Guadalupe Sanchez-Olivares

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.

Properties of the Entomoparasitic Nematodes (Heterorhabditis bacteriophora) Liquid Culture using a Helicoidal Ribbon Agitator as Rheometric System

The rheological parameters: flow behaviour index n, flow consistency index K and effective viscosity ηe were estimated for the entomoparasitic nematodes Heterorhabditis bacteriophora liquid broth at different culture maturation times. The nematode or nematodes were cultivated during 20 days in a bioreactor, and the growth media inside the bioreactor was enriched with protein and fat sources. Rheological parameters for the heterogeneous suspension were estimated with mixer principles employing a helical ribbon agitator fixed to a rheometer. As the culture matured, n decreased from 0.8 to 0.2 (-) and K increased up to 1200 mPa•sn; ηe showed a non-Newtonian (n<1) behaviour, ηe reached peak values of 0.32 Pa•s for a rotational speed of 0.5 revolutions per second (rps) and 0.048 Pa•s for 2.5 rps. Rheological properties reported here could be more reliable as compared to those reported for non-homogeneous liquid fermentations where estimations were performed with conventional geometries (i.e. concentric cylinders) which are appropriate for homogeneous systems but not for non-homogeneous ones.

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

Clay Minerals and Clay Mineral Water Dispersions — Properties and Applications

This chapter deals with the properties and applications of clay mineral water dispersions and clay minerals as flame retardant additives for polymers. Clay minerals, such as kao‐ linites, micas, and smectites, are the basic constituents of clay raw materials, which are classically employed in the ceramic industry to produce porcelain, fine ceramics, coarse ceramics, cements, electro-ceramics, tiles and refractories. These products are mainly used in sectors of economic importance, such as agriculture, civil engineering, and envi‐ ronment. A direct method to prepare clay mineral polymer composites is through disper‐ sion in water. Water dispersions of clay exhibit some interesting flow phenomena such as yield stress; i.e., the material behaves as a solid until a critical force applied on the materi‐ al forces it to flow. Water dispersions of clay have also been reported to be used to pre‐ pare materials with enhanced flame-retardant properties such as leather. On the other hand, direct melt compounding of clay mineral with different polymers as the composite matrix (HIPS, PP, and HDPE) to prepare a number of polymer composites with flameretardant properties has also been reported.