydraulic double-piston screen changer, continuous belt filter, or fully automatic laser-drilled rotary disc filter	Filtration fineness 80 to 150 micrometers, filter area matched to throughput	Removal of carbonized and infusible particles	Determines black speck count in the finished pellet
16. Pelletizing	Water ring die-face pelletizer or underwater pelletizer	Die hole diameter 2.8 to 4.0 millimeters, blade set matched to throughput	Melt cutting and cooling	Produces uniform pellet geometry
17. Pellet handling	Centrifugal pellet dryer, vibrating classifier, blending silo, metal detector	Silo volume for 4 to 12 hours of production	Drying, fines removal, batch homogenization, final safety check	Eliminates batch color variation and residual metal
18. Packing	Automatic weighing and bagging station	25 kilogram bags or 500 to 1000 kilogram big bags	Finished goods packaging	Traceable lot control

Two architectural principles run through this table. Buffers matter as much as machines: a drying silo and a blending silo absorb the natural short-term variation of a wet process and let the extruder run at steady state, which is worth more to pellet quality than any single upgrade elsewhere. And contamination should always be removed at the earliest stage where removal is physically possible, because every kilogram of soil that reaches the water loop must later be removed from the water at a much higher cost in energy, chemicals and sludge handling.

Infeed Conveying, Manual Sorting and Metal Removal

The infeed section looks unglamorous but sets the reliability ceiling for the whole plant. A chain plate conveyor with a hardened running surface handles baled film, wet material and the occasional stone without the belt damage that a rubber conveyor suffers. Belt width of 1000 to 1500 millimeters with a variable frequency drive running 3 to 12 meters per minute gives operators enough dwell time to work, and the drive speed becomes the primary throughput control for the entire line.

Manual sorting remains the most cost-effective removal method for a specific class of contaminant: large, rigid, non-target objects that no automated system reliably catches. Rope, wire bundles, wood, textiles, rigid containers, and the occasional tool or machine part all belong to this class, and any one of them can stop a shredder for an hour. A sorting platform with two to four positions, adequate lighting and a rejection chute directly beside each position is standard on printed and post-consumer film lines. On clean post-industrial trim it can be reduced to a single inspection position.

Magnetic separation should be treated as mandatory rather than optional. An overband magnet at 8000 to 12000 gauss over the infeed conveyor removes the great majority of loose ferrous material for a modest capital and near-zero operating cost, and it protects every blade downstream. Eddy current separation is the judgment call. It removes aluminum and other non-ferrous fragments, which matters when the stream contains foil laminate or hardware. On agricultural film and clean converter trim it is usually unnecessary; on mixed post-consumer film and printed laminate scrap it pays for itself in blade life and in the reduction of visible specks.

Shredding: Blade Steel, Screen Size and Throughput Matching

Shredding converts bales and large sheets into fragments that can be conveyed, metered and washed. For film, the output target is 60 to 150 millimeters, which is deliberately coarse. Over-shredding at this stage is a common and expensive mistake: fine film fragments increase surface area, absorb more water, carry more soil into the water loop and become harder to dewater, while offering no benefit that the wet crusher does not deliver more efficiently later.

Single-shaft shredders with a hydraulic pusher ram give the most consistent output size on film because the ram forces material against the rotor continuously, and the screen under the rotor sets the particle size directly. Double-shaft shredders handle mixed and heavily contaminated input with greater tolerance for foreign objects, at the cost of a wider particle size distribution. For agricultural film and heavy-duty sacks, a double-shaft machine ahead of the wet crusher is usually the more robust choice; for baled packaging film, single-shaft with a 100 to 150 millimeter screen is typical.

Blade steel selection is where the abrasion grading from earlier pays off. D2 and SKD-11 tool steel, hardened to 58 to 62 HRC, are the working standard for film shredding. On agricultural film with high sand content, blade life drops sharply and the practical countermeasures are a slightly lower rotor speed, a rotor design that allows blade rotation to a fresh cutting edge, and acceptance of a shorter re-sharpening interval. Expect 200 to 400 operating hours between blade services on heavily soiled agricultural film and roughly double that on clean packaging film.

Drive sizing follows throughput and stream difficulty. A 500 kilograms per hour film line typically uses 55 to 90 kilowatts at the shredder; a 1000 kilograms per hour line uses 110 to 160 kilowatts. Undersizing the shredder motor is a false economy, because the shredder is the stage most exposed to unpredictable input and the one whose stoppages cascade through the entire plant.

Dry Pre-Washing: Removing Grit Before It Reaches the Water Loop

Dry pre-washing is the stage most often omitted from budget line offers and the one that most reliably transforms the operating economics of an agricultural film plant. Its principle is simple: dry soil is far easier and cheaper to remove than wet soil, so remove it before adding water.

The equipment is a friction-based rotating drum or a beater-type machine with a perforated screen of 8 to 20 millimeters, running at 300 to 600 revolutions per minute. Shredded film enters, is beaten and tumbled against the screen, and dry soil, sand and powder pass through the perforations while the film continues forward. On agricultural film with 20 to 60 percent soil load, a well-designed dry pre-cleaning stage removes 40 to 60 percent of the total soil burden. On heavy-duty sacks, the same machine class doubles as a bag opener that shakes retained powder out of folds and seams.

The downstream benefits compound. Less soil in the water loop means smaller sedimentation basins, lower flocculant consumption, less sludge to dewater and dispose of, lower fresh water make-up, and dramatically less abrasive wear on wet crusher blades, pumps and screw conveyors. The stage also reduces the load on the hot wash tank, which means less heating energy per ton. For any stream above roughly 15 percent soil content, dry pre-cleaning is not an accessory; it is the stage that makes the rest of the line economical.

Wet Granulation: Knife Gap, Screen Aperture and Water Injection

The wet crusher performs the final size reduction, and it does so under continuous water spray for three reasons: water carries away released soil immediately, it suppresses dust, and it cools the cutting zone so that friction heat never approaches the 105 to 115 degrees Celsius softening range of LDPE.

Knife gap is the parameter that separates a well-maintained film crusher from a poor one. The working range is 0.3 to 0.8 millimeters between rotating and fixed blades. Below 0.3 millimeters the blades risk contact and the machine generates excessive fines; above 0.8 millimeters, thin film folds through the gap instead of being cut cleanly, producing long tails that wrap on the rotor and block the screen. On film lines running mixed thickness, 0.4 to 0.6 millimeters is a good default, checked and reset at every blade service.

Screen aperture of 30 to 60 millimeters suits film. Finer screens increase residence time in the cutting chamber, generate heat, and produce fines that are hard to dewater and that raise melt loss at the filter. Coarser screens pass pieces that the friction washer cannot scrub effectively and that later cause feeding irregularity. Water injection is typically 2 to 5 cubic meters per hour at the crusher on a 1000 kilograms per hour line, with the water recovered and returned to the treatment loop rather than discharged.

Rotor speed of 400 to 900 revolutions per minute and a drive of 55 to 132 kilowatts cover the normal capacity range. Rotor design matters more on film than on rigid material: a claw or scissor-cut rotor geometry cuts film progressively across the width rather than impacting it flat, which reduces both power draw and the tendency of thin film to wrap.

