Preparation and Morphology Studies of Core-Shell Type Waterborne Polyacrylate-Polyurethane Microspheres

Effects of Grafting Degree on the Formation of Waterborne Polyurethane-Acrylate Film with Hard Core-Soft Shell Structure

Waterborne polyurethane-acrylate (WPUA) grafted with polyurethane was prepared to improve the film-forming ability of hard-type acrylic latex. To balance the film-formation ability and hardness, the WPUA latex was designed with a hard core (polyacrylate) and soft shell (polyurethane). The grafting ratio was controlled through varying the content of 2-hydroxyethyl methacrylate (HEMA) used to cap the ends of the polyurethane prepolymer. The morphologies of the latex particles, film surface, and fracture surface of the film were characterized through transmission electron microscopy, atomic force microscopy, and scanning electron microscopy, respectively. An increase in the grafting ratio resulted in the enhanced miscibility of polyurethane and polyacrylate but reduced adhesion between particles and increased minimum film formation temperature. In addition, grafting was essential to obtain transparent WPUA films. Excessive grafting induced defects such as micropores within the film, leading to the decreased hardness and adhesive strength of the film. The optimal HEMA content for the preparation of a WPUA coating with excellent film-forming ability and high hardness in ambient conditions was noted to be 50%. The final WPUA film was prepared without coalescence agents that generate volatile organic compounds.

Preparation and Properties of Hydrophilic Rosin-Based Aromatic Polyurethane Microspheres

Hydrophilic aromatic polyurethane (HAPU) microspheres were prepared through dispersion polymerization of a rosin-based polyurethane dispersion with C=C and styrene (St). The effects of the monomer ratio (i.e., waterborne rosin-based aromatic polyurethane (WRPU) to St), dispersant level, and reaction temperature on the properties of the microspheres were investigated; the effects of pH and adsorption temperature on the adsorption capacity of Orange II were also studied. The microspheres were characterized using Fourier transform infrared spectroscopy, energy-dispersive spectrometry, thermogravimetric analysis, laser particle size analysis, and scanning electron microscopy. The results showed that HAPU microspheres have been successfully synthesized and the produced microspheres exhibited good thermal stability and monodispersion. The optimum reaction conditions for the preparation of the microspheres were determined as a monomer ratio (m _WRPU/m _St) of 6:4 with 8 wt % poly(vinyl pyrrolidine) (on the basis of the mixed monomer) at 80 °C for 8 h. Under these conditions, the average particle size of the synthetic microspheres was 120 nm and the particle size distribution index was 0.442. The microspheres' adsorption capacity for Orange II reached 17.53 mg·g^-1 when the solid-liquid ratio was 1 g·L^-1, with an initial concentration of 100 mg·L^-1 at pH 5, and the adsorption was conducted at 313 K for 3 h.

Waterborne epoxy-modified polyurethane-acrylate dispersions with nano-sized core-shell structure particles: synthesis, characterization, and their coating film properties

Waterborne epoxy-modified polyurethane-acrylate (EPUA) dispersions with nano-sized core-shell structure particles, with polyacrylate (PA) as core and epoxy-modified polyurethane (EPU) as shell, were successfully prepared via a two-step procedure. The waterborne EPU dispersions were first synthesized to serve as seeds, and then the butyl acrylate (BA) and methyl methacrylate (MMA) monomers were introduced into EPU particles to form polymeric core by radical polymerization under the assistance of ultrasonic treatment. Fourier transform infrared (FT-IR) spectroscopy revealed that the epoxy and PA components were successfully incorporated onto the chain of the PU and EPU to form EPU and EPUA, respectively. The transmission electron microscopy (TEM) photograph demonstrated that the EPUA particles have the core-shell structure. The as-prepared EPUA coating films exhibited good thermo-stability and mechanical properties, as revealed by thermogravimetric analysis (TGA) and tensile testing, respectively. The results of potentiodynamic polarization curves and immersion corrosion testing in 5 wt% NaCl aqueous solution both demonstrated that the anticorrosive properties of EPUA mainly depended on the mass content of PA, with the optimized value of 30 wt%.

Cellulose Acetate/Chitosan Multimicrospheres Preparation and Ranitidine Hydrochloride Release In Vitro

A noval cellulose acetate/chitosan multimicrospheres (CACM) was prepared by the method of w/o/w emulsion. The concentration of cellulose acetate (CA) and the ratio of CA/chitosan (CS) had influence on the CACM size, and appearance. Ranitidine hydrochloride loading, and releasing efficiency in vitro were investigated. The optimal condition for preparation of the microspheres was CA concentration at 2% and the ratio of CA/CS at 3/1. The microspheres size was 200-350 microm. The appearance of microspheres was spherical, porous, and nonaggregated. The highest loading efficiency was 21%. The ranitidine release from the CACM was 40% during 48 hr in buffers.