Eduardo Rogel-Hernández

A facile synthesis route for carboxyaryl-methacrylates: a way to obtain aromatic polyelectrolytes

This paper describes a flexible synthetic route for the preparation of the following methacrylic acid derivative monomers with aromatic spacers, including salicylic acid derivatives, in high yields: 2-methacryloyloxybenzoic acid (2-MBA), methyl-2-methacryloyloxybenzoate (M2-MB), 3-methacryloyloxybenzoic acid (3-MBA), methyl-3-methacryloyloxybenzoate (M3-MB), 4-methacryloyloxybenzoic acid (4-MBA), methyl-4-methacryloyloxybenzoate (M4-MB), 4-methacryloyloxy phenyl acetic acid (4-MPAA), methyl-4-methacryloyloxyphenylacetate (M4-MPA) and methyl-4-methacryloyloxyphenylpropionate (M4-MPP). The preparation of the respective aromatic polymers from these monomers by solution free-radical polymerization and their characterization are also described. The position of the substituent in the aromatic spacer ring plays a very important role in the properties of the polymers prepared. While for methyl-ester substitution the glass transition temperature increases from ortho to para isomers, in the case of carboxylic acid substitution this value decreases from ortho to para isomers. The four polymers prepared with free acid groups are hydrophobic polyelectrolytes, as shown by their behavior in aqueous NaCl solutions at different pH values, making them potential candidates for new pH sensitive materials.

Synthesis and polymerization of carboxyalkylmethacrylates: new hydrophobic polyelectrolytes

This paper describes the synthesis of the following methacrylic acid monomers with aliphatic spacers: methyl methacryloyloxyethanoate (MMOE), methyl 4-methacryloyloxybutanoate (M4MOB), methyl 6-methacryloyloxyhexanoate (M6MOH), methyl 10-methacryloyloxydecanoate (M10MOD), and methyl 11-methacryloyloxyundecanoate (M11MOU). The preparation of the respective linear polymers from these monomers, their characterization, and their conversion, via selective saponification, to five new hydrophobic polyelectrolytes are also described. With an increasing number of methylene spacers, the glass transition temperature of the polymers drops, as well as that of the polyelectrolytes, yielding polymeric materials with varied physical states. The developed hydrophobic polyelectrolytes show cloud points in aqueous NaCl solutions at different pH values, making them potential candidates for new pH-sensitive materials.

SYNTHESIS AND CHARACTERIZATION OF ASYMMETRIC ULTRAFILTRATION MEMBRANE MADE WITH RECYCLED POLYSTYRENE FOAM AND DIFFERENT ADDITIVES

This paper reports the synthesis and characterization of asymmetric ultrafiltration membrane made from recycled polystyrene foam (PS) with different additives and polyvinylpyrrolidone (PVP). The polystyrene is currently employed as packing, in fabrication of glasses and dishes. The recycled polystyrene is inexpensive and easy to acquire and, at less in Mexico, not a conscience exists of recycled. The membranes where prepared by phase inversion process from casting solution containing polystyrene as polymer, l-methyl-2-pyrrolidone (NMP) as solvent, and polyethylene glycol (PEG) of different molecular weights and dioctyl phthalate (DOP) as additives. The membranes where characterized in terms of pure water permeation (PWP), molecular weight cut off (MWCO), flux and membrane morphology. The results revealed that the addition of PEG with high molecular weights, produce membrane with higher pure water permeation. The presence of additives affects the surface roughness and membrane morphology.

