The global push for “Circular Fashion” has split textile recycling into two distinct technological paths: Mechanical Recycling (Fiber-to-Fiber) and Chemical Recycling (Polymer-to-Polymer). For plant operators, the choice of shredder determines the viability of the downstream process. This guide specifies the cutting geometry required for each pathway.
Related equipment: textile waste single shaft shredder.
1. Mechanical Recycling (Fiber Preservation)
Goal: Retain maximum fiber length to allow re-spinning into yarn.
Challenge: Standard shredders act as “scissors,” cutting fibers too short (<5mm), turning valuable cotton into low-grade insulation filler (downcycling).
The Solution: The “Garnett” Style Single-Shaft
Instead of aggressive shearing, mechanical recycling requires a “tearing” action.
- Rotor Configuration: High-density rotor with thousands of small, pointed teeth (pins) rather than large block knives.
- Action: The pins “comb” and pull the fabric apart, disentangling the weave rather than slicing it.
- Target Output: Fluffy fibrous mass with lengths of 15mm – 25mm.
- Downstream: Carding machines re-align these fibers for spinning.
Machine Requirement:
* Low Speed: < 60 RPM to reduce fiber breakage heat.
* Cooling: Air-cooled cutting chamber to prevent synthetic fibers (polyester) from melting and fusing.
2. Chemical Recycling (Surface Area Maximization)
Goal: Create uniform, small chips with high surface area to accelerate chemical depolymerization (Glycolysis/Hydrolysis).
Challenge: Inconsistent particle sizes cause uneven reaction rates in the reactor vessel. Large pieces don’t dissolve; dust clogs filtration.
The Solution: Precision Multi-Shaft Shearing
Chemical recyclers need “chip” geometry, not “fluff.”
- Rotor Configuration: Quad-shaft shredder (or granulator) with sharp, close-tolerance block knives.
- Action: Scissor-like clean cuts.
- Target Output: Uniform 10mm x 10mm squares.
- Why: Smaller, more uniform chips increase solvent-to-material contact and can improve reaction consistency. The realized benefit depends on chemistry, agitation, residence time, and filtration.
Comparative Specifications
| Parameter | Mechanical Recycling (Spinning) | Chemical Recycling (Depolymerization) |
|---|---|---|
| Target Output | Long Fibers (Fluff) | Uniform Chips (Confetti) |
| Critical Metric | Fiber Length (>15mm) | Surface Area & Uniformity |
| Screen Size | Open / No Screen (Garnett) | 10-12mm Rigid Screen |
| Blade Type | Tearing Pins / Spiked Cylinder | Sharp Shear Knives |
| Throughput | Lower (Gentle processing) | High (Aggressive cutting) |
Handling Difficult Materials
Elastic Fabrics (Spandex/Elastane)
- Issue: Stretchy fibers wrap around standard rotors (“winding”), stalling the machine.
- Fix: An Anti-Winding Spline Rotor. The rotor surface typically features a textured or splined shaft that prevents long elastane strands from tightening around the axis.
Post-Consumer Buttons & Zippers
- Protocol: Metal contaminants destroy fine shredder blades.
- Requirement: A Pre-Shredder (slow speed, high torque) to rip open bales and liberate metal, followed by an Overband Magnet and Eddy Current Separator before the material enters the fine-cutting granulator.
The Energycle Advantage
For mixed-material streams (e.g., Post-Consumer fast fashion), Energycle recommends a Two-Stage System:
1. Stage 1: Heavy-duty industrial shredder to open bales and size-reduce to 50mm.
2. Stage 2: Specialized Granulator (for chemical) or Tearing Line (for mechanical) to achieve final spec.
FAQ
Can I process carpet on a textile shredder?
Carpet (Nylon/PP face mostly) is extremely abrasive due to the calcium carbonate backing. You need Carbide-Tipped blades. Standard tool steel will dull in <50 hours.
What is the “melt point” risk?
Polyester (PET) melts at ~260°C, but softens earlier. If blades are dull, friction heat will fuse the chopped fabric into hard lumps (“popcorn”), ruining the batch for chemical recycling. Keep blades sharp!
References
[1] “Textile Recycling Technologies & Specs,” The Ellen MacArthur Foundation. Textile Recycling Technologies & Specs
[2] “Mechanical vs Chemical Recycling of Textiles,” European Environment Agency. Mechanical vs Chemical Recycling of Textiles
