Javier I. Amalvy

Application of dynamic speckle interferometry to the drying of coatings

In this work a new tool to study the drying of paints, based on an optical technique known as dynamic speckle interferometry is presented. The basic concepts of the technique are described and applied to the drying process of white solvent-borne and white water-borne paints (latex paint) following the time evolution of the activity of dynamic speckle patterns. For processing the data an alternative method based on the use of the second-order moment of the modified co-occurrence matrix of the time history of its intensity was used. The experimental results obtained were compared with the gravimetric technique and the resulting curves from the speckle-time evolution compared favorably with gravimetric drying curves. The results were also discussed on the basis of the knowledge of the coating drying process and factors related with the surface properties. Dynamic speckle interferometry seems to be a useful technique for assessing the time evolution of surfaces and, its sensitivity to refractive index changes helps to determine the start of different stages during the drying of latex paints. The dynamic speckle method tests mainly the activity on the surface and the measurements seem to confirm that the initial stage of drying is like a pure solvent. Finally, the study of different aspects of the drying process using this technique is proposed.

The role of nanocrystalline cellulose on the microstructure of foamed castor-oil polyurethane nanocomposites.

Nanocrystalline cellulose (CNC), obtained by sulphuric acid hydrolysis, was used to synthesize polyurethane foams (PUFs) based on a functionalized castor oil polyol and a Methylene diphenyl diisocyanate (MDI). Formulations with varying isocyanate index (FI) and NCO number were prepared. At 0.5 wt.%, SEMs of the fractured surface underlined that the CNC acted both as a nucleation agent and as a particulate surfactant with cell geometries and apparent density changing selectively. The chemical structure of the PUF (FTIR) changed after the incorporation of CNC by a relative change of the amount of urea, urethane and isocyanurate groups. A low NCO number and isocyanate index contributed to the migration of the CNC to the Hard Segment (HS), acting as reinforcement and improving substantially the compressive mechanical properties (Ec and σc improvements of 63 and 50%, respectively). For a high NCO number or isocyanate index, the CNC migrated to the Soft Segment (SS), without causing a reinforcement effect. The migration of the CNC was also detected with DSC, TGA and DMA, furtherly supporting the hypothesis that a low NCO number and index contributed both to the formation of a microstructure with a higher content of urethane groups.

A kinetic study in emulsion polymerization of polyurethane‐acrylate hybrids

Polyurethane (PU) anionomer having 2‐ethoxymethacrylate terminal groups was prepared in a methyl methacrylate/n‐butyl acrylate mixture as a reactive diluent, following a prepolymer mixing process. This prepolymer‐acrylic monomer mixture was chain extended in a water/surfactant solution using different dispersion speeds. Stability tests of PU‐acrylic monomer dispersions before polymerization were performed at different temperatures by following the particle size evolution. After the dispersion process the kinetics of batch emulsion polymerization at 70°C using different concentrations of initiator was investigated. Data are compared with published results of batch emulsion copolymerization of methyl methacrylate/n‐butyl acrylate. The effect of triethylamine, used in the prepolymer synthesis, on the emulsion polymerization of acrylic monomers was also studied. The kinetic results indicate that during emulsion polymerization of PU acrylic mixture, some coagulation takes place, mainly due to changes in ionic ...

Morphology and properties of neutralized chitosan-cellulose nanocrystals biocomposite films

Chitosan/cellulose nanocrystals (CH-CN) films were obtained by casting of dispersions, and treated with NaOH for neutralization proposes. The composition of films was varied from 1 to 10wt.% of CN. Changes in the morphology of the systems were correlated with the different properties studied. FTIR revealed the presence of a weak interaction between the polymer matrix and nanofiller, confirmed by a slightly increase in thermal stability. SEM images suggested that incorporating CN amounts higher than 3wt.% generates phase-segregated systems, and SAXS showed that CH avoid the typical organization of CN at concentrations below 5wt.%. Improved performance against water was obtained in composite materials comparing to the pure polymer matrix, as well as CH and CH-CN films did not show antibacterial activity demonstrating that remnant acetic acid, when no neutralization step is done, plays an important role in this property.

A density functional study of the adsorption of pyridine, 2-vinylpyridine, and 4-vinylpyridine onto a silica surface

Abstract The interaction of pyridine, 2-vinylpyridine, and 4-vinylpyridine with silica surfaces represented by model clusters is studied within the framework of the density functional theory to shed light on the different trend towards polymerization showed by the vinyl derivatives of pyridine. It is found that pyridine interacts more strongly with silica clusters than its derivatives, whereas 2-vinylpyridine, in its turn, exhibits a larger interaction energy than 4-vinylpyridine. It is also found that the interaction pattern is dominated in all cases by the formation of a hydrogen bond between the nitrogen atom and a hydroxyl group of the silica cluster, a second, very weak hydrogen bond is formed in some of the systems, though. A natural bond orbital analysis and the calculation of harmonic vibrational frequencies allow to confirm those findings. Finally, it is proposed that the trend of not forming nanocomposites when using 2-vinylpyridine is mainly due to the involvement of its vinyl group in a weak hydrogen bond to an oxygen atom of the silica surface avoiding to polymerize and not due to a weak acid–base interaction nor steric effects as it was previously supposed.

Starch / Polyvinyl Alcohol Blends Containing Polyurethane as Plasticizer

Gonzalez-Forte, Lucia del Sol. INIFTA (Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas). UNLP-CONICET; Argentina

Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications

A pH-sensitive blend of polyurethane (PU) and poly(2-(diethyl amino)ethyl methacrylate (PDEA) with good film-forming capacity was prepared from the corresponding aqueous dispersions. The polymer matrix was first characterized by using FTIR, DSC, water vapor transmission and water swelling capacity at different pHs. The drug release profile of films was evaluated using a vertical Franz Cell and theophylline as model drug. The water swelling degree increases from 54 to 180% when the pH of the medium is changed from 6 to 2, demonstrating the pH-responsive behavior of the film. The in-vitro release studies indicate that an anomalous transport mechanism governs the theophylline release.

A Microstructural Study of Acrylic-Modified Chitosan by Means of PALS and SAXS

Chemical modification of chitosan, specially grafting with different polymers is an important strategy in the production of bio-based materials with enhanced properties. In the present study, chitosan was grafted with n-butyl acrylate, in a surfactant-free emulsion polymerization. Stable dispersions with high grafting efficiency were obtained and the microstructure of the casted films was analyzed by positron annihilation lifetime spectroscopy and small angle X-ray scattering. Results are discussed in terms of the number and distribution of the grafting sites.

Drying paint by means of dynamic speckle patterns

The drying of paints was followed using the time evolution of the activity of dynamic speckle patterns. For processing the data an alternative method based in the use of the second order moment of the modified co-occurrence matrix of the time history of its intensity was used. The experimental results obtained were compared with gravimetrical techniques. The results are discussed on the basis of the knowledge of the coating drying process.