Miguel Angel Rodriguez-Perez

Functionalized graphene sheet filled silicone foam nanocomposites

In this article we report the successful manufacture of a novel functionalized graphene sheet (FGS)/silicone porous nanocomposite. Both the cellular microstructure and the properties of the porous nanocomposite were investigated in detail. The thermal properties show great stability and heat dissipation efficiency, highlighting their potential in applications with intense thermal requirements. Additionally, compression measurements indicate that there was a favourable interaction between the graphene nanosheets and the polymer.

Dynamic mechanical analysis of injection-moulded discs of polypropylene and untreated and silane-treated talc-filled polypropylene composites

Abstract Dynamic mechanical analysis (DMA) is used to study the dynamic mechanical properties of injection-moulded discs of polypropylene, talc-filled polypropylene composites and silane-treated talc-filled polypropylene composites. Silane addition in a very low proportion improves the adhesion between the filler and the polymer and enables composites to be used where otherwise they could not. Therefore, on the one hand, the composites have different properties due to the filler and the coupling agent, and on the other hand the injection processing induces a structure, resulting in inhomogeneity and anisotropy for the moulded discs. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques are used to help state the microscopic structure and justify the macroscopic properties measured with DMA.

Characterization of the cellular structure based on user-interactive image analysis procedures

This work addresses the development of a novel user-interactive image analysis computed technique to determine the main characteristics of the cellular structure of cellular materials with any density, morphology, and/or cell size from micrographs obtained from any source—scanning electron microscopy, optical microscopy, etc. The specific analyzed parameters are cell size (mean cell diameter), cell anisotropy, cell size distribution, and cell density. A comparison with several conventionally used methods is also presented in this work. The development of such application offers a quick (<3 min per micrograph) and complete characterization of the cellular structure, with reproducible results and good agreement with the typical manual measurement methods.

Prediction of the radiation term in the thermal conductivity of crosslinked closed cell polyolefin foams

The thermal conductivity and the cellular structure as well as the matrix polymer morphology of a collection of chemically crosslinked low-density closed cell polyolefin foams, manufactured by a high-pressure nitrogen gas solution process, have been studied. With the aid of a useful theoretical model, the relative contribution of each heat-transfer mechanism (conduction through the gas and solid phases and thermal radiation) has been evaluated. The thermal radiation can be calculated by using a theoretical model, which takes into account the dependence of this heat-transfer mechanism with cell size, foam thickness, chemical composition, and matrix polymer morphology. A simple equation, which can be used to predict the thermal conductivity of a given material, is presented.

Dynamic mechanical behavior of starch-based scaffolds in dry and physiologically simulated conditions: Effect of porosity and pore size

The three-dimensional scaffolds of a blend of starch and poly(L-lactic) acid, SPLA70, were produced using compression molding of polymer/salt mixture followed by leaching of salt. One series of scaffolds were prepared with varying polymer-to-salt ratio while keeping the salt size constant, and the other series of scaffolds were prepared with varying salt sizes while keeping the polymer-to-salt ratio constant. The X-ray microcomputed tomography and scanning electron microscopy assay were used to analyze the porous morphologies, porosity and distribution of porosity of the porous scaffolds. Salt-free and integrated SPLA70 scaffolds with porosities ranging from 74% to 82% and pore sizes of 125-250 to 500-1000 microm can be fabricated using the present fabrication technique. The water uptake of the SPLA70 scaffolds increases with increasing porosities and also with increasing pore size. In dry state, the storage modulus decreases with increasing porosity and also with increasing pore size. The normalized modulus values are related to normalized density of the scaffolds by a power-law function with an exponent between 2 and 3. For the immersed scaffolds under physiological conditions, the storage modulus was less dependent on porosity and pore size. However, the loss factor increased significantly compared with dry state measurements. The present study clearly shows that the mechanical performance of porous polymeric constructs in dry and in immersed state is completely different, and for comparison with biomechanical performance of tissues, the tests should ideally be performed in immersed state.

Effect of addition of EVA on the technical properties of extruded foam profiles of low‐density polyethylene/EVA blends

Some technical properties (static mechanical properties, dynamic mechanical properties, creep-recovery behavior, thermal expansion, and thermal conductivity) of low-density foams (50 kg/m3) made of blends of low-density polyethylene (LDPE) and the ethylene vinyl acetate copolymer (EVA) were studied as a function of the EVA proportion in the blends. These properties were compared with those of a foam made of a blend of EVA and ethylene propylene rubber (EPR). The knowledge of how the EVA proportion influences the behavior of these blend foam materials is a fundamental factor in order to obtain a wide range of polyolefin foams, with similar density, suitable for different applications.

Mechanical characterization of closed-cell polyolefin foams

Three different experimental techniques [compression experiments at low strain rates, instrumented falling-weight impact tests, and dynamic mechanical analysis (DMA)] have been used for the mechanical characterization of a collection of crosslinked closed-cell polyolefin foams of different chemical compositions, densities, and type of cellular structure. The experimental results that it is possible to obtain from each technique are shown, and related to the different applications of these materials. The relationships between the structure and the mechanical properties are also presented.

The Thermal Conductivity of a Polyethylene Foam Block Produced by a Compression Molding Process

The thermal conductivity of 10 mm thick low density polyethylene foam sheets cut from a block produced by a compression molding process has been studied in the temperature range between 24°C and 50°C. The cellular structure and the matrix polymer morphology have also been characterized to find out the main microscopic characteristics that influence on the foam properties. A previously developed theoretical model has been applied to compute the thermal conductivity of the foams under study. This model was successful in the considered temperature range. Moreover, the evolution of the thermal conductivity along the thickness of the foam block has also been considered and explained in terms of the structure of the materials.

Comparing the effect of carbon-based nanofillers on the physical properties of flexible polyurethane foams

Flexible polyurethane foams filled with a fixed amount of carbon-based nanofillers, in particular multiwall nanotubes and graphenes, have been studied to clarify the influence of the morphology and functional groups on the physical properties of these polymeric foams. The effect of the carbon nanoparticles on the microphase separation has been analyzed by FT-IR spectroscopy revealing a decrease in the degree of phase separation of the segments. Variations of the glass transition temperature and an improved thermal stability were observed due to the presence of the nanoparticles. The EMI shielding effectiveness of flexible PU foams has also been enhanced, in particular for FGS nanocomposite foams.

Carbon nanotubes provide self-extinguishing grade to silicone-based foams

This article examines the feasibility of using multiwall carbon nanotubes (MWCNTs) as a fire retardant in silicone-based foams. MWCNTs were mechanically blended with polydimethylsiloxane reactants without any previous functionalisation treatment. The flammability of the materials was characterised as a function of the filler content using a standard fire testing method. The limiting oxygen index of the composite increased as a function of nanotube content, attaining the self-extinguishing grade even at low mass fraction of the carbon nanotubes (0.5 wt%). Further thermal characterisation revealed increases in thermal dissipation efficiency and thermal degradation temperature. The different thermal and flame retardancy results were attributed to the formation of a CNT network throughout the sample. The formation of this network was attributed to a good dispersion of the CNTs via non-covalent CH–π interactions and to the surface tension of the gas–polymer interface during foaming.