Poster: Analysis of Ultra-High Molecular Weight Polyethylene (UHMWPE) by GPC and Viscometry

Alberto Ortín, Pilar del Hierro. Polymer Char, Valencia, Spain.

Abstract:

The unique mechanical and chemical resistance properties of UHMWPE are making this technical polymer grow in its range of applications and industrial importance. From an analytical point of view, it presents many challenges given the extremely long chains that result in solutions of very high viscosity. In this poster, analytical tools that are helpful to succeed in the analysis of UHMWPE are presented.

For high-temperature GPC analysis, the polymer needs to be dissolved at a very low concentration level so that the injected solution does not block the system frits or columns and a smooth and stable flow is maintained. Besides the limitations posed by the separation range of GPC columns, a precise Molecular Weight Distribution (MWD) can only be obtained by means of an extremely sensitive and stable detector. Infrared (IR) detection has proved to be successful in this kind of analysis, that is, when the injected mass has to be drastically reduced, by one or two orders of magnitude.

Measuring the Intrinsic Viscosity (IV) of UHMWPE is also a useful tool for production control and product development given the difficulties and limitations of other analytical techniques. The IVA instrument incorporates a robust two-capillary viscometer, together with a high-temperature autosampler, so that a fully-automated analysis of UHMWPE can be carried out conveniently and with high precision, overcoming the problems of the manual or semi-automated methods. By using the built-in IR detector, the actual injected mass of the sample going through the viscometer capillaries is quantified; thus, improving the accuracy and precision of the IV results.

Common to all analytical techniques is the requirement of handling the samples with care to prevent thermal or oxidative degradation during the dissolution and analysis steps. Guidelines on this and on good practices are explained in this work.