Cellular plastics consist of thin polymeric membranes separating small cavities or cells. The cells may be mostly closed and separate, mostly open and interconnecting, or a combination of the two. The percentage of open cells is indicative of the insulating quality of cellular plastics and is an important variable, requiring control during manufacture and evaluation after production. The ASTM Standard Test Method D2856 provides a procedure for determining the percentage of open cells using an older model of an air comparison pycnometer. This device is no longer manufactured. However, you can determine the percentage of open cells conveniently and with greater precision by performing a test which uses Micromeritics’ AccuPyc 1330 Pycnometer.
The test, conducted as described in this application note, is comparable in all respects with the ASTM standard method. As in the standard method, you cut a sample from the original material and determine the volume of the sample. This cut opens some of the closed cells. You then make a second cut of equal area on the same sample material and determine the volume again. The second cut allows you to compute a correction for the cells opened by the first cut. While the ASTM D2856 standard specifies air as the operating gas, dry nitrogen is satisfactory in all aspects. Dry air may be used if desired.
Cellular plastics consist of thin polymeric membranes separating small cavities or cells. The cells may be mostly closed and separate, mostly open and interconnecting, or a combination of the two. The percentage of open cells is indicative of the insulating quality of cellular plastics and is an important variable, requiring control during manufacture and evaluation after production. The ASTM Standard Test Method D2856 provides a procedure for determining the percentage of open cells using an older model of an air comparison pycnometer. This device is no longer manufactured. However, you can determine the percentage of open cells conveniently and with greater precision by performing a test which uses Micromeritics’ AccuPyc 1330 Pycnometer.
The test, conducted as described in this application note, is comparable in all respects with the ASTM standard method. As in the standard method, you cut a sample from the original material and determine the volume of the sample. This cut opens some of the closed cells. You then make a second cut of equal area on the same sample material and determine the volume again. The second cut allows you to compute a correction for the cells opened by the first cut. While the ASTM D2856 standard specifies air as the operating gas, dry nitrogen is satisfactory in all aspects. Dry air may be used if desired.
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