Float-Sink Separation as a Line Stage

Float-sink separation is the density sorting step that removes everything heavier than water from the polyolefin fraction. Wet flake enters a tank of water where LDPE, at 0.915 to 0.935 grams per cubic centimeter, floats and is carried forward by paddles and a surface skimmer to an inclined discharge screw, while PET, PVC, aluminum fragments, sand, stones and heavy organic matter sink to the bottom and are removed by a bottom screw conveyor. Because the density gap between LDPE and PET or PVC is very large, the separation efficiency for those contaminants is high with correct residence time and agitation.

For a printed and sticky film line, the design decisions at this stage are straightforward: two to three tanks in series rather than one, because each additional pass raises purity on material that entered the tank still holding soil; sufficient tank length, typically 3 to 6 meters per unit, to give flake time to reach its equilibrium buoyancy; and a bottom sediment removal system sized for the real grit load rather than a token screw. Detailed water level tuning and hydrodynamic optimization inside the tank are a separate engineering subject and are treated elsewhere; at line level, what matters is that the stage is sized for the incoming soil burden and is preceded by dry pre-cleaning so that it is not asked to do a job better done upstream.

High-Speed Friction Washing With Counter-Current Water Flow

Friction washing is the mechanical workhorse of the wet section. A vertical or horizontal rotor fitted with paddles spins at 700 to 1200 revolutions per minute inside a perforated screen of 3 to 8 millimeters, driving flake against flake and against the screen wall. The scrubbing action removes over 90 percent of loosely bound surface contamination, and the released soil escapes through the perforations with the water while the flake continues upward or forward.

Counter-current water flow is what turns a friction washer from a mixer into a washer. Water enters at the discharge end and flows against the direction of material travel, so the cleanest flake meets the cleanest water and the dirtiest incoming flake meets water that is already carrying soil out of the machine. The concentration gradient this creates is the reason counter-current friction washing consumes substantially less fresh water than co-current designs for the same cleanliness result. On a printed film line, two friction washers are standard: one immediately after float-sink separation to remove bulk soil, and one after the hot wash and rinse to strip loosened ink residue and chemical carry-over.

Three design details separate a durable machine from a maintenance problem. Paddle material and hardfacing determine wear life on abrasive agricultural film, and replaceable paddle tips are worth specifying. Screen open area determines how quickly released soil leaves the machine; too little open area and the soil simply recirculates with the flake. Finally, the housing must be arranged so that the machine can be opened for inspection without dismantling the drive, because friction washer screens need regular cleaning on any stream that carries fiber or plant matter.

On a 1000 kilograms per hour line, friction washers typically draw 30 to 55 kilowatts each. That is a significant share of the wet section power draw, which is another argument for removing dry soil upstream: a friction washer asked to remove 60 percent soil load consumes far more energy and wears far faster than one polishing flake that has already been pre-cleaned.

Hot Washing: Chemistry, Temperature and Residence Time for Ink and Grease

Hot washing is the stage that makes printed and greasy film economically recyclable, and it is non-negotiable for any stream carrying surface print or food residue. Cold friction washing removes soil; only hot caustic chemistry removes ink binders and saponifies fats.

The reactor is a heated, agitated vessel operating at 75 to 95 degrees Celsius with a caustic soda concentration of 0.5 to 2.0 percent, supplemented by a surfactant package to lower surface tension and keep detached ink dispersed in the water instead of redepositing on flake. Residence time is 10 to 20 minutes. Heating is by direct steam injection or by a thermal oil jacket, and the choice usually follows what utilities the plant already has: steam is faster to bring to temperature and simpler to control, while thermal oil avoids condensate dilution of the wash liquor.

The three process variables interact strongly, and understanding the trade-offs is the difference between a wash recipe that works and one that merely consumes chemicals. Temperature drives reaction rate, but the ceiling is set by LDPE softening near 105 to 115 degrees Celsius and, practically, by the point at which flake begins to agglomerate in the tank. Caustic concentration drives the chemical attack on ink binders, but excess caustic raises rinsing demand, neutralization load in the water treatment plant and the risk of residual alkalinity in the pellet. Residence time can substitute partially for both, which is why a larger reactor volume often outperforms an aggressive chemical recipe on the same stream.

Contamination Target	Temperature (degrees Celsius)	Caustic Soda (percent)	Surfactant Dosing	Residence Time (minutes)	Expected Removal	Notes
Nitrocellulose-based surface ink	80 to 90	0.8 to 1.5	Standard nonionic package	10 to 15	80 to 90 percent	Most alkali-sensitive ink family; easiest to remove
Polyurethane-based surface ink	85 to 95	1.5 to 2.0	Reinforced package with dispersant	15 to 20	60 to 80 percent	Alkali-resistant; needs the highest severity setting
Water-based ink	75 to 85	0.5 to 1.0	Standard package plus anti-redeposition agent	10 to 15	75 to 90 percent	Redeposition is the main risk; keep wash liquor clean
Reverse-printed laminate ink	85 to 95	1.5 to 2.0	Reinforced package	15 to 20	Below 20 percent	Ink is mechanically shielded; target color homogenization instead
Fats, oils and food residue	80 to 90	1.0 to 2.0	Degreasing surfactant	10 to 15	85 to 95 percent	Saponification is fast; watch foaming in the water loop
Pressure-sensitive adhesive residue	80 to 90	1.0 to 1.5	Solvent-assisted surfactant	15 to 20	50 to 75 percent	Combine with strong friction washing directly after the reactor
Paper label fiber and adhesive	75 to 85	0.5 to 1.0	Standard package	10 to 15	80 to 95 percent	Fiber must be removed from the water loop, not recirculated

Two operating disciplines determine whether the hot wash keeps performing after the first month. Wash liquor must be continuously bled and replenished, because detached ink and saponified grease accumulate until the liquor itself becomes the contamination source. And the rinse immediately after the reactor must be genuinely counter-current with fresh water on the final pass, otherwise alkaline carry-over follows the flake into the dryer, concentrates as water evaporates, and shows up as surface residue and elevated ash in the finished pellet.

Rinsing, Centrifugal Dewatering and Thermal Drying

The drying cascade has one job: deliver flake to the extruder or agglomerator below 1 percent moisture, using mechanical separation for as much of the water as possible because mechanical dewatering costs a fraction of what thermal evaporation costs.

Rinsing comes first. A rinse tank followed by a second friction washer removes chemical carry-over and any ink residue loosened but not detached in the reactor. Fresh water enters at this final stage and cascades backward through the earlier tanks, which is the standard counter-current arrangement for the whole wet section and the main reason a well-designed line uses so little make-up water.

Mechanical dewatering follows in a horizontal centrifugal dryer, sometimes called a squeezer or centrifuge, with the rotor at 700 to 1000 revolutions per minute inside a screen of 0.5 to 1.5 millimeters. Outlet moisture is typically 3 to 8 percent depending on flake size distribution and the amount of fines present. Fines hold water disproportionately, which is a further argument against over-shredding upstream. Drive power is 22 to 45 kilowatts on a 1000 kilograms per hour line.

Thermal drying finishes the job. A hot air pipe dryer with air at 80 to 120 degrees Celsius carries flake pneumatically while evaporating surface water, and a vertical drying silo downstream provides 15 to 40 minutes of residence at moderate temperature to equalize moisture through the batch. The silo is not optional on a high-capacity line: it is the buffer that decouples the inherently variable wet section from the extruder, and it is what allows the extruder to see a constant feed condition even when the washing line has a short interruption.

