Innovation through co-operation
Our UFAPOL range is composed of high quality anionic emulsifiers with specifications particularly accommodated for the high requirements of the emulsion polymer industry. Our UFAPOL range is characterised by low levels of electrolyte and non-reacted material, consistent and well defined raw material sources, very low levels of bi-products, light colour, good thermal, pH and electrolyte tolerance and they are readily biodegradable.
EMULSION POLYMERISATION
Among the many applications of surfactants their use in the paints, plastics and elastomer industries account for around 5% of the volume of surfactants consumed. The most important application in this field is the use of surfactants for the production of plastics and polymer dispersions by emulsion polymerisation. Surfactants also play an important role as dispersants for pigments and as additives for improving wetting properties of paint films.
Aqueous polymer dispersions for use as binders for emulsion paints, as dispersion-based adhesives, for paper coating, as textile auxiliaries and for leather finishes are produced by emulsion polymerisation. In emulsion polymerisation, synthetic surfactants assume the role of latex stabilisation, and basically has three emulsifying functions, namely: stabilising the monomer droplets at the beginning of the polymerisation, supplying surfactant micelles as the site of the polymerisation reaction and stabilising the polymerised latex particles pending transportation, storage and processing.
Polymer dispersions produced by emulsion polymerisation are generally made up of several monomers ( typical exceptions being: PolyVinylChloride and PolyVinylAcetate ), where the typical combinations are vinylacetate/acrylate, vinylacetate/ethylene, styrene/acrylate, vinyl chloride/ethylene/acrylate, and styrene/butadiene. These co-polymers usually consist of a hard component and a soft component. By combining different functional monomers it is possible to produce polymers with certain adhesion, cohesion or cross-linking properties. The properties of the polymer dispersion can also be influenced by the way in which the emulsifier is added. The most common methods are the batch process, monomer addition, the pre-emulsion process, the seed latex process and continuos emulsion polymerisation in stirred tank reactors or loop reactors.
THE EMULSIFIER SYSTEM
Surfactants for the production of polymer dispersions are based partly on native raw materials and partly on fossil raw materials. In recent years, the paint and lacquer industry has witnessed a clear trend towards surfactants based on renewable and biodegradable raw materials. The various surfactant types, such as anionic, cationic and nonionic surfactants, play roles of differing importance in emulsion polymerisation.
Nonionic surfactants generally have to be relatively high concentrated to form stable emulsions, and because of this they are mostly used in combination with protective colloids or anionic emulsifiers. In conjunction with ionic emulsifiers they reduce charge density at the particle surface. Because they are unaffected by electrolytes they act as chemical and steric stabilisers.
Anionic emulsifiers like fatty alcohol sulphates are distinguished by particularly good polymerisation behaviour and by the formation of fine-particle polymer dispersions, for example in the production of acrylate hydrosols for priming plaster and for the production of high gloss paints. Their foaming power commends their use in the production of latex foams. Fatty alcohol sulphates are biodegradable and meet the requirements of food laws. Fatty alcohol ether sulphates are more soluble in water than fatty alcohol sulphates and are largely unaffected by water hardness. With a low degree of ethoxilation, they show favourable foaming behaviour. The polymer particles produced with them are generally fine-particle, stable, pigment-compatible and low temperature-resistant dispersions. The growing preference for non-aromatic emulsifiers is leading increasingly to the replacement of alkyl phenol ether sulphates by fatty alcohol ether sulphates.
The large number of emulsifiers available makes it clear that the choice of the optimal emulsifier for a particular system is often difficult and requires considerable experience. Since not only the emulsifier, but also other process parameters have an influence on the result of the polymerisation and since the performance requirements which the polymer dispersions are expected to satisfy are very different, no general rules can be laid down as to the choice of the correct stabilising system.
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