Antonio Sanchez-Solis

Hierarchically Nanostructured Barium Sulfate Fibers

BaSO(4) nanostructures with controlled morphologies were successfully produced via one-step process through precipitation of BaSO(4) in aqueous and organic media. The synthesis is carried out by mixing solutions of BaCl(2) and Na(2)SO(4) in presence of EDTA (disodium ethylenediaminetetraacetic acid) at room temperature. The influence of the reaction conditions such as initial reactants concentration, pH, EDTA/[Ba(2+)] ratio and aging on the BaSO(4) nanoparticles organization is studied. Using EDTA in aqueous media, spherical secondary particles of 500 nm diameter are obtained, which are formed by 4 nm size primary particles. With dimethyl sulfoxide and small amounts of water (5%) and EDTA, the aging process allows the production of long homogeneous fibers, related to hierarchical organization of BaSO(4) nanoparticles. Direct observation of self-assembling of primary particles by HRTEM allows proposing a mechanism for fiber formation, which is based on multipolar attractions that lead to a brick-by-brick organization along a preferential orientation. Results evidence the role of EDTA as controlling agent of the morphology and primary and secondary mean particle size.

Influence of maleic anhydride grafting on the rheological properties of polyethylene terephthalate–styrene butadiene blends

Abstract The rheological properties of polyethylene terephthalate (PET)–styrene butadiene rubber (SBR) blends are studied in this work. The shear viscosity was measured in a special capillary device mounted on an injection-molding machine, which provides data on pressure and flow rate. Comparison of the viscosity of the PET–SBR physical blend with that of the blend of PET with maleic anhydride-functionalized SBR (SBRg) provides information on the effect of grafted maleic anhydride chains at the rubber–thermoplastic interface on the rheological properties of the blend. Shear viscosity is a function of the amount of compatibilizer and applied shear stress present in the preparation of the blends. A reduction in the particle size due to increasing screw speed was correlated with a reduction in the shear viscosity and an increase in the impact properties of the blend.

Effect of Montmorillonite Clay on the Burning Rate of High-Impact Polystyrene

The effect that montmorillonite clay has on the burning rate of high impact polystyrene (HIPS) is examined. Two clays are considered a pristine montmorillonite (MMT-Na+) and a montmorillonite clay intercalated with triphenyl phosphite (TPP). In addition to the burning rate tests, mechanical, impact and rheological properties are determined. Results show an increase of 55% in the burning rate of the nanocomposite when the neat MMT-Na+ clay is added. Thermal measurements indicate a diminishing HIPS decomposition temperature as the MMT-Na+ clay concentration rises. On the other hand, when TPP is incorporated in MMT-Na+ (MMT-i-TPP) and the clay is added to HIPS, a substantial reduction (42%) of the burning rate is observed, while the mechanical properties are kept at the level of those of the original HIPS. The system HIPS-MMT-i-TPP presents a steeper reduction in the viscosity as compared to HIPS in the high-temperature range.

Effect of cholesterol and triglycerides levels on the rheological behavior of human blood

Important public health problems worldwide such as obesity, diabetes, hyperlipidemia and coronary diseases are quite common. These problems arise from numerous factors, such as hyper-caloric diets, sedentary habits and other epigenetic factors. With respect to Mexico, the population reference values of total cholesterol in plasma are around 200 mg/dL. However, a large proportion has higher levels than this reference value. In this work, we analyze the rheological properties of human blood obtained from 20 donors, as a function of cholesterol and triglyceride levels, upon a protocol previously approved by the health authorities. Samples with high and low cholesterol and triglyceride levels were selected and analyzed by simple-continuous and linear-oscillatory shear flow. Rheometric properties were measured and related to the structure and composition of human blood. In addition, rheometric data were modeled by using several constitutive equations: Bautista-Manero-Puig (BMP) and the multimodal Maxwell equations to predict the flow behavior of human blood. Finally, a comparison was made among various models, namely, the BMP, Carreau and Quemada equations for simple shear rate flow. An important relationship was found between cholesterol, triglycerides and the structure of human blood. Results show that blood with high cholesterol levels (400 mg/dL) has flow properties fully different (higher viscosity and a more pseudo-plastic behavior) than blood with lower levels of cholesterol (tendency to Newtonian behavior or viscosity plateau at low shear rates).

Unsaturated polyester-clay slurry nanocomposites

Abstract In this work, nanocomposites were produced with an unsaturated polyester resin and sodium montmorillonite (MMT) slurry. Upon increasing the clay content [from 1 to 5 parts per hundred resin (phr)] increments of 57% and up to 120% were found in the flexural modulus, with respect to that of the resin alone. Using clay slurry, the cross-linking reaction was affected by the clay, in such a way that the gelation temperature and the thermal stability increased. Using transmission and scanning electron microscopy, resin intercalation into the MMT silicate layers was observed and the fracture morphology revealed the effect of the clay slurry on the nanocomposite morphology. Furthermore, shear and oscillatory rheological tests revealed the formation of a structure between resin and clay at low shear rates, and the presence of this structure was evidenced by X-ray photoelectron spectroscopy (XPS) measurements.

Burning Rate, Mechanical and Rheological Properties of HIPS-PET and Clay Nanocomposites

We analyze the effect of montmorillonite clay nanoparticles on the burning rate (BR), mechanical and rheological properties of high-impact polystyrene (HIPS) and blends of polyethylene terephthalate (PET) and HIPS produced by a twin-screw extrusion process. It is found that the BR of the HIPS-PET system is considerably reduced at relatively high clay concentrations. On the other hand, the increase in clay concentration in the HIPS matrix none leads to an unexpected rise in the BR. The degradation temperature is determined by measurements of complex viscosity as a function of temperature. It is found that degradation temperature decreases with clay concentration, particularly in the HIPS-PET-clay nanocomposite, diminishing by 28°C with respect to that of HIPS at high clay contents. This low degradation temperature means that a char layer is formed at lower temperatures, so the BR decreases as well. Mechanical properties are also affected, such as the fracture strain.

