The Effect of Reactor Conditions on High‐Impact Polypropylene Properties and Gas Phase Polymerization Kinetics

• Published in: Macromolecular reaction engineering Vol. 12; no. 4
• Main Authors: Cancelas, Aarón J., Yang, Lanti, Girod, Robin, de Heer, Jos, Kleppinger, Ralf, Delsman, Erik, Wang, Jingbo, Gahleitner, Markus, Monteil, Vincent, McKenna, Timothy F. L.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-08-2018; Wiley-VCH Verlag
• Subjects: Atomic force microscopy; Atomic properties; Atomic structure; Catalysis; Catalysts; Chemical Sciences; Copolymerization; Copolymers; Ethylene; high impact polypropylene; Isotacticity; kinetics; Mass transfer; Morphology; Polymerization; Polypropylene; properties; Properties (attributes); Propylene; Reaction kinetics; reactor; Rubber; Ziegler-Natta catalysts
• ISSN: 1862-832X; 1862-8338
• DOI: 10.1002/mren.201700063

High impact polypropylene (hiPP) powders are made in a 2.5 L semi‐batch gas‐phase reactor using a Ziegler–Natta catalyst and two sequential polymerization steps. The amount of copolymer, reactor temperature and pressure, the relative amounts of ethylene and propylene, and the presence of hydrogen are varied systematically to understand their impact on the copolymerization kinetics, hiPP properties, and on rubber distribution. Examples of discoveries are that the presence of hydrogen can reduce copolymerization activity, depending on the catalyst system, and that the fraction of crystalline copolymer decreases with 1) copolymer content in hiPP; and 2) copolymerization activity. The last implies a resistance to mass transfer of ethylene during copolymerization. To understand this phenomenon, atomic force microscopy analyses of hiPP samples with distinct morphology of the polypropylene matrix (isotactic polypropylene, iPP) and copolymer ethylene/propylene ratios are performed after microtoming. It is found that mesoparticles are the determining structure for the copolymer distribution, and that powders with more ethylene in the copolymer or an iPP matrix better suited for mass transfer had more rubber in the center of the mesoparticles. This indicates that the length scales of the mesoparticles that control transfer limitations for ethylene also impact the properties of the final impact copolymer.
The impact of rubber content, as well as of the relative crystalline and amorphous fractions in the rubber is considered in terms of the physical properties of high impact polypropylene powders, including powder flowability and mechanical properties. It appears that mass transfer resistance can explain certain observations.