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PubMed2005

Properties and structure of manganese oxide-coated clay.

In the environment, heavy metals are important contaminants that sorb to and accumulate in soils and sediments. Dominant minerals in the subsurface are oxides and clay, which occur as discrete particles and heterogeneous systems; these surfaces can significantly impact the mobility and bioavailability of metals through sorption. To better understand heterogeneous systems, amorphous (hydrous manganese oxide (HMO)) and crystalline manganese oxides (birnessite and pyrolusite) were coated on montmorillonite. However, the montmorillonite substrate potentially inhibited crystallization of the pyrolusite coating, and also resulted in a poorly crystalline birnessite. Mineralogy and morphology of the coated systems suggest an amorphous structure for HMO and uniform coverage for HMO and birnessite coatings; the presence of Si and Al indicates uncoated areas along intraplanar surfaces. The coating surface charge behaved similarly to that of discrete oxides and clay where the pH(znpc) of HMO- and birnessite-coated clay were 2.8 and 3.1, respectively. Surface area of the coated systems increased while the pore size distribution decreased as compared to the external surface area and pores of montmorillonite. X-ray absorption spectroscopy (XAS) revealed the local structural environment of Mn in the HMO- and birnessite-coated clay was consistent with the pure phase oxides: for HMO-coated clay 3.1 atoms of oxygen at 1.89 +/- 0.02 A in the first shell and 2.7 atoms of manganese at 2.85 +/- 0.02 in the second shell; and, for birnessite-coated clay 6 atoms of oxygen at 1.91 +/- 0.02 A in the first shell and 6 atoms of manganese at distance 2.99 +/- 0.02 A in the second shell. Overall, the surface properties suggest that the coating behaves like that of discrete oxides, an important sink for metal contaminants.

Journal Article↗
PubMed2005

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization.

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 degrees C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100-500 rpm) and time (15/60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of "honeycomb" particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20-22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5-7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Journal Article↗
PubMed2005

Relating clay yield stress to colloidal parameters.

The ability to predict rheological behavior of clay dispersions would be useful in formulating systems rheologically modified by clays as well as designing equipment to handle clay based materials. Deriving predictive equations for these materials has been hindered due to the various mechanisms by which clay systems develop microstructure. This work seeks to observe the relationship between the yield stress, tauy, and the zeta potential, zeta, and determine the nature of the particle interactions for dispersions of laponite (a synthetic clay) and dispersions of a mixture of naturally occurring kaolinites and bentonites. It is found that the relationship of tauy to zeta2 for clay suspensions is opposite to that found for homogeneously charged spheroidal colloids. This result can be traced to the type of particle interactions occurring, which for the systems studied appear to be edge-to-face attractions.

Journal Article↗
PubMed2005

Dispersion of organically modified clays within n-alcohols.

A method for formation of polymer-clay nanocomposites involves dispersion of the nanometer silicate layers of clays into a solvent, followed by dispersion into polymers. The dispersion of layered silicates within solvents affects the structure and properties of the nanocomposites. We report the dispersion of organically modified clays, used for formation of nanocomposites with organic polymers, within a range of alcohol solvents. Experiments involved stirring a mixture containing approximately 1 wt% of alkylammonium-modified clays in n-alcohols with general molecular structure RnOH, where n represents the number of carbons of alkyl chains, varying from 2 to 8. The clays precipitated from the dispersion when RnOH solvents with n<5 were used, however, they formed gels for solvents with n5. The increased dispersion was related to the decrease of polarity and hydrogen bonding force within solvents. X-ray diffraction for the dispersed clays indicated that the interlayer spaces (1.8 nm), formed by regular stacking of the silicate layers, expanded to a maximum of 3.0 nm after treatment with RnOH with n5. The interlayer expansion was due to the intercalation of n-alcohol molecules within the interlayer spaces. It is suggested that the alkyl chains of n-alcohols remain parallel to the silicate surface in the intercalate. Preliminary experiments on the influence of these alcohol solvents on the intercalation of polyol (polyether) are also reported.

Journal Article↗
PubMed2006

The impact of montmorillonite clay addition on the in vitro wear resistance of a glass-ionomer restorative.

