Presented at the 7th International Conference on Polyolefin Characterization (ICPC), 2018. Houston, TX, USA.
By T. González, B. Monrabal, E. López, A. Roig. Polymer Char, Valencia, Spain.
Industrial polymer samples may contain fillers, gels/crosslinked material, catalyst residues or are additivated with small-particle size carbon black as light stabilizer. In those cases, a filtration step is required prior to a Liquid Chromatography (LC) analysis to protect the life of the columns, and/or fouling the detector cells.
There are new instruments that may incorporate an in-line filter system prior to injection with a back-flush mode, which can be effective for most standard samples contaminated with small amounts of residues. However, when samples contain a significant amount of crosslinked material or inorganic residues, an external filtration apparatus is advised, and it is a must when the samples contain carbon black of very small-particle size, due to the difficulties of removing it with standard filtration elements.
Samples produced in batch reactors or pilot plants with reduced catalyst efficiency may also contain significant catalyst residues, which also need to be removed with an external filtration step. The most difficult case is the removal of fine carbon black particles in polyolefins, usually analyzed by high temperature GPC (Gel Permeation Chromatography), which is quite often used with a Light Scattering detector (LS). The presence of very small particles may damage frits or column packing, and the particles capable of passing through the column to the detector cell will result in a noisy baseline when using a LS detector. Thus, an efficient external filtration system is required in the analysis of these types of samples.
In this poster, it is investigated if the filtration process modifies the molecular structure of different polyethylene (PE) and polypropylene (PP) resins.