Project Details:

Efficiency and reproducibility of temperature rising elution fractionation (TREF)

The aims of this project are (1) to fractionate a given number of Polyethylene (PE) test samples with regard to their composition using a given experimental procedure, (2) to compare the quantity and chemical composition of the obtained fractions in the partner laboratories, (3) to compare the results with regard to influence of the instrumental setup and reproducibility and (4) to establish suitable conditions for the compositional fractionation of polyethylene. Finally conclusions shall be drawn with regard to the comparability of the results and the robustness of TREF procedures in daily routine.

TREF is a technique which fractionates semicrystalline polyolefins from solution according to composition and microstructure. The technique has been invented in the late 1970s. In TREF the polymer is dissolved in a suitable solvent at elevated temperatures. Subsequently the solution is slowly cooled down to crystallize the sample. In the third step the sample is eluted by fresh solvent at successively rising temperatures. The fractions are collected and analyzed after workup. The instrumental setup and experimental parameters which are used vary between the different laboratories. Crystallization and elution can be carried out either in a column which is packed with a porous support or in a reactor without packing. As there was no commercial instrumentation available until the late 90s the equipment which is used is in most cases in-house constructed. The steps of crystallization and elution are influenced by the concentration of the polymer, the dimensions of the reactor, the type of support used and the cooling rate. However there are no guidelines about these parameters and little information is available in the literature. Therefore the results from different laboratories are difficult to compare. Due to the pivotal importance of TREF for the compositional fractionation of polyethylene it is highly important to compare the results between different laboratories. TREF is used in various countries, ranging from industrialized nations to developing countries.