OBJECTIVES: The in vitro wear resistance of a glass-ionomer (GI) restorative ChemFil Superior (Dentsply DeTrey, Kanstanz, Germany) reinforced with either a pristine calcium montmorillonite (Ca-MMT) or an organically modified 12-amino-dodecanoicacid treated montmorillonite (ADA-MMT) clay was evaluated to investigate the potential of MMT reinforced GI restoratives as posterior filling materials. METHODS: The wear resistance of a GI restorative reinforced with 0.5-2.5 wt.% Ca-MMT and ADA-MMT was assessed for groups of four disc-shaped specimens using the OHSU oral wear simulator operating at 20 N abrasion and 90 N attrition forces for 50,000 cycles at a frequency of 1 Hz in the presence of a poppy seed and PMMA micro-sphere slurry. The wear facet of each specimen was quantified by measuring the mean wear depth and mean volumetric wear in the abrasion (40-60% of wear facet) and attrition (80-90%) regions in conjunction with the mean total wear depth and mean total volumetric wear. RESULTS: The addition of Ca-MMT clay resulted in a significant increase in the mean total volumetric wear and mean total wear depth of the GI restorative as the concentration of clay was increased utilising the one-way ANOVA and Tukey's test comparisons at a 95% significance level. When ADA-MMT clay was added to the GI no significant differences in mean total volumetric wear and mean total wear depth were evident (P<0.05). CONCLUSIONS: The addition of Ca-MMT clay to the GI restorative resulted in a significant decrease in the in vitro wear resistance. ADA-MMT clay additions to the powder element of the GI restorative did not significantly enhance the in vitro wear resistance.

Analysis of Variance↗
PubMed2006

Mechanism of smectic arrangement of montmorillonite and bentonite clay platelets incorporated in gels of poly(acrylamide) induced by the interaction with cationic surfactants.

Structure transitions, induced by the interaction with the cationic surfactant cetylpyridinium chloride in nanocomposite gels of poly(acrylamide) with incorporated suspensions of the two closely related layered clays bentonite and montmorillonite, were studied. Unexpectedly, different behaviors were revealed. X-ray diffraction measurements confirm that, due to the interaction with the surfactant, initially disordered bentonite platelets arrange into highly ordered structures incorporating alternating clay platelets and surfactant bilayers. The formation of these smectic structures also in the cross-linked polymer gels, upon addition of the surfactant, is explained by the existence of preformed, poorly ordered aggregates of the clay platelets in the suspensions before the gel formation. In the case of montmorillonite, smectic ordering of the disordered platelets in the presence of the surfactant is observed only after drying the suspensions and the clay-gel composites. Rheology studies of aqueous suspensions of the two clays, in the absence of both surfactant and gel, evidence a much higher viscosity for bentonite than for montmorillonite, suggesting smaller clay-aggregate size in the latter case. Qualitatively consistent results are obtained from optical micrographs.

Journal Article↗
PubMed2002

First-principles study of illite-smectite and implications for clay mineral systems.

Illite-smectite interstratified clay minerals are ubiquitous in sedimentary basins and they have been linked to the maturation, migration and trapping of hydrocarbons, rock cementation, evolution of porewater chemistry during diagenesis and the development of pore pressure. But, despite the importance of these clays, their structures are controversial. Two competing models exist, each with profoundly different consequences for the understanding of diagenetic processes: model A views such interstratified clays as a stacking of layers identical to endmember illite and smectite layers, implying discrete and independently formed units (fundamental particles), whereas model B views the clays as composed of crystallites with a unique structure that maintains coherency over much greater distances, in line with local charge balance about interlayers. Here we use first-principles density-functional theory to explore the energetics and structures of these two models for an illite-smectite interstratified clay mineral with a ratio of 1:1 and a Reichweite parameter of 1. We find that the total energy of model B is 2.3 kJ atom(-1) mol(-1) lower than that of model A, and that this energy difference can be traced to structural distortions in model A due to local charge imbalance. The greater stability of model B requires re-evaluation of the evolution of the smectite-to-illite sequence of clay minerals, including the nature of coexisting species, stability relations, growth mechanisms and the model of fundamental particles.

Journal Article↗
PubMed2004

Free energy, energy, and entropy of swelling in Cs-, Na-, and Sr-montmorillonite clays.

