Some test methods use a standard reference material to verify that a tester is functioning as intended during a weathering test method. Recently, a new lot of polystyrene material (referred to as “PS Lot 9”) has been approved for use as a standard reference material when running SAE J2527 (Automotive Exterior) and SAE J2412 (Automotive Interior). This material becomes more yellow over time; the amount of yellowing will indicate if the test is being performed correctly.

The use of PS is no longer mandatory in SAE J25257 or J2412. However, if one chooses to use this standard reference material, it should be done correctly. Here are some tips to keep in mind:

1. Make sure the proper optical filter is installed in the tester SAE J2527 can be run using the Extended UV-Q/B filter or the Daylight-B/B filter, and SAE J2412 can only be run using the Extended UV-Q/B filter. Use of any other filter will affect the yellowing of PS Lot 9.
2. Use the open-backed “mesh” specimen tray These test methods require use of the open-backed specimen tray. Using a solid back tray will affect the yellowing of the polystyrene material.
3. Completely fill the tray with specimens or blank panels If large gaps are present in the open-backed specimen tray, that will affect the temperature profile of the test and will affect the yellowing of the polystyrene material.
4. Mount the polystyrene in the “black panel” specimen holder The polystyrene material should always be mounted in a specimen holder without any backing, exposing it to air on both sides of the material. Additionally, it should be mounted next to the black panel temperature sensor in the tester.
5. Always perform color measurements using a standard white tile as backing Polystyrene is a clear material and the evaluation of the test is affected by the color of the material behind the polystyrene. Always back the polystyrene with a white standard tile when taking color measurements.

 Similar to specimen repositioning during a test, running PS Lot 9 in SAE J2527 and SAE J2412 is a best practice that laboratories should try and follow. But keep in mind that this material has only been tested for these two test methods, and the published limits should not be used when running any other test method.

Polystyrene is very sensitive to UV exposure as well as temperature, which is both good and bad for a reference material – tests can be performed quickly, but small changes in conditions can cause drastic changes on the outcome of the test. By following the tips above, this reference material can help you identify issues early in a test, saving you time and money.

In order to make use of polystyrene easier, we have created a tool you can use to see if your test is within limits. You can download it here.

If you want the certificate for the polystyrene with the limits in tabular form, you can find them here.