Dilute solution viscosity of polyethylene terephthalate (PET)

Introduction

The Viscotek Dilute Solution Viscosity (DSV) system provides fully automated determination of viscosity. The system features the Viscotek Y-501 Relative Viscometer, the semi-automated sample preparation (SASP) and injection system, software, and accessories to provide for the ultimate in automation, safety, precision, and accuracy. The DSV system provides excellent results for the solution viscosity of polyester terephthalate (PET) resins, as shown in this application communication.

Experimental

In this work, the samples were analyzed in two solvents, o-chlorophenol (OCP) and 3:2 Phenol:TCE. Sample preparation was made automatically on the SASP system with a correction for thermal expansion. The run conditions were as follows: The temperature was fixed at 30° C. The concentration was 0.500 g/dL. The total solvent usage per sample with duplicate injections and including washing was 50 mL. The time of analysis per injection was 5.5 minutes and the average standard deviation of analysis was less than 0.0003 dL/g. Both solvent dispensing and sample analysis were carried out in a closed loop system to minimize solvent exposure.

Measurements were made on duplicate preparation and duplicate injections from each vial to show the precision of both the viscometer and the sample preparation system.

Results

The exact concentrations of the PET/OCP samples are given in table 1. The precision of the thermal expansion correction from the room temperature concentration to the analytical temperature concentrations should be noted.

The phenol:tetrachloroethane (Phenol:TCE) proved to be a better solvent for dissolution of the samples. The SASP preparation system was used to prepare single volumes of each Phenol:TCE sample. Duplicate injections were made from each vial. The Viscotek Model Y-501 Relative Viscometer measures solution viscosities of the sample relative to the reference solvent simultaneously, thereby avoiding errors due to temperature fluctuation and solvent variations.

Table 2 gives the details the accuracy and precision of the Y-501 Viscometer for the OCP samples: The data for the samples run in 60% phenol / 40% TCE is shown in table 3. Note the reproducibility within each run.