Thursday, February 11, 2016

Melt Flow Index (ASTM D 1238)

To measure flow rate by extrusion Plastometer.

Specimen:

Any form which can be introduced into the cylinder bore may be used. e.g. powder, granules, strips of film. Conditioning required varies with material.

Procedure:

The apparatus is preheated to 190oC for PE. Material is put into the cylinder and the loaded piston (@ 43.25 psi) is put into place. After 5 minute the extrudate issuing from the orifice is cut off, flush and again one minute later. These cuts are discarded. Cuts for the test are taken at 1, 2, 3 or 6 minutes depending on the material or its flow rate. The melt index is calculated and recorded as gm/10 minute.

Significance:
It is primarily useful to raw material manufacturer as a method of controlling material uniformity. The melt index value is strongly indicative of relative “flowability” of various kinds and grades of PE. The ‘property’ measured by this test is basically melt viscosity or ‘rate of shear’. In general, the higher molecular weight materials are more resistant to flow.

2 comments:

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