Preparation and full characterization of cationic latex of styrene–butyl acrylate

Highly Uniform and Porous Polyurea Microspheres: Clean and Easy Preparation by Interface Polymerization, Palladium Incorporation, and High Catalytic Performance for Dye Degradation

Owing to their high specific surface area and low density, porous polymer materials are of great importance in a vast variety of applications, particularly as supports for enzymes and transition metals. Herein, highly uniform and porous polyurea microspheres (PPM), with size between 200 and 500 μm, are prepared by interfacial polymerization of toluene diisocyanate (TDI) in water through a simple microfluidic device composed of two tube lines, in one of which TDI is flowing and merged to the other with flowing aqueous phase, generating therefore TDI droplets at merging. The polymerization starts in the tube while flowing to the reactor and completed therein. This is a simple, easy and effective process for preparation of uniform PPM. Results demonstrate that the presence of polyvinyl alcohol in the aqueous flow is necessary to obtain uniform PPM. The size of PPM is readily adjustable by changing the polymerization conditions. In addition, palladium is incorporated in PPM to get the composite microspheres Pd@PPM, which are used as catalyst in degradation of methylene blue and rhodamine B. High performance and good reusability are demonstrated. Monodispersity, efficient dye degradation, easy recovery, and remarkable reusability make Pd@PPM a promising catalyst for dye degradation.

Colloidal Stability of Positively Charged Dispersions of Styrene and Acrylic Copolymers in the Presence of TiO2 and CaCO3

Increasing antibiotic resistance of several pathogenic microorganisms calls for alternative approaches to prevent spreading of bacterial diseases. We propose to employ for this purpose coatings obtained from positively charged latex dispersions. In this contribution we characterize aqueous mixed dispersions containing TiO2 or CaCO3 and methyl methacrylate-ethyl acrylate or styrene-ethyl acrylate copolymers synthesized using a cationic surfactant, cetyltrimethylammonium bromide as an emulsifier. Particle size, electrokinetic (ζ) potential of the mixed dispersions and the resulting thin films, as well as antimicrobial properties of the latter are described. The TiO2 and CaCO3 dispersions were stabilised with polyethyleneimine (PEI) and optimum pH for the mixed dispersions were chosen on the basis of ζ-potential measurements. For TiO2, the maximum ζ = +35 mV was found at pH 7.5, and for CaCO3, pH was set at 8.2 (ζ = +38 mV), to prevent its dissolution. In most 1:1 mixtures of TiO2 or CaCO3 with the cetyltrimethylammonium bromide (CTAB)-stabilised latex dispersions, two distinct particles populations were observed, corresponding to the bare latex and bare TiO2 or CaCO3 fractions. Films made of the mixed dispersions remained positively charged and showed antimicrobial activity similar or reduced with respect to the bare polymer films.

Antimicrobial dispersions and films from positively charged styrene and acrylic copolymers

Antimicrobial properties of methyl methacrylate - ethyl acrylate and styrene - ethyl acrylate copolymers, both as latexes and after film formation were tested. The polymers were synthesized using a cationic surfactant, cetytrimethylammonium bromide (CTAB) as an emulsifier, in presence of either a cationic or an anionic initiator. The resulting latex particles showed sizes between 50 and 320 nm (larger for the anionic initiator), and ζ-potential between +30 and +70 mV (more positive for the cationic initiator). Dialysis did not change significantly the size distribution and ζ-potential of the latexes, and most of them inhibited growth of Gram-negative (E. coli), Gram-positive (S. aureus, B. subtilis) and yeast (C. albicans). On the other hand, only few compositions were effective against Gram-negative P. aeruginosa. Both completely ("dry") and incompletely ("wet") formed films produced from the respective latexes showed similar, although less pronounced antimicrobial activity pattern. The analysis of streaming potential for the films confirmed that part of the positive surface charge brought by non-covalent binding of CTAB to the polymer chains, is lost during dialysis of the latexes and during rinsing, especially under high-shear flow. From the practical point of view, films with the best mechanical and antimicrobial properties can be achieved using polymers with high proportion of ethyl acrylate, while nature of the co-monomer and initiator do not play crucial roles.

Improvement in Wood Bonding Strength of Poly (Vinyl Acetate-Butyl Acrylate) Emulsion by Controlling the Amount of Redox Initiator

Polyvinyl acetate emulsion adhesive has been widely used due to its good bonding performance and environmentally friendly properties. Indeed, the bonding performance can be further improved by copolymerizing with other monomers. In this study, the effect of the adjunction of redox initiator (hydrogen peroxide–tartaric acid, H₂O₂–TA) on the properties of the poly (vinyl acetate-butyl acrylate) (P (VAc–BA)) emulsion adhesive was investigated. With increasing dosage, the reaction became more complete and the obtained film was more compact, as identified via SEM. The core-shell structure of the emulsion particles was confirmed via TEM. Results indicate that while the initiator content increased from 0.5 to 1.0%, a clearer core-shell structure was obtained and the bonding strength of the plywood improved from 2.34 to 2.97 MPa. With the further incorporation of H₂O₂–TA (i.e., 1.5%), the bonding performance deteriorated. The optimum wood bonding strength (2.97 MPa) of the prepared P (VAc-BA) emulsion adhesive was even better than that (2.55 MPa) of a commercial PVAc emulsion adhesive, suggesting its potential application for the wood industry.

Characterization of Heterocoagulation with Oppositely Charged Polymer Colloid Particles through Online Tracking of Light Transmittance

Heterocoagulation of colloid particles with opposite surface charge has been used for the preparation of composite microspheres with specifically designed suprastructure, such as those with raspberry-like surface morphology and core-shell microspheres, which are difficult to achieve through other techniques. Here we report our investigation on the heterocoagulation of cationic polystyrene (PS) particles with anionic poly(methyl methacrylate) (PMMA) particles by a novel technique, i.e., by following online the evolution of the light transmittance in the process with practically no disturbance of the dispersion and no post-treatment for the samples. Different heterocoagulations were conducted with PS and PMMA latexes with different latex mixing regimes and different particle sizes for both latexes. The evolution of the light transmittance in all of these processes, mainly with addition of anionic latex to cationic latex, was followed online. By combining TEM to detect the morphology of the composite microspheres formed and light scattering to follow the size evolution in the heterocoagulation, this work gives a clear picture of the heterocoagulation process. In addition, a set of mathematical equations are established in order to estimate the number ratio of the particles with opposite charge and the surface coverage percent of the large primary particle with the small ones. Results show that the particle size plays a key role in the process. The mechanism of the heterocoagulation process is discussed.