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A commercial SiO2 modified by the addition of a TiO2 layer on its surface and pore walls offers a support for metallocene‐based ethylene polymerization catalysts with a 35 % improved catalytic activity. The effect of such support modification on the catalyst particle fragmentation during polymerization reactions were assessed. This was performed by exposing the internal cross‐section of several SiO2 and Ti/SiO2‐based metallocene catalyst particles, polymerized at a wide range of reaction conditions, with a Focused‐Ion Beam Scanning Electron Microscope (FIB‐SEM), followed by a semi‐quantitative analysis of polymer, catalyst and macropores of each 2D image obtained. The titanation of the SiO2 lead to a support framework that fractures earlier and more efficiently. This was evidenced by the presence of several empty (polymer‐free) cracks along the support dense‐shell, found more extensively in the Ti‐modified polymerized catalyst particle, which also resulted in a more sustained polymerized particles macroporosity during the course of the reaction. [ABSTRACT FROM AUTHOR]

Performance enhancement of metallocene‐based olefin polymerization catalysts can be obtained, among others, by the chemical modification of their support. We investigated a titanated SiO2 (Ti/SiO2) as an improved support material for zirconocene catalysts, which lead to ∼35 % higher ethylene polymerization yields when compared to the unmodified SiO2‐supported metallocene. The improved catalytic performance of the modified catalyst was found to be related to the presence of a Ti‐based active site, second to the Zirconocene centers, as well as to a higher Lewis acidity in the titanated supported‐MAO, which improved the activation of the Zr‐based centers. The Ti active species were generated by reduction of the Ti/SiO2 support with the methylaluminoxane (MAO) co‐catalysts, which introduced oxygen vacancies (VO) and Ti3+ species, as confirmed by probe molecule Fourier Transform Infrared (FT‐IR) spectroscopy and UV‐Vis Diffuse Reflectance Spectroscopy (DRS). The higher Lewis acidity was linked to 5‐coordinated Ti4+, as detected by probe molecules FT‐IR spectroscopy. [ABSTRACT FROM AUTHOR]

Purpose: Post-sternotomy dehiscence and mediastinitis remains a serious complication in cardiothoracic surgery. The aim of this work is to report our experience over a period of 8 years in the surgical treatment and risk factor analyses of post-sternotomy dehiscence and mediastinitis. Methods: All patients treated for post-sternotomy dehiscence at our Thoracic Surgery Unit in the last 8 years were retrospectively collected. We identified 237 patients with post-sternotomy dehiscence/mediastinitis. Forty-two patients had simple fractures of the metal steel wires, 61 had an asymmetric sternotomy with multiple sternal fractures, 113 had a symmetric sternotomy with multiple sternal fractures, 14 had a failed Robicsek procedure, and 7 had sternal dehiscence with mediastinal abscess. Results: Different surgical techniques and materials were used to repair the sternum. In 21 patients, the first revision failed and a second reoperation was required. At multivariate analyses, we have identified risk factors for revision failure and in-hospital mortality. Mortality rate was significantly higher in patients who underwent more than one surgical revision (8% vs 19%, p < 0.001). Conclusions: Patients with sternal dehiscence are very fragile due to multiple preoperative comorbidities as reflected by postoperative morbidity and risk factors for in-hospital mortality. A correct evaluation of the characteristics of sternal dehiscence is important to guide the most appropriate repair strategy. Patients who need repeated sternal revisions had a higher mortality. Further randomized studies are needed to evaluate different techniques and medical devices to define the gold standard procedure to reduce significantly sternal wound complications in high-risk patients as defined by well-known risk factors. [ABSTRACT FROM AUTHOR]

We report a case of a patient who had a type A aortic dissection after previous coronary bypass grafting. The in-situ right mammary artery had been anastomosed with the left anterior descending artery, the left mammary artery had been anastomosed to the obtuse marginal, and a vein graft had been used for the right coronary artery. All grafts were patent. The patients underwent a Bentall procedure on perfused heart. (J Card Surg 2010;25:330-332) [ABSTRACT FROM AUTHOR]

In the field of olefin polymerization catalysis, metallocenes are heterogenized with methylaluminoxane onto silica supports to yield active catalysts. During olefin polymerization, these silica supports act as a framework to control the fragmentation stage, thereby influencing the final polymer product and preventing reactor fouling and fines formation. This study investigates the influence of different silica supports induced on the final polymer product. To study a broad range of silica supports from an industrial silica database, we utilize a hierarchical clustering method to cluster the supports based on their physical properties. From the clustering method, five supports representing the clusters and an industrial benchmark were analyzed at different polymerization stages using focused ion beam–scanning electron microscopy (FIB–SEM) and microcomputed tomography (microCT). This combined FIB‐SEM/microCT methodology revealed differences in both fragmentation behavior and polymer morphologies based on structural features, including macropores, mesopores, spray‐dried shells, spray‐dried spheres, and denser shells. The heterogeneity and ideal fragmentation behavior was further assessed by calculating the replication factor of each support, indicating that silica materials containing macropores and spray‐dried shells have an almost ideal replication phenomenon. This multiscale analysis revealed new understanding of catalyst fragmentation for different supports. This understanding could in the future be further developed by the addition of more supports or additional analysis of the supports to the industrial database. [ABSTRACT FROM AUTHOR]

Ziegler-type catalysts are the grand old workhorse of the polyolefin industry, yet their hierarchically complex nature complicates polymerization activity-catalyst structure relationships. In this work, the degree of catalyst framework fragmentation of a high-density polyethylene (HDPE) Ziegler-type catalyst was studied using ptychography X-ray-computed nanotomography (PXCT) in the early stages of ethylene polymerization under mild reaction conditions. An ensemble consisting of 434 fully reconstructed ethylene prepolymerized Ziegler catalyst particles prepared at a polymer yield of 3.4 g HDPE/g catalyst was imaged. This enabled a statistical route to study the heterogeneity in the degree of particle fragmentation and therefore local polymerization activity at an achieved 3-D spatial resolution of 74 nm without requiring invasive imaging tools. To study the degree of catalyst fragmentation within the ensemble, a fragmentation parameter was constructed based on a k -means clustering algorithm that relates the quantity of polyethylene formed to the average size of the spatially resolved catalyst fragments. With this classification method, we have identified particles that exhibit weak, moderate, and strong degrees of catalyst fragmentation, showing that there is a strong heterogeneity in the overall catalyst particle fragmentation and thus polymerization activity within the entire ensemble. This hints toward local mass transfer limitations or other deactivation phenomena. The methodology used here can be applied to all polyolefin catalysts, including metallocene and the Phillips catalysts to gain statistically relevant fundamental insights in the fragmentation behavior of an ensemble of catalyst particles., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Ziegler-Natta catalysts for olefin polymerization are intrinsically complex multi-component systems. The genesis of the active sites involves several simultaneous and sequential steps, making the individual steps and interconnections difficult to be unraveled in an unambiguous manner. In this work, we combine X-ray diffraction and spectroscopy to probe each step of the birth and life of a MgCl 2 -based Ziegler-Natta catalyst, namely the formation of high surface area MgCl 2 by dealcoholation of an alcoholate precursor, the TiCl 4 grafting, and the subsequent activation by triethylaluminum as co-catalyst. The so-prepared catalyst was tested towards ethylene polymerization, leading to the production of mainly crystalline high-density polyethylene. The use of operando characterization techniques allowed probing the transient details that are difficult to be dissected in the aftermath, but can radically affect the overall catalytic process., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)