| Abstract: | Variation in the results obtained in the Light Scattering Film (LSF) Test, also referred to as the Fog Test, presents problems both for the investigator as well as the formulator. The results are often confusing (two similar formulas will produce widely different results) and seldom repeatable. In the Fog Test high fog values are desired because high fog values mean less fog. The results of this study demonstrate that the standard deviation for multiple tests on the same sample decreases with increasing fog value. The values obtained when little LSF is produced (high fog values) vary only slightly while the values obtained for heavy LSF (low fog values) fluctuate as much as 30 points. Several explanations are offered for this lack of repeatability, but they condense down to the fact that all of the variables which affect the results are not presently controlled. The tests cited in this report were conducted using Di-2-ethylhexyl phthalate, Diisodecyl phthalate, and Di-(1-heptyl, nonyl, undecyl) phthalate as neat plasticizers from commerical suppliers. DOP was used because it is currently used by the SAE as an industry standard. The remaining two plasticizers were used because they are typically used in flexible PVC for automotive interiors. Results of this study confirm that the variations encountered in the LSF Test are inherent in the test itself and not due to the material being evaluated. Fluctuations which occur around a given LSF value occur to the same degree irrespective of the material producing the light scattering film. |
