LATEX FILM FORMATION

Investigations on the effect of reactive surfactants on latex film microstructure and properties via tracer diffusion

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 Obiettivo del progetto (Objective)

'Aqueous film forming polymer (latex) dispersions are widely used in the adhesive and coating industry. In recent years, significant research effort is devoted to the development of reactive surfactants for emulsion polymerization, with the aim of achieving better product performance in these water-based systems. They are devised to produce emulsions with better technical properties like emulsion stability, low water uptake of dry films, and better gloss. The reactive surfactant takes part in the polymerization and becomes a part of the polymer chain, and thus modifies the film formation process, the film microstructure as well as the film properties. So far, however, a clear molecular level understanding of how reactive surfactants influence the performance of coatings is missing. Thus, studies at molecular length scales performed on well-defined model systems, where the particle surfaces are modified with covalently attached surfactants, are important to understand the film formation process and tailoring film properties. In this project a systematic study on the influence of anionic reactive surfactants on latex film formation and film properties of Poly (butyl methacrylate) emulsions, employing a tracer diffusion technique (Forced Rayleigh scattering; FRS) is proposed. Reactive surfactants avoid surfactant migration to and aggregation at the polymer-substrate and the polymer-air interface and also modify the polymer interdiffusion between particles that is necessary to form a mechanically strong film. Both effects can be studied at molecular level with the FRS technique. The benefit of the proposed studies will be an improved understanding of the relationship between the nature of the interfacial membranes (depending upon the surfactant used) and the film formation process, helpful in the advancement of the control over film properties for better performing adhesives and coatings.'

Introduzione (Teaser)

Polymer films are used widely in coatings, paints and adhesives. EU-funded researchers are developing novel compounds to enhance film formation and performance while minimising the use of hazardous materials.

Descrizione progetto (Article)

Formation of films from water-based polymeric dispersions has become the processing method of choice in order to minimise the emission of volatile organic compounds (VOCs) produced from the use of organic solvents.

Processing requires the use of compounds to reduce the surface tension of water (surfactants) to enhance stability. However, surfactants tend to cause performance problems in the final coating due to their tendency to form surfactant clusters.

Recently, so-called reactive surfactants (surfmers) that become chemically attached to water-based film forming polymer (latex) dispersions during synthesis have been employed to inhibit clustering while retaining stability. However, most studies have focused on the macroscopic performance of the coatings as a result of surfmer use while investigation of molecular level solution microstructure and drying behaviour has been scarce.

European researchers initiated the LATEX FILM Formation project to fill this knowledge gap and open the door to additional functionality of polymer film coatings.

Researchers synthesised two surfmers structurally similar to the industry standard surfactant. The sulphonate surfmer, whose precursor was a renewable resource (an ingredient of cashew nut shell liquid), was characterised for this reporting period.

Tests demonstrated enhanced characteristics (in particular, lower critical micelle concentration) of the sulphonate surfmer compared to the industry standard and the ability to form stable latex dispersions, supporting its viability as an alternative surfactant. In addition, the coating produced using the sulphonate surfmer exhibited new and attractive functionalities.

Investigators developed a detailed molecular structural model of the co-polymer that gave insight into structure-function relationships and should be important in development of new surfmers.

Continuing research should lead to additional improved surfmers based on renewable resources. Exploitation of the results has the potential to further decrease VOC emissions and enhance functionality and performance of polymer film coatings.