Air temperature control matters because LDPE film is thin and heats quickly. Above roughly 120 degrees Celsius, thin film begins to soften, stick to duct walls and form lumps that block the system. Below 80 degrees Celsius, evaporation is too slow to reach the moisture target within the available residence time. The working window is narrow, and a properly tuned line uses a temperature sensor with closed-loop control rather than a fixed setpoint.

Agglomeration: Densifying Film Before the Extruder

Agglomeration solves the bulk density problem that defines film recycling. Dried film flake at 0.03 to 0.08 tons per cubic meter cannot feed a gravity-fed extruder throat reliably; the screw sees an inconsistent column of material, output surges, melt pressure oscillates and pellet geometry varies. The agglomerator raises bulk density to 0.30 to 0.45 tons per cubic meter, which is comfortably inside the range a single-screw extruder feeds without difficulty.

The machine is a high-speed rotor, typically 700 to 1000 revolutions per minute, inside a cylindrical chamber. Friction between the blades and the film raises the material to just below its melting point, at which stage the softened film sinters into irregular grains. A metered water quench is then injected, which shocks the mass, breaks it into free-flowing agglomerate and simultaneously flashes off remaining surface moisture. Drive power is substantial, typically 90 to 250 kilowatts depending on throughput, and this is one of the larger single energy consumers in the plant.

Two control problems dominate agglomerator operation on printed and sticky film. The first is temperature: the process window between good sintering and a solid melted mass inside the chamber is narrow, and the correct control strategy is closed-loop water quench timing based on motor load rather than on a fixed timer. The second is adhesive. Stretch film residue softens at 40 to 60 degrees Celsius, well below the sintering point, so it becomes tacky early in the cycle and can build up on the chamber wall. A water-jacketed housing, regular cleaning intervals and a slightly reduced batch size on adhesive-heavy streams are the practical countermeasures.

The alternative to agglomeration is a high-compaction force feeder integrated directly with the extruder, which densifies film continuously in a compaction screw ahead of the throat. Below roughly 500 kilograms per hour this is often the better answer: less energy, fewer moving parts, no separate machine. Above that throughput, and particularly on mixed film with variable thickness, a dedicated agglomerator generally produces steadier extruder output and a more uniform pellet, and it also gives the operator a buffer of densified material to run from.

Extrusion: Screw Geometry, Double-Stage Venting and Degassing

The extruder converts densified film into a homogeneous melt while removing everything volatile that survived the wet section. For printed and sticky LDPE film, three configuration choices dominate: screw geometry, venting arrangement and whether to use single-stage or two-stage extrusion.

Screw geometry for recycled film uses an L/D ratio of 30 to 36 to 1, considerably longer than a virgin film extruder, because the additional length provides residence time for devolatilization and homogenization of a feedstock whose melt index varies from flake to flake. A barrier screw with a mixing section in the metering zone gives better melt homogeneity, which matters directly for color consistency on printed material. Compression ratio is moderate, typically 3 to 1 to 3.5 to 1, since aggressive compression on a variable-density feed generates shear heat that pushes the melt toward the ink carbonization band.

Venting is where a film recycling extruder differs most from a standard machine. A double-stage vacuum vent arrangement operating at minus 0.08 to minus 0.095 megapascals removes residual moisture, volatile ink components and low-molecular-weight degradation products. The first vent takes the bulk of the moisture shortly after the melting zone; the second, further downstream, extracts the remaining volatiles from a fully molten and mixed material. Single-vent machines can handle clean post-industrial film, but on printed post-consumer material they produce porous pellets, visible surface bubbles and a persistent odor.

Temperature control is the discipline that keeps ink from carbonizing. The barrel profile below is a working baseline for printed LDPE film; note that it is deliberately conservative at the front and does not climb aggressively toward the die. Melt temperature should be measured, not assumed, and the target is 195 to 215 degrees Celsius.

Configuration	Barrel Zone Profile (degrees Celsius)	Screw Speed (revolutions per minute)	Target Melt Temperature (degrees Celsius)	Vacuum (megapascals)	Recommended Filtration Fineness
Clean post-industrial LDPE film, unprinted	170 / 185 / 195 / 205 / 210 / 205	80 to 140	205 to 215	Single vent, minus 0.06 to minus 0.08	120 to 150 micrometers, single stage
Printed post-industrial film	165 / 180 / 190 / 200 / 205 / 200	70 to 130	200 to 210	Double vent, minus 0.08 to minus 0.09	100 to 120 micrometers
Printed post-consumer packaging film	160 / 175 / 185 / 195 / 200 / 195	60 to 120	195 to 208	Double vent, minus 0.085 to minus 0.095	150 micrometers coarse plus 100 micrometers fine, two steps
Agricultural film with residual grit	160 / 175 / 185 / 195 / 200 / 195	60 to 110	195 to 205	Double vent, minus 0.085 to minus 0.095	150 to 200 micrometers first pass; continuous filter strongly advised
Stretch film with adhesive residue	160 / 175 / 185 / 195 / 200 / 195	60 to 120	195 to 208	Double vent, minus 0.085 to minus 0.095	100 to 120 micrometers
Mixed post-consumer film, high laminate content	160 / 175 / 185 / 195 / 200 / 195	60 to 110	195 to 205	Two-stage extrusion, minus 0.09 to minus 0.095 on stage two	150 micrometers plus 80 to 100 micrometers, two stages

Screw diameter follows the required throughput, and the pairing below is the standard sizing used on Polyretec film pelletizing configurations. A screw run near the top of its capacity band produces more shear heat and less homogeneous melt, so where output growth is planned, sizing one class up is usually the better decision.

Screw Diameter	Typical Output on LDPE Film (kilograms per hour)	Main Drive Power (kilowatts)	Suggested Application
100 millimeters	250 to 350	75 to 110	Small converter, in-house trim recovery, trial production
120 millimeters	400 to 550	110 to 160	Mid-size recycler, single-shift merchant pellet production
160 millimeters	700 to 1000	200 to 280	Continuous commercial recycling of post-consumer film
180 millimeters	1000 to 1500	280 to 400	Large-scale plant, multi-shift, integrated with a full washing line

Two-stage extrusion deserves its own note. In a two-stage system, the first extruder melts and homogenizes while the second extruder, fed from the first, builds the pressure needed to drive melt through fine filtration. The advantage is decoupling: filtration back pressure no longer forces the plasticizing screw into a high-shear operating point, so melt temperature stays lower and filtration can be finer. The trade-off is higher capital cost, more floor space and an additional drive to maintain. As a rule of thumb, specify two-stage extrusion when incoming contamination exceeds roughly 3 percent by weight, when laminate content is significant, or when the customer specification requires filtration finer than 100 micrometers on a soiled stream.

Melt Filtration Fineness and Screen Changer Selection

Melt filtration determines the black speck count of the finished pellet, and on printed film it is the single most consequential equipment choice after the extruder itself. The filter must capture carbonized ink particles, infusible laminate fragments, residual mineral matter and paper fiber, all while sustaining continuous operation on a contamination load that would blind a conventional screen within hours.

