Audrey Bonnefond

Morphology and properties of waterborne adhesives made from hybrid polyacrylic/montmorillonite clay colloidal dispersions showing improved tack and shear resistance

AbstractThe morphology and adhesive properties of waterborne films from n-butyl acrylate/methyl methacrylate/montmorillonite clay hybrid polymer latexes which were synthesized by miniemulsion polymerization in the presence of a reactive organoclay ((2-methacryloylethyl) hexadecyldimethylammonium modified montmorillonite, CMA16) were investigated. It was found by cryo-TEM analysis that the hybrid dispersions were a mixture of colloidal particles composed of a small fraction of free montmorillonite clay platelets, polymer latex particles, polymer particles to which one or more clay platelets where adhered onto its surface and a fraction of colloidal material consisted of a clay platelet with a polymer lob adhered to either side, in other words hybrid particles with a dumbbell-like morphology. The films made from these waterborne hybrid dispersions presented a homogeneous dispersion of the clay platelets and exfoliated morphology. The shear adhesion failure temperature (SAFT) and shear resistance of the hybrid latex films synthesized with CMA16 were better than those prepared with a commercial clay (Cloisite 30B), but presented a liquid-like probe-tack performance. When allyl methacrylate (AMA) was added in the formulation, SAFT and shear resistance improved, but the film had a very low energy of adhesion due to the excessively crosslinked matrix. In order to reduce crosslink density and thus improve the adhesion energy, small amounts of chain transfer agent, in this case n-dodecyl mercaptan (n-DDM), were used in the miniemulsion polymerization process. Adhesive films made from these waterborne hybrid dispersions showed excellent SAFT and shear resistance, and good energy of adhesion.

Surfactant-Free Miniemulsion Polymerization of n-BA/S Stabilized by NaMMT: Films with Improved Water Resistance

The use of sodium montmorillonite clay as a stabilizer in the surfactant-free emulsion polymerization of n-butyl acrylate/styrene (n-BA/S) was assessed. It was shown that the use of the clay alone did not yield the desired armored latex particles. A functional comonomer, that is, a phosphate ester of poly(ethylene glycol) monomethacrylate, was used to improve the interaction between the polymer and clay, thus allowing for the clay platelets to adhere to the surface of the polymer particles. The morphology of the films obtained for these two different scenarios was similar and resembled a honeycomb structure. However, their water-resistance properties differed drastically. The water absorption and water vapor permeation rate were much lower in the hybrid n-BA/S/clay films in the presence of the functional monomer than in the films obtained without the functional monomer.

New evidence for hybrid acrylic/TiO2 films inducing bacterial inactivation under low intensity simulated sunlight

This study addresses the preparation and characterization of hybrid films prepared from Titanium dioxide (TiO2) Pickering stabilized acrylic polymeric dispersion as well as their bacterial inactivation efficiency under sunlight irradiation. Complete bacterial inactivation under low intensity simulated solar light irradiation (55 mW/cm(2)) was observed within 240 min for the films containing 10 weight based on monomers (wbm) % of TiO2, whereas 360 min were needed for the films containing 20 wbm% of TiO2. The hybrid films showed repetitive Escherichia coli (E. coli) inactivation under light irradiation. TiO2 released from the films surfaces was measured by inductively coupled plasma mass spectrometry (IPC-MS), obtaining values of ∼ 0.5 and 1 ppb/cm(2) for the films containing 10 wbm% and 20 wbm% of TiO2, respectively, far below the allowed cytotoxicity level for TiO2 (200 ppb). Transmission electron microscopy (TEM) of the hybrid films showed that TiO2 nanoparticles (NPs) were located at the polymer particles surface forming a continuous inorganic network inside the film matrix. Atomic force microscopy (AFM) images showed differences in the TiO2 dispersion between the air-film and film-substrate interfaces. Films containing 10 wbm% of TiO2 had higher roughness (Rg) at both interfaces than the one containing 20 wbm% of TiO2 inducing an increase in the bacterial adhesion as well as the bacterial inactivation kinetics. The highly oxidative OH-radicals participating in the bacterial inactivation were determined by fluorescence.

Surfactant-free poly(methyl methacrylate)/poly(vinylamine) (PMMA/PVAm) amphiphilic core-shell polymer particles

Surfactant-free emulsion polymerization for the synthesis of poly(methyl methacrylate)/poly(vinylamine) (PMMA/PVAm) amphiphilic core-shell polymer particles is investigated in this work. Particularly, the effect of the PVAm molar mass and the tert-butyl hydroperoxide (TBHP)/PVAm molar ratio on the kinetics of reaction and particle nucleation is studied, and the morphology of the polymer particles carefully analyzed. Interestingly, decreasing the TBHP/PVAm molar ratio leads to faster kinetics of the polymerization reaction. Decreasing the molar mass of PVAm also yields faster kinetics. The morphology of the PMMA/PVAm polymer particles is core-shell like, and the PVAm chains are located at the surface of the polymer particles acting as stabilizer. Thus, the pH affects their morphology and the PVAm chains are fully extended at low pH and hence are swollen by water and have large size, whereas at high pH, the PVAm chains shrink and particle sizes are smaller.

New agitated and thermostatized cell for in situ monitoring of fast reactions by synchrotron SAXS.

A thermostatized and agitated sample cell for synchrotron small-angle X-ray scattering (SAXS) measurements of liquid samples (homogeneous or heterogeneous) has been developed. The cell is composed of a compact main body with inlet and outlet windows for the beams of light. The volume of the cell is approximately 0.8 ml and the distance between the windows is 5 mm to allow accurate SAXS measurements. The cell is thermostatized by means of a jacket that surrounds the sample holder and it is connected to a thermostatic bath. In addition, the cell has a top and a bottom lid that allow easy cleaning and maintenance without demounting the optical windows. The cell has been used to run SAXS measurements of liquid samples and, for the first time, a mini-emulsion polymerization reaction has been monitored by SAXS.