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Moisture in the polymer causes hydrolysis to occur. As the water molecule is heated, one of the hydrogen atoms breaks away and both the H+ and OH- ions look for pairs along the polymer chain. In hygroscopic polymers such as PC/ABS these ions break up the long polymer chains resulting in a lower average molecular weight. This drop in molecular weight results in a drop in overall material viscosity.

Because water has a molecular weight of only 18, it alone acts as a plasticizer which reduces the overall viscosity of the material. This is one reason we often recommend molders of non-hygroscopic materials ensure they remove surface moisture from their materials.

-Andy

note: The intensification ratio is a factor which is used to
convert the hydraulic pressure being applied to the hydraulic injection
cylinders into the actual pressure being applied to the polymer melt at the
front of the screw.

Attribute data has two different outcomes. An example of such an outcome would be a GO / NO-GO gauge which is used when testing parts. This test results in only two different outcomes, Pass or Fail.

Variables are those aspects measured using a scale. An example of this would be a dimension measured using calipers. This device provides a wide variety, or scale, of results based on the accuracy of the instrument and ability of the person taking the measurements.

-Andy

Polymer chain mobility is highly dependent on the length, or molecular weight, of the polymer chain. If most of the polymer chains have a similar molecular weight, or smaller distribution, then they are all more likely to soften at similar temperatures typically resulting in a more narrow temperature range at which the polymer can be processed.

Adversely, a broad molecular weight distribution often results in a wider processing window due to the mobility of some polymer chains while other chains remain highly entangled.

Semi-crystalline polymers with a narrow molecular weight distribution can often achieve a higher degree of crystallinity than polymers with a wide distribution. 

-Andy