IV Tester
The IV is determined by dissolving a small amount of PET in a solvent and measuring the time required for 100 ml of the
solution to flow through a capillary viscometer at a fixed temperature.
The flow time is compared to that for a standard solvent
under the same conditions. Concentration and time are then used to compute the Intrinsic Viscosity.
This test is a sensitive measure of the degradation of cellulose resulting from the action of heat; light; acids; alkalies;
oxidizing and reducing agents; and the like; used in its processing or purification.
The intrinsic viscosity value may be
converted to degree of polymerization (DP) or to intrinsic fluidity; if desired.
Solutions of cellulose are not Newtonian liquids; that is; their viscosity depends upon the rate-of-shear or velocity gradient
during measurement.
This effect is smaller for samples of low molecular mass (DP) and at low concentrations than for high-DP
samples and at high concentrations. For the celluloses and concentrations included within the limits set forth in this test
method; the effect of rate-of-shear is assumed to be negligible for referee purposes.
For other conditions and for research
purposes
this assumption may be invalid; but to discuss ways of accounting for this effect is beyond the scope of the present test
method.
- This test method covers the determination of the intrinsic viscosity of purified celluloses such as bleached wood pulps; cotton linters; and regenerated cellulose. It is applicable to all cellulose samples with an intrinsic viscosity of 15 dl/g or less. Most native (unpurified) celluloses have intrinsic viscosity values too high for measurement by this test method
- The IV is related to the composition and molecular weight of the PET resin and is a common descriptor of PET flowability. The Best Practice specifications for PET flake and pellets stipulate IV requirements for end products using recycled PET.
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