Recycling rules feel arbitrary until you have watched what happens at the other end. Why is a plastic liner such a problem? Why does wax ruin a load? Why does moisture get deducted so aggressively? All of it makes immediate sense once you understand the process your bales are feeding.
1 · The pulper
Bales go into what is essentially an enormous blender: a vessel of water with a rotor at the bottom. Mechanical agitation plus water breaks the bonds between fibres and the board disintegrates into a slurry, typically 4–6% fibre by weight.
This is the first and most important filter, and it explains the single biggest contamination rule. Anything that does not break down here has to be removed later, mechanically, at cost. Plastic film does not break down. It shreds into thousands of small pieces that are harder to remove than one large piece would have been.
2 · Coarse screening and ragging
A ragger — literally a rotating rope — pulls out the long stringy contaminants: film, strapping, wire, tape. It is remarkably effective and remarkably crude. Heavy contaminants drop out into a junk trap: staples, stones, the occasional hand tool.
Here is why your bale spec matters. A mill expects a certain contamination rate and has sized this equipment accordingly. Exceed it and throughput drops, which is why deductions for prohibitives are steep rather than proportional.
3 · Fine screening and cleaning
The slurry passes through progressively finer screens and through hydrocyclones, which spin out particles by density. This removes the small stuff: ink particles, adhesive fragments, grit, and — this is the relevant one — wax.
Wax-coated produce board is the classic dead end. Wax does not pulp and does not screen out cleanly. It melts, disperses, and redeposits on equipment and on the finished sheet as spots and voids. One pallet in a load can affect an entire run, which is why it is a hard rejection rather than a deduction.
| Contaminant | Removed at | Consequence if present |
|---|---|---|
| Plastic film | Ragger, partly | Shreds; raises reject rate and downtime |
| Metal banding | Junk trap | Equipment damage risk |
| Staples | Junk trap | Generally tolerated in small quantities |
| Polystyrene | Screens, poorly | Fragments persist into the sheet |
| Wax coating | Not reliably removed | Spots and voids; possible load rejection |
| Food grease | Not removed | Contaminates the water loop; odour in the sheet |
| Water | N/A — paid for as fibre | Direct deduction on every ton |
4 · Forming
The cleaned slurry sprays onto a moving wire mesh. Water drains, fibres interlock, and a continuous wet sheet forms. Fibre alignment here gives paper its grain direction, which is why board is stiffer in one axis than the other and why box design specifies score orientation.
5 · Pressing and drying
The sheet passes through press rolls, then over a long series of steam-heated cylinders. This is the energy-intensive step by a wide margin, and it is where the moisture deduction becomes obvious: every kilogram of water you ship arrives, gets paid for as fibre, and then has to be boiled off at the mill's expense.
6 · Corrugating
Flat liner and medium go to a corrugator. The medium is heated, fluted between rollers, glued and sandwiched between liners. Out comes combined board, which is then printed, slotted, scored and folded into boxes. Then, with luck, into a trailer, to a dock, and eventually back round to a yard like ours.
The fibre-length argument
Here is the thing that reframes the whole process. Every pass through a pulper shortens the fibres. Shorter fibres interlock less well, producing a weaker sheet. Corrugated can go round this loop roughly five to seven times before the fibre is too short to form strong board, at which point it is downgraded or lost.
Recycling is a finite number of lives. Reuse does not consume one.
So a box reused nine times and then recycled five times has delivered forty-five useful lives. The same box pulped immediately delivers five. Reuse is not an alternative to recycling — it is a multiplier on it, and that relationship is the single most underused fact in packaging sustainability.
What this should change about your dock
- Strip plastic liners before board reaches the baler. It takes seconds and it is the highest-value sorting action available.
- Separate wax-coated board at source. There is no outlet for it in a standard OCC stream.
- Keep collection under roof. You are paid for fibre, not water.
- Shake out void fill. Polystyrene left inside boxes is the most common avoidable contaminant we find.
- And before any of it — pull out the containers that could still be containers.
Our pieces are written by the people who do the work rather than by a content agency, which is why they contain more numbers and fewer adjectives than is fashionable. If a figure here does not match your experience, we would genuinely like to hear about it — two of our published coefficients have changed that way.