Properties of pet-pen blends produced by extrusion and injection blow- molding

In this work, blends made of polyethylene terephthalate (PET) and polyethylene 2,6 naphthalene dicarboxylate (PEN) were prepared by melt extrusion processed at several temperatures and residence times. The blends with composition up to 20 wt % PEN were characterized with regard to their degree of transesterification and their rheological properties. Subsequently, bottles were produced by injection-stretch blow-molding and their mechanical properties were measured. It was found that improved PET-PEN blends were produced at 270°C with a PET content of 15 and 20 wt % and residence time processing of 4 minutes. Both blends present a low degree of transesterification, block conformations, high shear viscosity and improved tensile properties.

Influence of X-ray opaque BaSO4 nanoparticles on the mechanical, thermal and rheological properties of polyoxymethylene nanocomposites

Abstract This work evaluates the influence of a radiopaque reinforcement, barium sulfate (BaSO4), on the mechanical, rheological and thermal properties of polyoxymethylene (POM). Nanocomposites of POM containing spherical nanoparticles of BaSO4 (0, 1, 2, 3 phr) were obtained by melt extrusion in a twin-screw equipment followed by injection molding. The mechanical, thermal and rheological properties of these nanocomposites and the dispersion state of the particles were investigated. Scanning and transmission electron microscopy revealed the morphology of the products. The main objective of this work is the production of nanocomposites with sulfate concentration enough to acquire radiopaque properties while maintaining the mechanical properties of the matrix. In this regard, mechanical and rheological properties were found similar to those of the polymer matrix, but radiopaque contrast tests revealed the influence of the nanoparticles concentration on the optical properties of the composites. The production of these nanocomposites suggests potential applications in the biomedical sector given their unique radio-opacity properties.

PET-MMT and PET-PEN-MMT Nanocomposites by Melt Extrusion

Polymer nanocomposites have attracted a great deal of interest in the scientific and industrial fields because of remarkable improvements achieved in the physical and mechanical properties at very low filler loadings. For example, the diffusion of gas molecules is largely retarded by the presence of randomly oriented clay particles. These new class of materials can be obtained by means of two main processes: in-situ polymerization of monomers in the presence of nanoparticles and the use of polymer processing techniques such as extrusion [Okamoto, M. 2006 and Suprakas, S. R. 2003]. The use of clay particles to produce nanocomposites is a usual practice; however, clay has to be usually organically modified to induce affinity with the polymer matrix [Kracalik, M. et al 2007; Vidotti, S. E. et al 2007]. The improvement of nanocomposite properties depends on different factors, for example, a good dispersion of clay particles in nano-scale within the polymer matrix. The nanocomposites obtained by melt extrusion require initially, an intercalation process of the polymer macromolecule into the clay galleries and finally clay exfoliation in the polymer matrix. This process is diffusion-controlled and requires long residence times under the pressure buildup produced inside the extruder. However, high residence times or high screw speeds may conduce to polymer degradation. Therefore, optimum process conditions need to be investigated in order to produce high performance nanocomposites. Moreover, it has been found that clay exfoliation may not be a sufficient condition to obtain optimum properties; clay platelets dispersion and polymer-clay interaction are also key features to consider. In this chapter, poly(ethylene terephthalate)-montmorillonite clay (PET-MMT) and poly(ethylene terephthalate)-poly(ethylene naphthalene 2,6-dicarboxylate)-montmorillonite clay (PET-PEN-MMT) nanocomposites were prepared and characterized. Maleic anhydride (MAH) is used as the compatibilizing agent in the blend and its effect is also studied. In both nanocomposite blends, optimum processing conditions were investigated to achieve improved tensile properties. The preparation of the PET-PEN polymer matrix also requires special care since a transesterification reaction between these two polymers is induced by

Analysis on the effect of nanographite obtained by an ultrasound technique in polypropylene compounds

In this work, the effect of inclusion of nanographite particles in a polypropylene (PP) matrix is studied. Nanographite particles were obtained through ultrasound exfoliation from graphite upon using a water-based hydrophobically modified alkali-swellable emulsion (HASE) associative polymer as a surfactant. Results indicate that exfoliation renders particle size distribution ranging from 3 to 3000 nanometers. Nanographite was blended with PP through two extrusion processes: twin screw and single screw, the latter includes the coupling to a static-mixer head, to generate extensional flows. Concurrently, ultrasonic waves are applied to the molten flow through ultrasonic transducers attached to the mixing head, which induces high particle dispersion and good particle distribution in the polymer matrix. It was found that at HASE concentration of 5% by weight and sonication time of 14 days (period of the exfoliation process), optimum tensile properties of the compound were achieved. Also, with respect to the PP matrix, the rate of thermal degradation decreased from 2.1 (PP) to 1.9 (% °C−1), melt temperature ranged from 442°C (PP) to 396°C, and melt index decreased from 7.4 (PP) to 6.2 (g/10 min). Raman spectroscopy confirmed the exfoliation process, rendering sizes ranged from graphite particles of few graphene layers to micron-sized particles. Rheological measurements of the compounds revealed that the extrusion-ultrasound process influences the viscosity, storage, and loss moduli. The dispersion and distribution of nanoparticles improved the electromagnetic radiation shield (approximately 35%). The dielectric constant changed from 2.21 (pristine PP) to 9.02 for the compounds, which enables a good level of electrostatic charge dissipation.