Thermal decomposition of some poly(β-hydroxyalkanoates)

The thermal decomposition of some polyhydroxyalkanoates (PHA) has been investigated by means of thermogravimetry and differential thermogravimetry. The thermal stability of the studied polyesters decreases slightly with increasing hydroxyvalerate (HV) comonomer. This result is different from those reported in the literature. Other results agree with reaction mechanisms proposed in the literature. The data from dynamic thermogravimetric experiments are consistent with a first order reaction, as would be expected from the reaction mechanism. Infrared spectra of the thermally degraded and undegraded copolymers are evidence of the cis-elimination mechanism. © 1999 Society of Chemical Industry     

Mycobacterium tuberculosis H37Rv Strain Increases the Frequency of CD3+TCR+ Macrophages and Affects Their Phenotype,but Not Their Migration Ability

In mycobacterial infections, the number of cells from two newly discovered subpopulations of CD3⁺ myeloid cells are increased at the infection site; one type expresses the T cell receptor (CD3⁺TCRαβ⁺) and the other does not (CD3⁺TCRαβ⁻). The role of Mycobacterium tuberculosis (Mtb) virulence in generating these subpopulations and the ability of these cells to migrate remains unclear. In this study, monocyte-derived macrophages (MDMs) infected in vitro with either a virulent (H37Rv) or an avirulent (H37Ra) Mtb strain were phenotypically characterized based on three MDM phenotypes (CD3⁻, CD3⁺TCRαβ⁺, and CD3⁺TCRαβ⁻); then, their migration ability upon Mtb infection was evaluated. We found no differences in the frequency of CD3⁺ MDMs at 24 h of infection with either Mtb strain. However, H37Rv infection increased the frequency of CD3⁺TCRαβ⁺ MDMs at a multiplicity of infection of 1 and altered the expression of CD1b, CD1c, and TNF on the surface of cells from both the CD3⁺ MDM subpopulations; it also modified the expression of CCR2, CXCR1, and CCR7, thus affecting CCL2 and IL-8 levels. Moreover, H37Rv infection decreased the migration ability of the CD3⁻ MDMs, but not CD3⁺ MDMs. These results confirm that the CD3⁺ macrophage subpopulations express chemokine receptors that respond to chemoattractants, facilitating cell migration. Together, these data suggest that CD3⁺ MDMs are a functional subpopulation involved in the immune response against Mtb.     

Dependence of the mechanical properties of woodflour–polymer composites on the moisture content

Woodflour of Eucaliptus saligna with two different chemical treatments (mercerization and esterification with maleic anhydride) was used as filler of an unsaturated polyester matrix. Woodflour was treated to increase the interfacial adhesion with the matrix, to improve the dispersion of the particles, and to decrease the water sorption properties of the final composite. The objective of this study was to determine the influence of the moisture content and the woodflour chemical modification on the physical and mechanical properties of the different composites. Results indicated that mechanical properties (compression and bending tests) were severely affected by moisture and chemical modifications. In wet conditions, the composites made from treated woodflour had the lowest flexural modulus and ultimate stress. It was found that this was a reversible effect, because the original values of the compression properties were recovered after drying. Temperature scans in dynamic mechanical tests showed that an irreversible change occurred during exposure to humid environments, probably due to the hydrolysis of the polyester matrix. Essentially, the same behavior was observed for matrix and composites; however, a wood-related transition overlapped the main transition in the case of wet composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2069–2076, 1998     

Simulation of a hydrogen production and purification system for a PEM fuel-cell using bioethanol as raw material

A process to produce “fuel-cell grade” hydrogen from ethanol steam reforming is analyzed from a thermodynamic point of view. The hydrogen purification process consists of WGS and COPROX reactors. Equations to evaluate the efficiency of the system, including the fuel cell, are presented. A heat exchange network is proposed in order to improve the exploitation of the available power. The effect of key variables such as the reformer temperature and the ethanol/water molar feed ratio on the fuel-cell efficiency is discussed. Results show that it is feasible to carry out the energy integration of the hydrogen catalytic production and purification—PEM fuel-cell system, using ethanol as raw material. The technology of “fuel-cell grade” hydrogen production using ethanol as raw material is a very attractive alternative to those technologies based in fossil fuels.     

Extracts of Haematoxylon brasiletto inhibit growth, verotoxin production, and adhesion of enterohemorrhagic Escherichia coli O157:H7 to HeLa cells

The extracts of 33 plants were evaluated for their effects on growth of Escherichia coli O157:H7 (EHEC). The extract of Haematoxylon brasiletto was the only one that effectively inhibited bacterial growth. The effects of ethanolic extracts of this plant on growth, verotoxin production, and adhesion of E. coli O157:H7 to HeLa cells were determined. The MBC for growth was 4 mg/ml. No verotoxin formation was detected at 1, 2, or 3 mg/ml. Preexposing bacteria and HeLa cells to various concentrations of extracts affected the adhesion between non-EHEC and HeLa cells. Partial purification of the active fraction suggested that polyphenols might play a role in the antimicrobial activity exhibited by H. brasiletto extracts.     

