Browsing by Author "Bento, A."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- Decorated MCM-41/polyethylene hybrids: crystalline details and viscoelastic behaviorPublication . Cerrada, María L.; Pérez, Ernesto; Lourenço, J. P.; Bento, A.; Ribeiro, M. R.Polyethylene-based nanocomposites have been prepared by in-situ polymerization of ethylene with mesostructured MCM-41. Different approaches are used to improve interfacial adhesion between components, high density polyethylene (HDPE) matrix and MCM-41. These consist either of the incorporation of UA in the polymer chains by copolymerization in a very small content or of the modification of MCM-41 surface with the system based on undecenoic acid, UA/triisobutylaluminum, TIBA, before polymerization. The materials attained exhibit minimal changes in the crystallinity resulting from first melting process although a slight increase of long spacing at room temperature is seen as MCM-41 is incorporated in the hybrids. Moreover, a confinement effect is noticed and, thus, a delay in the crystallization process of the macrochains within pores and channels is detected. These novel self-reinforced nanocomposites show higher stiffness than other similar hybrids with poorer interfacial adhesion. Accordingly, they exhibit an enhancement in their mechanical performance without changing the final processing temperature since Tm is the same for all of the specimens.
- Functionalization of mesoporous MCM-41 (Nano)particles: preparation methodologies, role on catalytic features, and dispersion within polyethylene nanocompositesPublication . Bento, A.; Lourenço, J. P.; Fernandes, A.; Cerrada, María L.; Rosário Ribeiro, M.MCM-41 micro- and nanoparticles are prepared and functionalized with silane coupling agents. These pristine and silane-decorated mesoporous MCM-41s are further used in the synthesis of MCM-41/ethylene nanocomposites by in situ polymerization, utilizing either supported or non-supported catalytic systems. The catalytic behavior of those systems is discussed, taking into consideration the effects of the particle size, surface characteristics, and functionalization. The results have shown that the initial surface state of MCM-41 is of paramount importance to achieve high catalytic activity if a polymerization catalyst is to be supported. Functionalization changes the surface chemistry, thus, a positive or negative effect may be observed, depending on the previous features of the surface. The particle size of MCM-41 and its functionalization affect its final dispersion within the polymeric matrix, this distribution is evaluated by SEM, TEM, and microhardness measurements.
- Gas permeability properties of decorated MCM-41/polyethylene hybrids prepared by in-situ polymerizationPublication . Bento, A.; Lourenço, J. P.; Fernandes, A.; Ribeiro, M. R.; Arranz-Andrés, J.; Lorenzo, V.; Cerrada, María L.Mixed matrix membranes, MMM, based on polyethylene,PE, and silica mesoporous material, MCM-41, have been prepared using these hybrid materials obtained by in situ polymerization in order to achieve higher permeability, selectivity or both magnitudes relative to the existing polymeric PE membranes. Different methodologies are used to enhance interfacial adhesion between components, PE matrix and MCM-41. These basically consist of promoting the modification of MCM-41 surface with undecenoic acid, UA/triisobutylaluminum, TIBA, system before the polymerization and of incorporating UA in the polymer chains by copolymerization. The influence of UA on the degradation behavior is evaluated for all of the hybrids and the transport properties, in terms of permeability and diffusivity coefficients as well as permselectivity at different gases and temperatures are checked in some of the resulting materials.
- HDPE/mesoporous silica nanocomposites by in-situ polymerisation: structural details and mechanical responsePublication . Bento, A.; Lourenço, J. P.; Fernandes, A.; Pérez, Ernesto; Cerrada, María L.; Ribeiro, M. R.Mesoporous silicas exhibit stable three-dimensional structures, made of ordered channels with well-defined geometries and dimensions at nanometer scale, able to host intercalation reactions.
- Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical propertiesPublication . Cerrada, M. L.; Bento, A.; Pérez, Ernesto; Lorenzo, V.; Lourenço, J. P.; Ribeiro, M. R.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.
- MCM-41 as Nanofiller in Polyethylene Hybrid MaterialsPublication . Ribeiro, M. R.; Campos, João M.; Bento, A.; Lourenço, J. P.; Pérez, Ernesto; Cerrada, María L.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.
- New HDPE/MCM41 nanocomposites with improved mechanical performance: synthesis and characterizatioPublication . Bento, A.; Lourenço, J. P.; Fernandes, A.; Pérez, Ernesto; Cerrada, María L.; Ribeiro, M. R.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.