Polystyrene reference materials have been used in accelerated weathering test methods for decades to demonstrate acceptable maintenance and operation of weathering test chambers. Round-robin testing of these reference chips helped to establish acceptable lower and upper limits of polystyrene yellowing (Δb*) for SAE test methods J1885 (interior) and J1960 (exterior). However, since J1885 and J1960 were converted into performance-based standards (J2412 and J2527, respectively), the use of polystyrene reference materials in those standards is now non-mandatory. In line with this trend, polystyrene weathering reference materials are also no longer required by most automotive OEMs. Several factors have contributed to this change:

1. The factors causing yellowing of polystyrene chips may not be the same factors that degrade automotive materials in production today.

2. Some OEMs have developed their own reference materials, which better represent the materials critical to their products’ appearance and performance.

3. Modern weathering test chambers are capable of more precise control of test parameters, making tests more repeatable and reproducible without the need for validation from reference materials.

4. Availability of the current approved lot of polystyrene (Lot #8) has dwindled to near zero, and approval of a new lot of PS (Lot #9) has taken longer than anticipated to have proper limits established and to be brought to market.

5. The aging effects of polystyrene in storage are unknown.

6. Meeting the established requirements for polystyrene is often challenging, regardless of test apparatus.
To read more about Q-Lab and to find more articles like this, please visit Q-Lab Blog.