Three technologies cover the practical range. A hydraulic double-piston screen changer is the economical baseline: two filter positions, hydraulic sliding, and a screen change that can be done without stopping the line, though with a brief pressure and flow disturbance. For clean and lightly printed film it is entirely adequate. A continuous belt filter advances a screen belt automatically as differential pressure rises, giving genuinely uninterrupted operation and much lower operator attention; it suits moderately contaminated post-consumer film and is the most common choice on merchant film recycling lines. A fully automatic laser-drilled rotary disc filter uses a perforated steel disc rather than a woven mesh, with a scraper that removes retained contamination continuously and discharges it, so the filtration element is self-cleaning and effectively permanent. Its advantages on heavily contaminated printed and agricultural film are very long service intervals, minimal melt loss compared with continuous screen belts, and stable back pressure that in turn stabilizes melt temperature.

Filtration Technology	Practical Fineness	Contamination Tolerance	Melt Loss	Operator Attention	Relative Investment	Best Fit
Hydraulic double-piston screen changer	100 to 200 micrometers	Low to medium	Medium, purge at each change	High, manual screen replacement	Low	Clean post-industrial film, in-house trim recovery
Continuous screen belt filter	80 to 150 micrometers	Medium to high	Medium, belt consumption is ongoing	Low	Medium	Printed post-consumer packaging film
Fully automatic laser-drilled rotary disc filter	80 to 150 micrometers	High to very high	Low, controlled discharge only	Very low	High	Heavily printed film, agricultural film, mixed post-consumer input
Two-step arrangement, coarse plus fine	150 micrometers then 100 micrometers	Very high	Low to medium	Low	High	Demanding pellet specifications from difficult input

The fineness decision should be made against the customer specification, not against an abstract quality ambition. On printed post-consumer film the recommended arrangement is two-step filtration at 150 micrometers followed by 100 micrometers, which captures the great majority of carbonized particles without the blinding rate that a single fine screen suffers. Agricultural film should start coarser, at 150 to 200 micrometers, because mineral grit that survived washing blinds fine screens within minutes. Chasing 60 micrometers on a soiled stream is a specification error that shows up as constant screen changes, high melt loss and disappointing net output.

Pelletizing Head, Pellet Cooling and Classification

Water ring die-face pelletizing is the standard choice for LDPE film. Melt is extruded through a die plate and cut immediately at the die face by rotating blades, while a ring of circulating water on the inside of the cutting chamber cools and transports the pellets. The reason it suits film is tolerance: recycled film melt carries variable viscosity and occasional inclusions, and a water ring head handles that variability with fewer stoppages than a system requiring tight, stable melt conditions. Die hole diameters of 2.8 to 4.0 millimeters produce the pellet size range that downstream converters expect.

Underwater pelletizing, in which the die face is fully submerged, produces a more uniform, more spherical pellet with lower fines generation and is the preferred choice where pellet geometry is part of the sale specification. It requires a more stable melt and a more sophisticated water and temperature control circuit, and it is less forgiving of the viscosity swings that come with mixed post-consumer film. Both are legitimate choices; the decision follows the pellet specification and the consistency of the input stream.

Downstream of the cutting head, pellets pass through a centrifugal pellet dryer and then over a vibrating classifier that removes oversize agglomerates, tails and fines. The classifier is a small piece of equipment with a large effect on customer satisfaction, because fines and tails are the defects that converters notice first when they load a hopper. Blade wear at the die face is the maintenance item to watch: worn blades leave tails, and tails are the leading cause of downstream feeding complaints on recycled pellet.

Homogenization, Metal Detection and Packing

The final block converts a variable production stream into a consistent commercial product. Its value is disproportionate to its cost, and it is the part of the line most often trimmed from a budget offer.

A blending silo holding four to twelve hours of production is the primary tool for color consistency. Printed film input varies bale to bale, and the resulting pellet color varies with it; a mass-flow blending silo averages those variations so that a customer receiving a twenty-ton lot sees one color rather than a sequence of shades. On printed film, where color difference is a live commercial issue, silo blending frequently makes the difference between a pellet that meets a converter’s specification and one that does not.

A metal detector on the packing line is the final safety check. Despite magnetic and eddy current separation upstream, occasional metallic particles find their way through, and a converter who finds metal in a recycled pellet lot does not usually order again. Modern detectors reject a short pellet slug around the detection event rather than stopping the line.

Packing is either 25 kilogram bags for smaller customers and export consolidation, or 500 to 1000 kilogram big bags for bulk supply. Automatic weighing with lot number printing supports traceability, which is increasingly a requirement rather than a courtesy: recycled content certification schemes require documented mass balance from input to output, and a packing station that records lot data automatically makes that documentation straightforward instead of a manual burden.

Polyretec Soft PP/PE Crushing and Washing Line for Film Streams

The wet front end of a printed and sticky film plant is built on the Polyretec Soft PP/PE Crushing and Washing Line, a configuration developed specifically for film, woven bags and agricultural film rather than adapted from a rigid plastics line. It covers the capacity range of 500 to 1500 kilograms per hour, and it can be supplied either as a flake-producing washing plant or with one-step pelletizing integrated directly downstream, so that washed flake goes straight into the extruder without an intermediate storage and re-handling step.

The distinguishing engineering features on this line all address the film-specific problems described earlier in this article. Dry pre-cleaning is available as an integral stage rather than an add-on, which is what makes agricultural film with high soil load economically processable. Blade steel and screen configurations in the shredding and wet crushing sections are selected against the abrasion grade of the intended stream. The wash section uses counter-current water flow throughout, with fresh water entering at the final rinse and cascading backward, which is what holds fresh water consumption inside the 0.5 to 1.5 cubic meters per ton band when a closed-loop treatment package is fitted. For printed and greasy streams, the heated wash reactor with caustic and surfactant dosing is integrated into the flow rather than bolted on, so residence time is designed rather than improvised.

The fully automated PP and PE film washing plant delivered in Taiwan around the PTW1000 configuration is the reference installation for the 1000 kilograms per hour class: continuous operation with centralized control, automatic dosing and integrated water treatment. Projects delivered in Mexico for LDPE film carrying sticker labels, built around a heavy-duty shredder and beater machine arrangement, and in Turkey for printed bags and film, cover the sticky and heavily printed ends of the same equipment family.

Parameter	500 kilograms per hour class	800 kilograms per hour class	1000 kilograms per hour class (PTW1000 reference)	1500 kilograms per hour class
Design throughput, washed flake	500 kilograms per hour	800 kilograms per hour	1000 kilograms per hour	1500 kilograms per hour
Target materials	LDPE and LLDPE film, PP woven bags	Printed packaging film, stretch film, woven bags	Printed post-consumer film, agricultural film, heavy-duty sacks	Mixed post-consumer film, agricultural film at scale
Infeed	Chain plate conveyor with sorting platform and overband magnet	Chain plate conveyor, sorting platform, magnet, optional eddy current	Chain plate conveyor, multi-position sorting, magnet plus eddy current	Chain plate conveyor, multi-position sorting, magnet plus eddy current
Shredding	Single-shaft, screen 100 to 150 millimeters	Single-shaft or double-shaft, screen 80 to 150 millimeters	Heavy-duty shredder, screen 60 to 150 millimeters	Heavy-duty shredder, screen 60 to 120 millimeters
Dry pre-cleaning	Optional	Recommended	Integrated beater and de-dusting drum	Integrated beater and de-dusting drum, extended
Wet crusher	Knife gap 0.3 to 0.8 millimeters, screen 40 to 60 millimeters	Knife gap 0.3 to 0.8 millimeters, screen 30 to 60 millimeters	Knife gap 0.3 to 0.8 millimeters, screen 30 to 60 millimeters	Knife gap 0.3 to 0.8 millimeters, screen 30 to 50 millimeters
Float-sink tanks	Two in series	Two in series	Two to three in series	Three in series
Friction washers	One, 700 to 1000 revolutions per minute	Two, 700 to 1200 revolutions per minute	Two, 700 to 1200 revolutions per minute, counter-current	Two to three, 700 to 1200 revolutions per minute, counter-current
Hot wash reactor	Optional, 75 to 90 degrees Celsius	Standard for printed film, 75 to 95 degrees Celsius	Standard, 75 to 95 degrees Celsius, caustic 0.5 to 2.0 percent	Standard, 75 to 95 degrees Celsius, extended residence volume
Dewatering	Centrifugal dryer, outlet 3 to 8 percent moisture	Centrifugal dryer, outlet 3 to 8 percent moisture	Centrifugal dryer plus pipe dryer, outlet below 1 percent	Centrifugal dryer plus pipe dryer and silo, outlet below 1 percent
Water treatment	Sedimentation plus filtration	Sedimentation, dissolved air flotation, filtration	Closed loop with dosing, 85 to 95 percent recirculation	Closed loop with dosing and sludge dewatering
Control	Centralized panel with programmable logic controller	Centralized panel, touch screen human-machine interface	Fully automated, recipe management, remote monitoring ready	Fully automated, recipe management, remote monitoring ready
One-step pelletizing option	Available	Available	Available	Available