A Monte Carlo method for grand canonical and grand isoshear ensemble simulations has been used to characterize the free energy, energy, and entropy of clay mineral swelling. The Monte Carlo approach was found to be more efficient at simulating water content fluctuations in the highly constrained clay environment than a previously developed molecular dynamics method. Swelling thermodynamics calculated for Cs-, Na-, and Sr-montmorillonite clays indicate a strong dependence of swelling on the interlayer ion identity, in agreement with various experimental measurements. The Sr clay swells most readily, and both the Na and Sr clays prefer expanded states (two-layer hydrate or greater) when in contact with bulk water. In contrast, swelling is inhibited in the Cs clay. Differences in swelling behavior are traced directly to the tendency of the different ions to hydrate. The swelling free energies are decomposed into their energetic and entropic components, revealing an overall energetic driving force for the swelling phenomena. Entropic effects provide a smaller, mediating role in the swelling processes. The results provide a unique molecular perspective on experimentally well-characterized swelling phenomena.

Journal Article↗
PubMed1999

Molecular characterization of high affinity, high capacity clays for the equilibrium sorption of ergotamine.

Ergot alkaloids (mycotoxins) produced by Claviceps and Neotyphodium species of fungi may contaminate animal feedstuffs and results in disease in livestock. In this study, diverse phyllosilicate clays and other adsorbent materials, differing in chemical and structural characteristics, were tested for their ability to sorb ergotamine, a prevalent ergot mycotoxin, from acidic solution. Results indicated minimal binding to those sorbents possessing low surface area, cation exchange capacity and inaccessible interlayer regions. Cetyl pyridinium-exchanged montmorillonite (organoclay) exhibited decreased propensity for ergotamine in acidic solution as compared with the unexchanged hydrophilic parent clay. The highest ergotamine sorption was observed with cation exchanged montmorillonite clays; whereas, when collapsed, these same clays sorbed very little ligand. Based on initial binding experiments, calcium and sodium montmorillonite clays were prioritized for further characterization, including: capacity, affinity, and heat (enthalpy) of adsorption. Computer models of energy-minimized ergotamine isomers and clay were used to illustrate possible mechanisms of ergot alkaloid sorption at interlayer sites. Additional studies are warranted to assess the stability of ergot alkaloid/clay complexes under alkaline conditions to further understand the mechanism of adsorption.

Adsorption↗
PubMed1990

Remobilization of toxic heavy metals adsorbed to bacterial wall-clay composites.

Significant quantities of Ag(I), Cu(II), and Cr(III) were bound to isolated Bacillus subtilis 168 walls, Escherichia coli K-12 envelopes, kaolinite and smectite clays, and the corresponding organic material-clay aggregates (1:1, wt/wt). These sorbed metals were leached with HNO3, Ca(NO3)2, EDTA, fulvic acid, and lysozyme at several concentrations over 48 h at room temperature. The remobilization of the sorbed metals depended on the physical properties of the organic and clay surfaces and on the character and concentration of the leaching agents. In general, the order of remobilization of metals was Cr much less than Ag less than Cu. Cr was very stable in the wall, clay, and composite systems; pH 3.0, 500 microM EDTA, 120-ppm [mg liter-1] fulvic acid, and 160-ppm Ca remobilized less than 32% (wt/wt) of sorbed Cr. Ag (45 to 87%) and Cu (up to 100%) were readily removed by these agents. Although each leaching agent was effective at mobilizing certain metals, elevated Ca or acidic pH produced the greatest overall mobility. The organic chelators were less effective. Lysozyme digestion of Bacillus walls remobilized Cu from walls and Cu-wall-kaolinite composites, but Ag, Cr, and smectite partially inhibited enzyme activity, and the metals remained insoluble. The extent of metal remobilization was not always dependent on increasing concentrations of leaching agents; for example, Ag mobility decreased with some clays and some composites treated with high fulvic acid, EDTA, and lysozyme concentrations. Sometimes the organic material-clay composites reacted in a manner distinctly different from that of their individual counterparts; e.g., 25% less Cu was remobilized from wall- and envelope-smectite composites than from walls, envelopes, or smectite individually in 500 microM EDTA. Alternatively, treatment with 160-ppm Ca removed 1.5 to 10 times more Ag from envelope-kaolinite composites than from the individual components. The particle size of the deposited metal may account for some of the stability changes; those metals that formed large, compact aggregates (Cr and Ag) as seen by transmission electron microscopy were less likely to be remobilized. In summary, it is apparent that remobilization of toxic heavy metals in sediments, soils, and the vadose zone is a complicated issue. Predictions based on single inorganic or organic component systems are too simplistic.

