Poster: Analysis of UHMWPE and Bimodal HDPE by Gel Permeation Chromatography in a quality control environment

By Esther López, Alberto Ortín, Benjamín Monrabal. Polymer Char, Spain.

Abstract:

High temperature gel permeation chromatography (GPC/SEC) is used in analytical laboratories to obtain the molar mass distribution (MMD) as the most important microstructural property to characterize polyolefins. The requirement of high temperature operation, together with the complexity of the technique, and fragility of columns has prevented in the past the availability of MMD analysis in manufacturing plant laboratories as routine process control tool.

In this poster, we have selected two polymers of high industrial importance, bimodal  HDPE and UHMWPE, as examples to present analytical tools and guidelines that are helpful to succeed in the characterization in a quality control environment.

Bimodal HDPE resins (blow molding, pipe …), being produced in a multireactor process, with selective incorporation of comonomers, demand a close control during the production, not obtained with just Melt Index and Density parameters. The analysis of the MMD and comonomer incorporation in a short time provides a significant improvement in control during grade changes. A study of precision and reproducibility obtained in the analysis of this type of samples is presented with a significant reduction of analysis time (45 minutes) of significant importance for quality control decisions.

From an analytical point of view, UHMWPE samples present many challenges given the extremely long chains that result in solutions of very high viscosity, the limitations by the separation range of GPC columns, the thermal degradation… In this work it has been studied the importance of sample preparation, the importance of shear degradation in the column, as well as the lack of proper separation of the high molar mass fractions due to the exclusion limit of the columns to obtain accurate MMD.