09 Aug 2024
Understanding Intrinsic Viscosity (IV) Measurement: The Key to Quality in Recycled PET
Explore the importance of Intrinsic Viscosity (IV) in recycled PET, how it influences material performance, suitable applications for different IV levels, and the techniques used to adjust IV for specific needs.
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What is intrinsic viscosity (IV)?
Intrinsic Viscosity (IV) for rPET measures the thickness and stretchiness of the melted plastic.
Imagine if you had a stretchy rubber band—if it’s really stretchy and doesn’t break easily, it’s like rPET with a high IV. That means the plastic is strong and can be used to make tough things like bottles that need to hold liquids without breaking.
If the IV is low, it’s like a rubber band that’s not very stretchy and breaks easily, meaning the plastic is less durable and is better suited for applications where high strength is not a critical requirement.
So, IV helps decide what kind of products the plastic can be used for, based on how strong and stretchy it is.
The IV is measured in special units called deciliters per gram (dL/g). To test PET, it is melted and its flow through a tiny hole is observed. If it flows slowly, it has a high IV (indicating greater thickness). If it flows quickly, it has a low IV (indicating lower thickness). This measurement helps determine how strong and stretchy the plastic will be.
Applications or products based on intrinsic viscosity (IV) Values
0.6 - 0.7 dL/g: PET is used for yarn and fiber applications. PET fibers and yarns are utilized to create polyester materials, which are then used in making carpets, clothing (such as dry-fit athletic wear), and mattress filling.
0.7 - 0.8 dL/g: This range is generally used for PET sheet applications. Sheets are manufactured in various ways and then undergo a thermal process to create trays, boxes with lids, and containers.
0.8 - 0.85 dL/g: This is the PET bottle grade, primarily used in injection molding to create bottle preforms. These preforms are then supplied to companies with stretch blow molding machines, which heat and blow the bottles.
Above 0.85 dL/g: This range is used for water jerry cans. These cans used to be made of polycarbonate, but PET is now commonly used.
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Possibilities for increasing and decreasing the IV value
When working with recycled PET, Solid State Polycondensation (SSP) is an important process used to adjust how strong and stretchy the plastic is. Here’s a simpler breakdown:
Increasing IV: To make rPET stronger and more flexible, it can go through SSP. This means heating the rPET in a special way without melting it. This heat helps to rebuild the long chains in the plastic, making it more durable and stretchy. This is useful for making high-quality products like sturdy bottles or tough packaging.
Decreasing IV: If the rPET is too strong or stretchy, it might need to be adjusted. Although SSP mainly helps increase IV, the general idea is to manage how the rPET is processed (like adjusting temperatures) to make it less stretchy or weaker if needed. This makes the plastic suitable for less demanding uses.
Why IV is more important for rPET, then to other recycled materials?
Intrinsic Viscosity is crucial for rPET because it determines the plastic’s strength and flexibility, which are essential for making high-quality products like bottles and containers.
For other plastics like rHDPE and rPP, IV is less critical. Instead, properties like melt flow rate or density are more relevant for assessing their quality and usability. Each type of recycled plastic has its own key metrics based on its specific applications and processing needs.
At Cirplus, we understand the critical role Intrinsic Viscosity (IV) plays in ensuring the quality and performance of recycled PET. That’s why we collaborate with top-tier partner laboratories to offer precise IV measurement services. Whether you're looking to verify the IV of your materials or adjust it to meet specific requirements, Cirplus is here to help you achieve the best results. Reach out to us today to learn more about how we can support your recycled PET needs.