We report in this paper the synthesis and characterization of a new class of biopolymer-clay nanocomposites based in the assembling of chitosan to sepiolite, which is a natural magnesium silicate showing a microfibrous texture. CHN and ICP/AES chemical analyses, XRD, FTIR spectroscopy, 13 C solid-state NMR, LT-SEM, and thermal analysis have been employed in the characterization of the resulting nanocomposites. The adsorption isotherm of chitosan on sepiolite in acidic medium reveals a significant coverage of the biopolymer at high equilibrium concentration values indicating a multilayer adsorption. The arrangement of chitosan chains on the surface of the silicate microfibers is discussed on the basis of physicochemical data obtained by application of the different techniques. The potentiometric response of this new type of bio-nanocomposites incorporated in carbon paste electrodes toward aqueous salt solutions was employed for the first time as a valuable technique for a rapid assessment of the ionexchange behaviors. Thermal behaviors and mechanical properties have been determined by DTA-TG and DMTA, respectively. As these materials are well-processed as self-supporting films, in view of their properties they show potential interest as membranes for different processes related to separation of ions and gases, as well as components in electrochemical devices (fuel-cell, potentiometric sensors).

In this paper we consider a family of penalized likelihood criteria for determining the rank of the cointegration space, the number of lags, and the form of the intercept in vector autoregressions with possibly integrated processes. The paper provides a general consistency result for a class of model determination procedures in which the penalty depends on a simple parameter count only.

Sizing glass fibers with silane coupling agents enhances the ad-hesion and the durability of the fiber/polymer matrix interface in composite materials. There are several tests to determine the inter-facial strength between a fiber and resin, but all of them present difficulties in interpreting the results and/or sample preparation. In this study, we observed the influence of different aminosilanes fiber coatings on the resistance of epoxy-based composite materials using a very easy fractographic test. In addition, we tried a new flu-orescence method to get information on a molecular level precisely at the interface. Strength was taken into account from two stand-points: (i) mechanical strength and (ii) the resistance to hydrolysis of the interface in oriented glass-reinforced epoxy-based composi-tes. Three silanes: γ -aminopropyltriethoxysilane, γ -Aminopropyl-methyldiethoxysilane, and γ -Aminopropyldimethylethoxysilane were used to obtain different molecular structures at the interface. It was concluded that: (i) the more accessible amine groups are, the higher the interface rigidity is; (ii) an interpenetrating network mechanism seems to be the most important for adhesion and there-fore to the interfacial strength; and (iii) the higher the degree of crosslinking in the silane coupling layer is, the higher the hydrolytic damage rate is.

The adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicating a great affinity of the MB towards the sepiolite; the adsorption is quantitative up to adsorption of MB of 0.1 mmol/g sepiolite. The differences observed in the absorption spectrum in the region 500-650 nm for different MB Ioadings are interpreted in terms of aggregation of MB molecules on the sepiolite surface with the formation of MB dimers, trimers and higher aggregates. The progressive coverage of the sepiolite surface by MB produces a sharp decrease in the viscosity of the gels, and the suspension becomes peptized for an MB loading of 0.21 mmol/g which corresponds to the adsorption of MB dimers. These results indicate that MB avoids particle-to-particle interactions. The viscosity decrease is parallel to the perturbation of the Si-OH groups on the sepiolite surface as observed by IR spectroscopy, suggesting that these silanol groups can also play an important role in the theological behaviour of aqueous sepiolite dispersions.

Commercial glass fibres were calcinated for the removal of organic matter, activated for surface silanol regeneration and silanizated with ,'-aminopropyltri-ethoxysilane. Two different activation methods were used: reflux with neutral water and reflux with 10% HCI aqueous solution. Acid treatments hydrolize Si-O bonds, greatly changing the composition of the glass and regenerating silanol groups, sorne of them being of intraglobular nature. Water treatment does not change appreciably the glass composition, but its surface free energy value is the lowest. The degree of silanization is the greatest for the acid activated samples and the lowest for the water activated one. The polar contribution to the total surface free energy, once the samples are silanizated, is the highest for the fibres activated with boiling water whilst the dispersion component is about the same for all of them. SEM observations indicate that for the greatest degree of coating, debonding of the filaments may induce a peeling-out fractural mechanism.Glass libres; Surface tensron; APES l. lntroduction

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The fluorescenc response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epox and in the epoxy bulk of a composite material was studied. The effect of two glass fibe surface treatments was investigated. Commercial E-glass fi ers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescen labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epox interface reflecte that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.

Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyltriethoxysilane (APTES) and the 3-aminopropylmethyldiethoxysilane (APDES) the reagents for preparing them at the proportion of (APTES/APDES): 1/0, 1/1 and 0/1. The 1-pyrene sulphonyl chloride (PSC) fluorescent moiety was chemically attached to the silanised substrate via the sulphonamide formation. The hydrolytic degradation phenomenon of the silane coupling layer was studied as a function of: (i) temperature, (ii) coating layer type and (iii) pH (4, 7 and 10). The hydrolytic damage in the coupling region of the silica microfibres composite materials occurs under an equilibrium process. It was obtained the activation energies (E a ) for the hydrolytic damage considering the rate to reach the equilibrium. The values of E a depended on the type of coating and on the pH. As a consequence, the rate of hydrolytic damage could be related to the proportion of Si silane -O-Si silane , while the OH − groups were thought to catalyse the reaction.