Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties

New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting endotherm. These results indicate that polyethylene macrochains can grow up during polymerization either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements. Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the final processing temperature

New HDPE/MCM41 nanocomposites with improved mechanical performance: synthesis and characterizatio

Ordered mesoporous silicas with a channel structure of well-defined geometries and dimensions at nanometer scale are excellent candidates to host intercalation reactions. In recent years, our research group has shown that mesoporous silicas of the M41S class combined with metallocene complexes give rise to excellent supported catalysts for ethylene polymerisation. Due to the support characteristics, the reaction is allowed to occur in the channels and in this way hybrid organic-inorganic materials can be prepared within a large range of nanofiller concentration. These HDPE/MCM-41 nanocomposites exhibit an improved mechanical performance and an easier degradability due to the additional role of MCM-41 as a promoter for PE degradation

MCM-41 as Nanofiller in Polyethylene Hybrid Materials

Mesoporous MCM-41 exhibits a stable framework structure, well-defined nanopores and a large surface area. When combined with metallocene polymerisation catalyst, these mesoporous materials, provide a unique route for preparing polyolefin-based nanocomposites by in situ polymerisation

UHMWPE/HDPE in-reactor blends, prepared by in situ polymerization: synthetic aspects and characterization

This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/ High Density Polyethylene, UHMWPE/HDPE, blends by in situ polymerization in a single reactor, through dual catalyst immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-immobilized in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated, under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way. Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated. Results have shown that these in-reactor UHMWPE/HDPE blends exhibit a complex thermal, mechanical and rheological behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.info:eu-repo/semantics/publishedVersio

Dual-Composite Right-Left Handed Transmission Lines for the Design of Compact Diplexers

In this study, the use of dual-composite right-left-handed (D-CRLH) transmission lines is proposed for the design of diplexers. The D-CRLH diplexers present advantages over conventional diplexers such as smaller size (especially in the ultra high frequency band). The design procedure and the design equations are presented in this paper. The non-linear phase response of a D-CRLH transmission line has been used to design diplexers at any arbitrary frequencies. Finally, two diplexers have been designed and manufactured: one for quite near frequencies and the other for further ones. The simulation results show good agreement with the measurements. A sensitivity analysis has been provided to show the robustness of this kind of circuits

Shape Analysis and Computational Fluid Simulations to Assess Feline Left Atrial Function and Thrombogenesis

In humans, there is a well-established relationship between atrial fibrillation (AF), blood flow abnormalities and thrombus formation, even if there is no clear consensus on the role of left atrial appendage (LAA) morphologies. Cats can also suffer heart diseases, often leading to an enlargement of the left atrium that promotes stagnant blood flow, activating the clotting process and promoting feline aortic thromboembolism. The majority of pathological feline hearts have echocardiographic evidence of abnormal left ventricular filling, usually assessed with 2D and Doppler echocardiography and standard imaging tools. Actually, veterinary professionals have limited access to advanced computational techniques that would enable a better understanding of feline heart pathologies with improved morphological and haemodynamic descriptors. In this work, we applied state-of-the-art image processing and computational fluid simulations based on micro-computed tomography images acquired in 24 cases, including normal cats and cats with varying severity of cardiomyopathy. The main goal of the study was to identify differences in the LA/LAA morphologies and blood flow patterns in the analysed cohorts with respect to thrombus formation and cardiac pathology. The obtained results show significant differences between normal and pathological feline hearts, as well as in thrombus vs non-thrombus cases and asymptomatic vs symptomatic cases, while it was not possible to discern in congestive heart failure with thrombus and from non-thrombus cases. Additionally, in-silico fluid simulations demonstrated lower LAA blood flow velocities and higher thrombotic risk in the thrombus cases