Polyretec New Generation Pelletizing Line for LDPE Film

Downstream of the washing plant, the Polyretec New Generation Pelletizing Line is the configuration built for thin-walled LDPE film and thick-walled PE and PP regrind. It is a robust-construction line intended for post-consumer waste rather than for clean in-house scrap, which shows in the details that matter on printed material: long L/D plasticizing, double-stage vacuum venting, generous filtration area and a control philosophy that holds melt temperature down instead of pushing throughput up.

The line is configured around the screw diameter that matches the required output, and each class carries the same architecture. Densification is by agglomerator or high-compaction force feeder according to throughput and stream type. Filtration is specified against the contamination grade of the input rather than sold as a fixed item, with hydraulic screen changers on clean streams and continuous or fully automatic laser-drilled rotary disc filters on heavily printed and soiled streams. Pelletizing is by water ring die-face head as standard for film, with underwater pelletizing available where pellet geometry is part of the specification.

Parameter	Screw 100 millimeters	Screw 120 millimeters	Screw 160 millimeters	Screw 180 millimeters
Output on LDPE film	250 to 350 kilograms per hour	400 to 550 kilograms per hour	700 to 1000 kilograms per hour	1000 to 1500 kilograms per hour
L/D ratio	30 to 36 to 1	30 to 36 to 1	30 to 36 to 1	30 to 36 to 1
Main drive power	75 to 110 kilowatts	110 to 160 kilowatts	200 to 280 kilowatts	280 to 400 kilowatts
Screw speed	60 to 140 revolutions per minute	60 to 140 revolutions per minute	60 to 130 revolutions per minute	60 to 120 revolutions per minute
Densification	Force feeder standard, agglomerator optional	Force feeder or agglomerator	Agglomerator standard	Agglomerator standard, extended chamber
Venting	Double-stage vacuum, minus 0.08 to minus 0.095 megapascals	Double-stage vacuum, minus 0.08 to minus 0.095 megapascals	Double-stage vacuum, minus 0.085 to minus 0.095 megapascals	Double-stage vacuum, minus 0.085 to minus 0.095 megapascals
Two-stage extrusion option	Available	Available	Recommended above 3 percent contamination	Recommended above 3 percent contamination
Melt filtration	Hydraulic screen changer, 120 to 150 micrometers	Continuous belt filter, 100 to 150 micrometers	Continuous or laser-drilled rotary disc, 80 to 150 micrometers	Laser-drilled rotary disc, 80 to 150 micrometers, two-step available
Pelletizing head	Water ring die-face, 2.8 to 3.5 millimeter die holes	Water ring die-face, 2.8 to 4.0 millimeter die holes	Water ring die-face or underwater	Water ring die-face or underwater
Pellet handling	Centrifugal dryer and vibrating classifier	Centrifugal dryer, classifier, silo	Centrifugal dryer, classifier, blending silo, metal detector	Centrifugal dryer, classifier, blending silo, metal detector
Control	Programmable logic controller with touch screen	Programmable logic controller with recipe storage	Full automation, data logging, remote support ready	Full automation, data logging, remote support ready

For projects that require compounding-grade homogenization of the recycled melt, for example when mineral filler, color masterbatch or a compatibilizer is dosed into the recyclate, Wanplas supplies matched twin-screw pelletizing systems that integrate directly with Polyretec washing lines, so the washed flake can be routed either to a single-screw film pelletizing line or to a twin-screw compounding step within the same plant layout.

Master Process Parameter Sheet for Printed and Sticky LDPE

The table below consolidates the working setpoints for a 1000 kilograms per hour printed and sticky LDPE film line into one reference sheet. These are commissioning starting points, refined during the trial run against the customer’s actual material.

Process Variable	Setpoint or Range	Measurement Point	Effect if Set Too Low	Effect if Set Too High
Shredder screen aperture	60 to 150 millimeters	Rotor screen	Excess fines, higher water carry-over	Oversize pieces overload the wet crusher
Wet crusher knife gap	0.4 to 0.6 millimeters typical	Blade set, checked at each service	Blade contact risk, excessive fines	Film folds instead of cutting, rotor wrapping
Friction washer speed	700 to 1200 revolutions per minute	Drive frequency	Incomplete surface cleaning	Fines generation, higher power draw and wear
Hot wash temperature	75 to 95 degrees Celsius	Reactor liquor	Ink and grease not released	Flake softening and agglomeration in the tank
Caustic soda concentration	0.5 to 2.0 percent	Liquor titration, per shift	Poor ink removal, gray haze	Rinsing burden, alkaline carry-over, ash increase
Hot wash residence time	10 to 20 minutes	Reactor volume against flow	Chemistry has no time to act	Reduced plant throughput
Centrifuge outlet moisture	3 to 8 percent	Sampling at discharge	Not achievable without excess energy	Thermal dryer overload, venting stress
Dryer air temperature	80 to 120 degrees Celsius	Duct sensor, closed loop	Moisture target missed	Film softening, duct blockage, lumps
Flake moisture at extruder	Below 1 percent	Sampling at silo outlet	Not applicable	Porous pellets, surging, vent flooding
Agglomerate bulk density	0.30 to 0.45 tons per cubic meter	Sampling at agglomerator discharge	Feeding instability and output surging	Over-sintering, lumps, energy waste
Melt temperature	195 to 215 degrees Celsius	Melt probe before the filter	Unmelted inclusions, high filter pressure	Ink carbonization, black specks, odor
Vacuum level	Minus 0.08 to minus 0.095 megapascals	Vent line gauge	Residual moisture and volatiles in the pellet	Melt drawn into the vent port
Filtration fineness	80 to 150 micrometers	Filter specification	High black speck count	Blinding, melt loss, back pressure spikes
Filter differential pressure	Change or advance at 6 to 10 megapascals	Pressure transducers before and after filter	Premature change, wasted screen	Melt temperature rise from back pressure

Recycled LDPE Pellet Quality Targets and Test Methods

A recycled pellet is a commercial product with a specification, and the line must be able to demonstrate that specification consistently. The table below sets out the property targets that converters typically ask for on recycled LDPE from printed film, together with the test method and the process lever that controls each property.

