Browsing by Author "Cerrada, María L."
Now showing 1 - 10 of 13
Results Per Page
Sort Options
- Biodegradable polyesters reinforced with mesoporous silica particlesPublication . Campos, João M.; Ribeiro, M. R.; Deffieux, A.; Péruch, F.; Lourenço, J. P.; Cerrada, María L.In recent years, the development of mechanically reinforced nanocomposites based on biodegradable polyester matrices has gained a strong incentive due to their potential use as biomaterials and to growing worldwide environmental concerns.
- 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.
- Hafnocene catalyst for polyethylene and its nanocomposites with SBA-15 by in situ polymerization: immobilization approaches, catalytic behavior and properties evaluationPublication . Ferreira, Ana E.; Cerrada, María L.; Pérez, Ernesto; Lorenzo, Vicente; Cramail, Henri; Lourenço, J. P.; Quijada, Raul; Ribeiro, M. RosárioA hafnocene catalyst combined with methylaluminoxane (MAO) has been used as catalytic complex for the preparation of a set of polyethylene homopolymers by in situ polymerization under homogenous conditions and of different nanocomposites with mesoporous SBA- 15 particles, the latter playing the dual role of catalyst support and nanofiller. Distinct immobilization approaches have been explored for obtainment of these nanocomposites. Moreover, catalytic features, thermal stability, melting and crystallization transitions and mechanical behavior have been evaluated for those 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 HDPE/MCM-41 nanocomposites: crystalline structure and viscoelastic behaviourPublication . Cerrada, María L.; Pérez, Ernesto; Lourenço, J. P.; Campos, João M.; Ribeiro, M. R.Polyethylene-based nanocomposites have been prepared by in situ polymerisation of ethylene with mesostructured MCM-41 within a large range of nanofiller concentrations. The structural, thermal and viscoelastic studies have shown that the use of mesoporous MCM-41 as catalyst carrier and its further presence in the final material is an effective route for the successful attainment of nanocomposites. Data shows that minimal changes in crystallinity are observed but crystallites become thicker as MCM-41 content is raised in the nanocomposites. A confinement effect is found and a delay in the crystallisation process of the macrochains within pores and channels is observed. These novel self-reinforced nanocomposites present an enhanced rigidity, which becomes more important as temperature is raised. Accordingly, they exhibit an improved mechanical performance without varying the final processing temperature since Tm is the same for all of the specimens. In agreement with other works, it is confirmed that the MCM-41 acts as promoter for polyethylene degradation, an easier degradability being observed in these nanocomposites.
- 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.
- Preparation and characterization of Santa Barbara Amorphous-15 particles functionalized with mercaptopropyl groups and of their composites with poly(lactic acid)Publication . Díez-Rodríguez, Tamara M.; Blázquez-Blázquez, Enrique; Martínez, Juan C.; Lourenço, João P.; Cerrada, María L.; Pérez, ErnestoSanta Barbara Amorphous-15 (SBA-15) particles functionalized with mercaptopropyl groups (named as SBASH) have been prepared by a synthetic one-pot approach, and then have been incorporated into poly(lactic acid) (PLA), comparing their characteristics with those shown by composites attained with neat SBA-15 (PLASBA). The silica including the mercaptopropyl groups exhibits a certain loss of regularity because of its functionalization, although displays a better interaction with PLA than the pristine SBA-15 particles in the resulting materials. These composites (PLASBASH and PLASBA) also show a thermal stability slightly higher than neat PLA. An important nucleation effect of SBASH silica in the crystallization of PLA has been deduced from cooling experiments as well as from the cold crystallization in heating runs and from the degree of crystallinity reached. Small Angle X-ray Scattering (SAXS) profiles show that the PLA long spacings are rather similar for the different composites and the neat PLA. Thus, crystal size is rather similar in all samples. Microhardness values show an evident effect of reinforcement in all the composites compared with that shown by neat PLA. Nevertheless, the increase in rigidity is smaller in the biobased PLASBASH composites, those containing the modified silica, than in the PLASBA materials with the pristine SBA-15 particles.