How to Improve PET Flake Viscosity with SSP Solid State Polycondensation

PET bottle flakes will lose intrinsic viscosity (IV) during recycling and extrusion. Low IV PET material cannot meet the high tensile requirement for cotton strap, packing band and rigid packaging. Solid State Polycondensation (SSP) is the most reliable technology to raise PET flake viscosity without melting the material

What causes IV drop of recycled PET flakes?

After sorting, washing and crushing, recycled PET flakes contain moisture and impurities. Hydrolysis happens under high temperature melt processing, breaking the molecular chain and reducing IV value.
Moisture in PET flakes is the main reason of molecular chain scission
Multiple re-extrusion further reduces viscosity
Low IV PET leads to weak packing strap, easy breakage during use

How does SSP solid state polycondensation work?

SSP reaction takes place at temperature below PET melting point. PET flakes are heated in a vacuum tumble dryer / solid state polycondensation reactor. The by-product ethylene glycol is continuously removed under vacuum condition. Longer molecular chains are formed, so the intrinsic viscosity increases steadily.
Our SSP tumble drum can process PET flakes and PET pellets, lifting IV from 0.60 up to 0.95 or higher according to customer target.

Key advantages of SSP technology for PET recycling

1. Stable IV control: Adjustable final viscosity for different end products, such as PET packing strap, fiber, sheet.
2. Low degradation: No melt extrusion during viscosity building, less yellowing.
3. Wide raw material compatibility: Works for washed PET bottle flakes, regrind PET.
4. Continuous & batch type options available for different production capacity.

Critical process parameters for PET SSP

Pre-crystallization: Prevent PET flakes from sticking together inside the reactor
Vacuum level: Deep vacuum to remove glycol condensate
Reaction temperature and holding time: The longer retention time, the higher final IV
Raw material dehumidification: Dry flakes before feeding into SSP drum

Typical end applications of SSP treated high IV PET

High viscosity PET after SSP treatment is widely used for:
✅ High strength PET cotton strap / packing band
✅ PET staple fiber
✅ Rigid PET sheet and thermoforming package
✅ Food-grade PET pellets

Conclusion

SSP solid state polycondensation is an essential process for PET recycling manufacturers to upgrade low-IV waste flakes into high-value raw material. Proper SSP equipment can help you get stable viscosity output and improve your product competitiveness.
If you are looking for PET SSP tumble drum or complete PET recycling line, contact HD Machine for technical solution and quotation.