Observed maternal strategies and children's health locus of control in low-income Mexican Americans.

This study examined the relationship among mothers' health locus of control (HLOC) beliefs, their socialization strategies, and their children's HLOC beliefs in 80 low-income Mexican American families. Maternal socialization strategies were assessed from videotaped interactions of mothers and children engaged in a structured task. Factor analysis of the coded strategies yielded 4 factors: Tell Answer, Teaching, Clarify, and Reinforce. Findings indicated that maternal-health-internally scores negatively predicted mothers' use of the Tell Answer strategies and positively predicted their use of Teaching strategies. Mothers who believed that Powerful Others (e.g., health professionals) controlled their health were more likely to use the Tell Answer strategy. In contrast, mothers who believed that health was due to chance were less likely to use Teaching. Maternal use of Teaching strategies predicted children's internal HLOC, whereas maternal Tell Answer strategies predicted children's external HLOC. Findings suggest that mothers' HLOC beliefs influence the socialization strategies they use and that these strategies are associated with children's HLOC beliefs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proteoglycans production by aortic vascular smooth muscle cells from hypertensive rats

Remodeling of large and small arteries contributes to the development and complications of hypertension. Artery structural changes in chronic sustained hypertension include vascular smooth muscle cells (VSMC) proliferation and extracellular matrix (ECM) modifications. Extracellular constituents such as proteoglycans (PGs), may modulate vascular stiffness and VSMC growth and differentiation. We examined the effect of growth factors on secreted and membrane-bound PGs synthesis by cultured aortic smooth muscle cells (SMC) from 12- to 14- week-old spontaneously hypertensive rats (SHR) and age-matched Wistar rats. After stimulation with platelet-derived growth factor (PDGF-BB), 10% fetal calf serum (FCS) or 0.1% FCS as control, PGs synthesis (dpm/ng DNA) was evaluated in the medium (M-ECM) and in the cell layer (PECM) by a double-isotopic label method using both [³H]-glucosamine and [³⁵S]-sodium sulfate which are incorporated into all complex carbohydrates or only into sulfated dysaccharides, respectively. Data are presented as percent of the control (0.1% FCS). SHR VSMC displayed a significantly greater synthesis of MECM [³H]-PGs than Wistar rat cells, with both treatments, but no differences in M-ECM [³⁵S] uptake were found in any case. In the P-ECM, both PDGF-BB and 10% FCS produced a greater effect on [³H]-PGs and sulfated PGs synthesis in VSMC from SHR. An important change seen in SHR cells was a significant decreased sulfation, assesed by [³⁵S]/[ ³H] ratio, in basal and stimulation conditions. Present results indicate the existence of changes in PGS synthesis and modulation in VSMC from a conduit-artery of SHR and support the pathophysiological role proposed for matrix proteoglycans in the vascular wall changes associated to hypertension and related vascular diseases as atherosclerosis.     

Surfactant-aided dispersion of polystyrene-functionalized carbon nanotubes in a nanostructured poly(styrene-b-isoprene-b-styrene) block copolymer

The synergistic effect of using polystyrene-grafted multi-walled carbon nanotubes (PSgMWCNT) and a surfactant in the dispersion of MWCNT in a self-assembled poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer is reported. The functionalization of MWCNT with polystyrene achieved by the grafting-from approach is not enough to disperse them in the SIS block copolymer. However, a high dispersion of PSgMWCNT in SIS is achieved when dodecanethiol (DT) was added through composite preparation, without affecting the SIS capacity to self-assemble in ordered cylinders. Suspensions of PSgMWCNT without DT and not functionalized MWCNT with DT presented low stability forming aggregates in less than 10 min. On the contrary, the stability of PSgMWCNT suspension in the presence of DT was dramatically enhanced to more than two weeks. This synergistic effect is due to interactions between PSgMWCNT and DT molecules, as proved by UV-Vis spectroscopy.     

Clays for polymeric nanocomposites

We discuss test methods and results for determining individual clay platelets shape, size, size distribution, elemental composition, and impurities. Commercial sodium salt varieties of natural, semisynthetic and synthetic clay (Cloisite®‐Na⁺, Somasif ME‐100, and Topy‐Na⁺, respectively) were analyzed. In this international collaboration, eight laboratories on three continents carried out the work within the VAMAS TWA‐33 activities. There are large differences between the three nanofillers as far as: (1) the platelet orthogonal dimensions, (2) chemical composition, and (3) contaminants (their diversity and quantity) are concerned. Elaborate purification of natural clays leaves behind 2–5 wt% of organic and mineral impurities, whose nature, shape, size, and chemistry depend on the clay origin. These contaminants affect nanocomposite performance, thus controlling their composition and quantity is essential. The article describes the developed methods, summarizes the preliminary results, discusses the encountered difficulties, and proposes methods for solving them. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers