Intrinsic Viscosity Drop

Viscosity Test

Dissolving the polymer in a solvent and measuring the flow time through a capillary tube yields the intrinsic viscosity value. This measurement is sensitive to changes in polymer molecular weight and serves to qualify materials for high stress applications. When analyzing the intrinsic viscosity drop, a difference of more than ten percent between the incoming pellet and the molded part indicates inadequate drying.

Run Control

Processors of recycled flake resin must monitor this drop to ensure that the material retains enough melt strength to be processed. Extrusion of bottle grade flakes into sheet requires a low intrinsic viscosity drop to prevent the melt from sagging or tearing during thermoforming. Virgin resin is much less prone to viscosity loss than regrind because it contains fewer contaminants and has not undergone multiple heating cycles.

Process Failure

Severe polymer degradation reduces the toughness of the finished product, leading to failure under impact. In bottle molding, this results in thin areas or crack propagation in the base of the bottle.