Today's KNOWLEDGE Share
♻️ Why Does the IV of Recycled PET Tend to Decrease?
Intrinsic Viscosity (IV) is one of the most critical parameters for PET performance.
Yet in recycled PET (rPET), IV loss is a common and often misunderstood issue.
So why does IV tend to decrease during recycling?
1.Thermal degradation during reprocessing
PET is sensitive to heat. During extrusion and re-melting, excessive temperature or long residence time can cause polymer chain scission, directly reducing molecular weight — and therefore IV.
2.Hydrolysis caused by residual moisture
Even small amounts of moisture can trigger hydrolytic degradation at high processing temperatures.
Without proper drying control, IV loss can occur rapidly and irreversibly.
3.Mechanical stress in multiple processing steps
Grinding, washing, extrusion, and filtration all introduce mechanical shear.
Each step slightly shortens polymer chains, and the cumulative effect becomes significant over multiple recycling cycles.
4.Contamination and material inconsistency
Non-PET polymers, additives, or degraded fractions can accelerate thermal and chemical degradation, making IV control more difficult and less predictable.
5.Limited ability to “recover” IV
Unlike virgin PET, recycled PET cannot regain molecular weight without controlled post-treatment processes (such as solid-state polymerization).
Without such steps, IV loss is structural — not cosmetic.
👉 Why this matters for buyers
Lower or unstable IV directly affects processing behavior, mechanical strength, and end-use performance — especially in bottle, sheet, and thermoforming applications.
This is why consistent IV control is often more important than simply targeting a nominal IV value.
Understanding why IV drops is the first step toward sourcing recycled PET that performs reliably — not just on paper, but in production.
Has IV stability been a key challenge in your PCR material evaluations?
source :Judy Shen
#RecycledPET
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