Flavio Vázquez

Properties of films obtained from aqueous polymer dispersions: study of drying rate and particle polydispersity effects

The formation of polymer films obtained from latexes and their structural features have been investigated with the aid of a Monte Carlo simulation modelling and atomic force microscopy. The effects of particle size polydispersity and solvent drying rate on film structure, permeability and roughness have been studied. It has been shown that slow drying permits the formation of films with relatively low porosity and smooth surfaces. Polydispersity in the particle size leads to a weakening of the particle layering and thereby to a reduction in film barrier properties. Theoretical calculations indicate the existence of a local nonlinear dependence of film surface roughness on drying velocity. The correlation between film surface roughness and porosity has also been established.

Synthesis and Characterization of Water-Borne Adhesives Based on 2-Ethylhexylacrylate-butylacrylate Copolymers Functionalized with Acrylic Acid

ABSTRACT A series of copolymers, based on 2-ethylhexylacrylate (2-EHA) and butylacrylate (BuA), and functionalized with small amounts of acrylic acid (AA) were synthesized by emulsion polymerization techniques and monodisperse latexes were obtained. Their average particle size and particle size distribution were determined by quasi-elastic light scattering and confirmed by transmission electron microscopy. The change in the adhesive properties (peel, shear, and tack) as a function of 2-EHA/BuA ratio was studied. An optimal balance between these three properties was determined at a 2-EHA/BuA ratio 10/90 wt/wt. The influence of the functionalization of these copolymers with AA was also evaluated when the comonomers ratio was kept constant. Good results were found at an AA content of 1 wt%.

Development of New Carpet Backings Based on Composite Polymer Particles

A series of composite latex particles were prepared by two stage emulsion polymerization. Monodisperse acrylic particles, with an average particle size Dpz = 160 nm, were firstly synthesized. The second step consisted of styrene addition. Micrographs of the nanostructured particles were obtained by transmission electron microscopy (TEM) and the dependence of the morphology on the polymer composition was studied. A transition from a homogeneous to ‘champignon’ morphology was detected by this way. The aqueous dispersions of the obtained composite particles were used to prepare carpet backings. Their mechanical performance was tested by industrial methods.

Pressure-Sensitive Adhesives Based on Nanostructured Latex Particles

Conceivably, when a polymer with two opposite properties is required, two different monomers may chemically be combined by a simple copolymerization reaction. One of the commonest techniques is to synthesize copolymers by an emulsion polymerization. The homogeneous particles obtained by this method simply show a balance between the individual properties of the homopolymers. In contrast, two-stage emulsion polymerization affords simultaneously an improvement of both opposing properties (synergy). In order to study the influence of particle structure on adhesion properties, a series of nanostructured particles based on a copolymer of vinyl acetate and butylacrylate P(VA-co-BuA) and polybutylacrylate (PBuA) were synthesized by semicontinuous emulsion polymerization. The particle size and P(VA-co-BuA)/P(BuA) ratio were varied. The obtained dispersions were characterized by quasi-elastic light scattering. The adhesion properties (tack, peel, and shear strength) of the particles were evaluated according to industrial methods. It was found that improved values of peel and tack were obtained when a P(VA-co-BuA) rigid core was enveloped with a thin shell made of PBuA. A strong influence of the particle size and PBuA content on the adhesion properties was detected. The best performance was found at large particle sizes and thick shells.

On the Adhesive Properties of Vinyl-Acrylic Latex Particles Functionalized with Acrylic Acid

ABSTRACT A series of pressure-sensitive adhesives, based on vinyl acetate (VA) and butyl acrylate (BuA) and functionalized with small amounts of acrylic acid (AA), were synthesized by semicontinuous emulsion polymerization. This technique allowed preparing latex particles with high monodispersity and pre-defined particle size. The influence of the VA/BuA ratio on the tack, peel, and shear strength of the coatings was investigated. To explain the dependence of adhesive properties (shear, peel, and tack) on particle composition, a Monte Carlo simulation based on a simple model was used to understand the film formation process. The simulation showed that dense adlayers were formed from dispersions containing a relative high content of BuA. Experimental testing showed that films with a low VA/BuA ratio (30/70) exhibited moderate values of shear resistance due to well-structured layers formation, with improved tack and peel properties. A positive influence of functionalization on the adhesive properties was observed at low AA content (1% w.) in coatings enriched in BuA, as a result of surface particle saturation with charged groups.

