Every percentage point of recovery matters when you're processing thousands of tons per year. If you purchase 1,000 tons of baled plastic and only sell 700 tons of finished product, the missing 300 tons represents material you paid for—plus the labor, energy, water, and disposal costs that went into processing it. Improving material recovery often delivers faster returns than chasing incremental throughput gains.
This guide explains what high recovery rates mean in real production environments, identifies where yield is commonly lost, and outlines the equipment choices and process controls that consistently push recovery above 95% on suitable feedstock.
Understanding Plastic Recycling Recovery Rate (Mass-Balance Method)
Two common mistakes inflate recovery numbers: counting water as product weight, and blaming the processing line for contaminants that were never recoverable polymer to begin with.
For accurate decision-making, use this mass-balance definition:
Polymer Recovery (%) = (Saleable polymer output ÷ Polymer content in feedstock) × 100
This requires estimating the actual polymer content in your inbound material through bale sampling, contamination audits, or supplier certifications. Report recovery excluding:
- Non-polymer contaminants (metal, stone, glass, wood)
- Non-target polymers (e.g., PVC in a PET stream)
- Water mass (report moisture separately; wet weights mask problems)
The Association of Plastic Recyclers (APR) publishes Model Bale Specifications that define acceptable versus prohibitive material in commercial bales—these specifications directly affect what you can realistically recover as saleable polymer.[1]
Common Yield Loss Points in Plastic Recycling Plants
Most avoidable yield loss comes from a short list of failure modes. When you measure them, you can fix them.
| Loss Point | What It Looks Like | Root Cause | Typical Solution |
|---|---|---|---|
| Fines & dust generation | Target polymer shows up as sludge; yield drops even when line runs smoothly | Impact crushing, dull knives, wrong screen selection, high-speed grinding on brittle material | Gentler size reduction sequence, controlled screening, knife maintenance schedule, wet grinding where appropriate |
| Separation errors | Float material sinks (or vice versa); reject stream looks too "clean" | Poor tank flow balance, inadequate wet-out, density drift from temperature or contamination, incorrect setpoints | Stabilized float-sink operation, staged separation, periodic sampling of reject streams |
| Filtration purge | Screen changer waste contains mostly polymer | Over-purging, premature screen changes, unstable melt pressure | Matched filtration strategy, pressure monitoring, predictable screen change intervals |
| Start-up & grade-change scrap | Extra gaylords of "off-spec" pellets; frequent line restarts | Inconsistent feeding, variable drying, melt temperature or pressure swings | Process stability (feed rate, drying, melt control), documented start-up procedures |
| Measurement error | Numbers don't match what you see on the floor | Moisture not measured, scales not calibrated, inconsistent record-keeping | Routine scale checks, moisture meters, simple mass-balance tracking |
Plastic Recycling Equipment Choices to Reduce Yield Loss
Size Reduction: Minimize Fines Creation
High yield starts before washing. Once you create dust, you lose material throughout the line, and no downstream separator can recover it.
Practical approaches that reduce fines:
- Use a low-speed first stage (such as a trituratore monoalbero) to reduce bulky items without shattering them
- Follow with a second-stage granulator only after geometry is controlled, and maintain knife sharpness on schedule
- Select screen size based on your wash system requirements and buyer specifications—overly fine sizing often creates more dust and higher carryover
When fines generation remains high despite process tuning and maintenance, upstream size-reduction equipment selection becomes the limiting factor—the knife configuration, rotor speed, and chamber design must match your specific material characteristics.
Separation: Monitor Reject Quality
If your float-sink reject stream looks too clean, your settings are likely wrong. The fastest diagnostic: take a timed sample of rejects, dry it, and weigh how much target polymer is leaving the system.
For rigid plastic streams, a staged approach (wash → float-sink → rinse) is common. For mixed bales, upstream bale quality matters as much as equipment—purchasing to APR-like specifications reduces unrecoverable material entering your plant.
Drying & Handling: Keep Moisture Out of Extrusion
Wet flakes create process instability that shows up as extra purge, screen loading fluctuations, and off-spec pellets. If you pelletize, treat dewatering as a yield tool, not just an energy-saving step.