Property	Typical Target	Test Method Basis	Controlled By
Melt flow rate at 190 degrees Celsius and 2.16 kilograms	0.3 to 2.0 grams per 10 minutes	Melt flow rate testing per ISO 1133	Input consistency, melt temperature, residence time
Density	0.918 to 0.930 grams per cubic centimeter	Immersion or gradient column per ISO 1183	Polymer purity, foreign polyolefin content
Moisture content	Below 0.1 percent	Loss on drying or Karl Fischer titration	Drying cascade and vacuum venting
Ash content	Below 1.5 percent	Muffle furnace incineration per ISO 3451	Washing efficiency, dry pre-cleaning, filtration
Black speck count	Counted per 100 grams against an agreed reference	Visual count on cast plaque or pressed film	Melt temperature control and filtration fineness
Color difference value	Agreed tolerance band against a reference pellet	Spectrophotometric color measurement	Hot wash efficiency and silo blending
Tensile strength retention	75 to 90 percent of virgin reference	Tensile testing per ISO 527	Thermal history, degradation control, contamination
Elongation at break	Agreed minimum against application	Tensile testing per ISO 527	Degradation control and foreign polymer content
Odor	Assessed against an agreed sensory scale	Internal panel assessment on heated sample	Hot wash degreasing and vacuum devolatilization
Pellet geometry and fines	Uniform pellet, minimal tails and fines	Sieve analysis and visual inspection	Cutter blade condition and classification

Two of these deserve particular attention on printed film. Ash content is the number that reveals whether the wet section is genuinely working, because it aggregates mineral soil, paper fiber, pigment and filler that survived the whole process. And black speck count is the property that most often triggers a customer complaint, which is why melt temperature discipline and filtration selection are treated as quality controls rather than as production settings.

Water Treatment, Sludge Handling and Air Emission Control

A film washing plant is a water plant with a polymer product, and the water treatment loop deserves the same engineering attention as the extruder. A well-designed closed loop recirculates 85 to 95 percent of process water, which is what keeps fresh water consumption in the 0.5 to 1.5 cubic meters per ton band even on soiled agricultural film.

The treatment train follows a standard sequence. Coarse solids settle in a sedimentation basin sized for the real grit load rather than a nominal one. Dissolved air flotation then removes suspended fines, emulsified grease and detached ink particles by attaching micro-bubbles to them and skimming the resulting float layer. Chemical dosing with a coagulant such as polyaluminum chloride followed by a polyacrylamide flocculant aggregates the remaining fine solids into settleable flocs. Filtration polishes the water before it returns to the process, and a bleed stream is discharged or sent for external treatment to prevent the accumulation of dissolved salts and organics.

Sludge handling is the part most often underestimated. On agricultural film, the sludge volume is substantial because most of what enters the plant as bale weight leaves as sludge, and wet sludge is expensive to transport. A filter press or screw press that raises sludge dry solids content materially reduces disposal cost and is a routine part of a properly specified line. Where dry pre-cleaning has removed 40 to 60 percent of soil before it ever reaches the water, the sludge burden falls proportionally, which is one more reason that stage repays its cost.

Air emissions come from two sources. The hot wash section releases steam carrying trace volatile organic compounds, and the extruder vacuum vents release moisture along with ink volatiles and low-molecular-weight degradation products. Both should be captured and treated rather than vented into the workshop. A condenser on the vacuum line recovers most of the moisture and condensable organics; activated carbon adsorption or a comparable treatment stage handles the remainder. Beyond regulatory compliance, this matters for the working environment, because ink volatiles in a workshop are the most common health and comfort complaint on printed film recycling plants.

Utility Consumption Benchmarks per Ton of Pellet

Utility consumption per ton of finished pellet is the honest way to compare line designs, because it is independent of scale, currency and local tariffs. The table below gives working benchmarks for LDPE film lines with a closed-loop water package.

Stream	Electrical Energy (kilowatt hours per ton of pellet)	Fresh Water (cubic meters per ton)	Caustic Soda (kilograms per ton)	Yield, Bale to Pellet	Sludge Generated
Clean post-industrial film, unprinted	280 to 360	0.3 to 0.8	Not required	88 to 95 percent	Very low
Printed post-industrial film	340 to 430	0.5 to 1.0	3 to 6	85 to 92 percent	Low
Printed post-consumer packaging film	400 to 500	0.8 to 1.3	5 to 10	60 to 75 percent	Medium
Stretch film with adhesive	380 to 470	0.6 to 1.1	4 to 8	70 to 85 percent	Low to medium
Heavy-duty industrial sacks	400 to 500	0.8 to 1.3	4 to 8	70 to 85 percent	Medium
Agricultural film, high soil load	450 to 550	1.0 to 1.5	3 to 7	45 to 65 percent	High to very high

Three observations follow from these numbers. Energy consumption is dominated by three consumers: the agglomerator, the extruder main drive and the hot wash heating load, which together typically account for 65 to 75 percent of plant demand. Water consumption is driven almost entirely by what leaves the system as sludge moisture and flake carry-over, not by tank volume, so a better sludge press reduces water consumption more effectively than a bigger recirculation pump. And yield, not utility cost, is the variable that dominates plant economics on soiled streams; a five-point yield improvement from better dry pre-cleaning is worth more than any plausible energy saving elsewhere.

Investment Level, Payback Window and Operating Economics

Because equipment pricing varies with configuration, scope and destination, the useful way to discuss investment is through an index rather than a figure. Setting a baseline 500 kilograms per hour LDPE film washing and pelletizing line at 100 points on a line investment index, the relative positions below hold across most project configurations.

Configuration	Line Investment Index (baseline 500 kilograms per hour LDPE film line = 100 points)	Installed Power Level	Operating Cost Level	Output Pellet Grade	Indicative Payback Window
500 kilograms per hour, washing only, flake output	62 to 72 points	Low	Low	Washed flake, sold as intermediate	18 to 30 months
500 kilograms per hour, washing plus pelletizing, baseline	100 points	Medium	Medium	General-purpose recycled LDPE pellet	16 to 28 months
1000 kilograms per hour, washing plus pelletizing	155 to 180 points	High	Medium	General-purpose to good-quality pellet	14 to 24 months
1000 kilograms per hour with hot wash and two-step filtration	185 to 215 points	High	Medium to high	Low black speck, controlled color pellet	14 to 26 months
1000 kilograms per hour agricultural film configuration with extended pre-cleaning	200 to 235 points	Very High	High	Filler and construction grade pellet	16 to 30 months
1500 kilograms per hour full configuration with two-stage extrusion	245 to 290 points	Very High	Medium per ton, High absolute	Premium recycled LDPE pellet	13 to 22 months

Payback windows above assume continuous multi-shift operation, a secured feedstock supply and a stable offtake for the finished pellet. All three assumptions deserve scrutiny before the equipment decision, because the most common cause of disappointing project economics is not equipment performance but feedstock availability: a line sized for 1500 kilograms per hour running at 600 kilograms per hour because the bales are not there carries the capital and the labor of the larger plant with the output of the smaller one.

