Inherent Viscosity

The inherent viscosity (I.V.) of a polyester material may be determined through a solution test or through a Gel Permeation Chromatography (GPC) test. The I.V. of a molded part is an indicator of the average molecular weight of a material. The molecular weight of a material determines physical properties such as tensile strength, stiffness and impact performance.

Processing and I.V.

Processing polyester-based materials will reduce the I.V. If drying and processing guidelines are followed, the I.V. of the molded part will exhibit only a slight drop. Improper drying, excessive residence times, excessive temperatures, or excessive use of regrind materials may cause unacceptable drops in I.V., reducing the properties of the material.

Determine Material Integrity

Eastman technical service labs are available to assist in the testing of molded parts. One of the first steps in any failure analysis should be the determination of the material integrity. Submit the failed part and, if possible, a sample of pellets from the material lot in question to Eastman technical service labs.

I.V. Results

Once you have the results from the I.V. testing, use the I.V. guide to evaluate them. The I.V. guide provides typical I.V. ranges for several Eastman materials after processing.

After I.V. Is Compared to the I.V. Guide

If the I.V. is acceptable, proceed with the field failure analysis.

If the I.V. is unacceptable, further analysis of processing conditions may be beneficial. A field technical service representative can provide assistance to ensure proper processing during the next material trial for the application.