Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Identifying Virgin Plastics

What is virgin plastic?
Put simply, it is a polymer in its pure form. Many polymers - such as PTFE, PEEK and Nylons - are used by adding a filler such as glass or carbon to enhance the material properties. In virgin plastic, no fillers have been added.

Despite ample data on the properties of various polymers, it is easy to understand that most end-users rely on the word of the supplier that the polymer they are paying for is the polymer they are getting.

Because many of the properties are inherently difficult to test, one would need to send the material to a lab for identification. And because the methods of identification are sometimes complex and require many types of tests, this can end up being an expensive affair. A client may be willing to undertake this expense one time, but if a component is supplied regularly, it would be cumbersome to test the materials each time a new lot is received. Hence, for the most part, clients accept the material test certificates (MTC) as provided by the supplier and trust that the parts supplied are from the lot corresponding with the MTC.

In our own experience, we have come across many instances of clients claiming they are using a certain polymer when in reality, the material they are being supplied is a cheaper variant of the polymer they think they are using.

A few examples of these are highlighted in the table below:

Polymer Substitute Price difference
PTFE Polypropylene, Polyethylene 4-5X
PCTFE PTFE, Polypropylene 10-20X
FEP Polypropylene, Polyethylene 40-50X
PA66 PA6 1.5-2X
PFA Polypropylene, Polyethylene 40-50X

In most cases, the criteria for this substitution is clearly price. We receive many samples from potential clients claiming to be either PEEK or PTFE. In some cases, a lab test is not even needed as it is visually obvious they are using another polymer.

In a few cases, the non-availability or the non-processability of the polymer leads to suppliers opting for substitutes. For example, the inability of UHMWPE to be easily injection moulded leads some processors to use LDPE or HDPE instead. Visually, it is difficult to tell these polymers apart, so the client accepts the alternate material without question.

Obviously, the performance of these materials cannot match up to the polymer originally chosen for the application.

In one case, we received samples from a client claiming they were PEEK and enquiring as to why they should have failed in his application. The part was a ball valve seat, procured from another vendor and had deformed after only a few months of performance. When we explained that the part was PEK, the client insisted that his supplier was giving him PEEK. When the part was sent to the lab and it was confirmed that the part was PEK, the client asked us to supply him the same part, but with virgin PEEK. When we explained that the price would be nearly double, they refused to accept, asking us to match the price they were already getting. Eventually, they returned to their original supplier, even though they knew the material being supplied was inferior. The commercial impact of using virgin PEEK was too high for them and they preferred using the cheaper variant and dealing with the rejections that came with this.

In an attempt to make the identification of certain polymers more transparent, we created the above infographic. Using this, basic tests can be performed to ensure that the polymer is as committed.

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