Inés Joekes

Use of tire rubber particles as addition to cement paste

Abstract The surface modification of powdered tire rubber to increase its adhesion to cement paste was studied. The particles were surface-treated with NaOH saturated aqueous solutions for 20 min. Scanning electron microscopy (S.E.M.), water absorption, density, flexural strength, compressive strength, abrasion resistance, modulus of elasticity and fracture energy measurements were performed using test specimens (water/cement ratio=0.36) containing 10% of as-received or 10% of NaOH-treated rubber. The results of fracture energy and flexural and compressive strength show that the addition of rubber particles improves the toughness and reduces the porosity of the specimens. Mass loss by abrasion (−1.2±0.4% for control specimens; −1.7±0.4%, using treated rubber and −4.0±1.2% using as-received rubber, after 600 cycles) and electron microscopic examination show that the NaOH surface treatment enhances the rubber–matrix adhesion. The use of thus treated tire rubber particles, as addition, instead of a coarse aggregate, in cement-based materials is promising for applications such as driveways or in road construction.

About photo-damage of human hair.

This paper reviews the current knowledge about human hair photodamage and the photodegradation mechanisms proposed in the literature. It is shown that there are still a number of questions without answer regarding this issue. For example, a better understanding of the hair structural changes caused by different radiation wavelengths is still lacking. We also find controversies about the effects of sun exposure on different hair types. Explanations to these questions are frequently sustained on the amount and type of melanin of each hair, but factors such as the absence of knowledge of melanin structure and of established methodologies to use in human hair studies make it difficult to reach a general agreement on these issues.

Ethanol fermentation of a diluted molasses medium by Saccharomyces cerevisiae immobilized on chrysotile

In this work, the catalytic role of chrysotile support on the acceleration of alcoholic fermentation under non-aseptic conditions by Saccharomyces cerevisiae was investigated. The fermentation medium employed consisted only of diluted sugar-cane molasses. In the batch fermentations process with immobilized yeasts, the initial rate of CO2 production increased roughly 27 % during the first 30 minutes, compared to systems containing no chrysotile. A study of continuous alcoholic fermentation with chrysotile in the reactor bed showed a higher ethanol production rate at the different dilution rates investigated compared to similar fermentations without chrysotile.

Continuous fermentation of sugar cane syrup using immobilized yeast cells

Several strains of Saccharomyces sp. and commercial Bakers yeast were immobilized by adhesion onto chrysotile, a fibrous magnesium silicate (Mg6Si4O10 (OH)8). The activity of the cells is higher when immobilized, mainly for fermentation of 30 to 50% w/v glucose solutions. In the medium containing 30% w/v glucose, the initial fermentation rate increased 1.2-2.5 times. Yields were in the range of 80.4 to 97.3% for the immobilized cells and 72.7 to 84.5% for the free cells. A packed bed reactor for continuous fermentation was set up using one of the tested strains immobilized onto chrysotile. An average productivity of 20 to 25 g.l(-1).h(-1) was obtained in the first 20 d, and an average of 16 g.l(-1).h(-1) was obtained after 50 d of operation.

Evaluation of Magnetorheological Suspensions Based on Carbonyl Iron Powders

The particle size distribution and magnetic susceptibility of some commercial carbonyl iron powders (code names CC, CS, HQ, OX and SM) were measured. The particle size of the powders increases as follows: HQ<SM<CC OX<CS. The magnetic susceptibility increases in the order: HQ OX SM CC CS. Magnetorheological suspensions (MRS) with 66% w/w of iron were prepared and their rheological properties were evaluated at no field, 100, 200 and 300 Oe. The yield stress under 300 Oe measured with strain-stress curves increases in the order: HQ OX<SM<CC<CS, showing direct correlation with the susceptibility. The plastic viscosity without field increases in the order: CS<CC<OX<SM<HQ, an inverse correlation with particle size. These results show that the particle size and/or size distribution can be another important property of the powders, together with magnetic susceptibility on the formulation of improved MRS.

Mapping phases of poly(vinyl alcohol) and poly(vinyl acetate) blends by FTIR microspectroscopy and optical fluorescence microscopy

Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) blends in compositions 9/1, 1/1, and 1/9 (w/w) show that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as PVA-richer domains by green fluorescence of fluorescein and PVAc-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in the solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed us to obtain spectra for both PVA-richer and PVAc-richer domains. These spectra demonstrated that partial miscibility could occur only for blends with a higher PVAc content and, in these cases, we observed interchain hydrogen-bonded carbonyl groups. Fluorescence microscopy of blends with this partial miscibility exhibited small interconnected domains produced by coalescence of droplets during the polymer phase separation process.

Continuous process for large-scale preparation of chiral alcohols with baker's yeast immobilized on chrysotile fibers

Abstract Bioreductions of prochiral ketones in a continuous process were carried out in a Packed-bed-reactor with bakers yeast ( Saccharomyces cerevisiae ) immobilized on chrysotile fibers (IMBY). The performance of the reactor was observed for 30 days, under a constant dilution rate of 1.7×10 −1 h −1 using ethylbenzoylformate as substrate. The steady state showed 2.9×10 −2 g l −1 h −1 of productivity, 50% chemical yield, and 90% ee (enantiometric excess). Using ethylacetoacetate at the same dilution rate for 8 days, the steady state showed 65% chemical yield and 95% ee. No significant change on the IMBY integrity was observed. The results show that chrysotile is an excellent carrier for immobilization of bakers yeast (BY) cells to be used in the continuous process of bioreduction

Aspergillus terreus CCT 3320 immobilized on chrysotile or cellulose/TiO2 for sulfide oxidation

Abstract The increasing interest in applying chiral sulfoxides in asymmetric syntheses requires their preparation on a large scale, which can be obtained by enantioselective enzymatic oxidation of sulfides. We have focused on the preparation of sulfoxides 1 – 6 using Aspergillus terreus CCT 3320 cells to oxidize the precursor sulfides. These biotransformations lead to enantiomeric excesses (ee) better than 95%. In order to improve the biocatalytic process, the cells were immobilized on two supports, chrysotile and on cellulose/TiO 2 . The immobilized cells showed a similar biocatalytic behavior in the conversion rate and in the sulfoxide enantiomeric excess. Scanning electron microscopy (SEM) micrographs show that the cells are intertwined with the fibers of both supports, allowing fast separation from the reaction media and easing the biocatalyst reuse. Supported cells stored for at least 3 months showed no loss of activity.

Adsorption of colloidal gold on colloidal iron oxides

Abstract Lateritic gold enrichment can be associated with the formation of colloidal gold and its interaction with the iron-oxide-rich medium. Adsorption of colloidal gold on synthetic goethite and hematite was measured at 25°C. The observed high affinity between the oppositely charged particles depends on the medium composition. The presence of citrate anions can inhibit mutual coagulation, while inert electrolytes enhance this effect.

Electron microscopic observations of human hair medulla

In the study of human hair, medulla is the less studied structure because it is believed that it has no influence on the fibre properties. The aim of this paper is to contribute to the better understanding of medulla morphology. Using reproducible methods for hair samples preparations allowed observing the inner fibre by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Three medulla subunits were observed in cryofractured samples. In addition, the application of plasma etching on samples allowed accessing chemical differences between them. Two kinds of medulla were identified using stereomicroscopy: thin and thick medulla. They were morphologically differentiated using TEM. These methods can be used to study systematically the effects of medulla on hair properties and to evaluate the efficiency of cosmetic products.