Separation of Polypropylene Polymers by Crystallization and Adsorption Techniques

fractionation of industrial polypropylene resins by crystallization or adsorption is a challenging task due to the existence of stereoregularity and the fact that homopolymer and propylene-rich copolymers are semicrystalline, as is the case with polyethylene homopolymer, which is usually present in complex polypropylene resins. The separation mechanisms involved in crystallization and adsorption techniques are investigated. Crystallization techniques and adsorption chromatography on graphitized carbon using a temperature gradient separate the full range of propylene ethylene copolymers following a U-shaped 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 better defines 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 complex high-impact polypropylene resins.