ASTM D1505:18 pdf free download – Standard Test Method for Density of Plastics by the Density-Gradient Technique.
9. Procedure
9. I Wet three representative test specimens with the less dense of the two liquids used in the tube and gently place them in the tube. Allow the tube and specimens to reach equilibrium. which will require 10 rnifl or more. Thin films of I to 2 mils in thickness require approximately I ½ h to settle, and rechecking after several hours is advisable (Note 4).
9.2 Read the height of each float and each specimen by a line through the individual center of volume and averaging the three values. When a cathetometer is used, measure the height of the floats and specimens from an arbitrary level using a line through their center of volume. If equilibrium is not obtained. the specimen may be imbibing the liquid.
9.3 Remove old samples without destroying the gradient by slowly withdrawing a wire screen basket attached to a long wire (Note 6). which is conveniently done by means of a clock motor. Withdraw the basket from the bottom of the tube and. after cleaning, return it to the bottom of the tube. It is essential that this procedure be performed at a slow enough rate (approximately 30 rninl3(X)-mm length of column) so that the density gradient is not disturbed.
NoTE f—Whenever it is observed that air bubbles are collecting on samples in the column, a vacuum applied to the column will correct thi%.
10. Calculation
10. I The densities of the samples may be determined graphically or by calculation from the levels to which the samples settle by either of the following methods:
10. I . I Graphical Calculaiion—Plot float position versus float density on a chart large enough to be read accurately to ± I mni and the desired precision of density. A minimum correlation factor of 0.995 shall be obtained to show the column is acceptable. Plot the positions of the unknown specimens on the chart and read their corresponding densities.
11. Report
11 . 1 Report the following information:
11 . 1 . 1 Density reported as D2’’, in grams per cubic centimetre. as the average for three representative test specimens
11 . 1 .2 Number of specimens tested if different than three,
11.1.3 Sensitivity of density gradient in grams per cubic centimetre per millimetre.
11 .1 .4 Complete identilication of the material tested, and
11.1.5 Date of the test.
12. Precision and Bias
12. I Specimens Molded in One Iiiboraiorv and Tesied in Several LLthoraiories—An interlaboratory test was run in I 9K I in which randomized density plaques were supplied to 22 Ia)ratories. Four polyethylene samples of nominal densities of 0.92 to 0.96 g/cm were molded in one lalratory. The data were analyzed using Practice E691. and the results are given in Table 2.