Insights from industry

Measuring Intrinsic Viscosity of PET Without Toxic Solvents

Toby Rogers, Sales Director at Lloyd Instruments, talks to AZoM about their PETPlus IV test system and the benefits it can bring to the PET market.

Could you please provide a brief introduction to the industry that Lloyd Instruments works within and outline the key drivers?

Lloyd Instruments are physical testing experts in a diverse range of industries such as automotive, aerospace, medical devices, food, pharma and electronics. However packaging continues to be our core market. The key drivers in all industries is a greater emphasis on quality, regulation and safety.

Can you briefly explain the technique or the theory behind the PETPlus IV testing system?

Traditionally the intrinsic viscosity of PET is measured by dissolving in toxic solvents. The ASTM D4603 capillary viscometer method is used to compare the viscosity of the solvent to the solvent/PET solution.



The solvents used to dissolve PET are extremely dangerous and highly toxic and include: Phenol/tetrachlorethane, Phenol/Dichlorobenzene, Dichloroacetic Acid, TrifloroaceticAcid and ortho-Chloropehnol.

The solution viscosity method requires relatively simple equipment – a glass capillary viscometer. However expensive laboratory facilities and high level laboratory staff are required to facilitate the use of dangerous solvents. Ongoing consumable costs of solvents and disposal costs are another disadvantage to the solution method. Therefore despite the relatively low cost of a glass capillary viscometer, the significant cost of infrastructure to handle solvents makes the cost and practicality prohibitive for PET processors.

The method we use with the PETPlus system is solvent-free and based on melt viscosity. First the PET is dried in the laboratory under vacuum.  

Once dried, the PET is placed into a sealed barrel with a die at the base. The melt is then forced through the narrow die at 295 Celsius for 17 minutes. The free space in the barrel is filled with moisture free nitrogen gas to ensure there is no degradation due to moisture.

Some simple melt systems on the market do not use nitrogen, this leads to significant variability in measurement due to moisture contamination from the atmosphere.

After extrusion, the PETPlus software performs a linear regression to obtain the polymer degradation rate and initial melt viscosity. This is then converted to IV using a formula developed by ICI. ICI were the pioneers in PET and developed the melt system due to issues with solvent safety but also because a melt system gives far more information about how the material will behave in the process. The ICI method also measures thermal degradation which is impossible when using solvents. This is a very useful parameter that can be used to improve processing.

What are the major advantages of the PETPlus IV test system and what makes that unique?

The solvents used in traditional measuring methods are extremely dangerous. The PETPlus system offers significantly improved safety for users.

There's also an issue of cost in that there are high consumable costs to buy the solvents, and there's an equivalent cost to dispose of those solvents. As the PETPlus system does not use solvents these costs are eliminated.

Another issue with traditional methods is the cost associated with setting up a lab facility. The rheometer needed to perform the traditional IV tests has a relatively low cost, but setting up the safety procedures and systems to handle those solvents is very expensive.

And you need a laboratory technician who is trained to handle solvents.

With the PETPlus system, you don't need any special qualifications to use it and there are no safety issues to consider.

Another main advantage of this system, is the ability to measure the thermal degradation of the PET material which allows the user to see how it might behave in an injection moulding machine.

What main industries primarily benefit from the PETPlus IV testing system?

Our core market is PET preform manufacturers and PET processors.

For preform manufactures the benefits are numerous. Inspection of incoming material can quickly be assessed to avoid expensive downtime in production. Similarly evaluating blends of virgin and recycled material can be done on site to allow optimization of raw material costs.

Manufacturers can evaluate IV directly from the production dryer prior to processing which gives an early warning signal of issues with drying.

Pre-form IV can be measured to optimise the IV drop across the process which can be related to acetaldehyde and the dangers it poses if it migrates from the PET to the beverage.

How has the market responded to the PETPlus IV test system?

Today we are seeing a push by several major brands to specify the PETPlus as standard for new pre-form manufacturing lines and we expect this trend to grow. The ability to rapidly and safely measure IV to control process parameters has been very well received by PET processors, although we have seen a healthy conservatism in the testing community, as the method used in the PETPlus system is unique and differs from the traditional measuring methods.

This being said, PTI (Plastics Technology Inc.) recently made a study comparing the PETPlus test method with the traditional test methods. The study showed that the data achieved from the PETPlus system is just as reliable and equally fit for measuring intrinsic viscosity in a PET processing environment

How do you see the market progressing over the next decade and how do you see Lloyd Instruments being a part of that progression?

One main factor is safety. The world is getting evermore safety conscious, especially in the food and drinks industry. This is an area where testing requirements will increase in the future.

There is always a commercial drive from the drinks makers to have unique bottles for marketing purposes. Each time they invent something new, it pushes the boundaries we need to test.

In addition, processors are always looking for ways to make their bottles lighter making it even more critical to test.

Where can our readers find out more about Lloyd Instruments and the PETPlus IV?

Our website: has a wealth of additional information on the PETPlus instrument and we are always ready to discuss our customer’s needs.

About Toby Rogers

Toby Rogers

Toby Rogers has 20 years technical and commercial experience in the materials testing industry.

During this time his major focus has been the measurement of IV using melt methods. This knowledge has been used to assist PET processors globally improve their process and reduce costs.

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.

Stuart Milne

Written by

Stuart Milne

Stuart graduated from the University of Wales, Institute Cardiff with a first-class honours degree in Industrial Product Design. After working on a start-up company involved in LED Lighting solutions, Stuart decided to take an opportunity with AZoNetwork. Over the past five years at AZoNetwork, Stuart has been involved in developing an industry leading range of products, enhancing client experience and improving internal systems designed to deliver significant value for clients hard earned marketing dollars. In his spare time Stuart likes to continue his love for art and design by creating art work and continuing his love for sketching. In the future Stuart, would like to continue his love for travel and explore new and exciting places.


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  1. JUAN AGUILAR JUAN AGUILAR El Salvador says:

    this equipment can be used also for Polyester Thread

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of

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