Polymer films cast from aqueous polymer dispersions typically suffer from an inherent lack of mechanical strength when compared to their solvent-borne counterparts. This drawback can be overcome by the use nanostructured hybrid particles that contain both a hard and soft phase. In this work, we demonstrate the use latex particles consisting of a soft core with a multilobed hard shell synthesized by seeded semicontinuous emulsion polymerization with the aim of maximizing the interconnectivity of the hard phase in the resulting polymer film, thus generating films with improved mechanical properties. Films with a minimum film formation temperature (MFFT) close to that of the soft phase are formed while obtaining a Young's modulus up to 4.5 times higher that of a standard homogeneous latex particle. The effect of annealing temperature on film morphology is also investigated, clearly demonstrating that a marked difference in mechanical properties is observed when a percolating network of the hard phase within the film is obtained.

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Mechanically strong films are generated from cellulose nanocrystal armored latex particles synthesized by emulsion polymerization.

Cellulose nanocrystals (CNCs) are unique, lightweight materials that possess high elastic modulus and tensile strength, making them of great interest in the formation of nanocomposite materials. However, efficient design of the composite material is essential in translating the mechanical properties of the individual CNCs into the nanocomposite film. In this work, we demonstrate the formation of structured CNC/acrylic dispersions by physical blending of the anionic CNCs with charged acrylic latex particles. By blending with large cationic latex particles, the CNCs adsorbed onto the acrylic latex surface while blending with small latex particles led to the inverse structure. Films were cast from these dispersions and the physical properties were compared with the aim of understanding the influence of the initial structure of the hybrid dispersion on the structure of the final film. A significant difference in the mechanical properties was observed based on the position of the CNCs in the initial dispersion. Adsorption of latex particles onto the CNC surface led to a random distribution of nonconnected CNCs, which contributed little to improving the Young’s modulus, while adsorption of CNC onto the latex led to a honeycomb CNC network and a large increase in the Young’s modulus. This work underlines the importance of particle structure on the structure and mechanical properties of nanostructured films.

Acrylic/alkyd hybrid latexes offer the potential to obtain hard films from waterborne polymer dispersions without using coalescing agents. However, despite being widely used commercially, the curing process of the alkyd resin used in such formulations, and its influence on the final film morphology, remain poorly understood. In this work, we explore the curing process and its influence on film morphology in alkyd/acrylic hybrid latexes by nanomechanical mapping of the film during curing. It is shown that, although acrylic domains aid oxygen diffusion and facilitate curing, the rate of curing was substantially lower in the interior. Nevertheless, homogeneous curing was achieved at long times. The role of primary and secondary catalysts in the process is also explored, finding that the variation of the rate of curing of the alkyd plays an influential role in the development of film structure due to phase migration of the two polymers as curing progresses. It is hoped this work goes some way to unraveling the mystery behind the curing process in acrylic/alkyd hybrid latex films.