FIPA for xylene soluble fraction of polypropylene and impact copolymer

Introduction

FIPA is a fast, precise and accurate analytical tool for routine process and quality control analysis. This technique provides quick and easy simultaneous measurements of Mw, IV, and % polymer for liquid samples. Therefore, it is ideal for the quantification step of a routine test called "Xylene Soluble". The Xylene Soluble (XS) test is designed to determine the amorphous content of polypropylene (PP) and impact copolymers like ethylene-propylene rubber (EPR). The accuracy and precision of the XS test is very important to the implementation of the process and product definitions of these materials. In this report, we will compare the Viscotek FIPA experimental procedures versus the traditional gravimetric method. We will illustrate the time and cost savings possible with the FIPA technique, plus the gain in molecular information from Viscotek Triple Detection technology. Finally, we will present the results from a % XS correlation study on a set of PP and EPR samples.

Experimental

The schematic 1 provides the outline comparison of the Viscotek FIPA and the traditional gravimetric procedures.

The XS sample preparation procedure is well established and somewhat empirical in nature, therefore, the Viscotek mini-prep method must follow closely the traditional protocol in order to preserve the chemistry of the extraction while reducing solvent and labour requirements.

Schematic 1: Comparing the Viscotek FIPA method for determining the xylene soluble fraction compared to the traditional gravimetric method.

For this analysis, the detector used was a Viscotek TDA model 302 with the columns and the detectors kept at 45 °C. The eluent was THF at a flow rate of 1.0 mL/min. The injection volume was 100 µL.

From 20 to 40 samples can be processed using the Viscotek XS method in an 8 hour shift. The time savings comes from the mini-prep automation and the ability of the FIPA system to keep up with the sample flow. The reduction in solvent usage is also substantial because the mini-prep requires only 25 mL of xylene instead of 100 to 400 mL in the traditional gravimetric method

Results

This 9 sample correlation study compares the results obtained by the Viscotek XS method and the traditional gravimetric method. Figure 1 is a plot of the % XS data from both analyses. In addition to the %XS data, the Viscotek FIPA system provides the molecular weight and the intrinsic viscosity of the XS fraction.

Figure 1: Correlation of the % XS by FIPA and gravimetric method.

Conclusion

The Viscotek FIPA XS technique is rapidly becoming the preferred method for many polypropylene producers and catalyst research organizations. This is driven by the speed, accuracy, precision and additional Mw and IV information offered by the new technology. Time and labour savings can easily pay for a system in less than a year even in a moderate sample load situation. There are also additional HS&E improvements associated the mini-prep and FIPA when compared to the open vessel operation of the traditional gravimetric analysis.