Abstract
Polypropylene (PP) is one of the most widely used polymers. In this paper, three types of PPs including random PP, impact PP, and impact PP with high clarity, were prepared through a 75 kg/h pilot-scale Spheripol II process. The three produced PPs were produced by the selection or combination the two loops and gas phase reactor and controlling the comonomer and hydrogen concentrations. The three prepared PPs then were pelleted with the clarified nucleating agent NX 8000 and tested for mechanical, thermal, and optical properties. Their molecular structures and rubber phase size were also investigated by GPC, 13C NMR, temperature rising elution fractionation (TREF), XRD, SEM analysis, etc. The results showed that the random PP (PP-1) and the impact PP with high clarity (PP-3) obtained excellent optical transparency with a haze of 12.5% and 13.5% due to their small rubber phase size (roughly ≤ 100 nm), while the impact PP (PP-2) obtained bad transparency with a haze of 98.8% due to the large rubber phase size (about 1 μm) caused by the poor thermal compatibility with the PP matrix. The rubber phase content and ethylene/propylene sequence distributions of the three PPs varied much and resulted in different impact strengths and stiffness properties. PP-2 had a high impact strength of 14.5 kJ/m2 due to the rubber phase generated in the gas phase reactor. Except for the optical transparency, PP-3 gained stiffness and toughness, with 914 MPa of flexural modulus and 25.1 kJ/m2 of impact strength due to the unique molecular structure of its rubber phase.
Highlights
Since the discovery of the Ziegler–Natta (Z-N) catalyst in the 1950s, the production of polyolefins with various chain microstructures and properties has continuously grown with the rapid development of catalyst technology combined with polymerization innovation [1–10]
PP-2 had a high impact strength of 14.5 kJ/m2 due to the rubber phase generated in the gas phase reactor
The results show that the three PPs possess different molecular chain microstructures, which result in various mechanical, thermal, and optical properties
Summary
Since the discovery of the Ziegler–Natta (Z-N) catalyst in the 1950s, the production of polyolefins with various chain microstructures and properties has continuously grown with the rapid development of catalyst technology combined with polymerization innovation [1–10]. Polypropylene (PP) is undoubtedly one of most used and robust material fields in the production and consumption market globally [11–15]. The global production of PP was about 56 million tons in 2016 and is estimated to reach 80 million tons by 2022 [16]. The first major breakthrough in the Z-N catalysts in 1968 was promoted by Montedison ( LyondellBasell) and Mitsui with the discovery of the milled MgCl2 support for ethylene polymerization [17–19]. This technology was adopted by the extra addition of internal and external electron donors to improve the isotacticity of PP without catalyst activity in the PP industry in the Polymers 2020, 12, 751; doi:10.3390/polym12040751 www.mdpi.com/journal/polymers
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