Virgilio Angel González

Chemical structure and compatibility of polyamide–chitin and chitosan blends

This work presents a comparative study of the compatibilization of four binary blends with slight differences in their chemical structures. The natural polymers chitin (QA) and chitosan (QN) are blended with polyamide 6 (PA6) and polyamide 66 (PA66). The results, obtained using differential scanning calorimetry, infrared spectroscopy, and light and scanning electron microscopy, gave the following compatibilization sequence: PA6/QN ≈ PA66/QN > PA6/QA > PA66/QA. This behavior could be related to the ability of QN to form hydrogen bonds and also to the capability of the packing of PA66.

Recently acquired HIV infection in Spain (2003-2005): introduction of the serological testing algorithm for recent HIV seroconversion.

Background: Identification of recent HIV infections provides a description of the current pattern of HIV transmission and, consequently, can help to design better preventive interventions. Our study shows the first implementation in Spain of the Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS) strategy. We assess the viability of introducing STARHS in our setting and describe the frequency and epidemiological characteristics of recent infections (RIs). Methods: Between 2003 and 2005, HIV-positive blood samples drawn for diagnostic purposes were collected from 28 Spanish laboratories to be tested using STARHS. Samples from patients with a previous HIV diagnosis, age <18 years, <200 CD4 cells/μL or clinical AIDS criteria were excluded from the analysis. Results: A total of 660 (19.2%) samples were classified as RI. Most people identified with RI were male (79.8%) with a median age of 33.1 years, and 62.5% occurred among men who have sex with men (MSM). Immigrants made up 26.5% of individuals identified with RIs, with 48.7% coming from South America. Among the individuals with RI, at least 16.5% had reported another sexually transmitted infection (STI) during the year before the HIV diagnosis. Conclusion: The study shows that the implementation of STARHS in our setting is feasible and has highlighted important features of the local HIV epidemic, such as the ongoing spread of HIV among MSM, the potential role of STIs in RIs and the vulnerability of immigrants as a new target population.

Fracture surface of plastic materials: the roughness exponent

In order to provide more evidence concerning the controversial topic, conjectured for the first time in the early 90’s, that the roughness exponent of the self-affine fracture surfaces has a value close to 0.8, the self-affine behavior of fracture surfaces of both, semi-crystalline polypropylene (PP) and amorphous polystyrene (PS) was analyzed. The topography of polymeric fracture surfaces was obtained using atomic force microscopy, AFM, and the corresponding height profiles were processed using the variable bandwidth method (standard deviation criteria) to obtain the roughness exponent of the surfaces. Prior to that, the appropriate AFM operating conditions, in contact mode, were found. The average roughness exponent was 0.770 ^ 0.09 for the fracture surfaces of polypropylene and 0.707 ^ 0.07 for polystyrene. These results agree with values for different materials often reported in the literature that support 0.8 has a possible ‘universal’ value. Hence, it is considered that our results are in good agreement with the conjectured value even for polymeric materials. q 2002 Elsevier Science Ltd. All rights reserved.

Synthesis, optical and structural properties of sanidic liquid crystal (cholesteryl)benzoate-ethynylene oligomers and polymer

(Cholesteryl)benzoateethynylene oligomers having 3, 5 and 7 repeat units and the homologue polymer were synthesized by a divergence–convergence approach by the Sonogashira–Heck reaction. Their chemical structure was analyzed by 1H, 13C NMR, UV-Vis, fluorescence spectroscopy and circular dichroism. X-Ray diffraction patterns of all the materials show only a first order peak at 2.05° in 2θ, indicative of a lamellar order within a distance of 4.3 nm. This is twice the calculated distance of a molecule in its more extended conformation, i.e. of 2.15 nm, and is consistent with a disordered Smectic A phase for the trimer and pentamer and a nematic phase for the heptamer and polymer. The most probable model of organization corresponds to a supramolecular assembly in bilayers, where the cholesteryl chains are oriented in an opposite sense, i.e. in a back-to-back “comb like” fashion, which is in agreement with AM1 semiempirical optimization and DFT theoretical calculations. Since the molecular shape of the materials is consistent with brick or board-like structures and the molecules are stacked in blocks randomly oriented as observed by High Resolution Transmission Microscopy, the (cholesteryl)benzoateethynylene materials could be described as Sanidic LCs as a general term to classify their mesomorphic behavior. Optical properties are discussed in terms of the conjugation length and the terminal groups, iodine or in one case, hydrogen. In general the results confirm that all the molecules assume in solution a more planar conformational geometry when passing from the ground to the excited state as confirmed by the theoretical calculations. Circular dichroism spectra measured were consistent with the observed structural properties.

STATISTICAL ASSESSMENT OF SELF-AFFINE METHODS APPLIED TO SHORT PROFILES

Considering the small range of values that the self-affine exponent can take (0 to 1), the accuracy and precision of its determination are very important when it is used as a characteristic related to the evolution of physical phenomena or to the morphological nature of objects. In this work, a careful statistical evaluation of four common self-affine determination methods, applied to synthetic small profiles (N = 512) is reported. Accuracy, precision, confidence in the linear interval selection and computation speed are the parameters used to evaluate box counting (BC), rescaled-range analysis (Zmax), covariance analysis (Zdev) and wavelet transform (Wt) methods applied to profiles synthesized using the Weierstrass-Mandelbrot function (WMf) and the middle point displacement (Mp) methods. The results show that the log-log plot from which the self-affine exponent is computed, does not have the linear form of the BC and Zmax methods; the Wt and Zstd are the most accurate while Wt has the lowest precision. In light of these results, it is recommended to use only the Zstd or Wt methods for sample sizes of more than 100 profiles.

Polyamide/Biopolymer Blends

Abstract We prepared blends of polyamide 66 (P66) and chitin (QA) and its derivative, chitosan (AN), via the solution-casting technique. For P66 with 60% QN content, differential scanning calorimeter analysis showed an 81% decrease in the heat of fusion. When 15% P66 was added, the infrared spectral band of the carbonyl functional groups of the non-deacetylated portion of QN showed about 6 cm-1 displacement from its normal position. In addition, the carbonyl band of the P66 amide was expanded and displaced to the higher wavenumbers when QN was added. This spectral modification could be attributed to intermolecular hydrogen bonding between components, and the expansion of the P66 band could indicate an increase in disorder in the functional groups, namely, a transformation of P66 from the crystalline to the amorphous state. For P66/QA blends, no displacement of the functional group bands was detected, indicating the probable absence of miscibility of these blends. The morphology of the blends after solvent evaporation at 30°C was analyzed, using a cross-polarized optical microscope and a scanning electron microscope.

Polyamide-6/Chitosan Blends. Preliminary Results

Polyamide-6 (Pa6) and chitosan blends were prepared via the solution casting technique, yielding partial miscibility between these two polymers. DSC analysis shows a 75% decrease in the heat of fusion for Pa6 with 60% chitosan content, corresponding to a 25% decrease in the degree of crystallinity. The infrared spectral band for the chitosan amide functional group shows a severe displacement from its normal position when Pa6 is added, more than 28 cm -1 for an addition of 25% of Pa6. This spectral modification and the crystallinity variation could be attributed to hydrogen bonding between components. The morphology of the blend after solvent evaporation at 30°C was analyzed using a cross polarized optical microscope and a scanning electron microscope.