Typical process components include a essiccatore centrifugo after washing, with additional thermal drying when product specifications demand it.
For plants consistently seeing moisture-related yield loss despite operational adjustments, the mechanical dewatering capacity—not thermal drying—often determines whether flakes enter extrusion dry enough to prevent purge spikes.
Filtration: Control Purge Through Process Stability
Filtration is where plants often discard good polymer unintentionally. The goal is not to run screens until failure; it's consistent pressure and predictable screen loading so you can change or clean screens with minimal polymer loss.
If pelletizing is part of your operation, match your filtration strategy to contamination level—post-industrial versus post-consumer material, presence of labels and adhesives, dirt content. Review the process options under sistemi di pellettizzazione della plastica when planning your filtration approach.
How to Run a Plastic Recycling Yield Audit
You don't need a full SCADA system to find the biggest yield leaks. Start with one shift and a spreadsheet.
| Fare un passo | What to Measure | Metodo | What It Reveals |
|---|---|---|---|
| 1 | Inbound mass | Weigh bales or bulk feed per shift | Baseline for mass balance |
| 2 | Inbound contamination estimate | Sample, sort, dry, weigh (manual audit) | Recoverable polymer versus non-polymer |
| 3 | Saleable output mass | Weigh bagged pellets or finished flakes (dry basis) | True output (exclude water weight) |
| 4 | Reject stream value | Timed sampling of float-sink rejects, dry and sort | Separation error rate |
| 5 | Sludge & fines loss | Track sludge cake mass; inspect for polymer content | Whether size reduction is too aggressive |
| 6 | Filtration purge composition | Sample purge; estimate polymer versus contaminant ratio | How much yield is leaving at screen changer |
Calculating the Financial Impact of Recovery Rate Improvements
Instead of assuming generic figures, run the audit and use your measured baseline.
Quick example for a 2,000 kg/h line:
- A 1% yield improvement = 20 kg/h additional saleable product
- Over 6,000 operating hours/year = 120 tons
- Multiply by your net contribution margin per ton (not just selling price—account for all variable costs)
This calculation shows the payback period for any equipment or process changes required to capture that yield.
Domande frequenti
Can every feedstock reach 98% recovery?
No. Recovery depends on how much target polymer is actually in the inbound stream and how stable your process runs. Clean post-industrial scrap can reach very high recovery. Heavily contaminated post-consumer streams can still perform well, but only with tight control over fines generation, separation, and purge.
Should we report recovery on wet or dry basis?
Always dry basis. Water weight hides problems and makes comparisons meaningless. If you sell flakes, measure and report moisture at discharge, then calculate on a dry basis.
Why does our reject stream contain so much target polymer?
Either your separation settings are incorrect, or the line is compensating for upstream quality issues (polymer mix, label contamination, dirt). Sample your rejects and weigh the target polymer fraction—this is usually the fastest way to diagnose the problem.
How do bale specifications affect our recovery rate?
Bale specs define what the market considers acceptable material versus prohibitive contamination. If you buy bales outside specification, you're paying for material that cannot become saleable polymer in your target stream. Tighter incoming specs typically improve both recovery and product quality.
What's the best way to reduce fines in our process?
Start with the first size-reduction step. Use lower-speed shredders before granulators, maintain knife sharpness, and select screen sizes that match your downstream requirements rather than defaulting to the finest available. Measure fines at each step to identify which equipment is generating them.
How often should we check our mass balance?
Weekly spot-checks catch problems early. Monthly full audits provide trend data. Any time you change feedstock, adjust equipment settings, or see yield drop, run an audit to identify where the loss is occurring.
References & Further Reading
- Association of Plastic Recyclers — Model Bale Specifications
- APR — PET Thermoforms Bale Specification (PDF)
- ISO 15270 — Plastics: Guidelines for the recovery and recycling of plastics waste
- Losses and emissions in polypropylene recycling (ScienceDirect, 2024) — Study documenting 85% PP yield with 6.6% loss at mechanical drying and 4.0% at wet grinding/friction washing stages