Triblock copolymers functionalized with quaternary ammonium salts as dehydrating agents for heavy and extra-heavy crude oils

ABSTRACT Block copolymers PEO-PPO-PEO α,ω-functionalized with tertiary aliphatic or aromatic amines were synthesized to obtain a new type of ammonium salt. The compounds were evaluated as demulsifying agents in extra-heavy and heavy Mexican crude oils, 7.5° and 17.8° API. The grafting at the copolymer ends with trioctylamine and quinoline demonstrated to be the best functionalization for increasing the demulsifying efficiency in both crude oils. It was evidenced, for copolymers functionalized with aliphatic amines, that the length of the alkyl chain of the amine plays an important role in the potential to remove emulsified water. Furthermore, it was observed that higher positive value of log P parameter has a strong correlation with the performance of block copolymers functionalized with aliphatic amines. In the case of aromatic amines, the atomic charge of nitrogen proved to be an important factor to provoke the coalescence of the water drops. Finally, the molecular mass of block copolymer was also evaluated, showing that copolymers with higher are more efficient to remove the water from crude oils with huge amounts of asphaltenes. GRAPHICAL ABSTRACT

Novel petroleum demulsifiers based on acrylic random copolymers

Abstract Although normally the copolymers used to remove water from crude oil have a block structure, two series of random acrylic copolymers were evaluated as petroleum demulsifiers. These acrylic copolymers, with two different butyl acrylate (BuA) and 2-ethylhexyl acrylate (2-EHA) contents, were synthesized by semi-continuous emulsion polymerization. Their weight-average molar mass () was varied by modifying the amount of chain transfer agent relative to the monomers from 0 to 8 wt%. FTIR and 13C-NMR spectroscopies confirmed that the conversion of the monomers was complete. The synthesized acrylic copolymers were subsequently evaluated as demulsifier agents in a Mexican heavy crude oil (10.24°API). Copolymers with 70 wt% butyl acrylate monomer and a weight-average molar mass above of 11 000 g mol−1 presented the greatest ability to remove emulsified water from the system. The demulsifying capability of the copolymer was evidenced to be strongly dependent on their molecular mass. Highlights Synthesis of random acrylic copolymers (BuA-co-2-EHA) of different average molar mass (). Evaluation of random acrylic copolymers as demulsifiers of heavy crude oil. Weight-average molar mass () and monomer composition play an important role on the performance of random acrylic copolymers as demulsifiers. GRAPHICAL ABSTRACT

Assessment of Novel Water-Borne Coatings Obtained from Composite Latex Particles and Reinforced with TiO2 Nanotubes

Novel, environmentally friendly waterborne coatings were obtained from the filmification of nanostructured latex particles reinforced with inorganic nanotubes. The latex used to form the coatings consists of core-shell particles with a shell functionalized with different amounts of acrylic acid (AA). This external polymer layer was doped, in some cases, with TiO2 nanotubes at three different concentrations: 100, 500 and 1000 ppm. The composite particles were synthesized in two steps by semi-continuous emulsion polymerization at 75°C. A series of films was prepared by employing core-shell particles with different sizes, core cross-linking and shell functionalization. The coatings obtained were characterized by infrared spectroscopy (FTIR), tapping mode atomic force microscopy (TM-AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Drying rates and tests were also performed to further evaluate these films. It was observed that the addition of small amounts of TiO2 nanotubes contributes to improve the application properties, mainly adhesion to metallic substrates and water impermeability. The resistance to thermal degradation was also strongly increased, as showed by the DSC and TGA analyses. GRAPHICAL ABSTRACT