How to Improve IV Loss in Recycled PET: Chain Extender Solutions for rPET Processing

Recycled PET (rPET) is widely used in pelletizing, fiber, sheet, strap, injection molding and other polyester processing applications. But during collection, washing, drying and repeated melt processing, PET molecular chains can be shortened by hydrolysis, thermal degradation and shear. The result is a lower intrinsic viscosity (IV), weaker melt strength and a narrower processing window.

For many recyclers and compounders, the practical question is simple: how can the IV of recycled PET be restored during extrusion without adding unnecessary process complexity?

BTCE-2013 is designed for this problem. It is a reactive chain extender for PET and other polyester systems, helping reconnect degraded molecular chains during melt processing, increase molecular weight, improve IV and support more stable extrusion.

Why IV drops in recycled PET

PET is sensitive to moisture and thermal history. Even small amounts of residual water can accelerate hydrolysis at processing temperatures. In recycling streams, IV loss is often caused by a combination of:

• Incomplete drying before extrusion.
• Multiple heat histories from previous processing.
• Hydrolytic degradation during washing, storage or melt processing.
• High shear in extrusion, pelletizing, sheet extrusion or injection molding.
• Mixed feedstock quality, including bottle flakes, fibers, films and industrial scrap.

When IV drops, processors may see unstable strand extrusion, weaker melt strength, lower mechanical performance, more brittle products, and greater variation between production batches.

What a PET chain extender does

A reactive chain extender works inside the melt. Functional groups react with PET chain ends and help rebuild molecular weight. In production terms, this can support:

• Higher IV and improved molecular weight recovery.
• Better melt strength for extrusion and downstream forming.
• More stable pelletizing, sheet extrusion, fiber spinning and injection molding.
• Improved tolerance to recycled content and variable feedstock quality.
• A wider processing window for rPET modification.

BTCE-2013 is the main chain-extension component in this solution. For applications where moisture sensitivity or long-term hydrolysis resistance is also important, BTPW-2 and BTWR-500 can be considered as supporting additives.

Extrusion trial: BTCE-2013 improved IV in PET bottle flake

In a customer-side 65 mm extrusion trial, PET bottle flake and high-clean PET pellets were processed with different chain extender systems. The trial used dual vacuum sections with a vacuum level around -0.085 MPa. Under the tested conditions, the 1# chain extender did not show a clear IV-building effect, while BTCE-2013 showed significant IV improvement.

PET bottle flake trial results

In this trial, 0.8% BTCE-2013 delivered the highest measured IV, reaching approximately 0.99 dL/g. This indicates strong chain-extension performance and meaningful recovery of melt-processing capability.

The data also shows that dosage and processing conditions both matter. A higher additive level does not always mean a higher IV result. Drying, screw speed, residence time, vacuum efficiency and dispersion all influence the final performance.

High-clean PET pellet trial results

For high-clean PET pellets, BTCE-2013 also increased IV from 0.682 dL/g to a maximum of 0.909 dL/g under the tested conditions.

A three-part additive strategy for recycled PET

For rPET processing, IV recovery is usually the first priority, but not the only one. Moisture sensitivity and hydrolysis resistance also influence long-term processing stability and product performance.

This does not mean every formulation needs all three products. In many rPET applications, BTCE-2013 is the core solution. BTPW-2 and BTWR-500 are selected when the application requires additional moisture-management or hydrolysis-resistance performance.

Application areas

BTCE-2013 can be considered for a wide range of PET recycling and polyester modification processes, including:

• PET bottle flake pelletizing.
• rPET extrusion and re-pelletizing.
• Recycled PET fiber and filament.
• PET sheet and thermoforming sheet.
• PET strapping.
• PET injection molding with recycled content.
• PET film and BOPET-related applications requiring melt stability.
• PET engineering plastic modification.
• PETG / APET processing where chain degradation needs to be controlled.
• Mixed recycled polyester streams where IV stability is a key requirement.

Processing notes for better IV recovery

To get consistent chain-extension performance, processors should pay attention to:

• Drying: PET should be dried sufficiently before extrusion.
• Vacuum: efficient vacuum venting helps remove moisture and volatiles.
• Dispersion: BTCE-2013 should be well dispersed in the PET melt.
• Residence time: reaction time should be long enough, but excessive heat history should be avoided.
• Dosage optimization: the best dosage depends on feedstock IV, moisture level, target IV and processing equipment.
• Lab confirmation: IV, MFR/MFI, torque, strand stability and mechanical properties should be checked before scale-up.

Conclusion

Recycled PET often loses IV because of hydrolysis, thermal history and chain scission. A reactive chain extender such as BTCE-2013 can help rebuild molecular weight during extrusion and improve processing stability.

In the extrusion trial described above, BTCE-2013 increased PET bottle flake IV to approximately 0.99 dL/g under the tested conditions and also improved the IV of high-clean PET pellets. For recyclers, compounders and PET processors, this provides a practical route to improve rPET value and expand application possibilities.

For formulation design, BTCE-2013 can be used as the main IV-recovery additive, while BTPW-2 and BTWR-500 can be selected as supporting additives when moisture sensitivity or hydrolysis resistance needs to be further improved.