Chemically recycled monomer feed streams from postconsumer plastic packaging waste are expected to contain impurities that act as catalyst poisons. This work investigates the impact of such impurities on a commercial fourth‐generation Ziegler–Natta catalyst system. A recycled monomer feed stream in two different procedures by adding representative catalyst poisons (pyridine and n‐butanol) in various quantities to the reactor setup is simulated. Measuring catalyst activity and molecular weight distribution (MWD) and performing kinetic and MWD deconvolution modeling, the impact of the catalyst poisons on polymer product properties at the microstructural level is evaluated. The results demonstrate that, beyond a certain concentration (120 ppm), catalyst poisons have a substantial impact on the activity levels of the catalyst system tested. MWD deconvolution modeling shows an influence of the poisons on the composition of the resulting polymer product in the form of a shift toward lower or higher molecular weights (depending on the procedure). This microstructural analysis highlights the importance of purifying chemically recycled monomer feed streams.
Several chemical properties which influence the printability for fused filament fabrication 3D‐printing are derived from analyses of commercially available filaments. In preliminary experiments, polymerization conditions are optimized and suitable monomers and selectivity control agents (donors) are selected. An experimental series in which propene is copolymerized with the comonomers 1‐butene and 1‐hexene with an industrial Ziegler–Natta catalyst will be discussed here. The experiments are planned using design of experiments. Based on a split‐plot design, the design is adapted for mixtures and the combination of homo‐ and copolymerization. The observed factors, besides the mixture composition, are hydrogen partial pressure and the amount of donor. The obtained polymers are analyzed by means of high‐temperature size exclusion chromatography, differential scanning calorimetry, and rheology. 1‐Butene copolymers show good printing results and promising properties almost matching the desired ones. The targeted polymer properties are achieved within certain limits. 1‐Hexene copolymers result in lower molecular masses while crystallinity remains slightly higher, which does not match with the desired profile. Beneficial properties are likely to be achieved within a wider factor range, for example, higher comonomer amount and lower hydrogen partial pressure.
Chemical recycling of plastic waste has promise as a complementary technology to increase eco-efficiency of plastics life cycles. Accumulation of impurities in feed streams can affect sensitive compounds such as the Ziegler-Natta catalyst systems commonly used to produce polyolefins such as high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). In a poison study, the influence of impurities-more specifically NO and N 2 O-on the catalyst system are investigated comprehensively in terms of kinetic behavior and activity rates. A product composition analysis gives insights into product properties such as molecular weight distribution (MWD), comonomer composition distribution (CCD), melting point, and crystallinity. By applying known modeling techniques (kinetic modeling, MWD, and CCD deconvolution modeling), information beyond analytical data is obtained. The results of the study show that both poisons significantly affect catalyst kinetics and reduce catalyst activity. N 2 O influences primarily the MWD, while NO poisoning strongly affects the CCD of LLDPE samples. Since the mechanical properties of the polymers produced depend on factors such as MWD and CCD, NO and N 2 O poisoning may reduce their processability and applicability.
Front Cover: Polypropylenes for 3D printing are synthesized based on a customized split‐plot design. The study investigate homo‐ and copolymers, with varying comonomer content and type. Furthermore, the amount of donor and the hydrogen partial‐pressure are observed factors. After evaluation and optimization of the analyzed material properties, filaments of the most promising polymers are produced and successfully used in fused filament fabrication printing. This is reported by Gunnar Spiegel and Christian Paulik in article 1900044.
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