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Industry: polymers and plastics · EPR

Radicals, ageing and failure analysis

Radicals form when polymers are heated, exposed to light or stressed mechanically. EPR shows how fast, tests how well a stabiliser works and helps explain why a part failed.

Contact us← Industry: polymers and plastics
What it tells you

The start of degradation

Polymers degrade through reactions in which radicals are formed, long before cracks, discolouration or embrittlement are visible. EPR (electron paramagnetic resonance) sees the radicals themselves. It shows when degradation starts, how quickly it proceeds, and how long a stabiliser can hold it back.

Radical signal against exposure for a polymer without stabiliser, where radicals build up early, and with a stabiliser, where they appear after a delay
Radical build-up with and without a stabiliser. Schematic illustration, not measured data.
Typical samples

Where it is used

  • Plastics, rubbers and elastomers, including carbon-black filled compounds
  • Coatings and paints, for example the activity of light stabilisers over the depth of a clear coat
  • Parts that have failed in service, and good parts for comparison
  • Polymers with radical inhibitors or stabilisers

Typical tasks are comparing stabilisers, testing how a formulation withstands heat or light, and finding out whether a failure came from degradation.

How it works

Comparing the failed and the good part

A small piece of the polymer is placed in the instrument, and the radical signal is recorded and compared with a reference of known spin number. Samples can be aged in steps, so that the build-up of radicals is followed. In a failure analysis, a failed part and a good reference part are compared for their radical levels and for traces of paramagnetic metals.

Three steps: take a failed part and a good reference part, compare their radical levels and metal traces by EPR, and look for hints on the cause
Failure analysis with EPR. Schematic illustration.
Why EPR

What it adds

  • Sees the radicals directly and selectively, in solid samples as they are
  • Early warning, before degradation is visible
  • Ranks stabilisers on the same scale
  • Benchtop instruments put the technique within reach of a quality or development laboratory
Good to know

Points that matter in practice

  • Carbon black and other fillers can give their own signals. Compare compounds with the same filler, and use a reference part
  • Radicals can decay in storage, so note the time between the exposure and the measurement
  • The link between the radical level and the performance of the part has to be established for your own material
  • EPR complements mechanical, chemical and microscopic analysis. It does not replace them
How MSY Consulting helps

From your question to a routine method

Send or bring representative samples. MSY Consulting runs feasibility measurements, helps you plan the ageing steps and the reference parts, and trains your team until the method is part of your routine.

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Contact

Let's talk about your application

Send an email describing your instrument and your application, and you will get a reply.

contact@msyconsulting.eu

MSY CONSULTING SAS · Wissembourg, France · LinkedIn