One further economic point applies specifically to printed film. Adding a properly sized hot wash section and a second filtration step raises capital cost by a modest percentage of the total line, but it moves the pellet from a dark, variable filler grade into a controlled light-gray general-purpose grade. That step change in product grade has a far larger effect on project returns than any equivalent saving on the mechanical sections, which is why the hot wash is the last place to economize on a printed film line.

Requirement to Line Configuration Selection Guide

The table below maps common project requirements to a recommended Polyretec line configuration. It is written the way a technical offer should be prepared: input stream first, then throughput, then the pellet grade the customer needs, and only then the equipment.

Input Stream	Required Output	Target Pellet Grade	Recommended Polyretec Configuration	Critical Options to Include
In-house printed film trim from a converter	250 to 350 kilograms per hour	Reusable in-house blend at 20 to 40 percent	New Generation Pelletizing Line, 100 millimeter screw, with force feeder	Double-stage venting, hydraulic screen changer at 120 to 150 micrometers
Printed post-industrial packaging film, low soil	400 to 550 kilograms per hour	Light gray general-purpose pellet	Soft PP/PE Crushing and Washing Line, 500 kilograms per hour class, with hot wash, plus 120 millimeter pelletizing line	Hot wash reactor, continuous belt filter at 100 to 120 micrometers
Printed post-consumer packaging film	700 to 1000 kilograms per hour	Controlled color, low black speck pellet	Soft PP/PE Crushing and Washing Line, 1000 kilograms per hour class, plus 160 millimeter pelletizing line	Two to three float tanks, hot wash with dosing, two-step filtration, blending silo
Agricultural film, 20 to 60 percent soil	700 to 1000 kilograms per hour	Construction and filler grade pellet	Soft PP/PE Crushing and Washing Line, 1000 kilograms per hour class with extended dry pre-cleaning, plus 160 millimeter pelletizing line	Beater and de-dusting drum, grit removal, abrasion-resistant blades, laser-drilled rotary disc filter, sludge press
Stretch and wrapping film with adhesive	400 to 700 kilograms per hour	General-purpose pellet with stable melt flow rate	Soft PP/PE Crushing and Washing Line, 800 kilograms per hour class, plus 120 to 160 millimeter pelletizing line	Water-jacketed densification housing, anti-bridging paddles, hot wash with solvent-assisted surfactant
Heavy-duty industrial sacks with powder residue	500 to 1000 kilograms per hour	General-purpose pellet, controlled ash	Soft PP/PE Crushing and Washing Line, 800 to 1000 kilograms per hour class, plus 160 millimeter pelletizing line	Bag opener with de-dusting, multi-stage rinsing, dissolved air flotation in the water loop
Mixed post-consumer film from municipal collection	1000 to 1500 kilograms per hour	Stable charcoal or gray pellet	Soft PP/PE Crushing and Washing Line, 1500 kilograms per hour class, plus 180 millimeter pelletizing line with two-stage extrusion	Eddy current separation, three float tanks, extended hot wash, two-step filtration, large blending silo
Film plus a filler or masterbatch dosing requirement	500 to 1000 kilograms per hour	Compounded recycled grade	Polyretec washing line feeding a matched twin-screw pelletizing system supplied by Wanplas	Gravimetric side feeding, melt filtration, underwater pelletizing

One guideline underlies every row: specify the wet section for the dirtiest material the plant will realistically buy, and specify the extrusion section for the pellet grade the plant intends to sell. Those are two different questions, and answering only one of them is how projects end up with a good extruder in front of an inadequate washing line, or the reverse.

Troubleshooting: Black Specks, Odor, Color Drift and Output Loss

The defects below are the ones that actually appear on printed and sticky film lines, listed with the diagnostic sequence that resolves them fastest. The general principle is to check the process condition before changing the equipment, because in the great majority of cases the root cause is a setpoint or a maintenance interval rather than a design flaw.

Symptom	Most Likely Cause	Secondary Causes	Diagnostic Check	Corrective Action
Black specks in the pellet	Melt temperature above the ink carbonization band	Filtration too coarse; screen overdue for change; dead spots in the barrel or die	Measure actual melt temperature at the probe, not the barrel setpoint; check filter differential pressure trend	Lower the barrel profile and screw speed; advance or change the filter; move to two-step filtration; inspect for stagnation zones
Gray haze on nominally washed flake	Ink redeposition from contaminated wash liquor	Insufficient liquor bleed; missing anti-redeposition agent	Sample and inspect liquor clarity; check bleed and make-up rates	Increase liquor bleed, add or adjust the surfactant package, improve dissolved air flotation performance
Batch-to-batch color variation	No effective homogenization after pelletizing	Bale-to-bale input variation; inconsistent hot wash performance	Compare color measurements across consecutive lots	Install or enlarge the blending silo; stabilize hot wash setpoints; pre-blend input bales
Odor in the finished pellet	Insufficient degreasing in the hot wash	Weak vacuum on the vents; melt temperature too high generating degradation products	Heated sample sensory check; verify vacuum gauge reading under load	Raise caustic concentration and residence time; service the vacuum system; lower the melt temperature
Porous pellets or steam at the die	Excess moisture entering the extruder	Vent port partially blocked; dryer air temperature too low; excessive fines holding water	Sample flake moisture at the silo outlet; inspect vent ports	Restore drying cascade performance; clean vents; reduce fines generation upstream
Output surging and unstable melt pressure	Feeding instability from low bulk density material	Bridging in the feeder; agglomerator producing inconsistent grain size	Observe the throat under load; check agglomerate bulk density by sampling	Tune agglomerator quench timing; fit anti-bridging paddles; verify feeder cooling
Feeder or hopper bridging on stretch film	Adhesive softening above 40 to 60 degrees Celsius	Compaction ratio too aggressive; feeder cooling inadequate	Measure feeder housing temperature during production	Hold the housing below 45 degrees Celsius with water jacket cooling; reduce compaction; add a scraper
Rapid melt filter blinding	Filtration specified finer than the stream supports	Residual grit from inadequate pre-cleaning; paper fiber carry-over	Inspect the retained contamination on a removed screen	Step the fineness back; add or restore dry pre-cleaning; improve rinsing and fiber removal in the water loop
High ash content in the pellet	Incomplete soil and powder removal	Short hot wash residence; float tank overloaded; sediment recirculating	Ash test on flake before extrusion to localize the stage	Restore dry pre-cleaning; clear tank sediment systems; extend residence time
Wet crusher wrapping and blocking	Knife gap too wide for thin film	Blunt blades; screen aperture too fine; insufficient water injection	Measure the gap at several points across the rotor	Reset the gap to 0.4 to 0.6 millimeters; sharpen or rotate blades; verify spray nozzles
Pellet tails and fines	Worn die-face cutter blades	Incorrect blade pressure; die holes partially blocked	Inspect the blade set and die face during a planned stop	Replace blades, reset pressure, clean the die plate, verify classifier operation
Falling throughput at constant settings	Progressive filter loading	Screw and barrel wear; feeder cooling loss; contamination grade drift in incoming bales	Trend filter pressure and specific energy per kilogram over a week	Restore filtration cycle; measure screw and barrel clearance at the next service; re-check input contamination

Application Industries and End Markets for Recycled LDPE

Recycled LDPE from printed and sticky film supports a broad set of end markets, and the pellet grade the line produces determines which of them are accessible. Understanding the destination in advance is what makes the specification decisions earlier in this article commercially rational.

