Clay nanoparticles enhance latex emulsion paints
Latex emulsion paints can be made more hardwearing and fire resistant by incorporating clay nanoparticles, according to research conducted at the University of Warwick, UK.
Applied as waterborne and automotive coatings, or as binding material in cement, mortar, asphalt, carpets and paper, the polymer-based paints are normally stabilised using low molecular weight and ionic soaps such as sodium lauryl sulphate, non-ionic soap lauryl alcohol polyethoxylate (Brij), or polymeric varieties such as polyvinyl pyrrolidone, polyacrylic acid or modifiedcellulose.
Dr Stefan Bon, Associate Professor of Polymer Chemistry, explains, ‘Limitations depend on applications, but in coatings, for example, the use of low molecular mass surfactants can lead to reduced gloss in polymer films and a higher susceptibility to water uptake. Moreover, people can have allergies to ionic soaps and there can be environmental restrictions.’
Bon and his team have coated the individual polymer latex particles in paint with laponite clay discs of approximately 25nm in diameter and one nanometre high to create an armoured layer. Miniemulsion droplets that consist of a variety of monomers – styrene, ethylhexyl methacrylate, lauryl methacrylate – are generated using ultrasound in the presence of laponite clay discs, which are dispersed in the water phase.
Bon says, ‘The clay particles like to adhere to the oil-water interface. Ultrasound homogenisation ensures that we can adhere, but also remove, clay particles, so we can define the size of the monomer droplets.’ These coated particles are then polymerised via free radical polymerisation.
Early trials have suggested that the resulting paint has higher thermal stability than conventional varieties. For example, 35% of a polystyrene film, which normally degrades at around 350ºC, remained stable at temperatures exceeding 500ºC.
There is also the potential for improved scratch resistance and flame retardancy, as well as self-healing properties. ‘Not only the overall amount [of laponite clay] plays a role, but also how it is located within the final polymer coating once applied. We will be investigating [this],’ says Bon.
Researchers suggest the new material may also be used to create novel sensors.
Bon adds, ‘This inorganic honeycomb has a very large surface area and therefore is interesting for chemical sensor applications [by perhaps burning away the polymer cores of the particles]. We are currently exploring this. The simplicity of the production of the armoured particle means the route can be scaled up easily.’
Dr Stefan Bon, email: S.Bon@warwick.ac.uk.