Expanded Polystyrene (EPS/Styrofoam) is mostly air by volume, so logistics often dominate the economics: a 53-foot trailer full of loose EPS can be volume-limited long before it is weight-limited. In many scenarios, recycling becomes financially viable only after densification. This guide compares three common solutions: Shredding, Cold Compaction, and Thermal Densification.
Related equipment: single shaft shredder.
1. The Foam Shredder (Volume Reduction Ratio: 3:1)
A foam shredder tears bulky packaging into 20-50mm flakes. It does not compress the material; it simply breaks the structure.
- Best For: Manufacturers who reuse foam in-house (e.g., as “bean bag” filler or mixed into lightweight concrete).
- Logistics Check: If you plan to ship the waste to a recycler, shredding is insufficient. You are still shipping mostly air, and freight costs will exceed the scrap value.
- Mechanism: Low-speed, high-torque shafts with “ripping” teeth.
2. The Cold Compactor (Ratio: 50:1)
Also known as a Screw Press, this machine physically squeezes the air out of the EPS.
- Mechanism: An auger screw pushes the foam flakes against a restricted gate. The friction and pressure fuse the beads into a solid “log” without melting them.
- Output: White, dense logs (300-400 kg/m³).
- Energy: Low (Electromechanical only).
- Best For: Fish boxes (wet EPS), Electronics packaging.
- Advantage: It does not degrade the polymer chains. The resulting logs can be easily re-ground and molded into new PS products.
3. The Thermal Densifier (Ratio: 90:1)
A “Melter” uses heat to liquefy the foam, removing almost all of the trapped air.
- Mechanism: Electric heaters or intense friction melt the EPS into a toothpaste-like consistency, which is extruded into an ingot.
- Output: Rock-hard “purged” ingots (600-700 kg/m³) that look like hard plastic.
- Energy: High (Heating elements).
- Best For: Mixed dirty foam, High-volume logistics.
- Advantage: Maximum truck weight. You can load 20 tons of densified ingots into a container, maximizing export value.
Comparison Matrix
| Metric | Shredder | Cold Compactor | Thermal Densifier |
|---|---|---|---|
| Reduction Ratio | 3:1 | 50:1 | 90:1 |
| Output Density | 10-20 kg/m³ | 250-400 kg/m³ | 600-700 kg/m³ |
| Energy Cost | Low | Medium | High |
| Odor/Fumes | None | None | Styrene Gas (Vent required) |
| Freight Viability | Poor | Good | Excellent |
Financial Analysis: The “Pay-Weight” Threshold
To sell recycled EPS (rEPS), you generally need a full truckload.
* Loose Foam: A 53′ truck holds ~1,000 lbs. Value = $0 (Cost to ship > Value of material).
* Cold Compacted: A 53′ truck holds ~35,000 lbs. Value = Profitable.
* Thermal Densified: A 53′ truck holds ~45,000+ lbs. Value = More profitable.
Recommendation:
* If you generate < 1 ton/month: Use a Shredder and reuse locally.
* If you generate > 5 tons/month: Invest in a Cold Compactor.
* If you generate > 20 tons/month or export: Invest in a Thermal Densifier.
FAQ
Can I run wet fish boxes in a thermal densifier?
No. The water turns to steam, causing dangerous “blowback” and voids in the ingot. Use a Cold Compactor (like the Energycle CP Series) or a specialized washer-dryer system first.
Does cold compaction degrade the plastic?
No. Cold compaction preserves the Molecular Weight (MW) of the polystyrene better than thermal densification, which adds “heat history.”
References
[1] “EPS Recycling Logistics,” Expanded Polystyrene Industry Alliance. EPS Recycling Logistics
[2] “Densification Technologies for Polymers,” Waste Management Journal. Densification Technologies for Polymers