Adsorption↗
PubMed1996

Bacterial diversity in a deep-subsurface clay environment.

The presence of bacteria in a deep clay sediment was analyzed in a 20-m-long core horizontally drilled from a mine gallery at a depth of 224 m in the Boom clay formation (Mol, Belgium). This clay deposit is the result of a marine sedimentary process that occurred 35 million years ago. Bacterial activities were estimated by measuring respiration on [14C]glucose. Using the same samples, universal primers for the genes coding for eubacterial 16S rRNA were used to amplify extracted DNA. PCR products were then cloned, sequenced, and analyzed by molecular phylogeny. Our data showed a decrease in bacterial densities as a function of distance from the gallery, with few bacteria detectable by culture at more than 80 cm from the gallery wall. PCR experiments showed the presence of bacteria in all samples, and phylogenetic analyses were then used to tentatively identify these organisms. Because of low bacterial densities in deep clay samples, direct counts and enumeration of viable bacteria on diverse culture media remained negative. All experiments, both cultures and PCR, demonstrated the difficulty of analyzing samples that contain only a few poorly active bacteria as it is difficult to avoid a small contamination by active bacteria during sampling. Since the porosity of the Boom clay formation is less than the expected size of bacteria, it is possible that some of the bacteria present in this 35-million-year-old deep clay deposit derive from cells initially trapped during the sedimentation process.

Bacteria↗
PubMed2002

Growth of iron(III)-reducing bacteria on clay minerals as the sole electron acceptor and comparison of growth yields on a variety of oxidized iron forms.

Smectite clay minerals are abundant in soils and sediments worldwide and are typically rich in Fe. While recent investigations have shown that the structural Fe(III) bound in clay minerals is reduced by microorganisms, previous studies have not tested growth with clay minerals as the sole electron acceptor. Here we have demonstrated that a pure culture of Shewanella oneidensis strain MR-1 as well as enrichment cultures of Fe(III)-reducing bacteria from rice paddy soil and subsurface sediments are capable of conserving energy for growth with the structural Fe(III) bound in smectite clay as the sole electron acceptor. Pure cultures of S. oneidensis were used for more detailed growth rate and yield experiments on various solid- and soluble-phase electron acceptors [smectite, Fe(III) oxyhydroxide FeOOH, Fe(III) citrate, and oxygen] in the same minimal medium. Growth was assessed as direct cell counts or as an increase in cell carbon (measured as particulate organic carbon). Cell counts showed that similar growth of S. oneidensis (10(8) cells ml(-1)) occurred with smectitic Fe(III) and on other Fe forms [amorphous Fe(III) oxyhydroxide, and Fe citrate] or oxygen as the electron acceptor. In contrast, cell yields of S. oneidensis measured as the increase in cell carbon were similar on all Fe forms tested while yields on oxygen were five times higher, in agreement with thermodynamic predictions. Over a range of particle loadings (0.5 to 4 g liter(-1)), the increase in cell number was highly correlated to the amount of structural Fe in smectite reduced. From phylogenetic analysis of the complete 16S rRNA gene sequences, a predominance of clones retrieved from the clay mineral-reducing enrichment cultures were most closely related to the low-G+C gram-positive members of the Bacteria (Clostridium and Desulfitobacterium) and the delta-Proteobacteria (members of the Geobacteraceae). Results indicate that growth with smectitic Fe(III) is similar in magnitude to that with Fe(III) oxide minerals and is dependent upon the mineral surface area available. Iron(III) bound in clay minerals should be considered an important electron acceptor supporting the growth of bacteria in soils or sedimentary environments.

Electrons↗
PubMed2005

Cat dissection vs. sculpting human structures in clay: an analysis of two approaches to undergraduate human anatomy laboratory education.

