Presented at the 6th International Conference on Polyolefin Characterization (ICPC), 2016. Shanghai, China.
Alberto Ortín, Jesús Montesinos, Benjamín Monrabal. Polymer Char, Spain.
Ethylene-Propylene copolymers, and also blends of polyethylene and polypropylene homopolymers, are important industrial products. The Molar Mass Distribution (MMD) of those complex materials is measured by High Temperature Gel Permeation Chromatography (HT-GPC), and the use of multiple band IR detection has proven very successful to study their chemical composition along the MMD.
Besides the analysis of the MMD and chemical composition of the whole material, it is also of interest to obtain the MMD of the individual components in a mixture. In this presentation, a data processing method is described to recover the MMD of the individual components in PP-PE binary mixtures, by using the data collected at multiple bands by a filter-based IR detector coupled to HT-GPC.
In the past, binary mixtures have been de-convoluted by combining data from, at least, two different detectors, while in this work a single yet multispectral detector is used. Drawbacks of combining data collected using several measuring cells, compensation of time/volume delay, differences in broadening of the chromatographic bands or dynamic response in the detector, are completely eliminated in this method. Unlike other approaches to deconvolution of chromatogram components based on curve fitting, this method does not require a-priori assumptions on peak shapes, and it is not necessary to assume the number of peaks in the mixture, so it is of more general application.
In other to show the performance of this deconvolution method, binary mixtures of polypropylene and polyethylene homopolymers at different ratios were analyzed by GPC-IR, as well as the individual components at equivalent concentration levels. The chromatograms and the resulting MMD obtained from the deconvolution or direct injection of individual components matched almost perfectly, even when the proportion of the minor component was low.
The methodology here presented can also be applied to other polyolefin binary mixtures such as polypropylene-polybutene which have been successfully analyzed by GPC with IR detection.