A. A. S. T. Delben

Evaluation of latex from five Hevea clones grown in São Paulo State, Brazil

Abstract Membranes of latex extracted from five clones of rubber tree (Hevea brasiliensis (Willd. ex Adr. de Juss) Muell.-Arg.) improved by selection and statistics methods have been prepared by air drying a 10% suspension in ammonia solution. TG–DTG and DSC, were used to characterize the membranes. The results obtained show no differences among latex from different clones.

Castor oil polyurethane containing silica nanoparticles as filling material of bone defect in rats

PURPOSE To evaluate the biologic behavior of the castor polymer containing silica nanoparticles as a bone substitute in diafisary defect. METHODS Twenty seven male Rattus norvegicus albinus Wistar lineage were submitted to bone defect filled with castor oil polymer. Three experimental groups had been formed with nine animals each: (1) castor oil polymer containing only calcium carbonate; (2) castor oil polymer with calcium carbonate and doped with 5% of silica nanoparticles; (3) castor polymer with calcium carbonate doped with 10% of silica nanoparticles; 3 animals of each group were submitted to euthanasia 15, 30 and 60 days after experimental procedure, and their femurs were removed to histological evaluation. RESULTS there was bone growth in all the studied groups, with a greater tendency of growth in the group 1. After 30 days all the groups presented similar results. After 60 days a greater amount of fibroblasts, osteoblasts, osteocytes and osteoclasts in group 3 was observed, with integrated activity of 3 kinds of cells involved in the bone activation-reabsorption-formation. CONCLUSIONS The castor polymer associated to the silica nanoparticles is biocompatible and allows osteoconduction. The presence of osteoprogenitors cells suggests silica osteoinduction capacity.

Thermal stability of fluorochloroindate glasses

New fluorindate glass compositions have been investigated in order to improve optical transmission as well as thermal properties. Chloride inclusion extends transmission of a fluoride matrix to longer wavelength in infrared region. In the present work thermal parameters of an IZnBS composition, based on InF3, ZnF2, BaF2 and SrF2, with various amounts of alkaline chlorides were investigated by differential scanning calorimetry. The chloride presence decreased all characteristic temperatures and increased both thermal stability and glass forming ability up to 10% of MCl content, where M=Li, Na, K and Rb. The presence of NaCl promoted glass phase separation. For samples containing same concentration of NaCl, this effect is accentuated for increasing the contents of SrF2.

Biocompatibility and osteogenesis of the castor bean polymer doped with silica (SiO2) or barium titanate (BaTiO3) nanoparticles

PURPOSE To evaluate the biocompatibility and osteogenesis of castor oil polymer doped with SiO2 or BaTiO3 nanoparticles. METHODS Twenty four male rats Wistar were submitted to bone defect filled with castor oil polymer. The animals were distributed in two experimental groups had been formed with 12 animals each: Group 1 - Castor oil polymer doped with 0.30 grams of SiO2 replacing 0.30 grams of CaCO3. Group 2 - Castor oil polymer doped with 0.30 grams of BaTiO3 replacing 0.30 grams of CaCO3. Euthanasia occurred 30 and 60 days after surgery and the femurs were sent to histological analysis and MEV. RESULTS The implants were biocompatible and allowed for progressive osteogenesis through osteoconduction in both observation periods. There was significant bone neoformation at 30 and 60 days in both groups within the histomorphometric evaluation, but group 1s osteogenesis was lesser in the 30 and 60-day periods observed when compared to the animals of group 2. The MEV morphometric evaluation evidenced a lesser percentage of osseous tissue filling within the BaTiO2-doped polymer. CONCLUSION The castor oil polymer doped with SiO2 or BaTiO3 remained biocompatible and allowed for progressive osteogenesis in both observation periods.

Spongolite : A hollow fibrous mineral from Mato Grosso do Sul State, Brazil

Abstract Spongolite from the State of Mato Grosso do Sul, Brazil, contains the remains of fossil sponges and hollow needles or microcapillaries with uniform surfaces. The central tunnels are ~1/10 to 1/2 of the cylinder’s diameter. The material is essentially X-ray amorphous though it contains small amounts of orthosilicic acids. The other main elements were Ti and Fe. Spongolite may have uses as a sorbent, as a bioavailable silicon source or, after blending with glass waste, it can be used in the fabrication of lightweight products having a closed-cell structure, potentially useful as an industrial insulator.

THERMAL PROPERTIES OF FLUORIDE GLASSES AND THEIR GEL PRECURSORS

Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.

New heavy halide glasses containing small amount of VIA compounds

New heavy halide glasses without fluorine have been synthesized as Pr3+ host materials for optical amplification at 1.3 micrometers or other active applications which require a phonon energy as low as possible. A relatively stable composition is 15CdCl2-10CdI2- 20PbI2-40PbBr2-15CsBr. However, this glass still undergoes the devitrification during fiber drawing process. A small amount of oxides and sulfides have been introduced in this system to decrease the crystallization tendency. The incorporation of 3 mole percent PbO in the base glass composition enlarges the thermal stability range. The stabilizing effect of CdO is more limited than that of PbO. Optimum results are observed when PbO substitutes PbBr2 rather than PbI2. The influence of several sulfides on glass stability was also investigated in the same glass. The additions of 5 mole percent of HgS, As2S3 and Sb2S3 appear favorable to glass formation. By comparison, attempts implemented with SeS2, PbS and CdS had no significant effect. An additional benefit of the introduction of oxides and sulfides is the decrease of the hygroscope character of the base glass. The optical transmission in the visible-IR spectrum shows no absorption at the pump and emission wavelengths, e.g. 1.0 and 1.3 micrometers , while the cut-off wavelength exceeds 10 micrometers for sample of 3 mm in thickness.

Critical problem of cadmium fluorochloride glass fiber drawing

Cadmium fluorochloride glass (CdFCl) is considered as a more favorable host for Pr3+ 1G4-3H5 transition than all-fluoride hosts, but it cannot be drawn easily into fibers. This critical problem is largely correlated with its special devitrification behavior and temperature dependence of viscosity. The high Avrami coefficients of crystallization obtained by isothermal method and by non-isothermal method suggest that nucleation rate increases during the crystallization. Meanwhile Avrami coefficients and activation energy values vary with the crystalline fraction. This corresponds to the formation of different phases during crystallization. The the ram XRD measurements performed from 210 to 320 degrees C confirm that chlorine-rich phases appear first at low temperature while the fluoride phases form lately. Comparison with fluorozirconate glass shows that CdFCl glass has a lower log (eta) - T slope. As a result the drawing temperature of the CdFCl glass is well above Tg, in the crystallization thermal range. These two factors explain the difficulties encountered in drawling CdFCl fibers from a preform. Drawing fibers directly from the melt should be an alternative method for CdFCl glasses.

Preparation of vitreous multicomponent fluoride films

Abstract Vitreous fluorozirconate films were obtained from bulk glass samples previously prepared by fusion. Bulk glass samples were heated between two plates at a constant rate, up to about 10°C above softening point and yet below crystallization onset temperature, under an applied load. Adherence of the films so obtained depended on heating rate and load and was good in vitreous silica, alumina and a series of metallic substrates. The films were stable and scanning electronic microscopy analysis revealed no crystallization. This technique can be applied to any stable fluoride composition.