Many human anatomy courses are taught using cat dissection. Alternatives are available, but information regarding learning outcomes is incomplete. In 2003, approximately 120 undergraduates enrolled in a human anatomy course were assigned to one of two treatment groups. In the control group, students performed cat dissections (emphasizing isolation and identification) of the muscular, digestive, and cardiovascular systems. In the experimental treatment group, students built clay sculptures of each human body system. Student learning was evaluated by using both low- and high-difficulty questions. On pre- and postexperiment control exams, there were no significant differences in student performance. On exams after a cat dissection vs. a human-clay sculpting experience, the students in the human-clay sculpting treatment group scored significantly higher than their classmates in the cat dissection group on both the low- and high-difficulty questions. Student attitudes toward dissection and taking future human anatomy courses were also measured. There were no differences in student attitudes at the beginning of the experiment; afterward, students exposed to a cat dissection experience viewed dissection more favorably than students in the human-clay sculpting treatment group. There were no treatment effects on student willingness to take future human anatomy courses. The experimental design makes it difficult to conclude precisely why students assigned to the human-clay sculpting experience performed better on exams, but as each method was performed in this particular human anatomy course, our data indicate that human-clay sculpting may be a viable alternative to cat dissection in an anatomy course in which the students focus on human anatomy.

Animals↗
PubMed1993

Effects of feeding aflatoxin-contaminated diets with and without clay to weanling and growing pigs on performance, liver function, and mineral metabolism.

Ninety-six crossbred weanling pigs (36 d of age, initial weight of 8.8 kg) were used in a three-phase study to determine the effects of feeding an aflatoxin-contaminated corn (AC) diet (922 ppb of aflatoxin B1) with and without sodium bentonite (clay) on performance, liver function, and mineral metabolism. In the nursery phase, control corn (NC) or AC was fed in corn-soybean meal diets with and without 1% clay for 6 wk. Compared with NC, AC decreased ADFI and ADG (P < .01) and increased serum activities of gamma-glutamyltransferase (P < .01) and alkaline phosphatase (P < .05). In the growing phase, 48 pigs from the nursery phase were fed NC but continued on their respective clay treatments for 5 wk. Pigs previously fed AC had higher (P < .01) ADFI and lower (P < .05) gain/feed, serum Ca, K, and glucose; ADG, other serum values, and liver minerals were not affected by treatments. In the metabolism phase, 24 barrows from the nursery phase were continued on the same corn and clay treatments for two 4-d total collections of urine and feces. Feeding AC increased (P < .05) P and Na absorption. The addition of clay lowered Mg and Na absorption (P < .01) for both AC and NC. Significant interactions for many minerals indicated that the effects on mineral metabolism were more pronounced when AC was fed. Serum and liver mineral concentrations were generally unaffected by the treatments in all phases. Feeding clay with AC results in partial restoration of performance and liver function without greatly influencing mineral metabolism.

Aflatoxin B1↗
PubMed1993

Effectiveness of different types of clay for reducing the detrimental effects of aflatoxin-contaminated diets on performance and serum profiles of weanling pigs.

Three trials were conducted with recently weaned pigs (n = 198) to determine the effects of feeding different types of clay in conjunction with aflatoxin-contaminated diets. In Trial 1, pigs (n = 54; trial length 4 wk) were assigned to either an uncontaminated treatment (NC), 800 ppb of aflatoxin from contaminated corn (AC), or AC with one of four clays. In Trial 2 (n = 81; trial length 5 wk), pigs were assigned to NC, AC (500 ppb of aflatoxin from rice starch), or AC with one of seven types of clay. In both trials, pigs fed AC had decreased ADG and gain:feed ratios (P < .05) compared with controls. The clays differed in their ability to produce gains similar to those of controls. The clays did reduce changes in the serum measurements normally affected by aflatoxin, including albumin, total protein, gamma glutamyltransferase (GGT), and alkaline phosphatase (ALP) levels, in a manner similar to their effect on ADG. In Trial 3, pigs (n = 63) were assigned to one of seven diets for 4 wk: NC, AC (800 ppb of aflatoxin) with no clay, AC with one of four levels of a treated Ca bentonite (.25, .5, 1, and 2%), or AC and .5% hydrated sodium calcium aluminosilicate. The addition of treated Ca bentonite to AC improved ADG (P < .05) and ADFI (P < .01) linearly. Gain:feed ratios were not affected by treatments. The inclusion of treated Ca bentonite to the AC diet linearly decreased aspartate aminotransferase (AST) levels and quadratically decreased ALP and GGT levels (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxins↗
PubMed2000

[Experimental study of esophageal covered stent for prevention of migration: use of clay to simulate stenosis of the esophagogastric junction or anastomosis site].