Synthesis of hydrophobic weak-acid monomers by enzymatic action and their polymerization to obtain hydrophobic polyelectrolytes

We have prepared a series of carboxyalkyl methacrylates from the corresponding methoxy protected acids using pig liver esterase. From a set of these methacrylate derivatives with 3, 4, 5 and 7 methylenes as spacers, the enzymatic reaction exhibits a substrate selectivity for the terminal ester group of the molecule containing a short side-chain (3 methylenes); however, selectivity decreases as the length of the side-chain increases, resulting in partial cleavage of both ester groups in the methacrylates containing 4, 5 and 7 methylenes. This was probably due to the poor water solubility of the substrates, since the use of a tensoactive compound improved the selectivity of hydrolysis and yield. Furthermore, for side chains with 7 methylenes, hydrolysis of both esters groups is considerable (even in the presence of a tensoactive compound); therefore, the procedure is not recommended for highly hydrophobic molecules. Using the obtained carboxyalkyl methacrylates, polyelectrolytes were prepared by free radical polymerization. A pH-dependent phase-separation behavior was presented by the materials, making them suitable for applications in areas such as controlled drug release.

EFFECT OF THE MEMBRANE CHARACTERISTICS AND OPERATION MODES, IN THE FOULING OF ULTRAFILTRATION MEMBRANES BY NATURAL ORGANIC MATTER (NOM)

Membrane fouling by natural organic matter (NOM) is a major problem in ultrafiltration (UF) water treatment. The objective of this study was to evaluate the effects of operations modes on natural organic matter fouling, rejection and flux decline during UF. A comparison of constant pressure and constant flux tests confirmed that modest constant flux provided the most beneficial conditions. As general observation hydrophilic membranes were less prone to NOM fouling.

Preparation and characterization of PVA/PASA-PVA/PDDAB bipolar membrane

Bipolar membranes (BMP) were prepared by bonding together separate anion and cation exchange membrane. For the preparation of the cation selective layer, aqueous solution of PVA [poly(vinyl alcohol)], and PASA [poly(anetholesulfonic acid sodium salt)], where the ratio of PVA/PASA was changed for the control of the membrane charge density, were cast for negatively charged membranes. These membranes were annealed at 100 oC for 45 min and cross-linked in an aqueous solution containing 10% Na2SO4, 1.5% H2SO4, and 0.5% glutaraldehyde in order to control water content of the gel membranes. The anion selective layers were prepared by dispersing a solution of PVA and PDDAB [poly(diallyldiethylammonium bromide)] in DMF, where the ratio of PVA/PDDAB was changed for the membrane charge density control. The electrical resistance of BMP formed by this methodology was slightly increased while the selectivity decreased, while their permselectivity did not change with the acid or alkaline post-treatment.

Microplastics on sandy beaches of the Baja California Peninsula, Mexico

Microplastics have become a concern in recent years because of their negative impact on marine and freshwater environments. Twenty-one sandy beach sites were sampled to investigate the occurrence and distribution of microplastics on the sandy beaches of the Baja California Peninsula, Mexico, as well as their spectroscopic characterization and morphology. Microplastics were separated using the density method and identified using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR). The mean abundance of microplastics in the samples was 135 ± 92 particles kg−1, and fiber was the most abundant microplastic found in the samples, comprising 91% of the total microplastics identified. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis of the microplastics showed that the main polymers found in microplastics were polyacrylic, polyacrylamide, polyethylene terephthalate, polyesters, and nylon.

Electro-Cross-Flow Ultrafiltration System for the Rejection of Nickel Ions from Aqueous Solution, and Sugeno Fuzzy Model Simulation

An empirical model was developed using the experimental results, to predict the removal of nickel ions under the effect of an external electric field applied to an ultrafiltration membrane, electroultrafiltration (EUF) process. Two commercial membranes from Millipore PLCC5 (regenerated cellulose, 5 kDa) and PBCC5 (polyethersulfone, 5 kDa) were selected to conduct the experiments. The rejection of nickel ions increases with an increment of the applied voltage. The maximum rejection of the metal was found to be 60% obtained with the PBCC5 membrane and applying a potential difference of 3.5 and 4.5 V. The results have shown that the application of an external electric field increases the removal capacity of UF membranes and enhances EUF system efficiency. The experimental data for removal of nickel ions in the system were analyzed using the Takagi–Sugeno–Kang (TKS) fuzzy model. The goodness of fit for the TKS fuzzy model used was at least 98%.