Refuse sacks and general packaging film. The largest single outlet for recycled LDPE from post-consumer film. Blend ratios of 30 to 100 percent recycled content are routine, color tolerance is wide, and mechanical requirements are moderate. Black speck count matters less here than melt flow consistency, because unstable melt flow causes bubble instability in film blowing.

Construction and agricultural film. Damp-proof membranes, concrete curing film, temporary protection film and silage film accept recycled content at 20 to 80 percent. The gray or charcoal color that printed film naturally produces is not an obstacle in these applications, and in some of them it is preferred.

Drip irrigation tubing and agricultural pipe. Recycled LDPE and LLDPE blends are widely used in irrigation tubing, typically at 20 to 60 percent inclusion. Consistency of melt flow rate and freedom from hard inclusions matter here, because inclusions cause wall defects and emitter blockages.

Injection molded crates, pallets and general parts. Thick-section injection moldings tolerate higher contamination and lower optical quality than film applications, which makes them the natural home for pellets from difficult input. Impact performance is the property to watch, and it is controlled mainly by foreign polymer content and thermal history.

Pipe outer layers and cable ducting. Multi-layer pipe constructions use recycled polyolefin in the non-critical outer layer, with a virgin inner layer meeting the performance specification. This is a growing outlet as recycled content targets tighten across construction supply chains.

Compounded and filled grades. Where a recycled pellet needs mineral filler, color adjustment or a compatibilizer for use in a specific molded part, the recyclate becomes a compounding feedstock. For these projects, Wanplas supplies matched twin-screw pelletizing systems that integrate directly with Polyretec washing lines, so a plant can serve both the film pellet market and the compounded grade market from one washed flake stream.

Standards, Certification and Documentation

Recycled material sold into regulated or brand-owner supply chains needs documentation, not just quality. The framework below is what a serious recycling plant should be able to demonstrate.

Quality management. ISO 9001 provides the documented process control, traceability and corrective action framework that converters increasingly audit before placing volume orders. For a recycling plant, the practical value is lot traceability from bale to bag.

Environmental management. ISO 14001 covers water discharge, sludge disposal and air emission management. On a film washing plant, where water and sludge are the dominant environmental interfaces, this is a substantive standard rather than a paper exercise.

Recycled content verification. Third-party recycled content certification schemes verify the mass balance between input waste and output recyclate, and the Global Recycled Standard is the most widely recognized framework for tracking recycled content through a supply chain. Both depend on documented input weights, output weights and loss accounting, which is why automatic weighing and lot recording at the packing station is worth specifying from the start.

Machinery safety. Equipment supplied into the European market must meet the applicable machinery directive requirements and carry CE marking, covering guarding, emergency stop architecture, electrical safety and noise. For a plant with high-speed rotors, hot caustic liquor and molten polymer, these are the provisions that protect operators in daily practice.

Polyretec supplies complete technical documentation with each line, including process flow diagrams, electrical schematics, equipment manuals, spare parts lists and commissioning records, so that certification audits and internal maintenance planning both have a documented basis.

Trial Runs, Installation, Training and Lifetime Support

No two film waste streams are identical, which is why the single most useful step before a line purchase is a trial run on the customer’s own material. Polyretec accepts customer material samples for laboratory and pilot testing, and the trial produces the data that a specification should be built on: achievable ink removal, realistic yield from bale to pellet, ash content, moisture behavior, filtration loading rate and the melt temperature window that keeps black specks under control. A specification written from a trial run on real material is a different document from one written from a bale description.

Turnkey delivery. Lines are supplied as complete turnkey projects covering layout design, equipment manufacture, water treatment integration, electrical and control integration, and utility interface definition. A film recycling plant has more interfaces between stages than most plastics machinery installations, and single-source responsibility for those interfaces removes the coordination gap where projects usually lose time.

Testing before shipment. Equipment is tested before dispatch, and where the customer supplies material, the line can be run on the actual feedstock so that both parties see the result before the machinery leaves the factory rather than after it arrives.

Installation and commissioning. Polyretec engineers attend site for installation supervision and commissioning, taking the line from mechanical completion through water loop filling, chemical dosing calibration, extruder start-up and first pellet production. With a team of more than 24 engineers and project experience across more than 50 countries, commissioning is a routine operation rather than an experiment.

Operator training. Training covers the setpoint logic behind each stage rather than only button sequences, because the operator who understands why the knife gap is 0.5 millimeters and why the melt temperature ceiling is 215 degrees Celsius is the one who keeps the pellet inside specification a year later. Training includes blade service, screen changing, dosing control, water loop maintenance and troubleshooting the defect table above.

Spare parts and after-sales support. As a Wanplas factory, Polyretec applies the group service commitment of USD 500 free parts per year, with free replacement of parts damaged within the warranty period. Wear parts on a film line, blades, screens, paddles and filter elements, are stocked as standard items rather than made to order. Technical support is available remotely through the line control system where the customer network permits, which resolves most process questions without a site visit.

Open factory policy. Wanplas operates an open factory policy across its factories, and buyers are welcome to visit Polyretec to inspect equipment under construction, watch a line running on real material and speak directly with the engineers who will commission their project. For a capital purchase of this size, a factory visit answers questions that no specification document can.

Frequently Asked Questions

Conclusion: Specify the Line for the Worst Bale You Will Ever Buy

The best LDPE film pelletizing line for printed and sticky film waste is the one specified against the hardest material the plant will realistically process, not the cleanest sample in the negotiation. Every stage in the chain covered here exists to solve a specific physical problem: dry pre-cleaning removes soil before it becomes an expensive water problem; float-sink separation removes everything denser than water; counter-current friction washing strips bound surface contamination; hot washing with caustic and surfactant attacks ink binders and grease that mechanical action cannot touch; the drying cascade protects the extruder; agglomeration solves the bulk density gap; double-stage venting removes what the wet section left behind; and melt filtration catches what nothing else could. Remove any one of these and the pellet tells the story.

The parameters that matter most are few and specific. Keep melt temperature between 195 and 215 degrees Celsius so ink volatilizes instead of carbonizing. Give the hot wash 10 to 20 minutes at 75 to 95 degrees Celsius with 0.5 to 2.0 percent caustic and a matched surfactant. Deliver flake to the extruder below 1 percent moisture and at 0.30 to 0.45 tons per cubic meter bulk density. Filter at 80 to 150 micrometers, in two steps on difficult streams. Close the water loop to recirculate 85 to 95 percent. Get those right and a printed post-consumer film stream produces a controlled light-gray pellet with ash below 1.5 percent and tensile strength retention of 75 to 90 percent, at 380 to 550 kilowatt hours and 0.5 to 1.5 cubic meters of fresh water per ton.

Polyretec, a Wanplas factory, has been building plastic recycling equipment since 2010 and has delivered more than 100 projects across more than 50 countries, with printed film, sticker-loaded film and agricultural film among its recurring specialties. Lines are supplied turnkey, tested before shipment, installed and commissioned by Polyretec engineers, and supported afterward with operator training, remote technical assistance and the Wanplas commitment of USD 500 free parts per year.

If you are evaluating a line for printed or sticky LDPE film, the most productive next step is to send a representative sample of your worst material together with your target output and the pellet specification your customers ask for. Polyretec will run a trial, report the achievable ink removal, yield, ash content and filtration loading, and return a line configuration built on those measured results rather than on assumptions. You are also welcome to visit the factory, see a comparable line running on real film waste, and talk the configuration through with the engineers who will commission it.