Published in: Macromolecular Chemistry and Physics.
Volume 215, 2014, Pages 1818-1828.
Authors: B. Monrabal, L. Romero.
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The fractionation of industrial polypropylene resins by crystallization or adsorption is a challenging task due to the existence of stereo-regularity and the fact that homopolymer and propylene-rich copolymers are semi-crystalline, as it is the case with polyethylene homopolymer which is usually present in complex polypropylene resins. The separation mechanisms involved in crystallization and adsorption techniques have been investigated. Crystallization techniques and adsorption chromatography on graphitized carbon using temperature gradient, separate the full range of propylene-ethylene copolymers following a U-shape curve and cannot provide unequivocal compositional results. The addition of an infrared detector to measure the level of branches at each elution temperature provides a new dimension that defines better the separated components. A step further in separation is using cross-fractionation chromatography (composition followed by molar mass separation) which makes use of all the mechanisms investigated to provide the most extended separation of the complex high impact polypropylene resins.