Margarita Victoria García-Garduño

Rheological properties of styrene-butadiene copolymer-reinforced asphalt

Rheological properties of styrene-butadiene copolymer-reinforced asphalt were investigated. A percolation-like model was used to fit dynamical experimental data, and a comparison with the Kerner-Takayanagi model is presented. In addition, a frequency-composition-temperature correspondence principle is proposed. This correspondence principle allows the prediction of the rheological behavior of an asphalt-based composite within a wide range of compositions, provided a narrow composition range at different frequencies and temperatures is previously known.

Development of hybrid materials consisting of SiO2 microparticles embedded in phenolic-formaldehydic resin polymer matrices

Abstract A phenolic-formaldehydic resin (PFR) of the Novolac-type and modified by the incorporation of carboxylic end groups (MPFR), is used to influence the morphological and optical properties of sol-gel synthesized SiO 2 materials. Silica microparticles are formed from the hydrolysis of silicon alkoxide solutions in ethanol and in the presence of polymerizing PFR or MPFR resins, hence rendering a final product consisting of SiO 2 globules entangled inside a resin network. Under appropriate experimental conditions, chemical unions are established between silanol groups anchored on the surface of the SiO 2 particles and MPFR carboxylic chains, to provide SiO 2 /MPFR core-shell compounds. The presence of PFR or MPFR resins during the SiO 2 sol-gel production influences: (i) the size of SiO 2 particles; and (ii) the transparency, translucency or opacity properties of the final hybrid products. Either one of the latter optical conditions is established by the amounts of reactants used to prepare a given hybrid specimen. FTIR, TGA and SEM are employed to determine the chemical and textural properties of SiO 2 /PFR and SiO 2 /MPFR solids. Results confirmed the existence of chemical bonds at the interface between silica and MPFR resin, as well as superior properties of these hybrid materials with respect to pure PFR or MPFR polymerized materials.

Morphology and elastic properties of PP/EVA polymer blends

Several polypropylene-ethylene vinyl acetate (PP/EVA) copolymers with compositions ranging from 90/10 to 10/90 PP/EVA were prepared and characterized in terms of their morphology by transmission and scanning electron microscopy, and their mechanical properties were also studied. The results show a wide range of spatial structures which correlate well to the corresponding measurements of elastic modulus of the blends.

Morphological characterization of polybutadiene-cellulose diacetate composites

Abstract A composite material, prepared by mixing polybutadiene (PBd) (commercial sample) and cellulose diacetate (DAC) chemically functionalized in our laboratory, was studied. In this composite, DAC is a bio-degradable modifying material (with a concentration between 5 and 15 vol%), while the PBd is the continuous phase. The addition of a small amount of the modifier drastically changes the properties of the continuous matrix. Due to the semi-rigid character of the DAC molecule and the very small miscibility between these polymers, the discrete phase formed by DAC is anisotropic, leading to a strong modification of the mechanical properties of the material. In order to improve the adhesion between the two phases, the DAC molecules were chemically functionalized. This is an important feature for good performance of the composite in terms of its mechanical properties.

Hybrid materials based on functionalised epoxy resin networks

Purpose – The purpose of this paper is to describe how sol‐gel synthesised silica particles are used to modify the characteristics (especially the thermal and mechanical properties) of either an epoxy resin (ER) or a −COOH‐functionalised ER (FER) substrate. In the systems studied here, spherical silica particles are embedded in ER or FER thermosetting polymeric substrates for producing translucent solid materials. There arise covalent unions between the SiO2 silanol surface groups of the particles and the functionalised FER ends, thus rendering SiO2‐FER core‐shell compounds.Design/methodology/approach – The characterisation results confirm the affinity existing between ER and SiO2 particles as well as the existence of chemical bonds at the interface between the silica and FER phases.Findings – An efficient and durable application against corrosion of metallic materials has been developed through the preparation and application of thin surface films made of finely disseminated SiO2 colloidal particles, whi...

Influence of the Preparation Technique on the Morphological Characterization of Polymeric Blends

Abstract Morphology-property relationships are among the parameters which determine the practical use of polymer blends. However, very few reports in the literature realize that the preparation technique of the samples for being examined by a particular methodology, is crucial for the final results. Indeed, in the case of Electron Microscopy, for instance, for the studies of polymer and copolymer blends, very little care is taken in analyzing the effect of, for example, using dissolution for preparing samples or how a microtomy process could affect the observation. Accordingly, in this work a study of the influence of different preparation techniques for SEM (Scanning Electron Microscopy) analysis of Ethylene Vynil Acetate/Polypropylene blends (EVA/PP), including a discussion on the relevance of various physical or chemical factors affecting the observation, is presented.

Crystallographic characterization of eggshells as scaffolds for bone regeneration

The aim of this work was to characterize six different eggshell types as future osseous regeneration scaffolds. The study design was cross-sectional observational. The study was conducted in the Laboratory of Materials and the chemical analysis in the Faculty of Chemistry, UNAM, Mexico. Fifty samples of fresh eggs were obtained, 10 from each species (hen, turkey, duck, dove and quail). Square-shaped pieces of about 2 x 2 cm were obtained from the eggshells by means of a high-speed handpiece with a # 701 carbide bur. From the total of eggshell pieces, the ones coming from fresh eggs were included, and the ones showing signs of fracture or spots were excluded. Their morphology was analyzed with a low vacuum scanning electron microscope (JEOL 5200), with an accelerating voltage of 20 kV. The chemical elemental analysis was performed with an EDAX energy dispersive spectrometer (EDS) and the chemical composition was determined by means of a Siemens diffractometer. All of the eggshells were constituted by calcium carbonates, and their outer structure was less porous than the inner one, sometimes with granules and cuticles firmly attached to the inner surface of the eggshell. The eggshell major chemical components were mainly: oxygen, calcium, phosphorous, magnesium, sulfur and carbon. There are no significant quantities of sulfur (S) in the turkey and quail eggshells. These kinds of eggshells have not been tested yet as a scaffold, but it is expected that they may be used soon in bone regeneration once the organic part is removed. Eggshells are largely waste material. The authors anknowledge the technical support to Chem. Rafael Ivan Puente Lee

SEM Morphological Study and Transparency Properties of Hybrid SiO2 - Phenolic Resin Materials

Hybrid materials consisting of SiO2 microspheres immersed in two kinds of phenolic-formaldehydic resin matrices of the Novolac-type: (i) a typical one (PFR) and a chemically modified one (MPFR) are synthesized in situ through the sol-gel process. SiO2 globules of diverse sizes are entangled inside PFR or MPFR matrices to produce opaque, transparent or translucent solid materials, characteristics that depend on the amounts of silicon alkoxide and PFR or MPFR components employed for their syntheses. The ensuing hybrid substrates show chemical unions between the SiO2 silanol surface groups and the MPFR carboxylic chains thus rendering SiO2-MPFR core-shell compounds. Spectroscopic results confirm the existence of these chemical bonds across the interface between silica microspheres and MPFR matrix, while SEM observations provide the picture of solid materials depicting heterogeneous or homogeneous morphologies. The transparency properties of SiO2-MPFR solids is greatly influenced by the light scattering caused by inhomogeneities of the network, i.e. the transparency is poor when the size of SiO2 particles is large as well as when their distribution is not homogeneous inside the MPFR matrix, on the other hand, if the SiO2 globules are sufficiently small and if they are homogeneously distributed throughout the substrate then the transparency is high. These morphological characteristics of SiO2 MPFR materials are contrasted with those of a conventional hybrid material made of unmodified phenolic resin (PFR) and silica microspheres (SiO2-PFR).