This test method has been described in an earlier publication; it has been adopted in the United Kingdom as Method 102-D of British Standard 2782 (1956) and in the United States by ASTM.
One advantage of the Vicat softening point (VSP) test is that it can be carried out on small specimens. It was therefore of interest to establish correlations between VSP values and test results by ASTM Method D 648 and B.S. 2782 Method 102-C (softening test on cantilever specimens) for a range of thermoplastics. The VSP test is not suitable for highly crosslinked materials since they cannot accommodate an indentation of 1 mm. Measurements of
It is well known that test results by ASTM Method D 648 are affected by stress in the test specimens, and this may be a large effect if the specimens are injection molded. It was found that VSP values are not so affected, and the VSP therefore gives a measure of intrinsic softening behavior. Comparison with Method D 648 test results gives some measure of molding stresses.
Reproducibility of VSP results on crystalline plastics tends to be poor compared with the reproducibility attainable on amorphous thermoplastics. A variant of the test has advantages, namely, the use of a large area indenter (