PURPOSE: An inner-covered Spiral Z-stent (IC-SZ) developed by our group was examined for its effectiveness in preventing migration by experimental comparison with commercially available esophageal covered stents. MATERIALS AND METHODS: The following six types of stents were used: inner-covered Spiral Z-stents with diameters of 16 mm (small IC-SZ) and 19 mm (large IC-SZ), outer-covered Spiral Z-stent (OC-SZ), covered Wallstent, covered Ultraflex stent, and Cook Z-stent. Experimental models were prepared using clay to simulate stenosis of the esophagogastric junction or anastomosis site due to tumor, and each stent was placed in the clay. After the stent had been fully expanded with a balloon catheter, one of its ends was pulled until the stent migrated out of the clay, and the traction force was measured. The inner cavity of the stent placed in the clay was observed using an endoscope. RESULTS: The mean maximal traction force required to pull the stents out of the clay were as follows, in decreasing order: 4.14 +/- 0.39 kg for the large IC-SZ, 4.12 +/- 0.83 kg for the small IC-SZ, 3.64 +/- 0.44 kg for the Cook Z-stent (p < 0.05), 3.34 +/- 0.62 kg for the covered Ultraflex stent (p < 0.05), 1.53 +/- 0.43 kg for the OC-SZ (p < 0.01), and 0.56 +/- 0.16 kg for the covered Wallstent (p < 0.01). The force required to pull out the large IC-SZ stent was the greatest, showing a significant difference from the values for the other four types of stents (excluding the small IC-SZ). Observation using an endoscope revealed that the wire of the IC-SZ stent was almost entirely embedded in the clay, whereas the wires of other stents were not. CONCLUSION: The IC-SZ stent may be less likely to migrate than other esophageal covered stents.

Biomechanical Phenomena↗
PubMed1989

[Adsorption potency of 2 clays, smectite and kaolin on bacterial enterotoxins. In vitro study in cell culture and in the intestine of newborn mice].

The use of clays in the treatment of enterocolitis is justified by their ability to adsorb viruses, biliary acids and bacterial toxins secreted into the intestinal lumen. We have studied the in vitro inactivation of the LT toxins of Vibrio cholerae and E. coli, the ST toxin of ETEC and the verotoxin of EHEC. These various toxins were incubated with two types of clays, smectite and kaolin, to investigate the influence of dose, pH variations and the duration of contact of the clays with the toxins. Irrespective of their presence or absence in the supernatant, the biological activity of the toxins was assessed in cell culture and in the newborn mouse test. Both clays inactivated the LT toxin. Smectite was more efficient than kaolin as it was active immediately especially at the pH of intestinal chyme. The LT toxins were adsorbed on the clays by hydrogen bonding. This permitted the segregation of the toxins and prevented them from being fixed to the membrane receptors on the cells. The two clays were ineffective against the verotoxin of EHEC when the pH was alkaline although they were more efficient at acid pH. ST toxin of ETEC was slightly adsorbed by smectite and kaolin.

Adsorption↗
PubMed2004

Organic-inorganic hybrids from renewable plant oils and clay.

This study deals with the preparation and properties of a new class of organic-inorganic hybrids from renewable resources. The hybrids were synthesized by an acid-catalyzed curing of epoxidized triglycerides in the presence of an organophilic montmorillonite (a modified clay). The mechanical properties were improved by the incorporation of clay in the oil-based polymer matrix. The reinforcement effect due to the addition of clay was confirmed by dynamic viscoelasticity analysis. The hybrids showed relatively high thermal stability. The co-curing of epoxidized soybean and linseed oils in the presence of clay produced hybrids with controlled mechanical and coating properties. The barrier property of the hybrid towards water vapor was superior to that of the oil polymer. The development of the present hybrids consisting of inexpensive renewable resources, triglyceride and clay is expected to contribute to global sustainability.

Aluminum Silicates↗