X2.2.13.1 Purging does not replace cleaning. After purging,
the equipment must be cleaned properly to avoid the effects of
contamination, resin buildup, and so forth, as discussed previously.
X2.2.14 Melt Density—It is important that the correct melt
density be used, that is, 0.7636 g/cm3 for PE at 190°C and
0.7386 g/cm3 for PP at 230°C. These values may be different
for copolymers or when additives are incorporated into the
resin. Small errors in these values can affect the end results. If
not known, the melt density can be determined as described at
the end of Footnote A of Table 1.
X2.2.15 Piston (Flag) Travel Distance—The setting of the
proper piston travel distance (6.35 6 0.25 mm for MFRs up to
10 g/10 min and 25.40 6 0.25 mm for MFRs greater than 10
g/10 min) is important in Procedure B. The reproducibility of
Procedure B is better if these parameters are strictly adhered to.
A calibrated distance verification device will be required to
maintain the proper piston travel.
X2.2.16 Calculation Factors—When trouble shooting, always
check the calculations and the factors used.
X2.2.17 Power (Electrical) Fluctuation—Constant power
(voltage) is important to maintain the temperature desired.
Periodic changes in voltage will cause changes in the temperature
of the unit, creating test values that fluctuate because of
inconsistent sample temperatures. Though this is a rare situation,
this fluctuation has been found to cause erratic test results.